kundu

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Author name code: kundu
ADS astronomy entries on 2022-09-14
author:"Kundu, M.R."

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Title: Microflares and the Statistics of X-ray Flares
Authors: Hannah, I. G.; Hudson, H. S.; Battaglia, M.; Christe, S.;
Kašparová, J.; Krucker, S.; Kundu, M. R.; Veronig, A.
2011SSRv..159..263H Altcode: 2011SSRv..tmp..262H; 2011SSRv..tmp...87H; 2011arXiv1108.6203H;
2011SSRv..tmp..243H; 2011SSRv..tmp..163H
This review surveys the statistics of solar X-ray flares, emphasising
the new views that RHESSI has given us of the weaker events (the
microflares). The new data reveal that these microflares strongly
resemble more energetic events in most respects; they occur solely
within active regions and exhibit high-temperature/nonthermal emissions
in approximately the same proportion as major events. We discuss the
distributions of flare parameters (e.g., peak flux) and how these
parameters correlate, for instance via the Neupert effect. We also
highlight the systematic biases involved in intercomparing data
representing many decades of event magnitude. The intermittency of
the flare/microflare occurrence, both in space and in time, argues
that these discrete events do not explain general coronal heating,
either in active regions or in the quiet Sun.

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Title: The Relationship Between Solar Radio and Hard X-ray Emission
Authors: White, S. M.; Benz, A. O.; Christe, S.; Fárník, F.; Kundu,
M. R.; Mann, G.; Ning, Z.; Raulin, J. -P.; Silva-Válio, A. V. R.;
Saint-Hilaire, P.; Vilmer, N.; Warmuth, A.
2011SSRv..159..225W Altcode: 2011SSRv..tmp..263W; 2011SSRv..tmp..244W; 2011SSRv..tmp..164W;
2011arXiv1109.6629W; 2011SSRv..tmp...88W
This review discusses the complementary relationship between radio
and hard X-ray observations of the Sun using primarily results from
the era of the Reuven Ramaty High Energy Solar Spectroscopic Imager
satellite. A primary focus of joint radio and hard X-ray studies of
solar flares uses observations of nonthermal gyrosynchrotron emission
at radio wavelengths and bremsstrahlung hard X-rays to study the
properties of electrons accelerated in the main flare site, since
it is well established that these two emissions show very similar
temporal behavior. A quantitative prescription is given for comparing
the electron energy distributions derived separately from the two
wavelength ranges: this is an important application with the potential
for measuring the magnetic field strength in the flaring region, and
reveals significant differences between the electrons in different
energy ranges. Examples of the use of simultaneous data from the two
wavelength ranges to derive physical conditions are then discussed,
including the case of microflares, and the comparison of images at
radio and hard X-ray wavelengths is presented. There have been puzzling
results obtained from observations of solar flares at millimeter
and submillimeter wavelengths, and the comparison of these results
with corresponding hard X-ray data is presented. Finally, the review
discusses the association of hard X-ray releases with radio emission at
decimeter and meter wavelengths, which is dominated by plasma emission
(at lower frequencies) and electron cyclotron maser emission (at
higher frequencies), both coherent emission mechanisms that require
small numbers of energetic electrons. These comparisons show broad
general associations but detailed correspondence remains more elusive.

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Title: Sunspots at centimeter wavelengths
Authors: Kundu, Mukul R.; Lee, Jeongwoo
2011IAUS..273..265K Altcode:
The early solar observations of Covington (1947) established a good
relation between 10.7 cm solar flux and the presence of sunspots on
solar disk. The first spatially resolved observation with a two-element
interferometer at arc min resolution by Kundu (1959) found that the
radio source at 3 cm has a core-halo structure; the core is highly
polarized and corresponds to the umbra of a sunspot with magnetic fields
of several hundred gauss, and the halo corresponds to the diffuse
penumbra or plage region. The coronal temperature of the core was
interpreted as due to gyroresonance opacity produced by acceleration of
electrons gyrating in a magnetic field. Since the opacity is produced
at resonant layers where the frequency matches harmonics of the
gyrofrequency, the radio observation could be utilized to measure the
coronal magnetic field. Since this simple interferometric observation,
the next step for solar astronomers was to use arc second resolution
offered by large arrays at cm wavelengths such as Westerbrock Synthesis
Radio Telescope and the Very Large Array, which were primarily built for
cosmic radio research. Currently, the Owens Valley Solar Array operating
in the range 1-18 GHz and the Nobeyama Radio Heliograph at 17 and 34 GHz
are the only solar dedicated radio telescopes. Using these telescopes
at multiple wavelengths it is now possible to explore three dimensional
structure of sunspot associated radio sources and therefore of coronal
magnetic fields. We shall present these measurements at wavelengths
ranging from 1.7 cm to 90 cm and associated theoretical developments.

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Title: The IAU Early French Radio Astronomy Project
Authors: Orchiston, Wayne; Boischot, A.; Delannoy, J.; Kundu, M.;
Lequeux, J.; Pick, M.; Steinberg, J.
2011AAS...21714608O Altcode: 2011BAAS...4314608O
In 2006 an ambitious project was launched under the auspices of the
IAU Working Group on Historic Radio Astronomy to document important
developments in French radio astronomy from 1901 through to the
1960s, in a series of papers published, in English, in the Journal
of Astronomical History and Heritage. This successful project has now
come to an end with the sixth and final paper in the series about to
be published (and a new WG project, on the history of early Japanese
radio astronomy, has just been launched). In this paper we discuss
Nordmann's abortive attempt to detect solar radio emission in 1901, and
the important roles played by staff from the École Normale Supérieure
and the Institut d'Astrophysique in Paris during the 1940s through
60s in developing new radio astronomy instrumentation and pursuing a
range of solar and non-solar research projects in Paris itself and
at field stations established at Marcoussis, Nançay and the Haute
Provence Observatory.

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Title: High-Energy Emission from a Solar Flare in Hard X-rays and
Microwaves
Authors: Kundu, M. R.; Grechnev, V. V.; White, S. M.; Schmahl, E. J.;
Meshalkina, N. S.; Kashapova, L. K.
2009SoPh..260..135K Altcode: 2009arXiv0908.0385K
We investigate accelerated electron energy spectra for different sources
in a large flare using simultaneous observations obtained with two
instruments, the Nobeyama Radio Heliograph (NoRH) at 17 and 34 GHz,
and the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI)
at hard X-rays. This flare is one of the few in which emission up to
energies exceeding 200 keV can be imaged in hard X-rays. Furthermore,
we can investigate the spectra of individual sources up to this
energy. We discuss and compare the HXR and microwave spectra and
morphology. Although the event overall appears to correspond to the
standard scenario with magnetic reconnection under an eruptive filament,
several of its features do not seem to be consistent with popular flare
models. In particular we find that (1) microwave emissions might be
optically thick at high frequencies despite a low peak frequency in
the total flux radio spectrum, presumably due to the inhomogeneity
of the emitting source; (2) magnetic fields in high-frequency radio
sources might be stronger than sometimes assumed; (3) sources spread
over a very large volume can show matching evolution in their hard
X-ray spectra that may provide a challenge to acceleration models. Our
results emphasize the importance of studies of sunspot-associated flares
and total flux measurements of radio bursts in the millimeter range.

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Title: Highlighting the history of French radio astronomy. 4:
Early solar research at the École Normale Supérieure, Narcoussis
and Nançay
Authors: Orchiston, Wayne; Steinberg, Jean-Louis; Kundu, Mukul; Arsac,
Jacques; Blum, Émile-Jacques; Boischot, André
2009JAHH...12..175O Altcode:
The first tentative steps in solar radio astronomy took place during
the 1940s and early 1950s as physicists and engineers in a number of
countries used recycled World War II equipment to investigate the flux
levels and polarisation of solar bursts and emission from the quiet
Sun, and sought to understand the connection between this emission and
optical features in the solar photosphere and chromosphere. There was
also an abiding interest in the terrestrial effects of this solar radio
emission. Among these solar pioneers were French radio astronomers from
the École Normale Supérieure in Paris. In this paper we review the
early solar observations made by them from Paris, Marcoussis and Nançay
prior to the construction of a number of innovative multi-element
solar interferometers at the Nançay field station in the mid-1950s.

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Title: Mitigation of geogenic arsenic bearing groundwaters: Assessing
the importance of risk substitution arising from waterborne pathogens
Authors: Mondal, Debapriya; Polya, David A.; Giri, A. K.; Banerjee,
M.; Hegan, A.; Rodriguez-Lado, L.; Bradford, W.; Banerjee, N.; Kundu,
M.; Ganguli, B.
2009GeCAS..73Q.893M Altcode:
No abstract at ADS

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Title: High-Energy Emission from a Solar Flare in Hard X-Rays and
Microwaves
Authors: Kundu, Mukul R.; Grechnev, V. V.; White, S. M.; Schmahl,
E. J.; Meshalkina, N. S.; Kashapova, L. K.
2009SPD....40.1920K Altcode:
We investigate accelerated electron energy spectra for different sources
in a large flare using simultaneous observations obtained with two
instruments, the Nobeyama Radio Heliograph (NoRH) at 17 and 34 GHz,
and the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI)
at hard X-rays. This flare is one of the few in which emission up to
energies exceeding 200 keV can be imaged in hard X-rays. Furthermore,
we can investigate the spectra of individual sources up to this
energy. We discuss and compare the HXR and microwave spectra and
morphology. Although the event overall appears to correspond to the
standard scenario with magnetic reconnection under an eruptive filament,
several of its features do not seem to be consistent with popular flare
models. In particular we find that (1) microwave emissions might be
optically thick at high frequencies despite a low peak frequency in
the total flux radio spectrum, presumably due to the inhomogeneity
of the emitting source; (2) magnetic fields in high-frequency radio
sources might be stronger than sometimes assumed; (3) sources spread
over a very large volume can show matching evolution in their hard
X-ray spectra that may provide a challenge to acceleration models. Our
results emphasize the importance of studies of sunspot-associated flares
and total flux measurements of radio bursts in the millimeter range.

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Title: Advances in Solar Radio Astronomy
Authors: Kundu, Mukul R.
2007AAS...210.3801K Altcode: 2007BAAS...39..152K
The development of research in Solar Radio Astronomy over the years
will be presented. Starting with the early years of solar radio research
when discoveries were frequently made,we discuss the evolution of solar
radio research into an integral component of solar physics research. We
continue with a discussion of contributions made by radio instruments
to those made by space solar missions and show that the combined
observations are complementary as well as fundamental in nature,
especially when it applies to high energy solar phenomena.

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Title: The Morphology of Decimetric Emission from Solar Flares:
GMRT Observations
Authors: Kundu, M. R.; White, S. M.; Garaimov, V. I.; Subramanian,
P.; Ananthakrishnan, S.; Janardhan, P.
2006SoPh..236..369K Altcode: 2006SoPh..tmp....7K
Observations of a solar flare at 617 MHz with the Giant Meter-wave
Radio Telescope (GMRT) are used to study the morphology of flare radio
emission at decimetric wavelengths. There has been very little imaging
in the 500 - 1000 MHz frequency range, but it is of great interest,
since it corresponds to densities at which energy is believed to be
released in solar flares. This event has a very distinctive morphology
at 617 MHz: the radio emission is clearly resolved by the 30″ beam
into arc-shaped sources seeming to lie at the tops of long loops,
anchored at one end in the active region in which the flare occurs,
with the other end lying some 200 000 km away in a region of quiet solar
atmosphere. Microwave images show fairly conventional behaviour for the
flare in the active region: it consists of two compact sources overlying
regions of opposite magnetic polarity in the photosphere. The decimetric
emission is confined to the period leading up to the impulsive phase of
the flare, and does not extend over a wide frequency range. This fact
suggests a flare mechanism in which the magnetic field at considerable
height in the corona is destabilized a few minutes prior to the main
energy release lower in the corona. The radio morphology also suggests
that the radiating electrons are trapped near the tops of magnetic
loops, and therefore may have pitch angles near 90˚.

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Title: Microwave and Hard X-ray Imaging Observations of Energetic
Electrons in Solar Flares: Event of 2003 June 17
Authors: Kundu, Mukul R.; Schmahl, E. J.; White, S. M.
2006SPD....37.1306K Altcode: 2006BAAS...38..241K
We discuss one large flare using simultaneous observations obtained
with two instruments--Nobeyama Radio Heliograph (NoRH) at 17 and
34 GHz, and Reuven Ramaty High Energy Solar Spectroscopic imager
(RHESSI) in the context of flare models. As we know energetic electrons
accelerated to nonthermal energies are seen via microwave and hard X-ray
emission from the solar corona. Imaging observations are necessary to
study the energetic electrons in flare events. Nonthermal microwave
emission during large solar flares is produced by gyrosynchrotron
mechanism which involves coronal magnetic fields of at least a few
hundred gauss and electrons of energy of a few hundred keV. Hard
X-ray emission, on the other hand, is produced by bremsstrahlung from
beamed or trapped electrons of a few to hundreds of keV energy. The
two different methods of mapping energetic flare electrons therefore
complement each other, and provide good means of testing flare models
which have been abundant in the recent literature. The RHESSI HXR
and NoRH microwave imaging observations of the flare of 2003 June 17
are used here as an example. The flare in question was of class M6.8,
and it was observed in AR 10386, a beta-gamma-delta region, two days
after its east-limb passage.

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Title: Radio and Hard X-Ray Imaging Observations of the M5.7 Flare
of 2002 March 14
Authors: Schmahl, E. J.; Kundu, M. R.; Garaimov, V. I.
2006ApJ...643.1271S Altcode:
We describe a flare of GOES class M5.7 that was observed simultaneously
by RHESSI (Ramaty High Energy Solar Spectroscopic Imager) and NoRH
(Nobeyama Radio Heliograph). The flare occurred in AR 9866 located near
the disk center. The hard X-ray (HXR), microwave, EIT, and TRACE 195 Å
observations indicate that the flaring region consisted of a complex
of multiple loops. In the microwave domain the source morphology,
the timing, the polarization characteristics, and the photospheric
magnetic fields clearly indicate that it is of a class characterized
as a “double loop” configuration, meaning two systems of magnetic
flux, each consisting of many smaller loops. The observations suggest
the existence of a small loop system created by the emergence of new
flux, which interacts with an old flux system, and of a remote flare
site that is observed primarily in radio. The former is the main flare
site where we observe microwave, HXR, and EUV emissions. In HXR there
are two main identifiable loop systems. The first is an elongated one
filled with energetic electrons primarily emitting lower energy (12-25
keV) HXR with a colocated microwave source; this source has distinct
footpoints at higher X-ray energies. The second loop system is implied
by compact HXR sources in opposite magnetic polarities separated by a
distance greater than the length of the first loop system. Spectroscopic
analysis of the RHESSI data shows that the spectrum can be fitted with
a thick-target model with a thermal component and a broken power-law
component of the electron energy distribution. This model is used to
address the thermal/nonthermal and radio/HXR electron number problems.

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Title: Nobeyama radio heliograph observations of RHESSI microflares
Authors: Kundu, M. R.; Schmahl, E. J.; Grigis, P. C.; Garaimov, V. I.;
Shibasaki, K.
2006A&A...451..691K Altcode:
Aims.We present a summary of the analysis of thirty microflares,
observed simultaneously by the Ramaty High Energy Solar Spectroscopic
Imager (RHESSI) in hard X-rays and by Nobeyama RadioHeliograph (NoRH)
in microwaves (17 GHz). Methods: .We used microflares observed
by RHESSI in the energy range 3-25 keV, and for larger events, up
to 35 keV. The observations were made 2002, May 2-6. Results:
.We describe the imaging characteristics of these microflares including
their locations in hard X-rays and microwaves and the relative positions
of the micro-flaring sources. We discuss the brightness temperatures,
emission measures and their hard X-ray spectral properties. We see
small (mini) flaring loops clearly in NoRH and RHESSI images. The
microwave emission often seems to come from the RHESSI foot points
(for higher energies), and from the entire small (mini) flaring loop
(for lower energies). Sometimes the two (microwave and hard X-ray)
sources coincide, at other times they are at opposite ends of a mini
flaring loop. Typically, the hard X-ray spectrum of the microwave
associated RHESSI microflares can be fit by an isothermal component at
low energies (below 10 or 12 keV) and a nonthermal component at higher
energies (above 12 keV). Conclusions: .Microflares in hard X-rays
and in microwaves behave like normal flares in many respects. They can
have both thermal and nonthermal components appearing in bremsstrahlung
and gyrosynchrotron radiation.

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Title: Flare-Associated Decimeter TypeIV Bursts at High Frequencies
Authors: Kundu, M. R.; White, S. M.; Hori, K.; Schmahl, E. J.
2006AGUSMSH24A..06K Altcode:
Type IV radio bursts are broadband continuum events associated with
solar flares that typically occur after the impulsive phase, can last
for tens of minutes and are usually confined to low frequencies, below
200 MHz. However some flares show clear evidence for strong Type IV-like
emission that is confined to high frequencies, around 1 GHz. Type IV
events require nonthermal electrons and imply the presence of either
long-lived energetic electrons trapped in coronal loops, or else
ongoing acceleration lasting for tens of minutes following a flare. If,
as is widely believed, the emission mechanism of Type IV bursts is
plasma emission, then the high- frequency events require electrons at
densities of over 3 109 cm-3, far higher densities than are involved
in the low frequency Type IV bursts. We present a sample of such high
frequency Type IV bursts and analyze their properties and association
with other flare phenomena, and discuss their possible sources.

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Title: A Study of Accelerated Electrons in Solar Flares Using
Microwave and X-Ray Observations
Authors: Grechnev, Victor V.; Kundu, Mukul R.; Nindos, Alexander
2006PASJ...58...47G Altcode:
We consider manifestations of accelerated electrons in microwave and
hard X-ray emissions from solar flares. To meet our objectives, we
discuss two events -- those of 1999 March 16 and February 16. The first
event is a short-duration burst, while the second is a long-duration
event. An analysis of the first event leads to the conclusion that: 1)
a seemingly single-loop configuration can actually be a double-loop
one, and 2) it is possible that the pitch-angle distribution of
the radio-emitting electrons can be anisotropic with practically no
non-zero pitch angles. The second event shows seemingly intersecting
flaring loops, and the formation of a post-eruptive arcade that can
proceed as a series of double-loop interactions. From these and other
published results, we conclude that: 1) double-loop configurations
can be responsible for flares showing diverse morphologies and time
profiles; 2) the pitch-angle distribution of accelerated electrons can
be strongly anisotropic, with an excess of small angles, contributing
to a rather narrow energy range of the microwave-emitting electrons.

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Title: Microwave and Hard X ray Imaging of Energetic Electrons in
Solar Flares: Event of 2003 June 17
Authors: Kundu, M. R.; Schmahl, E. J.; White, S. M.
2006IAUS..233..334K Altcode:
We discuss a large flare that was observed simultaneously by
RHESSI in hard X-rays and by the Nobeyama Radio Heliograph (NoRH)
in microwaves. The imaging observations made both by RHESSI and NoRH
show many interesting features which may be relevant for producing
realistic flare models.

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Title: RHESSI &amp; Nobeyama Imaging Observations of the X 2.7 Flare
of 2003 Nov 3, 00:58 UT
Authors: Kundu, M. R.; Schmahl, E. J.; Garaimov, V. I.; White, S. M.
2005AGUSMSP52A..02K Altcode:
We describe the RHESSI HXR and Nobeyama (NoRH) microwave imaging
observations of an X-class event that was observed during the great
solar activity period of Oct 19--Nov 10, 2003. The flare in question of
class X 2.7 was observed in AR 0488 (position N08W66) on 2003 Nov 3,
00:58:33 UT, with a large peak at 01:15:25 UT, and ending at 03:08:19
UT. The maximum fluxes at 17 and 34 GHz are respectively 678 and 536
SFU. Besides the peak at 01:15 there are two other peaks at approx
01:20 and 01:32:30 UT. In NoRP data the peak at 01:20 is the most
dominant at frequencies 9.40, 3.75, 2.0 GHz. At 1.0 GHz the emission
prior to this peak is fluctuating and a peak with fluctuations exists
at around 01:05 UT. The third peak at 01:32:30 UT is spiky and it
is nonthermal with a turnover frequency between 17 and 34 GHz. One
significant property of the HXR emission (below 12 keV) during the
period 01:00 - 01:08 is that the preflare emission, in projection,
lies close to and above the W-limb, although the associated microwave
source is on the disk. There are two preflare sources (RHESSI at
12-25 keV, and NoRH at 17 and 34 Ghz), but it is not clear how they
are related. The RHESSI source seems to coincide in position with the
EIT flaring source at its apex. The morphological structure seems to
suggest that we are dealing with a loop-top HXR source situated at
the top of the EIT flaring loop and flaring sources at 17 and 34 GHz,
whose morphology suggests a complex flaring arcade structure.

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Title: RHESSI and radio imaging observations of microflares
Authors: Kundu, M. R.; Trottet, G.; Garaimov, V. I.; Grigis, P. C.;
Schmahl, E. J.
2005AdSpR..35.1778K Altcode:
We present an analysis of five microflares, three observed
simultaneously by RHESSI in hard X-rays and Nobeyama RadioHeliograph
(NoRH) in microwaves (17 GHz) and two observed by RHESSI and Nancay
RadioHeliograph (NRH) at metric wavelengths (150-450 MHz). Since we
have no radio imaging telescopes simultaneously operating at microwave
and meter wavelengths in the same time zone, we are obliged to use a
different set of metric events in contrast to that used for comparison
with the two radio wavelengths. We are interested in using the locations
and other imaging characteristics of the events from both RHESSI and
radio observations instead of just temporal correlation. So we have
used the Nancay (France) metric radioheliograph at 150-450 MHz for
this purpose. Here we describe the properties of five events - three
in microwaves and two at metric wavelengths. We discuss the brightness
temperatures, emission measures and the hard X-ray spectral properties
of these microevents. One sees small (mini) flaring loops clearly in
NoRH and RHESSI images. The microwave emission often seems to come from
the RHESSI foot points (for higher energies), and from the entire small
(mini) flaring loop (for lower energies).The RHESSI microflares seem
to be associated in position with metric type III bursts. Frequently,
the hard X-ray spectrum of the microwave associated RHESSI microflares
can be fit by a thermal component at low energies (∼3-12 keV) and
a nonthermal component at higher energies (∼12-20 keV).

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Title: Multi-wavelength study of a coronal mass ejection: a flare
event from AR#9393
Authors: Manoharan, P. K.; Kundu, M. R.
2005AdSpR..35...70M Altcode:
The active region, AR#9393, produced a number of intense flares
during March-April 2001. In this paper, we report the analysis of an
X1.1 flare event of April 2, 2001 and its associated coronal mass
ejection. The timing and location of the Hα eruption,
radio burst activities, and the onset of mass ejection suggest an
energy release that occurred close to the surface of the sun. At
this region, as shown by the magnetogram, X-ray and EUV images, the
field configuration was complex and the 3-D extrapolation revealed the
presence of a magnetic null point. Results also suggest that the energy
release is followed by the magnetic reconnection between the low-lying
loops near the separator point and outlying loops. This study provides
the support for the magnetic break-out process to trigger the energy
release in eruptive flare event.

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Title: The configuration of simple short-duration solar microwave
bursts
Authors: Kundu, M. R.; Nindos, A.; Grechnev, V. V.
2004A&A...420..351K Altcode:
Using data from the Nobeyama Radioheliograph (NoRH) we study the
source configuration of four simple short-duration 17 and 34 GHz
bursts which have also been observed partially by the Yohkoh Soft X-ray
Telescope (SXT). Two events are consistent with a single flaring loop
configuration. In one of them the flaring loop is resolved in the SXT
images. We derive a self-consistent model for this event by comparing
the radio observations with gyrosynchrotron model loop calculations. Our
best-fit model is able to reproduce both the observed flaring loop
shape as well as the fluxes and structures of the radio emission at
the peak of the event. The flaring loop is relatively small having a
footpoint separation of 16 arcsec and maximum height of 7.7 arcsec. The
variation of the magnetic field along the loop is small (800 G at
the footpoints and 665 G at loop top) and the loop is filled with
electrons with energies up to 10 MeV. The other two bursts show two
radio sources; one source being cospatial with a compact bright soft
X-ray loop associated with a patch of parasitic magnetic polarity whose
photospheric magnetic flux increases before the flares while the other
source is not prominent at any other wavelength range. The two sources
are connected with diffuse loop-like soft X-ray emission. We infer that
these bursts originate from the interaction of two sets of loops with
different sizes. Therefore the simple short duration microwave bursts
we studied do not always appear in the same configuration. Contrary
to previous results not all of them appear as single-loop events. It
is possible that some events are caused by two interacting loops.

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Title: RHESSI and Microwave Imaging Observations of Two Solar Flares
Authors: Kundu, M. R.; Schmahl, E. J.; Garaimov, V. I.
2004AAS...204.5402K Altcode: 2004BAAS...36R.757K
We present hard X-ray (RHESSI) and microwave (NoRH) imaging observations
of two solar flares of M-class observed on March 14 and March 12
of 2002, one located near the disk center and the other near the
E-limb. For the March 14 event (near disk center), both hard X-ray and
microwave observations indicate that the flaring region consisted of a
complex of multiple loops. In microwaves its spatial configuration has
a double-loop structure; at the main flare site (primary flaring loop)
we observe microwave, HXR, EUV emissions and at a remote site (connected
to main site by a long loop) we observe microwaves only due to a strong
magnetic field. Some HXR foot point sources (in 25-100 KeV bands) have
co-located microwave footpoint sources. The hard X-ray spectrum can be
fitted with a thick target model with a thermal component and a broken
power-law component. The March 12 E-limb event was fully observed by
Nobeyama Radio Heliograph (NoRH), but in hard X-rays it was observed
only from around the peak until the end of flare, because of RHESSI
night time. In hard X-rays (6-50 KeV) it was clearly a coronal source
located above an EIT loop, and it seems to have significant motion in
the post flare period. In microwaves it was also a coronal source in
both 17 and 34 GHz. Due to the relatively poor resolution of NoRH, the
overall source size in radio is large, encompassing the RHESSI source
at the start and end of its motion. The spatial maximum of the 17 GHz
source appears at a coronal height below the HXR source. The microwave
source also shows motion, along with the expansion of the EIT flaring
loop. The hard-ray spectral properties of the flare will be discussed.

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Title: Radio Observations of Rapid Acceleration in a Slow Filament
Eruption/Fast Coronal Mass Ejection Event
Authors: Kundu, M. R.; White, S. M.; Garaimov, V. I.; Manoharan,
P. K.; Subramanian, P.; Ananthakrishnan, S.; Janardhan, P.
2004ApJ...607..530K Altcode:
We discuss a filament eruption/coronal mass ejection (CME) event
associated with a flare of GOES class M2.8 that occurred on 2001
November 17. This event was observed by the Nobeyama Radio Heliograph
(NoRH) at 17 and 34 GHz. NoRH observed the filament during its eruption
both as a dark feature against the solar disk and a bright feature
above the solar limb. The high cadence of the radio data allows us to
follow the motion of the filament at high time resolution to a height
of more than half a solar radius. The filament eruption shows a very
gradual onset and then a rapid acceleration phase coincident with
the launch of a fast halo CME. Soft X-ray and extreme-ultraviolet
(EUV) images show heating in a long loop underneath the filament
prior to the flare. The NoRH height-time plot of the filament shows
a roughly constant gradual acceleration for 1 hr, followed by a
very abrupt acceleration coincident with the impulsive phase of
the associated flare, and then a phase of constant velocity or much
slower acceleration. This pattern is identical to that recently found
to occur in the motion of flare-associated CMEs, which also show a
sharp acceleration phase closely tied to the impulsive phase of the
flare. When the rapid acceleration occurs in this event, the flare
site and the filament are separated by ~0.5 Rsolar, making
it unlikely that a disturbance propagates from one location to the
other. Models in which a disruption of the large-scale coronal magnetic
field simultaneously permits the acceleration of the filament and the
flare energy release seem to be a better explanation for this event.

---------------------------------------------------------
Title: Nobeyama Radioheliograph and RHESSI Observations of the X1.5
Flare of 2002 April 21
Authors: Kundu, M. R.; Garaimov, V. I.; White, S. M.; Krucker, S.
2004ApJ...600.1052K Altcode:
We present an overview of the radio observations of the X1.5 flare of
2002 April 21 and complementary data from other wavelengths. This flare
was fairly well observed by the Ramaty High Energy Spectroscopic Imager
(RHESSI) spacecraft and fully observed by the Nobeyama Radioheliograph
(NoRH) at 17 and 34 GHz. This long-duration event lasted more than 2
hr and featured a beautiful arcade of rising loops on the limb visible
at X-ray, EUV, and radio wavelengths. The main flare was preceded by
a small event 90 minutes earlier showing a long EUV loop connecting
well-separated radio and hard X-ray sources. The main flare itself
starts with a compact radio and hard X-ray source at the eastern end of
the region that develops into emission close to the solar surface (and
well inside the solar limb) over a large region to the northwest. As
the flare proceeds, a large set of loops is seen to rise well above the
solar limb. Distinct regions of radio emission with very different time
behavior can be identified in the radio images, and, in particular,
a peculiar nonthermal source seen in radio and hard X-rays low in the
corona at the base of the arcade is seen to turn on 30 minutes after
the start of the impulsive phase. At about the same time, an extremely
intense burst of coherent radio emission is seen from 500 to 2000 MHz;
we speculate that this lower-frequency burst is produced by electrons
that are accelerated in the nonthermal source at the base of the arcade
and injected into the loop system where they radiate plasma emission
in the 1010 cm-3 density plasma at the top of
the arcade of loops. This event is striking as a demonstration of
the many ways in which a flare can produce radio emission, and the
combined data at different wavelengths reveal a diversity of energy
release and nonthermal acceleration sites.

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Title: Long Term Variation of Solar Corona from SOHO/EIT Observations
Authors: Zhang, Jie; Kundu, Mukul R.
2004IAUS..223..157Z Altcode: 2005IAUS..223..157Z
We present the long term variation of solar corona based on SOHO/EIT
observations from 1996 to 2004. EIT provides diagnostics of bulk corona
in three channels with overlapping temperature range from 0.5 MK to 2.7
MK and with high spatial resolution. We find that the coronal emission
measure increases by a factor of 4 from 2.0times10^{27} cm^{-5} at the
solar minimum to 8.0times10^{27} cm^{-5} at the solar maximum. In the
meantime, the overall temperature of the corona increases from 1.3 MK
to 1.7 MK

---------------------------------------------------------
Title: RHESSI and Microwave Imaging Observations of Two Solar Flares
Authors: Kundu, M. R.; Schmahl, E. J.; Garaimov, V. I.
2004IAUS..223..425K Altcode: 2005IAUS..223..425K
We describe two flares of GOES class M5.7 and 1.5 which were observed
simultaneously by RHESSI (Ramaty High Energy Solar Spectroscopic
Imager) and NoRH (Nobeyama Radio Heliograph). Both flares exhibit
slow motions suggestive of changing magnetic shear, loop expansion,
or gradual reconnection. One flare is clearly a coronal hard X-ray
and microwave flare.

---------------------------------------------------------
Title: Microwave and hard x-ray imaging observations of a complex
M flare
Authors: Schmahl, E.; Kundu, M.; Garaimov, V.
2004cosp...35..872S Altcode: 2004cosp.meet..872S
We describe a flare of GOES class M5.7 which was observed simultaneously
by RHESSI and NoRH (Nobeyama Radio Heliograph). The flare occurred
in active region AR 9866 located near disk center. Both hard X-ray
and microwave observations indicate that the flaring region consisted
of a complex of multiple loops. In the microwave domain it clearly is
of a class characterized by a double loop configuration: a small loop
created by the emergence of a new flux interacting with an old flux,
which is the main flare site meaning that this is the site where we
observe microwave, HXR, EUV emissions, and a remote flare site which
is observed only in radio. In HXR there are clearly three loops,
two of which have distinct foot points with co-located microwave s
source in one foot point; the third loop is large and filled with
energetic electrons primarily emitting lower energy (12-25 keV)
HXR. The successive energization of the loops gives the illusion of
re-orientation with time of RHESSI flaring loops. There is a second peak
in flaring emission in both microwaves and HXR, which also shows up as
a short duration weak continuum in dynamic spectra (in the frequency
range 30-500 MHz, 01:50-01:57 UT). We have carried out spectroscopic
analysis of the flare event using RHESSI data. We find that the data
can be fitted with a thick- target model with a thermal component and a
broken power-law component with a spectral break at an electron energy
of 40 keV. The total emission measure rises from the start of the flare
to a maximum of ∼ 1.5 × 1049 cm-3. The electron
energy distribution below 40 keV is initially harder (δ ∼ 4) than the
distribution above the break, but it softens in the middle of the flare,
and then hardens in the last few minutes of the flare. The upper slope
remains more constant, hardening slightly from δ ∼ 6 at the beginning
to 5 near the end. This trend is paralleled by the gradual filling in
of a loop between footpoints in the 24-30 keV band, followed by the
fading of the loop source between the footpoints. In keeping with this,
the 37-55 keV images show a near-constant morphology. Viewed overall,
the successive loops inferred from microwaves and HXR appear to show
a decrease of magnetic shear as the flare.

---------------------------------------------------------
Title: Radio imaging observations of hard x-ray microflares observed
by RHESSI
Authors: Kundu, M.; Trottet, G.; Garaimov, V.; Grigis, P.
2004cosp...35..877K Altcode: 2004cosp.meet..877K
We describe the properties of two sets of microflares observed
simultaneously by RHESSI (Ramaty High Energy Solar Spectroscopic
Imager) in hard X-rays and by two radio imaging instruments--NoRH
(Nobeyama Radio Heliograph) in microwaves (17 GHz) and NRH (Nancay Radio
Heliograph) at metric wavelengths. The two sets of events occurred in
two different time zones, and as a result we do not have simultaneous
imaging data in microwaves and metric wavlengths for the same RHESSI
events. We'll discuss four events--two observed by NoRH in microwaves
and two observed by NRH in meter waves, along with RHESSI events. The
microwave (17 GHz) events occurred in AR 9934 at 03:58 UT May 3,
2002 and at 05:08 UT May 4, 2002. We have detected microwave (17 &amp;
34 GHz) emissions in association with RHESSI microflares in the energy
range 3-50 keV. The microwave emission comes from footpoints for higher
energies, and from the entire mini or small flaring loop for lower
energies. The relative positions of microwaves and hard X-rays are as
they should be in normal flares. Sometimes the two sources coincide,
at other times the two sources are at opposite ends of the flaring
loop. One sees the mini flaring loops clearly in NoRH images. RHESSI
maps at the time of maximum X-ray emission during the event of May 3,
2002 clearly show an X-ray loop in the range 3-6 keV and two footpoints
of the loop in the 6-12 and 12-25 keV ranges. These footpoints are
located above opposite magnetic polarities as seen in overlays of
hard X-ray images on the MDI images. The MDI magnetograms taken
before the microflares show rapid evolution of the magnetic field,
including sometimes the emergence of a new region. The hard X-ray
spectrum of microwave associated RHESSI microflares can be fit by
a thermal component (EM ∼ 3× 1046 cm-3) at
low energies (3-6 keV) and a nonthermal component (with slope -3.2)
at higher energies. The two metric events imaged by NRH occurred
on August 5 and September 3, 2003, one located on the disk and the
other at the limb. The RHESSI microflare sources are compact. They
are accompanied by a series of metric type III bursts at 150-410 MHz
originating from sources located above the RHESSI HXR source. Their
source positions show frequency dispersion as expected from plasma
radiation sources. The properties of these microflare sources in hard
X-rays, microwave and meter wavelengths will be discussed.

---------------------------------------------------------
Title: Radio Observations of Rapid Acceleration in a Slow Filament
Eruption/Fast CME Event
Authors: Kundu, M. R.; White, S. M.; Garaimov, V. I.; Manoharan,
P. K.; Subramanian, P.; Ananthakrishnan, S.; Janardhan, P.
2003AGUFMSH21A..06K Altcode:
We discuss a filament eruption/coronal mass ejection (CME) associated
flare event of GOES class M2.8 that occurred on November 17, 2001. This
event was observed simultaneously by Nobeyama RadioHeliograph (NoRH)
at 17 and 34 GHz and by the Giant Meterwave Radio Telescope (GMRT)
in India at 1060 MHz. The flare occurred in active region 9704 at
S18E41. NoRH observes the filament during its eruption both as a dark
feature against the solar disk and a bright feature above the solar
limb. The filament eruption shows a very gradual onset and then a rapid
acceleration phase coincident with the launch of a fast halo CME. The
flare on the disk in microwaves has a gradual rise, a broad maximum
and a gradual decay. At 1060 MHz, its time profile had three impulsive
peaks. The NoRH height--time plot of the filament shows a roughly
constant gradual acceleration for an hour, followed by a very abrupt
acceleration coincident with the impulsive phase of the associated
flare. Soft X-ray images show heating in a long loop underneath the
filament prior to the flare. The impulsive behavior of 1060 MHz emission
combined with high brightness temperatures indicated the existence of
nonthermal electrons in loops that clearly are not the same as the
loops containing the microwave-emitting electrons. The latter are
dominated by thermal bremsstrahlung and agree well with the EUV and
soft X-ray loops. This study is consistent with recent findings that
the rapid acceleration of flare--associated CMEs is closely tied to the
impulsive phase of the flare. A trigger is required to cause the rapid
acceleration to occur at the same time as the flare even though the
two events are spatially well separated. We speculate that this trigger
is provided by some kind of reconnection in the multiple flux systems
that exist between the flaring active region and the erupting filament.

---------------------------------------------------------
Title: Giant Meterwave Radio Telescope observations of an M2.8 flare:
Insights into the initiation of a flare-coronal mass ejection event
Authors: Subramanian, Prasad; Ananthakrishnan, S.; Janardhan, P.;
Kundu, M. R.; White, S. M.; Garaimov, V. I.
2003SoPh..218..247S Altcode: 2003astro.ph..9661S
We present the first observations of a solar flare with the GMRT. An
M2.8 flare observed at 1060 MHz with the GMRT on 17 November 2001 was
associated with a prominence eruption observed at 17 GHz by the Nobeyama
radioheliograph and the initiation of a fast partial halo CME observed
with the LASCO C2 coronagraph. Towards the start of the eruption,
we find evidence for reconnection above the prominence. Subsequently,
we find evidence for rapid growth of a vertical current sheet below
the erupting arcade, which is accompanied by the flare and prominence
eruption.

---------------------------------------------------------
Title: Radio and Hard X-Ray Images of High-Energy Electrons in an
X-Class Solar Flare
Authors: White, S. M.; Krucker, S.; Shibasaki, K.; Yokoyama, T.;
Shimojo, M.; Kundu, M. R.
2003ApJ...595L.111W Altcode:
We present the first comparison between radio images of high-energy
electrons accelerated by a solar flare and images of hard X-rays
produced by the same electrons at photon energies above 100 keV. The
images indicate that the high-energy X-rays originate at the footpoints
of the loops dominating the radio emission. The radio and hard X-ray
light curves match each other well and are quantitatively consistent
with an origin in a single population of nonthermal electrons with
a power-law index of around 4.5-5. The high-frequency radio spectral
index suggests a flatter energy spectrum, but this is ruled out by the
X-ray spectrum up to 8 MeV. The preflare radio images show a large
hot long-lived loop not visible at other wavelengths. Flare radio
brightness temperatures exceed 109 K, and the peak in the
radio spectrum is as high as 35 GHz: both these two features and the
hard X-ray data require very high densities of nonthermal electrons,
possibly as high as 1010 cm-3 above 20 keV at
the peak of the flare.

---------------------------------------------------------
Title: Coronal Structure of a Flaring Region and Associated Coronal
Mass Ejection
Authors: Manoharan, P. K.; Kundu, M. R.
2003ApJ...592..597M Altcode:
We report the multiwavelength investigations of an eruptive flare
event that occurred on 2001 April 2 at about 11 UT. The manifestations
associated with this flare event have been studied from the near-Sun
region to about 0.5 AU. The Hα images from the Meudon Spectroheliograph
reveal a fast spectacular eruption of plasmoids from the flare site
to the west and a Moreton wave disturbance propagating toward the
south. A bright, fast, wide coronal mass ejection (CME) associated with
this eruptive event was imaged by SOHO/LASCO and the remote-sensing
interplanetary scintillation technique. The radio measurements from the
Nançay Radioheliograph and Tremsdorf Radio Telescope have been useful
in identifying the radio signatures of the CME's initiation. The metric
type II radio bursts produced at the time of CME onset also propagate
toward the west, and their positions coincide with the magnetic null
point, which was located at the southwest part of NOAA active region
9393. The timings and positions of the radio bursts, the Hα eruption,
and the CME onset as well as the magnetic field configuration suggest
a release of energy at the null point, and as indicated by the Moreton
wave, the eruption starts close to the chromospheric or low coronal
level. The results support the “breakout” scenario proposed by
S. Antiochos and coworkers, and they are also suggestive that the
energy release is followed by magnetic reconnection between the
low-lying loops near the separatrix and the loop system above them.

---------------------------------------------------------
Title: RHESSI and Microwave Imaging Observations of Two Microflares
Authors: Garaimov, V. I.; Kundu, M. R.; Grigis, P. C.
2003SPD....34.1603G Altcode: 2003BAAS...35..833G
We describe two microflares which occurred in the AR 9934 at 03:58
UT May 3, 2002 and at 05:08 UT May 4, 2002. AR 9934 was a complex
region which contained a sunspot with a strong negative polarity of
the magnetic field on the north side and a bipolar region on the south
side. Analysis of the MDI images shows fast evolution of the south
part of the region. TRACE images show many small loops in the south
part of AR and the complex loop which connected the north sunspot to
the south side of the region. We have observations of both of these
events by Nobeyama Radio Heliograph and RHESSI. The NoRH 17 GHz maps
show loop like structure of the radio source which has a maximum above
the sunspot land it connects to the south side of AR. RHESSI maps
superimposed on the NoRH maps show that X-ray emission in the range
3-25 keV are located inside the radio contours. During both events hard
X-ray emission was located in the south part of the AR. RHESSI maps
corresponding to the maximum X-ray emission during the event of May 3,
2002 clearly show an X-ray loop in the range 3-6 keV and two footpoints
of the loop in the 6-12 and 12-25 keV ranges. These footpoints are
located above opposite magnetic polarities as seen in overlays of
hard X-ray images on the MDI image. Also hard X-ray emission seems
to be brighter from the northern footpoint than from the other. The
hard X-ray images of the event of May 4, 2002 shows a small X-ray loop
(smaller than size of the loop in the previous event), located close
to the same position relative to the active region. We calculated the
hard X-ray spectrum, temperature and emission measure for both events.

---------------------------------------------------------
Title: Quasi-periodic Pulsations in a Solar Microwave Burst
Authors: Grechnev, V. V.; White, S. M.; Kundu, M. R.
2003ApJ...588.1163G Altcode:
Quasi-periodic pulsations in solar flares can provide important
information on physical conditions in flaring regions. In this paper, we
study a microwave burst that showed deep quasi-periodic pulsations. The
most dramatic feature of this event has been discussed by Asai and
coworkers. In the second of four bursts during the flare, strongly
modulated pulsations appear in radio images from the eastern end of a
long loop and in hard X-rays from the western end of the loop. We show,
in addition, that (1) at least five distinct radio sources with very
different time profiles can be identified, including emission from
the long loop connecting the modulated radio and X-ray sources; (2)
substructure is also present in the radio emission from the eastern
end of the long loop during the first burst of the flare, but with
timescales shorter than in the second burst; (3) radio modulations
are seen at the western end of the loop during the second burst but
at a level some 20 times weaker than at the eastern end; (4) these
radio modulations at the western end of the loop, like the hard X-ray
modulations at the same location, appear to lead the modulations at the
eastern end by about 0.5 s, but all have the same period. The period of
the modulation can be explained by MHD oscillations of the loop ~120"
long connecting the sources: both oscillations that change the magnetic
field strength in the loop, such as propagating fast-mode waves, and
torsional oscillations that change the direction of the magnetic field
in the loop can explain the observed properties of the modulation of
the radio emission. An impulsive reconnection episode is a plausible
source of oscillating fast-mode waves and is consistent with some other
aspects of the event. However, it is difficult to reconcile the strength
of the radio modulations at the eastern end of the loop with their delay
relative to the emissions at the western end, where the modulation is
observed to be much weaker. If the electrons originate at the western
end where the main energy release seems to occur, and the modulation is
imposed on them there before they propagate 1010 cm to the
other end of the loop, any effects due to a spread in electron energies
or pitch angles would lead to a spread in propagation times that should
smooth out the modulation of the radio emission from the remote source,
as should any trapping of electrons in the loop: yet the radio emission
from the eastern end of the loop shows much stronger modulation than
the radio and hard X-ray emission from the western end of the loop.

---------------------------------------------------------
Title: Nobeyama Radio Heliograph and RHESSI Observations of the X1.5
Flare of April 21, 2002
Authors: Kundu, M. R.; Garaimov, V. I.; White, S. M.; Krucker, S.
2003SPD....34.1812K Altcode: 2003BAAS...35..841K
We present radio observations of the X1.5 flare of April 21, 2002, and
complementary data from other wavelengths. This flare was fairly well
observed by the spacecraft RHESSI and fully observed by the Nobeyama
Radio Heliograph at 17 and 34 GHz. This long-duration event lasted
more than 2 hours and features a beautful arcade of rising loops on
the limb visible at X-ray, EUV and radio wavelengths. The main flare
was preceded by a small event 90 minutes earlier showing a long EUV
loop connecting well-separated radio and hard X-ray sources. The main
flare itself starts with a compact radio and hard X-ray source at the
eastern end of the region that is followed by emission close to the
solar surface (well inside the solar limb) over a large region to the
northwest. As the flare proceeds a large set of loops is seen to rise
well above the solar limb. Distinct regions of radio emission with very
different time behaviour can be identified in the radio images, and in
particular a peculiar nonthermal 17 GHz source low in the corona at the
base of the arcade is seen to turn on 30 minutes after the start of the
impulsive phase. At about the same time an extremely intense burst of
coherent radio emission is seen from 500 to 2000 MHz: we speculate that
this lower-frequency burst is located at the top of the arcade of loops.

---------------------------------------------------------
Title: Distinctive spatial configuration of a class of microwave
flaring sources
Authors: Kundu, M. R.; Garaimov, V. I.
2003AdSpR..32.2497K Altcode:
We discuss a class of microwave flares whose source regions exhibit a
distinctive spatial configuration; the primaryenergy release in these
flares results from the interaction between emerging magnetic flux and
an existing overlying region. Such events typically exhibit radio, X-ray
and EUV emission at the main flare site (the site of interaction) and
in addition radio emission at a remote site up to 1 × 10 5
km away in another active region. We have identified and studied more
than a dozen microwave flares in this class, in order to arrive at
some general conclusions on reconnection and energy release in such
solar flares. Typically, these flares show a gradual rise showing
many subsidiary peaks in both radio and hard X-ray light curves with
a quasi-oscillatory nature with periods of 5-6 seconds, a bright
compact X-ray &amp; EUV emitting loop in the main flare source, a
delay of the radio emission from the remote source relative to the
main X-ray-emitting source. The magnetic field in the main flare site
changes sharply at the time of the flare, and the remote site appears
to be magnetically connected to the main flare site.

---------------------------------------------------------
Title: Radio observations of explosive energy releases on the Sun
Authors: Kundu, M. R.; White, S. M.
2003dysu.book..288K Altcode:
This chapter is devoted to a discussion of the radio observations
of explosive energy releases (normal flares and small-scale energy
releases) on the Sun. Radio imaging observations of solar flares and
coronal transients and the relationship of radio phenomena with those
observed in hard and soft X-rays, and underlying physics are discussed.

---------------------------------------------------------
Title: Distinctive spatial configuration of a class of microwave
flaring sources
Authors: Kundu, M. R.; Garaimov, V. I.
2002ESASP.506..319K Altcode: 2002ESPM...10..319K; 2002svco.conf..319K
We discuss a particular spatial configuration of a class of microwave
flaring regions in which the primary energy release results from the
interaction between emerging magnetic flux and an existing overlying
region. Such events typically exhibit radio and X-ray emission at the
main flare site (the site of interaction) and in addition radio emission
at a remote site up to 1×105 km away in another active
region. We have identified and studied more than a dozen microwave
flares in this class, in order to arrive at some general conclusions
on reconnection and energy release in such solar flares.

---------------------------------------------------------
Title: The Physical Properties of a Flaring Loop
Authors: White, S. M.; Kundu, M. R.; Garaimov, V. I.; Yokoyama, T.;
Sato, J.
2002ApJ...576..505W Altcode:
We use high-resolution radio observations to study the physical
parameters of a flaring loop. The loop is visible at radio wavelengths
because of gyrosynchrotron emission by nonthermal electrons (energies
typically above several hundred keV) accelerated by the flare. We are
able to measure the loop thickness and length with a precision on the
order of 1". We find that the loop length increases from about 60"
initially to about 80" in the decay phase of the event. The loop
(averaged along its length) initially is no more than 3" wide. The
soft and hard X-ray data obtained with the Soft X-Ray Telescope and
Hard X-Ray Telescope on the Yohkoh satellite are consistent with the
same loop as observed at radio wavelengths (although the soft X-ray
morphology has some small differences early in the event). This event
was accompanied by a coronal mass ejection and a coronal dimming
visible in Solar and Heliospheric Observatory Extreme-Ultraviolet
Imaging Telescope images, so it involved a very large volume of the
corona, yet the radio observations clearly indicate that much of the
energy release in the low corona was restricted to a region apparently
no more than 2000 km across. As the event proceeds, the loop develops a
bright feature at the loop top in both the radio and soft X-ray images
that cannot be reproduced in gyrosynchrotron loop models in which the
electron distribution has relaxed by pitch angle scattering to fill
the loop. This prevents us from using the flare properties to measure
the magnetic field strength and variation along the loop. The bright
loop-top source may require that trapping of electrons take place at
the loop top late in the event.

---------------------------------------------------------
Title: Multiple-loop structure of a solar flare from Microwave,
EUV and X-ray Imaging Data
Authors: Garaimov, V. I.; Kundu, M. R.
2002SoPh..207..355G Altcode:
We present the results of an analysis of a flare event of importance
M2.8 that occurred at 00:56 UT 28 August 1999. The analysis is based
upon observations made with the Nobeyama radioheliograph (NoRH) and
polarimeters (NoRP), TRACE, SOHO/MDI, EIT, and Yohkoh/SXT. The images
show a very complex flaring region. Pre-flare TRACE and EIT images
at 00:24 UT show a small brightening in the region before the flare
occurred. The active region in which the flare occurred had evolving
magnetic fields, and new magnetic flux seems to have emerged. The
X-ray and radio time profiles for this event show a double-peaked
structure. The polarimeter data showed that the maximum radio emission
(1200 s.f.u.) occurred at 9.4 GHz. At 17 GHz the NoRH images appear to
show four different radio sources including the main spot and the main
flare loop. Most of the microwave emission seems to originate from the
main flare loop. Comparison of BATSE and microwave time profiles at 17
and 34 GHz from the main sunspot source shows that these profiles have
similar structures and they coincide with the hard X-ray peaks. The
maximum of the flare loop emission was delayed by 10 s relative to the
second maximum of the sunspot associated flare emission. Analysis of SXT
images during the post-flare phase shows a complex morphology - several
intersecting loops and changes in the shape of the main flare loop.

---------------------------------------------------------
Title: Multiwavelength Study of a Coronal Mass Ejection: Eruption
from AR#9393
Authors: Manoharan, P. K.; Kundu, M. R.
2002AAS...200.3610M Altcode: 2002BAAS...34..694M
We report the investigation of one of the coronal mass ejections
unleashed by the largest active region, AR9393, of the current
solar cycle. This mass ejection was associated with an X1.1 flare
that occurred on April 2, 2001 at about 11 UT and also showed small
effect in terms of energetic particle. The analysis of H-alpha images
obtained from the Meudon spectroheliograph shows a fast eruption
towards the north-west direction and wave-like propagation from the
eruption site. The acceleration of the ejecta results in a speed of
about 150-200 km/s close to the disk. The associated radio emission
observed with the Nancay Radioheliograph in the frequency range
160-327 MHz shows radio emitting regions moving towards north with
time and with increasing wavelength. The mass ejection observed with
the coronagraphs on board LASCO/ SOHO is consistent with the eruption
seen in the H-alpha. We discuss the formation and morphology of the
ejection and its interplanetary consequences.

---------------------------------------------------------
Title: Distinctive Spatial Configuration of a Class of Microwave
Flaring Sources
Authors: Kundu, M.; Garaimov, V. I.
2002AAS...200.6806K Altcode: 2002BAAS...34..756K
We discuss a particular spatial configuration of a special class of
microwave flaring regions (first identified by Hanaoka) in which the
primary energy release results from the interaction between emerging
magnetic flux and an existing overlying region. Such events typically
exhibit radio and X-ray emission at the main flare site (the site of
interaction) and in addition radio emission at a remote site up to 2 x
105 km away in another active region. We have identified and studied
more than a dozen microwave flares in this class, in order to arrive
at some general conclusions on reconnection and energy release in
such solar flares. Typically, these flares show a gradual rise showing
many subsidiary peaks in both radio and hard X-ray light curves with
a quasi-oscillatory nature with periods of 5-6 seconds, the presence
of a bright compact X-ray-emitting loop in the main flare source,
a delay of the radio emission from the remote source relative to the
main X-ray-emitting source, higher circular polarization in the radio
emission of the remote source than in the main source, and stronger
photospheric magnetic field in the remote source. We show that the
magnetic field in the main flare site changes sharply at the time of
the flare, and that the remote site is magnetically connected to the
main flare site sometimes only up to the time of the main impulsive
phase, at which point the magnetic connection to the remote site may
be broken and further flare manifestations are largely confined to the
main flare site. This severing of the magnetic connection between two
well-separated active regions may be an intrinsic part of the energy
release in this flare.

---------------------------------------------------------
Title: Multiple-loop structure of a solar flare from Microwave,
EUV and X-ray Imaging Data.
Authors: Garaimov, V.; Kundu, M.
2002AAS...200.6805G Altcode: 2002BAAS...34..755G
We present the results of the analysis of a flare event of importance
M2.8 that occurred at 00:56 UT Aug 28, 1999. The analysis is based
upon observations made with the Nobeyama Radio Heliograph(NoRH) and
Polarimeters(NoRP), TRACE, SOHO/MDI, EIT and Yohkoh/SXT. The images
show a very complex flaring region. Pre-flare TRACE and EIT images
at 00:24 UT show a small brightening in the region before the flare
occurred. The active region in which the flare occurred had evolving
magnetic fields, and new magnetic flux seems to have emerged.The
X-ray and radio time profiles for this event show a double peaked
structure. The polarimeter data showed that the maximum radio emission
(1200 sfu) occurred at 9.4 GHz. At 17 GHz the NoRH images appear to
show four different radio sources including the main spot and the main
flare loop. Most of the microwave emission seems to originate from the
main flare loop. Comparison of BATSE and microwave time profiles at
17 and 34 GHz from the main sunspot source shows that these profiles
have similar structures and they coincide with the hard X-ray peaks. The
maximum of the flare loop emission was delayed by 10 sec relative to the
second maximum of the sunspot associated flare emission. Analysis of SXT
images during the post-flare phase shows a complex morphology - several
intersecting loops and changes in the shape of the main flare loop.

---------------------------------------------------------
Title: Multiwavelength study of a coronal mass ejection: Eruption
from AR#9393
Authors: Manoharan, P.; Kundu, M.
2002cosp...34E1014M Altcode: 2002cosp.meetE1014M
We report the investigation of one of the coronal mass ejections
unleashed by the largest active region, AR9393, of the current solar
cycle. This mass ejection was associated with an X1.1 flare that
occurred on April 2, 2001 at about 11 UT and also with energetic
particle flux. The analysis of H-alpha images obtained from the Meudon
spectroheliograph shows a fast eruption towards the north-west direction
and wavelike propagation from the eruption site. The acceleration of the
ejecta results in a speed of about 150-200 km/s close to the disk. The
associated radio emission observed with the Nancay Radioheliograph
in the frequency range 160-327 MHz shows radio emitting regions
moving towards north with time and with increasing wavelength. The
mass ejection observed with the coronagraphs on board LASCO/ SOHO
is consistent with the eruption seen in the H-alpha. We discuss
the formation and morphology of the ejection and its interplanetary
consequences.

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Title: Radio observations of high energy solar flares
Authors: Kundu, Mukul R.
2002HiA....12..379K Altcode:
In this paper we discuss some recent observations of radio emission
produced by high energy electrons resulting from solar flares. We
discuss the spatial structure of simple weak spiky burst emissions
observed simultaneously, at 17 and 34 GHz with the Nobeyama Radio
Heliograph (NoRH). Using simultaneous imaging observations obtained
by Yohkoh/HXT and SXT along with NoRH 17&amp;34 GHz observations,
we attempt to model a relatively stronger and longer flare using
gyrosynchrotron mechanism for the flaring radio emission.

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Title: Multiple-Loop Structure of a Solar Flare from Microwave,
EUV and X-Ray Imaging Data
Authors: Garaimov, V. I.; Kundu, M. R.
2002mwoc.conf..233G Altcode:
We present the results of analysis of a flare event of importance
M2.8 that occurred at 00:56 UT Aug 28, 1999. The analysis is based
upon observations made with the Nobeyama Radio Heliograph(NoRH) and
Polarimeters(NoRP), TRACE, SOHO/MDI,EIT and Yohkoh/SXT. MDI, TRACE,
EIT, Soft X-ray and radio images show a very complex structure of the
flaring region. Pre-flare TRACE and EIT images at 00:24UT show a small
brightening in the region before the flare occurred. The active region
in which the flare occurred had changing magnetic fields, and a new
magnetic flux seems to have emerged. The X-Ray and radio time profiles
for this event show a double peaked structure. The polarimeter data
showed that the maximum radio emission (1200sfu) occurred at 9.4 GHz. At
17GHz there appears to be four different radio sources including the
main spot and the main flare loop. Most of the microwave emission seems
to originate from the main flare loop. Comparison of BATSE and microwave
time profiles at 17 and 34GHz from the main sunspot source shows that
these profiles have similar structures and they coincide with the Hard
X-ray peaks. The maximum of the flare loop emission was delayed by 10
sec relative to the second maximum of the sunspot associated flare
emission. Analysis of SXT images during the post-flare phase shows
a complex morphology - several intersecting loops and changes in the
shape of the main flare loop. Implications of the complex morphology
of both radio and X-ray flaring sources will be discussed.

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Title: Distinctive Spatial Configuration of a Class of Microwave
Flaring Sources
Authors: Kundu, M.; Garaimov, V.
2002cosp...34E.632K Altcode: 2002cosp.meetE.632K
We discuss a particular spatial configuration of a class of microwave
flaring regions in which the primary energy release results from the
interaction between emerging magnetic flux and an existing overlying
region. Such events typically exhibit radio and X-ray emission at the
main flare site (the site of interaction) and in addition radio emission
at a remote site up to 2 × 105 km away in another active region. We
have identified and studied more than a dozen microwave flares in this
class, in order to arrive at some general conclusions on reconnection
and energy release in such solar flares. Typically, these flares show
a gradual rise showing many subsidiary peaks in both radio and hard
X-ray light curves with a quasi-oscillatory nature with periods of 5-6
seconds, the presence of a bright compact X-ray-emitting loop in the
main flare source, a delay of the radio emission from the remote source
relative to the main Xray-emitting source, higher circular polarization
in the radio emission of the remote source than in the main source,
and stronger photospheric magnetic field in the remote source. We show
that the magnetic field in the main flare site changes sharply at the
time of the flare, and that the remote site is magnetically connected to
the main flare site sometimes only up to the time of the main impulsive
phase, at which point the magnetic connection to the remote site may
be broken and further flare manifestations are largely confined to the
main flare site. This severing of the magnetic connection between two
well-separated active regions may be an intrinsic part of the energy
release in such flare.

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Title: Double Loop Configuration of a Flaring Region from Microwave,
Extreme-Ultraviolet, and X-Ray Imaging Data
Authors: Kundu, M. R.; Grechnev, V. V.; Garaimov, V. I.; White, S. M.
2001ApJ...563..389K Altcode:
We use extensive multiwavelength data to study a flare belonging
to the interacting-loop class of events identified by Hanaoka. The
class of flares is identified morphologically from the presence of
two well-separated radio sources in 17 GHz images (in this event,
160" apart), with only one source showing soft X-ray emission. This
event shows many of the other properties apparently shared by this
class of flares: a gradual rise showing many subsidiary peaks in both
radio and hard X-ray light curves with a quasi-oscillatory nature,
the presence of a bright compact X-ray-emitting loop in the main flare
source, a delay of the radio emission from the remote source relative
to the main X-ray-emitting source, higher circular polarization in
the radio emission of the remote source than in the main source,
and stronger photospheric magnetic field in the remote source. The
new results of our analysis are that we are able to show, using a
sequence of magnetograms, that the magnetic field in the main flare
site changes sharply at the time of the flare, and further we argue
that the remote site is magnetically connected to the main flare
site only up to the time of the main impulsive phase, at which point
we believe the magnetic connection to the remote site was broken
and further flare manifestations are largely confined to the main
flare site. This severing of the magnetic connection between two
well-separated active regions may be an intrinsic part of the energy
release in this flare. The region around the main flare site also
exhibits rotation in the magnetogram in the period leading up to the
flare. Radio and hard X-ray oscillations with periods of order 5-10
s are observed in the rise phase of this event. If they are due to
transverse oscillations of the flare loop at the Alfvén speed, then
the density in the loop is inferred to be of order 1011
cm-3 and to increase with time as expected.

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Title: Reconciling Extreme-Ultraviolet and Radio Observations of
the Sun's Corona
Authors: Zhang, J.; Kundu, M. R.; White, S. M.; Dere, K. P.; Newmark,
J. S.
2001ApJ...561..396Z Altcode:
The Sun's corona, which is composed of plasma at a temperature of a few
millions of degrees, can be best viewed in two electromagnetic domains,
one from wavelengths of a few angstroms to hundreds of angstroms
(in the soft X-ray and EUV domain), the other from wavelengths
of a few centimeters to several tens of centimeters (in the radio
domain). In this paper, we present a quantitative comparison of coronal
observations made in these two domains with high spatial resolution
over the full disk of the Sun. The EUV observations were taken with the
EIT (Extreme-Ultraviolet Imaging Telescope) on board SOHO (Solar and
Heliospheric Observatory), and the radio observations were taken with
the VLA (Very Large Array). The two sets of images show very similar
morphologies, indicating that the different wavelengths originate from
common solar features. We predict radio fluxes using the temperature
and emission measure of the corona calculated from EIT observations,
adopting Meyer's table of coronal abundances for the calculations. In
each of the seven observations investigated, there always exists a
good linear correlation in the pixel-by-pixel correlation plot between
the predicted and the observed radio flux for coronal features over a
wide range of flux variation. Nevertheless, the predicted radio flux
is systematically larger than that observed by a factor of 2.0+/-0.2,
on average. We attribute the difference to the underestimation of the
abundance of Fe relative to H in the abundances adopted by Meyer. On
this basis, we place the absolute Fe abundance in the corona at
7.8×10-5, which has an enrichment factor of 2.4 relative
to the accepted photospheric Fe abundance.

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Title: Possible Radio Evidence of Magnetic Reconnection in Solar
Flares
Authors: Kundu, Mukul R.; Grechnev, Victor V.
2001APS..DPPLM1002K Altcode:
We present possible radio evidence of magnetic reconnection in
solar flares.We discuss one specific solar flare -an LDE event of
GOES class M3.2 that was observed with the Nobeyama Radio Heliograph
(NoRH) in Japan as well as with the Soft X-ray telescope aboard the
satellite Yohkoh.The event was also observed in H-alpha and with metric
dynamic spectrum analyzers.Our evidence is based upon the facts that
we observed a bright microwave source-blob at 17 and 34 GHz near the
intersection of two apparently intersecting flaring loops or as a
loop-top source above the flaring loop.The bright microwave source
is clearly nonthermal and its time profile is similar to that of the
flaring foot point microwave sources; and in the late decay phase of
the event the microwave source structure is similar to that of the
corresponding SXR source. The event was accompanied by a Moreton wave
(evidence of shock wave ) and a type II radio burst (a consequence
of the shock).We discuss the observations in relation to a specific
flare model that involves magnetic reconnection.

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Title: Metric Radio Emission Associated with X-Ray Plasmoid Ejections
Authors: Kundu, M. R.; Nindos, A.; Vilmer, N.; Klein, K. -L.; Shibata,
K.; Ohyama, M.
2001ApJ...559..443K Altcode:
In this paper we report the first detection of metric/decimetric
radio emission associated with two soft X-ray plasmoid ejecta events
that occurred during two limb flares observed by the Yohkoh SXT. In
the first event a loop started to rise slowly (~10 km s-1)
before the beginning of the hard X-ray impulsive phase of the flare. At
about the onset of the impulsive flare, there was acceleration of the
ejecta, resulting in a speed of 130 km s-1 and finally to
~200 km s-1. The associated radio emission was observed with
the Nançay radioheliograph (NRH) in the frequency range of 230-450
MHz. It was an unpolarized continuum that lasted 8-10 minutes. The 410
MHz source was located close to the height where the plasmoid was last
identified in the SXT images. In the second event an eruption resulted
in the expansion of a large-scale, looplike feature and the development
of two plasmoid ejecta which moved in different directions. The speed of
the ejecta was 60-100 km s-1. In this event, the associated
radio emission was a long-lasting (about 2 hr) continuum observed from
450 to 164 MHz. The onset of the low-frequency emission was delayed
with respect to the onset of the high-frequency emission. In both
cases the radio sources were located above the soft X-ray ejecta in
the general direction of the prolongation of the ejecta movement. In
both cases the radio emission comes from nonthermal electrons which
are accelerated in close relationship with the propagation of the X-ray
plasmoid: as the plasmoid reaches higher altitudes, it interacts with
increasingly more extended magnetic field lines and new coronal sites
of production of nonthermal electrons are created.

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Title: On the Temporal Relationship between Coronal Mass Ejections
and Flares
Authors: Zhang, J.; Dere, K. P.; Howard, R. A.; Kundu, M. R.; White,
S. M.
2001ApJ...559..452Z Altcode:
The temporal relationship between coronal mass ejections (CMEs) and
associated solar flares is of great importance to understanding the
origin of CMEs, but it has been difficult to study owing to the nature
of CME detection. In this paper, we investigate this issue using the
Large Angle and Spectrometric Coronagraph and the EUV Imaging Telescope
observations combined with GOES soft X-ray observations. We present
four well-observed events whose source regions are close to the limb
such that we are able to directly measure the CMEs' initial evolution
in the low corona (~1-3 Rsolar) without any extrapolation;
this height range was not available in previous space-based coronagraph
observations. The velocity-time profiles show that kinematic evolution
of three of the four CMEs can be described in a three-phase scenario:
the initiation phase, impulsive acceleration phase, and propagation
phase. The initiation phase is characterized by a slow ascension
with a speed less than 80 km s-1 for a period of tens of
minutes. The initiation phase always occurs before the onset of the
associated flare. Following the initiation phase, the CMEs display an
impulsive acceleration phase that coincides very well with the flares'
rise phase lasting for a few to tens of minutes. The acceleration of
CMEs ceases near the peak time of the soft X-ray flares. The CMEs then
undergo a propagation phase, which is characterized by a constant speed
or slowly decreasing in speed. The acceleration rates in the impulsive
acceleration phase are in the range of 100-500 m s-2. One CME
(on 1997 November 6, associated with an X9.4 flare) does not show an
initiation phase. It has an extremely large acceleration rate of 7300 m
s-2. The possible causes of CME initiation and acceleration
in connection with flares are explored.

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Title: A Multiwavelength Study of Three Solar Flares
Authors: Kundu, M. R.; Nindos, A.; White, S. M.; Grechnev, V. V.
2001ApJ...557..880K Altcode:
In this paper we seek a self-consistent model for three strong limb
flares observed at 17 and 34 GHz by the Nobeyama radioheliograph and
also in soft X-rays and hard X-rays by the Yohkoh SXT (Soft X-Ray
Telescope) and HXT (Hard X-Ray Telescope) instruments. Additional
radio spectral data were provided by the Nobeyama polarimeter. The
flare geometry is simple, with one well-defined flaring loop in each
event. The 17 and 34 GHz emissions are optically thin gyrosynchrotron
radiation from energetic electrons that outlines the flaring loops and
peaks close to the loop tops. We infer that the variation of magnetic
field along the loops is very small. We try to reproduce the observed
radio morphologies and fluxes using a model gyrosynchrotron loop. The
results of our modeling rely on the model magnetic field geometry that
we choose. Although the exact loop geometry cannot be constrained from
a two-dimensional snapshot, we choose for simplicity a line-dipole
magnetic field, and the model field lines are circular. The SXT/HXT
images are used to provide the physical parameters of the model
loops. The high-frequency polarimeter data give the energy spectral
index of the radio-emitting electrons. We could not reconcile the
observed radio morphologies and fluxes using classic dipole magnetic
field models. The best-fit model that uses the same input parameters
for both frequencies and partly reconciles the observed 17 and 34 GHz
morphologies and fluxes is produced when we invoke a magnetic field with
constant strength along the model loop. These model loops have uniform
thickness. The derived densities of the radio-emitting electrons are
(1-6)×104 cm-3 with energy limits between 60
and 5000 keV. These models are the best fits we can get under the best
assumptions we can justify, but they do not in fact match the radio
morphologies very well; their problems and limitations are discussed.

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Title: Seemingly intersecting flaring loops in microwaves: Possible
radio evidence for reconnection
Authors: Kundu, M. R.; Grechnev, V. V.
2001EP&S...53..585K Altcode:
We present possible radio evidence of magnetic reconnection in a
solar flare—an LDE event of GOES class M3.2 that was observed on
1999 February 16 on the disk. Our evidence is based upon the facts
that we observed a bright microwave source-blob at 17 and 34 GHz near
the intersection of two seemingly intersecting flaring loops or as a
loop-top source above one flaring loop. The bright microwave source
is clearly non-thermal and its time profile is similar to those of
the flaring footpoint microwave sources; and in the late decay phase
of the event the microwave source structure is similar to that of the
corresponding SXR source.

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Title: Double Loop Configuration of a Flaring Region from Microwave,
EUV and X-ray Imaging Data
Authors: Garaimov, V. I.; Kundu, M. R.; Grechnev, V. V.; White, S. M.
2001AGUSM..SP51A04G Altcode:
We present the results of a study of a flare of importance M1.7 that
was observed with the Nobeyama Radio Heliograph (NoRH), SOHO/EIT
and MDI and Yohkoh/HXT &amp; SXT. The flare ocurred in a complex of
two active regions AR~8741 and AR~8739, which were separated by ~ 3
arc min. The main flaring region was AR~8741, which consisted of two
compact oppositely polarized components as judged by MDI magnetogram
data. 17~GHz and 34~GHz microwave emissions as well as EUV, and
hard and soft X-ray emissions from the flare originated primarily
from the vicinity of the compact components of opposite polarity in
AR~8741. There was some 17~GHz flaring emission from AR~8739. Clearly,
we are dealing with a large magnetic loop connecting AR~8741 and
AR~8739, as well as a compact loop in AR~8741 which was the main flare
site. One of the magnetic components of the compact loop increased
in field strength approximately 1 hour prior to the flare onset. MDI
magnetograms showed some other changes in the magnetic fields associated
with the compact loop. We suggest that the interaction of the compact
loop with the large loop was responsible for causing the flare. The
radio source structures at 17 and 34 GHz along with EUV, hard and soft
X-ray source structures of the flaring region will be presented.

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Title: The Physical Properties of a Flaring Coronal Loop
Authors: White, S. M.; Kundu, M. R.; Garaimov, V. I.; Yokoyama, T.
2001AGUSM..SP42A06W Altcode:
We present high resolution radio and X-ray images of emission from
nonthermal electrons trapped in a flaring coronal loop and measure
various physical properties of the loop, including the loop thickness
as a function of position along the loop and intensity profiles along
the loop. Gyrosynchrotron modelling provides a complementary method
for inferring parameters such as the magnetic field variation along the
loop, and we compare the results of the two approaches. Both agree that
there is little variation in magnetic field strength along the loop;
this purely radio measurement thus supports the same inference derived
from measurements of EUV and X-ray loop thicknesses.

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Title: Intersecting Flaring Loops in Microwaves: Possible Radio
Evidence for Magnetic Reconnection
Authors: Kundu, M. R.; Grechnev, V. V.
2001AGUSM..SP51A05K Altcode:
We present possible radio evidence of magnetic reconnection in a solar
flare - an LDE event of GOES class M3.2 that was observed on 1999
February 16 on the disk. Our evidence is based upon the facts that we
observed a bright microwave source - a bright blob at 17 and 34~GHz
near the intersection of two apparently intersecting flaring loops
or as a loop-top source above one flaring loop. The bright microwave
source is clearly nonthermal and its time profile is similar to those
of the flaring footpoint microwave sources, and in the late decay
phase of the event the microwave source structure is similar to that
of the corresponding SXR source. The loop-top microwave source shows
a movement of order 10 km/s, similar to that observed by Yohkoh in
soft X-rays in one LDE event which was considered to be a reconnection
event. It is important to note that in the late decay phase this event
was associated with CGRO/BATSE 100-300 keV energy electrons which appear
to originate primarily from the footpoints of one flaring loop. There
are data available in Hα from Hida observatory in Japan which show
an ejection during this apparent reconnection event.

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Title: A Radio Study of the Evolution of Spatial Structure of an
Active Region and Flare Productivity
Authors: Kundu, M. R.; White, S. M.; Shibasaki, K.; Raulin, J. -P.
2001ApJS..133..467K Altcode:
We present the results of a radio study of the evolution of an active
region through its flare productivity. The radio study was carried out
with data obtained by the Nobeyama Radio Heliograph at 17 GHz. We chose
the active region AR 7515, which appeared at the east limb on 1993 May
23 and then evolved during its passage across the disk. We followed
its evolution until June 2. This region produced many small flares. We
consider this region to be a typical active region in the sense that it
did not produce any large flares, but a large number of weak flares. We
investigate the optical and magnetic development of the region and show
how this affects the locations of the flaring activity. We discuss
a number of events in detail in order to investigate the roles of
nonthermal and thermal radio emission in the flares. The nonthermal
gyrosynchrotron emission generally occurs in regions of strong magnetic
fields, is generally circularly polarized, and often varies rapidly in
time. On the other hand, gradual radio components tend to be thermal and
only weakly polarized, if at all. An interesting aspect of evolution
of the flares in this region is that many of the flares in the early
phase of the evolution show strong but brief nonthermal radio emission
in the impulsive phase followed by gradual thermal emission, whereas
in the last 3 days more gradual events without a strong spike of radio
emission in the impulsive phase tend to be seen. Correspondingly, the
flare images suggest that the radio sources are more compact during
the early phases and more extended in the last half of the period
covered. The most dominant component of the preflare region is often
not the component that undergoes immediate flaring. Sometimes a number
of components in the preflare region participate in the flare process
together. We speculate that these component sources are unresolved
compact bipolar loops that flare in sequence. Loop-loop interactions
occurring at many different sites at the same time seems to be a less
plausible explanation of these events.

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Title: Spatial Structure of Simple Spiky Bursts at
Microwave/Millimeter Wavelengths
Authors: Kundu, M. R.; White, S. M.; Shibasaki, K.; Sakurai, T.;
Grechnev, V. V.
2001ApJ...547.1090K Altcode:
We present the results of a study of spatial structure of sources
of microwave and millimeter bursts with simple spiky time profiles
at 17 and 34 GHz, similar to those found to be common at 3 mm
wavelength. These bursts are of short duration, with fast 2-4 s rise
time to peak, followed by a rapid exponential decay. When mapped at
high spatial resolution with the Nobeyama Radio Heliograph (NoRH), the
radio images show direct evidence that the radio sources are compact
bipolar loops: source sizes are less than 5" and three of the five
events studied show closely spaced oppositely polarized components in
the circular polarization maps. All five events are located directly
over magnetic neutral lines in the photosphere. The soft X-ray behavior
is not entirely consistent with the Neupert effect in these events,
since all five events show a rise in the soft X-ray flux well before
any nonthermal electrons are present in the corona and the ratio of
peak soft X-ray flux to peak radio 17 GHz flux may vary by many orders
of magnitude from one event to the next. The abrupt time profiles
of these events and their physical properties are consistent with a
single-loop scenario in which magnetic energy release and acceleration
of nonthermal electrons are confined to a compact localized region.

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Title: Spatial Distribution and Temporal Evolution of Coronal
Bright Points
Authors: Zhang, Jie; Kundu, Mukul R.; White, Stephen M.
2001SoPh..198..347Z Altcode:
We present a statistical study of the spatial distribution and temporal
evolution of coronal bright points (BPs) by analyzing a continuous
set of observations of a quiet-Sun region of size 780” × 780”
over a period of 55 hours. The main data set consists of observations
taken by EIT (the Extreme-ultraviolet Imaging Telescope on board
the SOHO spacecraft) in its Fe xii 195 Å channel which is sensitive
to coronal plasma of temperature ∼ 1.5 MK; we also use soft X-ray
observations by SXT (Soft X-ray Telescope on the Yohkoh spacecraft)
which is sensitive to coronal plasma of temperature &gt; 2.5 MK. The
flux histogram for all pixels in EIT 195 Å images indicates that BPs
have a power law flux distribution extending down to a level of 3σ (σ,
root mean square deviation) above the average flux of the quiet Sun,
while the bulk quiet Sun has a Gaussian-like flux distribution. Using a
3σ intensity threshold, we find a spatial density of one BP per 90 Mm
× 90 Mm area, or equivalently 800 BPs for the entire solar surface at
any moment. The average size of a BP is 110 Mm2. About 1.4%
of the quiet-Sun area is covered by bright points and the radiation
from all BPs is only about 5% of that from the whole quiet Sun. Thus,
the atmosphere above quiet-Sun regions is not energetically dominated
by BPs. During the 55-hour period of EIT observations, we identify 48
full-life-cycle BPs which can be tracked from their initial appearance
to final disappearance. The average lifetime of these BPs is 20 hours,
which is much longer than the previously reported 8 hours based on
Skylab X-ray observations (Golub et al., 1974). We also see shorter
life times and smaller numbers of BPs in the soft X-ray images than
in the EIT 195 Å observations, suggesting that the temperature of
BPs is generally below 2 MK.

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Title: The Absolute Abundance of Iron in the Solar Corona (CD-ROM
Directory: contribs/white)
Authors: White, S. M.; Thomas, R. J.; Brosius, J. W.; Kundu, M. R.
2001ASPC..223.1361W Altcode: 2001csss...11.1361W
No abstract at ADS

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Title: Nonthermal Flare Emission from MEV-Energy Electrons at 17,
34, and 86 GHZ
Authors: Kundu, M. R.; White, S. M.; Shibasaki, K.; Sakurai, T.
2000ApJ...545.1084K Altcode:
We present analyses of two solar flares observed with high spatial
resolution at 86 GHz with the BIMA millimeter-wavelength telescope
and at 17 and 34 GHz with the Nobeyama radioheliograph. The flares
were observed on 1998 November 24 and 1999 May 1. At millimeter
wavelengths these are impulsive events, and therefore they must be
produced by MeV-energy electrons. The present study using simultaneous
observations of two flares at 86, 34, and 17 GHz provides an excellent
opportunity to study high-energy electrons with high spatial resolution
observations at three optically thin frequencies. The morphology of
millimeter emission can reveal both the properties of the MeV-energy
electrons and the nature of the coronal magnetic field lines where they
radiate. One of the two events we present is the first clear case of a
λ=3 mm source in which both footpoints of a loop are detected. In the
second event the polarization image at 17 GHz also suggests a bipolar
or looplike morphology. Such morphological observations can be used
to constrain the nature of the magnetic field in the solar corona.

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Title: Solar Flare Physics
Authors: Schmahl, Edward J.; Kundu, Mukul R.
2000STIN...0104608S Altcode:
During the past year we have been working with the HESSI (High Energy
Solar Spectroscopic Imager) team in preparation for launch in early
2001. HESSI has as its primary scientific goal photometric imaging
and spectroscopy of solar flares in hard X-rays and gamma-rays with
an approx. 2 sec angular resolution, approx. keV energy resolution and
approx. 2 s time resolution over the 6 keV to 15 MeV energy range. We
have performed tests of the imager using a specially designed experiment
which exploits the second-harmonic response of HESSI's sub-collimators
to an artificial X-ray source at a distance of 1550 cm from its front
grids. Figures show the response to X-rays at energies in the range
where HESSI is expected to image solar flares. To prepare the team
and the solar user community for imaging flares with HESSI, we have
written a description of the major imaging concepts. This paper will
be submitted for publication in a referred journal.

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Title: Radio Detection of a Rapid Disturbance Launched by a Solar
Flare
Authors: Janardhan, P.; White, S. M.; Kundu, M. R.
2000SPD....31.0243J Altcode: 2000BAAS...32Q1290J
This paper reports 333 MHz observations of motion associated with
a solar flare at a speed of 26000 km s-1. The motion
is seen from a radio source which suddenly starts moving during the
flare. At its peak the radio source covers a quiet region of dimension
500 arcsec. The disturbance itself does not seem to radiate, but it
excites coronal features which continue to radiate after it passes. The
inferred velocity is larger than any previously inferred velocity of a
disturbance in the solar atmosphere apart from freely-streaming beams
of accelerated electrons. The observed motion of the source at a fixed
frequency, low polarization and moderate bandwidth are more consistent
with the typical properties of moving Type IV radio bursts than with
classical coronal--shock--associated Type II bursts.

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Title: Soft X-Ray and Gyroresonance Emission above Sunspots
Authors: Nindos, A.; Kundu, M. R.; White, S. M.; Shibasaki, K.;
Gopalswamy, N.
2000ApJS..130..485N Altcode:
Using Yohkoh SXT and Nobeyama 17 GHz data, we have studied the soft
X-ray and microwave emission above several stable, large sunspots
near central meridian passage. Our study confirms the well-known fact
that soft X-ray emission is depressed above sunspots. It also shows
that the distribution of their soft X-ray intensity is not uniform;
usually the darkest pixels are associated with the umbra or the far
edges of the leading part of the penumbra while the following part
of the penumbra may contain higher intensity pixels associated with
brighter loops. For the first time, we present a systematic survey
of the temperatures and emission measures of the soft X-ray material
above sunspots. Sunspots always contain the lowest temperatures and
emission measures in the active regions. The mean umbral temperature
is 1.8×106 K, and the mean penumbral temperature is
2.4×106 K. The mean umbral and penumbral emission measures
are logEM=26.60 cm-5 and logEM=27.00 cm-5,
respectively. The differences between the umbral and penumbral plasma
temperatures are physically significant. The higher penumbral values
imply that the loops associated with the penumbrae are generally hotter
and denser than the loops associated with the umbrae. The highest
sunspot temperatures and emission measures are still lower than the
average active region parameters but higher than the quiet-Sun plasma
parameters. The coronal radiative energy loss rate above the umbrae
is 15% higher than the radiative loss rate of the quiet-Sun plasma
but a factor of 8.3 lower than the typical active region radiative
loss rate. The radio emission comes from the gyroresonance mechanism,
and, as expected, it is sensitive to the magnetic field rather than
the soft X-ray-emitting plasma.

---------------------------------------------------------
Title: The Absolute Abundance of Iron in the Solar Corona
Authors: White, S. M.; Thomas, R. J.; Brosius, J. W.; Kundu, M. R.
2000ApJ...534L.203W Altcode: 2000astro.ph..4007W
We present a measurement of the abundance of Fe relative to H
in the solar corona using a technique that differs from previous
spectroscopic and solar wind measurements. Our method combines EUV line
data from the Coronal Diagnostic Spectrometer (CDS) on the Solar and
Heliospheric Observatory with thermal bremsstrahlung radio data from
the VLA. The coronal Fe abundance is derived by equating the thermal
bremsstrahlung radio emission calculated from the EUV Fe line data to
that observed with the VLA, treating the Fe/H abundance as the sole
unknown. We apply this technique to a compact cool active region and
find Fe/H=1.56×10-4, or about 4 times its value in the solar
photosphere. Uncertainties in the CDS radiometric calibration, the VLA
intensity measurements, the atomic parameters, and the assumptions
made in the spectral analysis yield net uncertainties of ~20%. This
result implies that low first ionization potential elements such as
Fe are enhanced in the solar corona relative to photospheric values.

---------------------------------------------------------
Title: Microwave/Millimeter Wavelength Bursts with Simple Spiky
Time Profiles
Authors: Kundu, M. R.; White, S. M.; Shibasaki, K.; Sakurai, T.
2000SPD....31.0242K Altcode: 2000BAAS...32..818K
We report the detection at 17 and 34 GHz of microwave and millimeter
bursts which have simple spiky time profiles similar to those found to
be common at λ = 3 mm. These bursts are of short duration, with fast
2 - 4 sec rise time to peak, followed by an exponential decay. These
bursts can be of any intensity, from 1 sfu to 10's of sfu; they are
very strongly polarized (&gt; 50%), and they have similar properties
regardless of the nature of the active region in which the bursts
originate. The bursts seem to originate in compact sources which are
generally unresolved with 15" and 7" resolution of the Nobeyama Radio
Heliograph at 17 and 34 GHz respectively. We provide both direct and
indirect evidence that these compact sources are low-lying bipolar
loops. The direct evidence follows from the physical appearance of
the loop as well as from the bipolar nature of the loop. The indirect
evidence follows from the offset in position of the footpoint emission
in microwaves and hard X-rays, implying a compact asymmetric loop with
microwaves originating from the stronger magnetic field foot point
and the hard X-rays originating from the weaker field foot point.

---------------------------------------------------------
Title: The Absolute Abundance of Iron in the Solar Corona
Authors: White, S. M.; Thomas, R. J.; Brosius, J. W.; Kundu, M. R.
2000SPD....31.1301W Altcode: 2000BAAS...32Q.845W
We present a measurement of the abundance of Fe relative to H in the
solar corona using a technique which differs from previous spectroscopic
and solar wind measurements. Our method combines EUV line data from the
CDS spectrometer on SOHO with thermal bremsstrahlung radio data from
the VLA. The coronal Fe abundance is derived by equating the thermal
bremsstrahlung radio emission calculated from the EUV Fe line data to
that observed with the VLA, treating the Fe/H abundance as the sole
unknown. We apply this technique to a compact cool active region and
find Fe/H = 1.56 x 10-4, or about 4 times its value in the
solar photosphere. Uncertainties in the CDS radiometric calibration, the
VLA intensity measurements, the atomic parameters, and the assumptions
made in the spectral analysis yield net uncertainties of order 20%. This
result implies that low first ionization potential elements such as
Fe are enhanced in the solar corona relative to photospheric values.

---------------------------------------------------------
Title: Observations and models of a flaring loop.
Authors: Nindos, A.; White, S. M.; Kundu, M. R.; Gary, D. E.
2000BAAS...32..818N Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Observations and Models of a Flaring Loop
Authors: Nindos, A.; White, S. M.; Kundu, M. R.; Gary, D. E.
2000SPD....31.0243N Altcode:
Simultaneous images of a flaring loop at two frequencies are used to
model the magnetic structure of the loop and the energy distribution of
the radiating electrons. The imaging data were obtained with the VLA at
5 and 15 GHz. Additional spectral data were provided by the OVRO Solar
Array at several frequencies between 2 GHz and 15 GHz. At 15 GHz, the
flare emission was optically thin and came from the footpoints of the
flaring loop, while at 5 GHz the loop itself was outlined. Most of the
5 GHz emission was optically thick and its spatial maximum was close
to the loop top. A striking feature of the observations is that the 5
GHz emission does not reach down to the 15 GHz footpoints. We compare
the observations with calculations of gyrosynchrotron emission from an
inhomogeneous magnetic loop in order to determine the conditions in the
flaring loop. The best fit to the OVRO fluxes was reached with a model
flaring loop with photospheric footpoint magnetic field strength of 870
G. The thickness of the model loop was small compared to its footpoint
separation. The energy spectral index of the energetic electrons was 3.7
and their number density was 7.9 x 107 cm-3. The
low and high energy cutoffs of the nonthermal electrons were 8 and
210 keV. The 5 GHz emission in this model is at low harmonics (3--7)
and harmonic effects are responsible for the weak 5 GHz emission at
the footpoints. The absence of electrons above 210 keV is necessary in
this model to explain why no emission is observed from the loop top at
15 GHz. That model reproduced well the high frequency part of the OVRO
flux spectrum as well as the VLA spatial structure. Thus comparisons
between the spatially--resolved observations and models reveal the
three-dimensional structure of the loop geometry.

---------------------------------------------------------
Title: LASCO and EIT observations of CMEs associated with flares
Authors: Zhang, J.; Dere, K. P.; Howard, R. A.; Kundu, M. R.; White,
S. M.
2000SPD....31.0906Z Altcode: 2000BAAS...32..841Z
Coronal mass ejections (CME) and flares are two primary causes
of adverse space weather. These two solar eruptive phenomenon are
often observed to be associated with each other. Yet the relationship
between them is not well known. With unprecedented LASCO (Large-Angle
and Spectrometric Coronagraph) and EIT (Extreme-ultraviolet Imaging
Telescope) observations combined with simultaneous HXT (Hard X-ray
Telescope), GOES and other flare observations, we pursue to make a
comprehensive study on the spatial, temporal and energetic relationship
between CMEs and flares. In order to make accurate measurement of the
onset time of CMEs, we primarily select CME events whose source regions
are close to the limb and which are well observed by LASCO/C1 from
1.1 to 3 solar radii. Although a flare occurs in a rather small area
of active region, the CME's source region often covers much larger
longitudinal and latitudinal extension. Some CMEs occur simultaneously
with flare (within only a few minutes), however, some CMEs occur
well before the flares (more than 30 minutes earlier). Fast CMEs are
associated with strong flares. These studies are aimed to understand
the initiation process of solar eruptive phenomenon, and to fit a
variety of observational aspects into a consistent picture.

---------------------------------------------------------
Title: Observations and Models of a Flaring Loop
Authors: Nindos, A.; White, S. M.; Kundu, M. R.; Gary, D. E.
2000ApJ...533.1053N Altcode:
Simultaneous images of a flaring loop at two frequencies are used to
model the magnetic structure of the loop and the energy distribution of
the radiating electrons. The imaging data were obtained with the VLA at
5 and 15 GHz. Additional spectral data were provided by the Owens Valley
Radio Observatory (OVRO) solar array at several frequencies between
2 and 15 GHz. At 15 GHz, the flare emission was optically thin and
came from the footpoints of the flaring loop, while at 5 GHz the loop
itself was outlined. Most of the 5 GHz emission was optically thick,
and its spatial maximum was close to the loop top. A striking feature
of the observations is that the 5 GHz emission does not reach down to
the 15 GHz footpoints. We compare the observations with calculations of
gyrosynchrotron emission from an inhomogeneous magnetic loop in order
to determine the conditions in the flaring loop. The best fit to the
OVRO fluxes was reached with a model flaring loop with photospheric
footpoint magnetic field strength of 870 G. The thickness of the
model loop was small compared with its footpoint separation. The
energy spectral index of the energetic electrons was 3.7, and their
number density was 7.9×107 cm-3. The low- and
high-energy cutoffs of the nonthermal electrons were 8 and 210 keV,
respectively. The 5 GHz emission in this model is at low harmonics
(3-7), and harmonic effects are responsible for the weak 5 GHz emission
at the footpoints. The absence of electrons above 210 keV is necessary
in this model to explain why no emission is observed from the loop
top at 15 GHz. That model reproduced well the high-frequency part of
the OVRO flux spectrum as well as the VLA spatial structure. Thus,
comparisons between the spatially resolved observations and models
reveal the three-dimensional structure of the loop geometry.

---------------------------------------------------------
Title: Radio Detection of a Rapid Disturbance Launched by a Solar
Flare
Authors: White, S. M.; Janardhan, P.; Kundu, M. R.
2000ApJ...533L.167W Altcode:
We report the direct observation of motion associated with a solar
flare at a speed of 26,000 km s-1. The motion is seen from
a radio source at 0.33 GHz, which suddenly starts moving during the
flare. At its peak, the radio source covers a quiet region of dimension
500". Emission from any given location is sporadic. The disturbance
itself does not seem to radiate, but it excites coronal features
that continue to radiate after it passes. The inferred velocity is
larger than any previously inferred velocity of a disturbance in the
solar atmosphere apart from freely streaming beams of accelerated
electrons. The observed motion of the source at a fixed frequency,
low polarization, and moderate bandwidth are more consistent with the
typical properties of moving type IV radio bursts than with classical
coronal shock-associated type II bursts, but any disturbance at such a
high velocity must be highly supersonic and should drive a shock. We
speculate that the disturbance is associated with the realignment of
magnetic fields connecting different portions of an active region.

---------------------------------------------------------
Title: Solar Flare Physics
Authors: Schmahl, Edward J.; Kundu, Mukul R.
2000STIN...0034022S Altcode:
In the extended portion of this grant (January 1-March 31, 2000),
we have continued our previous efforts (January 1-December 31,
1999) in studies of Fourier imaging methods applied to hard X-ray
flares. In particular, we have performed theoretical analysis of the
"Forward-Fitting" method in collaboration with Dr. Markus Aschwanden,
(Lockheed-Martin Palo Alto Research lab) in support of the HESSI (High
Energy Solar Spectroscopic Imager) mission to enable rapid imaging of
solar flares in hard X-rays.

---------------------------------------------------------
Title: Nonthermal Flare Emission from MeV-Energy Electrons at 17,
34, and 86, GHz
Authors: Kundu, M. R.; White, S. M.; Shibasaki, K.; Sakurai, T.
2000ASPC..206..307K Altcode: 2000hesp.conf..307K
No abstract at ADS

---------------------------------------------------------
Title: Radio Emissions from the Sun's Corona
Authors: Kundu, Mukul R.
2000IAUJD...7E...6K Altcode:
A review of recent observations of coronal radio emissions will
be presented, with particular reference to flares and weak coronal
transients, and their relationships to emissions in other spectral
domains.The radio emissions to be discussed are obtained with large
radio interferometers such as the Very Large Array (VLA) in USA,the
Nobeyama Radio Heliograph (NoRH) in Japan,the Berkeley-Illinois-Maryland
Millimeter Array (BIMA), and the Nancay(France) metric radio
heliograph. Selected imaging observations of solar flares and transients
at all wavelengths will be emphasized, providing information on the
structure and spatial location of flaring radio sources with respect
to flaring soft X-ray loops and hard X-ray sources. Observational
evidence will be presented on acceleration of electrons to MeV energies
and of the existence of different energetic electron populations in
solar flares.

---------------------------------------------------------
Title: Millimeter-Interferometer Observations of Flares in Conjunction
with HESSI
Authors: White, S. M.; Kundu, M. R.
2000ASPC..206..335W Altcode: 2000hesp.conf..335W
No abstract at ADS

---------------------------------------------------------
Title: Two-Temperature Coronal Models from SOHO/EIT Observations
Authors: Zhang, J.; White, S. M.; Kundu, M. R.
1999ApJ...527..977Z Altcode:
We present a method for deriving a two-thermal-component approximation
to the differential emission measure distribution of plasma in the
Sun's corona in the temperature range to which the Extreme-Ultraviolet
Imaging Telescope (EIT) on the Solar and Heliospheric Observatory
(SOHO) spacecraft is sensitive. EIT takes high-resolution full-disk
coronal images in three of its four optimized channels by observing
emission lines of highly ionized Fe whose formation temperatures
overlap and cover the range from 0.7 to 2.8 MK. It is straightforward
to show that the traditional single-temperature models based on
the ratio of a pair of EIT images at different wavelengths are not
able adequately to represent the plasma contributing to all three
wavelength ranges. In this paper, we develop a modified image-ratio
method that results in a two-thermal-component model for the plasma
producing the coronal emission observed by EIT. The products of this
method are two temperature and two emission measure full-disk maps
of the Sun's corona, with the full resolution of the EIT telescope,
in two temperature regimes: one from 0.8 to 1.6 MK and the other from
1.6 to 2.6 MK. The two-component solutions are tested using a series
of model differential emission measures (DEMs) from the CHIANTI atomic
database package. This method appears to produce realistic results in
all regions of the Sun's atmosphere with the exception of coronal holes,
where very cool Si VII/Mg VII lines (&lt;0.7 MK) contribute more to
the EIT 284 Å image than the otherwise dominant hot Fe XV lines and
result in unrealistically high temperatures for the hot component
there. We demonstrate that while the raw EIT images are dominated
by the spatial distribution of emission measure in the corona, the
temperature maps often emphasize fine structure, which is less visible
in the flux images. The emission measure of the hot component is always
larger than that of the cool component. On the disk there appears to
be a firm lower limit to the integrated column emission measure along
any line of sight, including toward coronal holes. There is no overall
correlation between temperature and emission measure.

---------------------------------------------------------
Title: Microwave and Extreme Ultraviolet Observations of Solar
Polar Regions
Authors: Nindos, A.; Kundu, M. R.; White, S. M.; Gary, D. E.;
Shibasaki, K.; Dere, K. P.
1999ApJ...527..415N Altcode:
The poles of the Sun are brighter than the rest of the quiet Sun's
emission in a limited range of radio frequencies from 17 GHz to 87
GHz. We have studied microwave images of the quiet Sun made with
the Nobeyama radioheliograph at 17 GHz. They show that the so-called
polar-cap brightening consists of two components: a diffuse component
of 1500 K excess brightness and patchy compact sources with localized
excess brightness of about 3500 K. We test the reality of the compact
sources using the maximum entropy method deconvolution. The total flux
and the number of compact polar sources as well as the north-south
extent of the diffuse polar emission are larger in the pole that is
closest to the Earth. We compared the microwave polar emission with
nearly simultaneous SOHO EIT images taken in the lines of He II at 304
Å and Fe XII at 195 Å. No one-to-one correlation between the compact
radio sources and the bright EUV features was found: most of the radio
emission arises between the plumes visible to EIT. The boundaries of
the polar-cap brightenings did not match exactly the boundaries of the
coronal holes as seen in either the Fe XII 195 Å images or the He II
304 Å images. The temporal variations of the compact microwave sources
did not correspond to any significant changes in EUV emission. On the
other hand, most He II 304 Å changing features were associated with the
diffuse polar microwave emission, which was practically constant. Our
data suggest that the origin of the polar brightening is not coronal;
it seems that the bulk of the patchy radio emission comes from heights
below the 80,000 K layer.

---------------------------------------------------------
Title: A Microwave Study of Coronal and Chromospheric Ejecta
Authors: Nindos, A.; Kundu, M. R.; Raulin, J. -P.; Shibasaki, K.;
White, S. M.; Nitta, N.; Shibata, K.; Shimojo, M.
1999spro.proc..135N Altcode:
We have studied the radio properties of 18 X-ray coronal jets (observed
by the Yohkoh SXT) using Nobeyama 17 GHz data. We also searched for
chromospheric ejecta (Hα surges) during the time intervals that the
X-ray images were available. Microwave emission was associated with the
majority of the X-ray jets. The radio emission came from the base or
the lower part of the jets. We detected radio emission from almost all
jets which showed flare-like activity at their footpoints. The 17 GHz
time profiles were gradual and unpolarized, implying that the emission
was thermal. When possible, we computed the physical properties of the
X-ray-emitting ejected plasma. In one two-sided-loop type jet and one
anemone-type jet, the observed microwave fluxes from the lower part of
the jets were well above the fluxes predicted from the computed electron
temperatures and emission measures of the soft X-ray-emitting material
on the basis of thermal free-free emission. We interpreted the large
discrepancies in terms of the presence of lower temperature material
which cannot be detected by the SXT but produces strong microwave
free-free emission. This is the first time that such material is
observed in two-sided-loop type jets. Thus our observations confirm the
theoretical prediction by Yokoyama and Shibata (1996). We detected no
cool material at the base of the jets. We also observed an Hα surge
which was not associated with an X-ray jet and showed no signatures on
the SXT images but was detected with the Nobeyama Radioheliograph. The
emission of the microwave surge-associated source was free-free from the
chromospheric plasma. Constraints for the surge density were derived.

---------------------------------------------------------
Title: Solar Flare Physics
Authors: Schmahl, Edward J.; Kundu, Mukul R.
1999STIN...0025246S Altcode:
We have continued our previous efforts in studies of fourier imaging
methods applied to hard X-ray flares. We have performed physical and
theoretical analysis of rotating collimator grids submitted to GSFC for
the HESSI (High Energy Solar Spectroscopic Imager) mission involving
the imaging of solar flares in hard X-rays. In the following pages we
present analysis of several different imaging techniques, and focus on
the one (The Polar Representation) that shows the greatest promise in
minimizing storage requirements and maximizing the speed of map making.

---------------------------------------------------------
Title: Active Region Emissions and Coronal Field Extrapolations
Authors: Lee, J.; White, S. M.; Kundu, M. R.; Mikic, Z.
1999spro.proc...65L Altcode:
With vector magnetographs set to fly on the Solar--B mission,
the extrapolation of photospheric magnetic fields into the corona
will be increasingly important. As the techniques of coronal field
extrapolations grow more sophisticated, we require a more powerful means
to test them and to make full use of the information they contain. Radio
data can play an important role in testing extrapolation methods. In
this paper, we discuss a new test of coronal field extrapolation using
the concept of field line connectivity. The motivating idea is that
temperature should be nearly uniform on a given magnetic field line
due to the rapid transport of physical quantities along field lines
in the corona. Optically--thick gyroresonance emission provides
the temperature on a surface of known magnetic field strength in
the corona. As a consequence, we may expect that radio intensities
observed at different frequencies at points connected by field
lines should show a good correlation. This suggests that a test
of a magnetic field extrapolation model is whether the field--line
connectivity it predicts shows such a correlation. A second application
of field--line connectivity is to try to understand the relationship
between physical quantities in the photosphere at the footpoints of
magnetic field lines and the heating process in the corona on the same
field lines. If a particular magnetic quantity, such as shear, plays
a role in coronal heating then one expects the coronal extension of
field lines passing through peaks in this quantity will show the highest
coronal temperatures. This idea can be used to test candidate coronal
heating mechanisms. We demonstrate these ideas using the combination of
high--resolution VLA observations of a complex active region together
with state--of--the--art nonlinear force--free field modeling.

---------------------------------------------------------
Title: Radio Observations of Weak Coronal Transients
Authors: Kundu, M. R.
1999spro.proc..111K Altcode:
In this review we discuss radio observations of weak coronal
transients. We concentrate on the transient events observed primarily by
Yohkoh/SXT and to a smaller extent by SOHO/EIT. The radio observations
are those obtained with the Very Large Array (VLA) in microwaves,
the Nancay (France) metric radioheliograph at 150 - 450 MHz and the
Nobeyama RadioHeliograph (NRH) at 17 GHz. We discuss the observational
characteristics of X-ray bright point flares at meter wavelengths and
in microwaves, and provide evidence that both thermal and nonthermal
processes occur in these small scale flaring events. Similarly, radio
observations of X-ray jets in microwaves and at meter wavelengths
provide evidence for both thermal and nonthermal processes in these
dynamic coronal phenomena. Nonthermal radio emission in the form
of metric type III bursts is produced by electron beams propagating
along the jet, whereas microwave emission comes mostly from the jet
base. We discuss active region transient brightenings (ARTB's) and
show that their radio emission can be purely thermal, thermal gyro-
resonance or nonthermal gyrosynchrotron radiation. We discuss one
form (radio-selected) of quiet Sun transient brightenings located far
from active regions. We provide evidence that weak plasma ejections
following flares is observed at metric wavelengths in the form of
transient continuum emission. Finally, we discuss the time-varying
polar brightenings at 17 GHz, and their relationship to polar erupting
plumes observed by SOHO-EIT.

---------------------------------------------------------
Title: Multiple Components in the Millimeter Emission of a Solar Flare
Authors: Raulin, J. -P.; White, S. M.; Kundu, M. R.; Silva, A. V. R.;
Shibasaki, K.
1999ApJ...522..547R Altcode:
We analyze a small flare using imaging data at millimeter, microwave,
and soft X-ray wavelengths and microwave and hard X-ray spectral
observations. The remarkable aspect of this flare is evidence for
the presence of MeV-energy electrons, which are responsible for the
nonthermal millimeter emission, at a time when no hard X-rays from
lower energy electrons are detected. This occurs during a smoothly
varying phase, which is seen at radio wavelengths to last several
minutes and is the brightest phase at millimeter wavelengths but is
undetected in hard X-rays: it follows a brief spike of emission at
flare onset, which has the more usual properties of impulsive events and
features nonthermal microwave, millimeter, and hard X-ray emission. We
interpretthe phase that is brightest at millimeter wavelengths as being
due to efficient trapping of a relatively small number of nonthermal
electrons, whereas during the hard X-ray emission, trapping is much
less efficient, and the decay time is much shorter at all energies,
which leads to a larger ratio of hard X-ray flux to radio flux. As
in many previous events studied at millimeter wavelengths, there is a
discrepancy between the electron energy spectral indices inferred from
the milllimeter and hard X-ray data during the impulsive phase when both
are detected: again it appears that the energy spectrum at 1 MeV must be
significantly flatter than at several hundred keV and below. However,
there are problems in reconciling quantitatively the energy spectra
for the hard X-ray-emitting and radio-emitting components: based on
the most plausible parameters, the radio-emitting electrons should
produce most of the hard X-rays. One solution to this contradiction
is to invoke a coronal magnetic field stronger than seems likely based
on the photospheric magnetic field.

---------------------------------------------------------
Title: Radio and X-Ray Imaging Observations of a Continuum Burst
Authors: Kundu, M. R.; Raulin, J. P.; Nitta, N.; Raoult, A.
1999ApJ...522.1100K Altcode:
We study a metric continuum burst observed on 1993 February 18, and
its X-ray signatures from imaging observations in radio and X-rays
using the Nançay radioheliograph and the Yohkoh Soft X-Ray Telescope
(SXT). The event in question was associated with weak type III bursts;
these were detected at only one frequency (164 MHz), except for one
burst (at 10:58:05 UT), which was observed over a broad frequency range
(164-435 MHz). We believe that the early metric continuum burst is an
extension of the microwave continuum which was observed at frequencies
as high as 5 GHz, and its onset at ~10:50 UT is associated with the
development of an X-ray-emitting diffuse loop system which appears to
advance with a speed of ~50-100 km s-1. The observed type
III bursts seem to correspond to the repeated occurrence/appearance of
a collimated jet emanating from the loop system that is responsible for
the continuum burst. A few minutes prior to the main continuum onset
there is a soft X-ray ejection from the main flare region. The main
continuum has a brightness temperature greater than 108 K;
it is unpolarized, and it shows dispersion in position with frequency
and moves with speeds of ~50 km s-1 at 236-410 MHz. The SXT
images reveal that this initially ejected soft X-ray-emitting hot plasma
seems to gradually fill up the loop system with hot material. This hot
plasma must contain enough energetic electrons of energy greater than
several tens of keV, which are responsible for producing the metric
continuum burst by plasma radiation mechanism.

---------------------------------------------------------
Title: A Microwave Study of Coronal Ejecta
Authors: Kundu, M. R.; Nindos, A.; Raulin, J. -P.; Shibasaki, K.;
White, S. M.; Nitta, N.; Shibata, K.; Shimojo, M.
1999ApJ...520..391K Altcode:
Using Nobeyama 17 GHz data, we have studied the radio properties of
19 coronal jets identified in Yohkoh soft X-ray imaging telescope
(SXT) X-ray observations. The radio data provide information on the
physical conditions in the jets, which complements the data from the
X-ray surveys. Microwave emission was associated with the majority of
the X-ray jets in our sample. The radio emission typically came from
the base or the base and lower part of the jets. We detected radio
emission from almost all jets that showed flarelike activity at their
bases. The jets that were not associated with radio emission did not
show any significant increase in X-ray emission at their bases. The
strongest radio emission came from two of the largest jets in our
sample. Our data show a general correlation between the X-ray jet
fluxes and the associated radio fluxes. The 17 GHz time profiles were
gradual and unpolarized, implying that the emission was thermal. In a
two-sided-loop jet (1992 July 22 event) and one anemone-type jet (1993
February 9 event), the observed microwave fluxes from the lower part
of the jets were well above the fluxes calculated from the computed
physical parameters of the soft X-ray-emitting material on the basis
of thermal free-free emission. We interpret the large discrepancies
in terms of the presence of lower temperature material, which cannot
be detected by the SXT (the SXT is most sensitive to hot plasma above
2×106 K), but which produces strong microwave free-free
emission. This is the first time that such material has been observed
in two-sided-loop-type jets. We also observed motion of a jet-associated
microwave source with a velocity of 55 km s-1. The microwave
motion occurred after the appearance of the X-ray jet. There is clear
evidence that the microwave emission of that source was associated
with the jet and not with the associated small flare.

---------------------------------------------------------
Title: Microwave and Extreme Ultraviolet Observations of Solar
Polar Regions
Authors: Nindos, A.; Kundu, M. R.; White, S. M.; Gary, D. E.;
Shibasaki, K.; Dere, K. P.
1999AAS...194.3207N Altcode: 1999BAAS...31..871N
The radio emission of solar poles is brighter than the rest of the
quiet Sun's emission in a limited range of frequencies from 17 GHz to
87 GHz. We have studied microwave images of the quiet Sun made with
the Nobeyama Radioheliograph at 17 GHz. They show that the so-called
polar-cap brightening consists of two components: a diffuse component
of 1500 K excess brightness, and patchy compact sources with localized
excess brightness of about 3500 K. The total flux and the number of
compact polar sources as well as the North-South extent of the diffuse
polar emission are larger in the pole which is closest to the Earth. We
compared the microwave polar emission with nearly simultaneous SoHO EIT
images taken in the lines of He ii at 304 Angstroms and Fe xii at 195
Angstroms. No one-to-one correlation between the compact radio sources
and the bright EUV features was found: most of the radio emission arises
between the plumes visible to EIT. The boundaries of the polar-cap
brightenings did not match exactly the boundaries of the coronal holes
as seen in the Fe xii 195 Angstroms images. The temporal variations of
the compact microwave sources did not correspond to any significant
changes in EUV emission. On the other hand, most He ii 304 Angstroms
changing features were associated with the diffuse polar microwave
emission which was practically constant. Our data suggest that the
origin of the polar brightening is not coronal; it seems that the bulk
of the patchy radio emission comes from heights below the 80000 K layer.

---------------------------------------------------------
Title: A Microwave Study of Coronal Ejecta
Authors: Kundu, M. R.; Nindos, A.; Raulin, J. -P.; Shibasaki, K.;
White, S. M.; Nitta, N.; Shibata, K.; Shimojo, M.
1999AAS...194.1704K Altcode: 1999BAAS...31..853K
Using Nobeyama 17 GHz data, we have studied the radio properties
of 19 coronal jets identified in Yohkoh SXT X-ray observations. The
radio data provide information on the physical conditions in the jets
which complements the data from the X-ray surveys. Microwave emission
was associated with the majority of the X-ray jets in our sample. The
radio emission typically came from the base or the base and lower part
of the jets. We detected radio emission from almost all jets which
showed flare-like activity at their bases. The jets which were not
associated with radio emission did not show any significant increase
in X-ray emission at their bases. The strongest radio emission came
from two of the largest jets in our sample. Our data show a general
correlation between the X-ray jet fluxes and the associated radio
fluxes. The 17 GHz time profiles were gradual and unpolarized, implying
that the emission was thermal. In a two-sided-loop jet (July 22, 1992
event) and one anemone-type jet (February 9, 1993 event), the observed
microwave fluxes from the lower part of the jets were well above the
fluxes calculated from the computed physical parameters of the soft
X-ray-emitting material on the basis of thermal free-free emission. We
interpret the large discrepancies in terms of the presence of lower
temperature material which cannot be detected by the SXT (the SXT is
most sensitive to hot plasma above 2 x 10(6) K) but which produces
strong microwave free-free emission. This is the first time that
such material has been observed in two-sided-loop type jets. We also
observed motion of a jet-associated microwave source with a velocity
of 55 km/sec. The microwave motion occurred after the appearance of
the X-ray jet. There is clear evidence that the microwave emission of
that source was associated with the jet and not with the associated
small flare.

---------------------------------------------------------
Title: The Sun's Corona viewed from EUV and Radio Wavelengths
Authors: Zhang, J.; Kundu, M. R.; White, S. W.
1999AAS...194.1608Z Altcode: 1999BAAS...31..851Z
The Sun's Corona, which is composed of a few million degree plasma,
can be best viewed in two electro-magnetic wavelength domains, one
from a few Angstrom to hundreds of Angstrom (in Soft X-ray and EUV
domains), the other from a few centimeter to several tens of centimeter
wavelengths (in radio domain). In this paper, we present the detailed
and quantitative comparison of corona observations made in these two
domains with high spatial resolution and full view of the Sun. The
EUV observations were taken with EIT (Extreme Ultraviolet Imager) on
board SOHO (Solar and Heliospheric Observatory) in Fe spectral lines
centered at 171, 195 and 284 Angstrom, respectively; while the radio
observations were taken with the VLA (Very Large Array) at 6 and 20 cm,
and NRH (Nobeyama Radio Heliograph) at 1.8 cm (17 Ghz), respectively. We
have found that there exists excellent morphological similarity of
corona features between these two sets of observations. However,
the quantitative comparisons have revealed that the predicted radio
flux from EUV observations based on traditional assumptions is always
higher than that observed directly by radio instruments, by a factor
of 4 to 6. The discrepancy is probably due to the underestimation of
coronal ion abundance (e.g. Meyer's abundance) by a factor of 4 to 6.

---------------------------------------------------------
Title: Millimeter Imaging Observations of High Energy Electrons in
Solar Flares
Authors: White, S. M.; Kundu, M. R.
1999AAS...194.8009W Altcode: 1999BAAS...31..966W
The 10-element BIMA array will be used in to image solar flares at
millimeter wavelengths during campaign periods in the upcoming solar
maximum. Since millimeter emission in the impulsive phase of flares
comes from electrons with energies typically in excess of 1 MeV,
these observations complement observations of lower energy electrons
at other wavelengths. Recent BIMA flare data will be presented and
plans for the near future will be discussed.

---------------------------------------------------------
Title: A Study of Microwave-selected Coronal Transient Brightenings
Authors: Nindos, A.; Kundu, M. R.; White, S. M.
1999ApJ...513..983N Altcode:
We present the results of a search for radio-selected transient
brightenings (TBs) in the solar atmosphere as a complement to the
more common X-ray-selected surveys. The Sun was generally quiet during
the observations, making these data sensitive to weak TBs both in and
outside active regions. Five small impulsive events were identified
in a set of VLA observations at 4.5, 1.5, and 0.33 GHz and compared
with soft X-ray images from Yohkoh and EUV images from SOHO/EIT. Four
of the events were located at the edges of an active region, but one
was located 100" away in a quiet region of the atmosphere. Possible
emission mechanisms for these brightenings are investigated. The time
profiles of the radio TBs show impulsive peaks, while the corresponding
soft X-ray profiles are gradual. The impulsive radio peaks were
up to 35% polarized. Our data favor an interpretation in terms of
gyrosynchrotron radiation from mildly relativistic electrons. A small
number of nonthermal electrons with spectral index 3 can explain the
observed properties of the TBs. Thus, nonthermal TBs can be found away
from active regions. Two of the microwave TBs also show evidence for
type III radio emission at 327 MHz.

---------------------------------------------------------
Title: A Test for Coronal Magnetic Field Extrapolations
Authors: Lee, Jeongwoo; White, Stephen M.; Kundu, Mukul R.; Mikić ,
Zoran; McClymont, A. N.
1999ApJ...510..413L Altcode:
As models for the physical properties of the corona above solar
active regions grow more sophisticated, we will require better
means for testing them. In this paper we discuss and apply such a
test to a magnetic field model for an active region. This test is
based on the expectation that the temperatures at different points
on a given magnetic field line should be well correlated because of
the rapid transport of heat along field lines in the corona. We use
radio observations of an active region to measure the temperatures
on field lines as they cross two isogauss surfaces (at 430 and
750 G) in the corona. The field lines and isogauss surfaces are
derived from a coronal magnetic field model obtained via a nonlinear
force-free field extrapolation of a photospheric vector magnetogram;
for comparison, we also investigate a potential-field extrapolation
of the same magnetogram. In a region in which strongly sheared fields
are present, the nonlinear force-free field model does indeed show
a good correlation between the temperatures in the two surfaces at
points on the same field line, while the potential-field model does
not. This diagnostic acts both as a test of the magnetic field model
as well as of the interpretation of the radio data, and we show how
this test can also aid in understanding the radio data.

---------------------------------------------------------
Title: University of Maryland, Department of Astronomy, College Park,
Maryland 20742. Report for the period 1 Oct 1997 - 30 Sep 1998.
Authors: Kundu, M. R.
1999BAAS...31..194K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Solar Flare Physics
Authors: Schmahl, Edward J.; Kundu, Mukul R.
1998STIN...9914342S Altcode:
We have continued our previous efforts in studies of fourier imaging
methods applied to hard X-ray flares. We have performed physical
and theoretical analysis of rotating collimator grids submitted
to GSFC(Goddard Space Flight Center) for the High Energy Solar
Spectroscopic Imager (HESSI). We have produced simulation algorithms
which are currently being used to test imaging software and hardware
for HESSI. We have developed Maximum-Entropy, Maximum-Likelihood,
and "CLEAN" methods for reconstructing HESSI images from count-rate
profiles. This work is expected to continue through the launch of
HESSI in July, 2000. Section 1 shows a poster presentation "Image
Reconstruction from HESSI Photon Lists" at the Solar Physics Division
Meeting, June 1998; Section 2 shows the text and viewgraphs prepared
for "Imaging Simulations" at HESSI's Preliminary Design Review on July
30, 1998.

---------------------------------------------------------
Title: The Height Structure of the Solar Atmosphere from the
Extreme-Ultraviolet Perspective
Authors: Zhang, Jie; White, S. M.; Kundu, M. R.
1998ApJ...504L.127Z Altcode: 1998astro.ph..7175Z
We investigate the structure of the solar chromosphere and transition
region using full Sun images obtained with the Extreme-Ultraviolet
Imaging Telescope (EIT) aboard the Solar and Heliospheric Observatory
spacecraft. The limb seen in the EIT coronal images (taken in
lines of Fe IX/X at 171 Å, Fe XII at 195 Å, and Fe XV at 284 Å)
is an absorption limb predicted by models to occur at the top of the
chromosphere where the density of neutral hydrogen becomes significant
(~1010 cm-3). The transition-region limb seen
in He II λ304 images is an emission limb. We find that (1) the limb
is higher at the poles than at the equator both in the coronal images
(by 1300+/-650 km) and the 304 Å images (by 3500+/-1200 km), and (2)
the 304 Å limb is significantly higher than the limb in the coronal
images. The height difference is 3100+/-1200 km at the equator and
6600+/-1200 km at the poles. We suggest that the elevation of the
304 Å limb above the limb in the coronal images may be due to the
upper surface of the chromosphere being bumpy, possibly because of
the presence of spicules. The polar extension is consistent with a
reduced heat input to the chromosphere in the polar coronal holes
compared with the quiet-Sun atmosphere at the equator.

---------------------------------------------------------
Title: Coronal Currents, Magnetic Fields, and Heating in a Solar
Active Region
Authors: Lee, Jeongwoo; McClymont, A. N.; Mikić, Zoran; White,
Stephen M.; Kundu, Mukul R.
1998ApJ...501..853L Altcode:
We compare microwave images of a solar active region with
state-of-the-art fully nonlinear force-free extrapolations of the
photospheric fields in order to study the link between coronal currents
and heating of the corona. This extrapolation fully takes into account
the nonuniform distribution of electric currents observed in the
photosphere and its role in the coronal magnetic structure. We carry
out the comparison for AR 6615, a complex region observed with the
VLA on 1991 May 7. Under the assumption that the microwave emission
is dominated by optically thick gyroresonance radiation, we may use
the radio images to infer the temperature of the corona at different
heights and locations. This is then compared with heating models based
on the observed current distribution. We are able to reproduce the radio
images remarkably well with a model in which temperature is structured
along magnetic field lines, depends on the current on the field line,
and increases with height in a manner similar to that inferred from
static heated loop models. This result implies a direct link between
electric currents and coronal heating.

---------------------------------------------------------
Title: Spatial Structure of Solar Coronal Magnetic Loops Revealed
by Transient Microwave Brightenings
Authors: Zhang, J.; Gopalswamy, N.; Kundu, M. R.; Schmahl, E. J.;
Lemen, J. R.
1998SoPh..180..285Z Altcode:
We present the measurement of magnetic field gradient in magnetic
loops in the solar corona, based on the multi-wavelength Very Large
Array observations of two transient microwave brightenings (TMBs)
in the solar active region 7135. The events were observed at 2 cm
(spatial resolution ∼ 2=) and 3.6 cm (spatial resolution ∼ 3=)
with a temporal resolution of 3.3 s in a time-sharing mode. Soft X-ray
data (spatial resolution ∼ 2.5=) were available from the Soft X-ray
Telescope on board the Yohkoh satellite. The three-dimensional structure
of simple magnetic loops, where the transient brightenings occurred,
were traced out by these observations. The 2-cm and 3.6-cm sources
were very compact, located near the footpoint of the magnetic loops
seen in the X-ray images. For the two events reported in this paper,
the projected angular separation between the centroids of 2 and 3.6-cm
sources is about 2.3= and 3.1=, respectively. We interpret that the 2
and 3.6-cm sources come from thermal gyro-resonance emission. The 2-cm
emission is at the 3rd harmonic originating from the gyro-resonance
layer where the magnetic field is 1800 G. The 3.6-cm emission is at
the 2nd harmonic, originating from the gyro-resonance layer with a
magnetic field of 1500 G. The estimated magnetic field gradient near
the footpoint of the magnetic loop is about 0.09 G km=1 and
0.12 G km=1 for the two events. These values are smaller
than those observed in the photosphere and chromosphere by at least
a factor of 2.

---------------------------------------------------------
Title: Microwave Mode Coupling Above Active Regions as a Coronal
Density Diagnostic
Authors: Lee, Jeongwoo; White, Stephen M.; Kundu, M. R.; Mikić,
Zoran; McClymont, A. N.
1998SoPh..180..193L Altcode:
It is well recognized that the phenomenon of depolarization (the
conversion of polarized radio emission into unpolarized emission) of
microwaves over solar active regions can be used to infer the coronal
electron density once the coronal magnetic field is known. In this
paper we explore this technique using an active region for which we
have excellent radio data showing depolarization at two frequencies,
and for which we have an excellent magnetic field model which has been
tested against observations. We show that this technique for obtaining
coronal densities is very sensitive to a number of factors. When Cohen's
(1960) theory where depolarization is due to magnetic field rotation
alone is used, the result is particularly sensitive to the location
of the surface on which the magnetic field is orthogonal to the line
of sight. Depending on whether we take into account the presence
of electric currents in the photosphere or not, their extrapolation
into the corona can result in very different heights being deduced
for the location of the depolarization strip, and this changes the
density which is then deduced from the depolarization condition. Such
extreme sensitivity to the magnetic field model requires that field
extrapolations be able to accurately predict the polarity of magnetic
fields up to coronal heights as high as ∼ 105 km in order
to exploit depolarization as a density diagnostic.

---------------------------------------------------------
Title: Microwave and Soft X-ray Study of Solar Active Region Evolution
Authors: Lara, A.; Gopalswamy, N.; Kundu, M. R.; Pérez-Enríquez,
R.; Koshiishi, H.; Enome, S.
1998SoPh..178..353L Altcode:
We have studied the properties and evolution of several active
regions observed at multiple wavelengths over a period of about 10
days. We have used simultaneous microwave (1.5 and 17 GHz) and soft
X-ray measurements made with the Very Large Array (VLA), the Nobeyama
Radio Heliograph (NRH) and the Soft X-ray Telescope (SXT) on board
the Yohkoh spacecraft, as well as photospheric magnetograms from
KPNO. This is the first detailed comparison between observations at
radio wavelengths differing by one order of magnitude. We have performed
morphological and quantitative studies of active region properties by
making inter-comparison between observations at different wavelengths
and tracking the day-to-day variations. We have found good general
agreement between the 1.5 and 17 GHz radio maps and the soft X-rays
images. The 17 GHz emission is consistent with thermal bremsstrahlung
(free-free) emission from electrons at coronal temperatures plus a small
component coming from plasma at lower temperatures. We did not find
any systematic limb darkening of the microwave emission from active
regions. We discuss the difference between the observed microwave
brightness temperature and the one expected from X-ray data and in
terms of emission of a low temperature plasma at the transition region
level. We found a coronal optical thickness of ∼ 10-3
and ∼ 1 for radiation at 17 and 1.5 GHz, respectively. We have
also estimated the typical coronal values of emission measure (∼
5 × 1028 cm-5), electron temperature (∼
4.5 × 1066 K) and density (∼ 1.2 × 109
cm3). Assuming that the emission mechanism at 17 GHz is
due to thermal free-free emission, we calculated the magnetic field
in the source region using the observed degree of polarization. From
the degree of polarization, we infer that the 17 GHz radiation is
confined to the low-lying inner loop system of the active region. We
also extrapolated the photospheric magnetic field distribution to the
coronal level and found it to be in good agreement with the coronal
magnetic field distribution obtained from microwave observations.

---------------------------------------------------------
Title: Two-Sided-Loop Type X-ray Jets and Metric Radio Bursts
Authors: Kundu, M. R.; Raulin, J. -P.; Nitta, N.; Shibata, K.;
Shimojo, M.
1998SoPh..178..173K Altcode: 1998SoPh..178..611K
We have searched for nonthermal radio signatures in the form of metric
type III bursts in conjunction with two-sided-loop-type X-ray jets
observed by the Yohkoh/SXT experiment. We have found no evidence of
type III bursts in association with this particular type of X-ray jets
in contrast to the positive evidence of type III's in association
with anemone-type X-ray jets. This result is consistent with the
simulation results of Yokoyama and Shibata (1995), which show that
anemone-type jets are produced by vertical/oblique plasma flow whereas
the two-sided-loop-type jets are produced by horizontal plasma flow.

---------------------------------------------------------
Title: The Emergence of a Solar Active Region
Authors: White, S. M.; Lee, J.; Kundu, M. R.; SOHO/MDI Team
1998ASPC..155..130W Altcode: 1998sasp.conf..130W
No abstract at ADS

---------------------------------------------------------
Title: Type-III metric and microwave burst observations of coronal
X-ray jets
Authors: Kundu, M.
1998ESASP.421..179K Altcode: 1998sjcp.conf..179K
No abstract at ADS

---------------------------------------------------------
Title: The Solar Atmosphere Above a Sunspot
Authors: Zlotnik, E. Ya.; White, S. M.; Kundu, M. R.
1998ASPC..155..135Z Altcode: 1998sasp.conf..135Z
No abstract at ADS

---------------------------------------------------------
Title: Synoptic Radio Observations
Authors: Schmahl, E. J.; Kundu, M. R.
1998ASPC..140..387S Altcode: 1998ssp..conf..387S
No abstract at ADS

---------------------------------------------------------
Title: University of Maryland, Department of Astronomy, College Park,
Maryland 20742. Report for the period 1 Oct 1996 - 30 Sep 1997.
Authors: Kundu, M. R.
1998BAAS...30..233K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A Search for Hard X-ray Emission from Active Stars Using
CGRO/BATSE
Authors: White, S. M.; Harmon, B. A.; Lim, J.; Kundu, M. R.
1998ASPC..154.1192W Altcode: 1998csss...10.1192W
We report the results of a search for &gt; 20 keV photons from active
stars using CGRO/BATSE Earth-occultation observations. Twelve of
the "usual suspects" together with 12 "placebo" locations have been
analyzed using the BATSE software for occultation analysis developed
at NASA/MSFC. There are four detections at the nominal 5sigma level,
and eight at the 3sigma level. However the strongest detection (that of
AB Dor) shows clear evidence for contamination from the nearby strong
source LMC X-4. 18 of the 24 fields yield positive fluxes, indicating a
clear bias in the results, and possibly indicating the presence of weak
background hard X-ray sources detectable by BATSE in long-term studies.

---------------------------------------------------------
Title: Fast Time Structure during Transient Microwave Brightenings:
Evidence for Nonthermal Processes
Authors: Gopalswamy, N.; Zhang, J.; Kundu, M. R.; Schmahl, E. J.;
Lemen, J. R.
1997ApJ...491L.115G Altcode: 1997astro.ph.10200G
Transient microwave brightenings (TMBs) are small-scale energy releases
from the periphery of sunspot umbrae with a flux density 2 orders
of magnitude smaller than that from a typical flare. Gopalswamy et
al. first reported the detection of the TMBs, and it was pointed out
that the radio emission implied a region of very high magnetic field
so that the emission mechanism has to be gyroresonance or nonthermal
gyrosynchrotron, but not free-free emission. It was not possible to
decide between gyroresonance and gyrosynchrotron processes because
of the low time resolution (30 s) used in the data analysis. We have
since performed a detailed analysis of the Very Large Array data with
full time resolution (3.3 s) at two wavelengths (2 and 3.6 cm), and we
can now adequately address the question of the emission mechanism of
the TMBs. We find that nonthermal processes indeed take place during
the TMBs. We present evidence for nonthermal emission in the form of
temporal and spatial structure of the TMBs. The fast time structure
cannot be explained by a thermodynamic cooling time and therefore
requires a nonthermal process. Using the physical parameters obtained
from X-ray and radio observations, we determine the magnetic field
parameters of the loop and estimate the energy released during the
TMBs. The impulsive components of TMBs imply an energy release rate
of ~1.3×1022 ergs s-1, so the thermal energy
content of the TMBs could be less than ~1024 ergs.

---------------------------------------------------------
Title: Detection of Microwave Emission from Coronal X-Ray Jets
Authors: Kundu, M. R.; Shibasaki, K.; Nitta, N.
1997ApJ...491L.121K Altcode:
We present evidence of the detection of microwave emission at 17 GHz in
association with coronal X-ray jets. We present two typical cases--one
on the disk (1995 March 31) and the other at the limb (1992 August
25). For the disk event we see 17 GHz emission from the upper part of
the jet base (active region loop or loops), but no emission from the
collimated X-ray jet itself, implying that it must be optically thin
at 17 GHz. For the limb event, we see the base of the jet as well as
the bottom part of the jet itself, implying that the optical depth is
higher at the bottom part (obviously because of higher electron density)
than at the top. We believe that the 17 GHz emission is thermal,
because it is gradual and unpolarized, and that the heating process
that gives rise to the jet X-ray plasma also results in the 17 GHz
emission. The calculated 17 GHz flux densities seem to agree with the
observed values within a factor of 2. We consider this disagreement
to be quite reasonable in view of the various uncertainties involved
in computing the emission in both radio and X-rays.

---------------------------------------------------------
Title: X-Ray and Radio Studies of a Coronal Eruption: Shock Wave,
Plasmoid, and Coronal Mass Ejection
Authors: Gopalswamy, N.; Kundu, M. R.; Manoharan, P. K.; Raoult, A.;
Nitta, N.; Zarka, P.
1997ApJ...486.1036G Altcode:
On 1994 July 31, a fast (900 km s-1) eruptive structure
was observed in X-rays, followed by a slower plasmoid (180 km
s-1). They were associated with a coronal mass ejection,
prominence eruption, and a host of metric radio bursts. The X-ray
structure seems to be a part of a white light coronal mass ejections
(CME), as inferred from the white light images of July 30 and 31. A type
II burst was observed at the leading edge of the X-ray eruption, while a
type IV burst was spatially associated with the detached plasmoid. The
type III radio bursts occurred on thin overdense structures associated
with the eruption. We detected the rise of plasma levels because
of mass addition to the type III burst sources as a result of the
eruption. This event further clarifies the manifestation of a CME in
X-rays. We identify the X-ray eruption as the driver of the coronal
shock wave. This provides answer to the long-standing question regarding
the origin of coronal and interplanetary shock waves. We have also found
evidence to support the idea that herringbone bursts are produced when
the coronal shock wave crosses open magnetic field lines.

---------------------------------------------------------
Title: Radio Observations of Gyroresonance Emission from Coronal
Magnetic Fields
Authors: White, S. M.; Kundu, M. R.
1997SoPh..174...31W Altcode:
We review the basic characteristics of thermal gyroresonance (also known
as cyclotron) emission from solar active regions, and show how radio
observations combined with our understanding of the basic mechanism
can reveal much of the magnetic and thermal structure of the corona
over active regions.

---------------------------------------------------------
Title: Signatures of Coronal Currents in Microwave Images
Authors: Lee, Jeongwoo; White, Stephen M.; Gopalswamy, N.; Kundu, M. R.
1997SoPh..174..175L Altcode:
Microwave emission from solar active regions at frequencies above 4
GHz is dominated by gyroresonance opacity in strong coronal magnetic
fields, which allows us to use radio observations to measure coronal
magnetic field strengths. In this paper we demonstrate one powerful
consequence of this fact: the ability to identify coronal currents
from their signatures in microwave images. Specifically, we compare
potential-field (i.e., current-free) extrapolations of photospheric
magnetic fields with microwave images and are able to identify regions
where the potential extrapolation fails to predict the magnetic field
strength required to explain the microwave images. Comparison with
photospheric vector magnetic field observations indicates that the
location inferred for coronal currents agrees with that implied by the
presence of vertical currents in the photosphere. The location, over
a neutral line exhibiting strong shear, is also apparently associated
with strong heating.

---------------------------------------------------------
Title: Solar Flare Physics
Authors: Schmahl, Edward J.; Kundu, Mukul R.
1997umd..rept.....S Altcode: 1997STIN...9892889S
We have continued our previous efforts in studies of fourier imaging
methods applied to hard X-ray flares. We have performed physical
and theoretical analysis of rotating collimator grids submitted to
GSFC for future space or suborbital missions involving the imaging
of solar flares in hard X-rays. In particular, we have simulated the
performance of the High Energy Solar Spectroscopic Imager (HESSI),
using pseudo-flare images provided. We have computed count rates that
HESSI would record for these simulated flares, and reconstructed images
from the count rates.

---------------------------------------------------------
Title: Modeling of a Microwave Burst Emission
Authors: Preka-Papadema, P.; Alissandrakis, C. E.; Dennis, B. R.;
Kundu, M. R.
1997SoPh..172..233P Altcode: 1997ESPM....8..233P
We applied model computations on a microwave burst observed with
the Westerbork Synthesis Radio Telescope (WSRT) at 6 cm. We used
additional data from Hα, soft and hard X-rays in order to reproduce
the flaring loop and to compute the microwave total intensity and
circular polarization. We examined both cases of thin and thick
target. The computations show a large emission source in an optically
thick loop. We compare our results with the observation.

---------------------------------------------------------
Title: Radio Observations of the Emergence of a Solar Active Region
Authors: White, S. M.; Lee, J.; Kundu, M. R.
1997SPD....28.0603W Altcode: 1997BAAS...29..910W
On July 6 1996 a solar active region abruptly began to emerge through
the solar photosphere. This region was eventually to produce the first
X-class flare since 1993. We happened to be observing the region with
the VLA during its emergence, and present a preliminary report on
the observations in this paper. The radio data are the only means for
observing the magnetic fields of the emerging region in the corona,
and can thus be used to test models for the structure of emerging
magnetic fields. In this case, we do not see any evidence for strong
coronal fields during the initial emergence, indicating that the field
lines diverge rapidly above the photosphere as expected from simple
theory. We follow the emergence of flux over several days and discuss
the implications of these observations for theories of flux emergence.

---------------------------------------------------------
Title: Tracking a CME from Cradle to Grave: A Multi-wavelength
Analysis of the February 6-7, 1997 Event
Authors: Gopalswamy, N.; Kundu, M. R.; Hanaoka, Y.; Kosugi, T.; Hudson,
H.; Nitta, N.; Thompson, B.; Gurman, J.; Plunkett, S.; Howard, R.;
Burkepile, J.
1997SPD....28.0501G Altcode: 1997BAAS...29..908G
The partially earth-directed coronal mass ejection (CME) event of 1997
February 6-7 originated from the southwest quadrant of the sun. The
CME accelerated from 170 km/s to about 830 km/s when it reached a
distance of 25 solar radii. The CME was an arcade eruption followed
by bright prominence core structures. The prominence core was tracked
continuously from the solar surface to the interplanetary medium by
combining data from the Nobeyama radioheliograph (microwaves), Mauna Loa
Solar Observatory (He 10830 { Angstroms}), SOHO/EIT (EUV) and SOHO/LASCO
(white light). The CME was accompanied by an arcade formation, fully
observed by the YOHKOH/SXT (soft X-rays) and SOHO/EIT (EUV). The X-ray
and EUV observations suggest that the reconnection proceeded from
the northwest end to the southeast end of a filament channel. In the
SOHO/EIT images, the the feet of the soft X-ray arcade were observed
as EUV ribbons. The CME event also caused a medium sized geomagnetic
storm: The hourly equatorial Dst values attained storm level during
18:00-19:00 UT on February 09. This means the disturbance took about
2.25 days to reach the Earth. The first signatures of an IP shock was
a pressure jump in the WIND data around 13:00 UT on Feb 09, 1997 which
lasted for about 14 hours, followed by flux rope signatures. This CME
event confirms a number of ideas about CMEs: The three part structure
(frontal bright arcade, dark cavity and prominence core), disappearing
filament, elongated arcade formation, and terrestrial effects. We make
use of the excellent data coverage from the solar surface to the Earth
to address a number of issues regarding the origin and propagation of
the geoeffective solar disturbances. We benefited from discussions at
the first SOHO-Yohkoh Coordinated Data Analysis Workshop, held March
3-7, 1997, at Goddard Space Flight Center.

---------------------------------------------------------
Title: Currents, Magnetic Fields and Heating in a Solar Active Region
Authors: Lee, J.; McClymont, A. N.; Mikic, Z.; White, S. M.; Kundu,
M. R.
1997SPD....28.1602L Altcode: 1997BAAS...29R.920L
We have compared high-quality microwave images of the radio emission
from the corona above an active region with state-of-the-art nonlinear
force-free extrapolations of the photospheric magnetic field. The radio
images, which are dominated by the opacity provided by the coronal
magnetic fields, show excess magnetic field in locations consistent
with the expected location of coronal currents. We test the hypothesis
that the degree of heating on a given coronal magnetic flux tube is
related to the current flowing through it by comparing model radio
brightness distributions at different frequencies with the actual
observations. In the model we assume that temperature is distributed
along the field lines according to quasi-static loop models, and that
there is effectively no diffusion across the field lines. This coronal
heating model is able to reproduce the radio brightness distributions
remarkably well.

---------------------------------------------------------
Title: Multi-wavelength Observations of Transient Microwave
Brightenings in a Solar Active Region
Authors: Zhang, Jie; Gopalswamy, N.; Kundu, M. R.; Schmahl, E. J.;
Lemen, J. R.
1997SPD....28.0163Z Altcode: 1997BAAS...29..891Z
We present multi-wavelength Very Large Array observations of two
transient microwave brightenings (TMBs) in the solar active region
7135. The events were observed at 2 cm (spatial resolution ~ 2”) and
3.6 cm (spatial resolution ~ 3”) with a temporal resolution of 3.3 s
in a time-sharing mode. Soft X-ray data (about 5” spatial resolution)
were available from the Soft X-ray Telescope on board the YOHKOH
satellite. The 2 cm and 3.6 cm emission sources were very compact,
located near the footpoint of the magnetic loops seen in the X-ray
images. The TMBs traced out the three dimensional structure of the
magnetic loops where the transient brightenings occurred. For the
two events reported in this paper, the projected angular separation
between the centroids of 2 and 3.6 cm source is about 2.3” and 3.1”,
respectively. We interpret the spatial and temporal distributions
as implying that the 2 and 3.6 cm flux is mainly due to thermal
gyro-resonance emmision. The 2 cm emission seems to be at the 3rd
gyro-harmonic coming from the 1800 G gyro-resonance layer. The 3.6 cm
emission seems to be at both the 2nd and 3rd harmonics, originating
from gyro-resonance layers with a magnetic field of 1500 G and 1000
G, respectively. However, the two gyro-resonance layers for 3.6 cm
emission are not resolved with the current spatial resolution. The
estimated magnetic field gradient near the footpoint of the magnetic
loop is about 0.17 G km(-1) and 0.22 G km(-1) for the two events.

---------------------------------------------------------
Title: Microwave Radio Emission from Coronal X-ray Jets
Authors: Kundu, M. R.; Shibasaki, K.; Nitta, N.
1997SPD....28.0142K Altcode: 1997BAAS...29..887K
We report the first detection of microwave emission from coronal
X-ray jets using simultaneously obtained imaging data at 17 GHz
(Nobeyama Radioheliograph data) and in X-rays (Yohkoh/SXT data). We
present detailed results for one jet on the disk and another at the
limb. The 17 GHz emission in the disk event originates from the base
(a loop or a system of loops) of the jet, and for the limb jet the
microwave emission comes from the base as well as from a part of the
X-ray jet. We believe that the collimated jet is optically thin at 17
GHz in most cases. We have investigated more than two dozen jet events
and found 17 GHz emission in at least 70% of the cases. The 17 GHz
emission is unpolarized. We interpret the microwave emission as thermal,
related to the heating of the plasma responsible for the X-ray jet.

---------------------------------------------------------
Title: University of Maryland, Department of Astronomy, College Park,
Maryland 20742. Report for the period 1 Oct 1995 - 30 Sep 1996.
Authors: Kundu, M. R.
1997BAAS...29..232K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A Multi-Wavelength Analysis of the February 6/7, 1997 Coronal
Mass Ejection
Authors: Plunkett, S. P.; Gopalswamy, N.; Kundu, M. R.; Howard, R. A.;
Thompson, B. J.; Gurman, J. B.; Lepping, R. P.; Hudson, H. S.; Nitta,
N.; Hansoka, Y.; Kosugi, T.; Burkepile, J. T.
1997ESASP.404..615P Altcode: 1997cswn.conf..615P
No abstract at ADS

---------------------------------------------------------
Title: Radio Observations of Coronal X-ray Jets
Authors: Kundu, Mukul R.
1997IAUJD..19E...5K Altcode:
Among many discoveries, the Yohkoh/SXT experiment has discovered X-ray
jets which are transitory X-ray enhancements with well-collimated
motion (Shibata et al. 1992, PASJ,161,L173). In many cases, the jets
are associated with small flares at or near their foot points and the
motion appears to be a real flow of plasma at temperatures of a few
million degrees. We have detected microwave radio emission at 17 GHz
from these coronal jets, which appears to be thermal in nature. The
microwave emission appears to be associated mainly with the base of the
jets although in some cases the jets (which may be optically thin at 17
GHz) produce microwave emission. We have found evidence of non-thermal
radio emission from jets in the form of metric type III bursts. The
type III bursts are spatially and temporally coincident with the X-ray
jets.The implications of both sets of observations will be discussed.

---------------------------------------------------------
Title: Radio and X-Ray Studies of a Coronal Mass Ejection Associated
with a Very Slow Prominence Eruption
Authors: Gopalswamy, N.; Hanaoka, Y.; Kundu, M. R.; Enome, S.; Lemen,
J. R.; Akioka, M.; Lara, A.
1997ApJ...475..348G Altcode:
We report on the observations of an X-ray coronal mass ejection
(CME) with its three part structure: frontal loop, coronal cavity,
and the eruptive prominence core. The prominence core was observed in
microwaves, and the frontal loop was observed in X-rays. A coronal
volume much larger than that occupied by the prominence seems to be
affected by the eruption. Formation of an arcade structure was also
observed beneath the erupting prominence. X-ray enhancement at the
arcade persisted for several hours similar to long decay events. At
the apex of the arcade there was a bright knot, which we interpret
as the reconnection region from which the filament gets detached. We
determined the trajectories of the frontal loop and the prominence core
and found them to have very different characteristics. The CME showed an
extremely small acceleration, while the prominence had a linear motion
in the beginning followed by an exponential rise. However, during the
several hours of simultaneous observation, the prominence did not catch
up with the frontal loop. We determined the evolution of the CME mass,
which increased by a factor of 4 during our observations. We discuss
the implications of the observations in the general context of coronal
mass ejections.

---------------------------------------------------------
Title: A Giant Prominence Eruption Observed by Nobeyama
Radioheliograph and YOHKOH Spacecraft
Authors: Gopalswamy, N.; Hanaoka, Y.; Kundu, M. R.; Shibasaki, K.;
Koshiishi, H.; Enome, S.; Lemen, J. R.
1997IAUJD..19E...4G Altcode:
The results of an investigation of a giant prominence which erupted from
the northwest limb of the Sun on 1994 April 05, will be reported. The
event could be traced back to a large prominence of March 19, 1994
above the east limb. The filament was located in the north-south
direction when it appeared on the disk. At about 23:00 UT on April 05,
the filament started slowly rising and then accelerated. The speed of
the prominence was was only 75 km s^{-1} when it reached a height of
about 0.5 R_ odot above the surface. Preliminary examination shows that
the eruption caused a geomagnetic storm on April 07 at 20:00 UT. We
study the dynamical and physical properties of the erupting prominence
and obtain physical parameters of the prominence plasma. In X-rays, the
region of eruption was relatively faint. After the eruption, however,
there was a large void at the previous location of the prominence and
an arcade formed progressively spreading from south to north along
the limb. Based on the X-ray and radio observations, we determine the
characteristics of the pre- and post-eruption structures.

---------------------------------------------------------
Title: Radio Continuum and Type III Bursts Associated with Coronal
X-Ray Structures
Authors: Raulin, J. P.; Kundu, M. R.; Nitta, N.; Raoult, A.
1996ApJ...472..874R Altcode:
In this paper, we report the detection of a metric continuum burst
source at the top of a coronal loop observed in soft X-rays. The
continuum burst was probably a flare continuum that lasted more than
1 hr. This is the first observation of such metric continuum emission
produced by energetic electrons with high-spatial resolution imaging
instruments in both X-rays and radio. The nonthermal radio emission
appears to be associated with the rupture of a part of the loop
top and the ejection of soft X-ray plasma at the top of the coronal
loop. We have also identified X-ray coronal structures in which type
III emitting electron beams propagate. The metric continuum is most
likely caused by second-harmonic plasma emission, and the electron
density in the soft X-ray structure where type Ills are observed is
close to the critical plasma density derived from radio observations.

---------------------------------------------------------
Title: Radio and X-ray Imaging Observations of Solar Flares and
Coronal Transients
Authors: Kundu, M. R.
1996SoPh..169..389K Altcode:
We present a review of selected studies based upon simultaneous radio
and X-ray observations of solar flares and coronal transients. We use
primarily the observations made with large radio imaging instruments
(VLA, BIMA, Nobeyama, and Nançay) along with Yohkoh/SXT and HXT and
CGRO experiments. We review the recent work on millimeter imaging
of solar flares, microwave and hard X-ray observations of footpoint
emission from flaring loops, metric type IV continuum bursts, and
coronal X-ray structures. We discuss the recent studies on thermal
and nonthermal processes in coronal transients such as XBP flares,
coronal X-ray jets, and active region transient brightenings.

---------------------------------------------------------
Title: Observation and model calculations of sunspot ring structure
at 8.46GHz
Authors: Gopalswarmy, N.; Raulin, J. P.; Kundu, M. R.; Hildebrandt,
J.; Krueger, A.; Hofmann, A.
1996A&A...316L..25G Altcode:
We present Very Large Array (VLA) observations of AR 7542 which
demonstrate the existence of definite ring and horse-shoe structures
of a sunspot in intensity (I) and polarization (V) at 8.46GHz (3.5cm
wavelength) and compare them with model calculations of gyroresonance
radiation. The VLA measurements have been made on three different days
in July 1993 when AR 7542 was at three different longitudes which allows
us to study the effect of viewing angle on sunspot-associated microwave
emission. Model calculations of gyroresonance radiation have been
carried out using a modified dipole model corresponding to the observed
photospheric magnetic field strength and average temperature/electron
density distributions consistent with soft X-ray and EUV observations
(for the lower atmosphere) as well as theoretical assumptions (for
the corona). The calculated I and V maps were found to be generally
consistent with the radio observations. We obtain information on the
magnetic scale length in vertical and horizontal directions above
the sunspot and about the distribution of other plasma parameters
(temperature, density) inside the radio source region.

---------------------------------------------------------
Title: Yohkoh/SXT observations of a coronal mass ejection near the
solar surface
Authors: Gopalswamy, N.; Kundu, M. R.; Hanaoka, Y.; Enome, S.; Lemen,
J. R.; Akioka, M.
1996NewA....1..207G Altcode:
We report the observations of a coronal mass ejection (CME) using
the Soft X-ray Telescope on board the Yohkoh Mission. The CME had
the familiar three part structure (frontal loop, prominence core
and a cavity). The erupting prominence was observed by the Nobeyama
radioheliograph. We were able to determine the mass of the CME (2.6
× 1014 g) from X-ray observations which seems to be at
the lower end of the range of CME masses reported before from white
light observations. This is the first time the mass of a CME has been
determined from X-ray observations. The height of onset of the CME
was 0.3R⊙. The CME moved much faster than the erupting
prominence while its acceleration was smaller than that of the erupting
prominence. J. Leonard Culhane

---------------------------------------------------------
Title: Comprehensive Multiwavelength Observations of the 1992 January
7 Solar Flare
Authors: Silva, Adriana V. R.; White, Stephen M.; Lin, Robert P.;
de Pater, Imke; Gary, Dale E.; McTiernan, James M.; Hudson, Hugh S.;
Doyle, J. Gerry; Hagyard, Mona J.; Kundu, Mukul R.
1996ApJS..106..621S Altcode:
Observations of a solar flare that occurred at 2022 UT on 1992
January 7, during the 1991 December/1992 January Max `91 campaign,
are presented. This flare was observed simultaneously in Hα, radio
(at microwave and millimeter wavelengths), and soft and hard X-rays
(by the Yohkoh spacecraft) with high spatial and moderate spectral
resolution. A comparison of magneto grams before and after the flare
shows evidence of the emergence of new magnetic flux of opposite
polarity at the flare site. Although this flare was only of moderate
size (GOES classification C8.9 and Hα importance SF), it exhibited
several distinct bursts and at least 10 spatially distinct hard/soft
X-ray sources. Cospatial Hα brightenings suggest that most of the
X-ray sources are located at footpoints of magnetic loops. Two of the
hard X-ray sources have no Hα counterparts and are therefore believed
to be located at loop tops. The flare consisted of three bursts
of particle acceleration followed by a purely thermal phase. High
spectral resolution Ca XIX line profiles indicate upflows shortly
after the second acceleration phase. Analysis of the microwave/hard
X-ray/soft X-ray emission from individual sources provides information
on the radio emission mechanisms, the energetic electron population,
the magnetic field strength, and the plasma density. These parameters
were estimated for the two microwave sources observed during the
third acceleration burst; these sources were simultaneously detected
in soft X-rays, and one of the sources is also seen in hard X-ray
maps. Although the microwave emission is consistent with the gyro
synchrotron mechanism, the millimeter emission, which peaks during the
thermal phase when all nonthermal activity has ceased, is likely due
to thermal bremsstrahlung from the soft X-ray emitting hot plasma. The
energy lost to collisions by the energetic (&gt;15 keV) electrons
and the energy contained in the thermal plasma are calculated for
each source. The energy injected by the nonthermal electrons from all
sources is estimated to be 1030 ergs. Only the soft X-ray
sources with gradual time profiles seem to show the Neupert effect.

---------------------------------------------------------
Title: A Model for Active Region Emission at Centimeter Wavelengths
Authors: Nindos, A.; Alissandrakis, C. E.; Gelfreikh, G. B.; Kundu,
M. R.; Dere, K. P.; Korzhavin, A. N.; Bogod, V. M.
1996SoPh..166...55N Altcode:
We present multi-frequency observations and model computations of the
microwave emission of a solar active region. The radio observations
were obtained with the RATAN-600 at several wavelengths between 0.8
and 31.6 cm and with the VLA at 6 and 20 cm. The active region was
also observed in the EUV O Iv lines by the HRTS instrument aboard
the Space Shuttle Spacelab-2 mission. These lines are formed in the
chromosphere-corona transition region and their intensity ratio is
sensitive to pressure. Photospheric magnetograms provided both the
longitudinal and the transverse component of the magnetic field. The
microwave observations were checked against model computations
taking into account both the free-free and the gyro-resonance emission
mechanisms and using the pressure data from the O IV lines. The magnetic
field was computed through constant-α force-free extrapolations of
the longitudinal photospheric field. We computed both the flux from
2 to 20 cm and the spatial structure of the microwave emission at 6
and 20 cm. The comparison of the computed and observed flux spectra
allowed us to estimate the magnetic field strength at the base of the
transition region and in the low corona, as well as the values of the
conductive flux and the height of the base of the transition region. The
model maps at 6 cm and 20 cm showed that α was not constant above the
active region; the same conclusion was reached on the basis of the
photospheric observations. The use of pressure measurements allowed
us to identify microwave structures which were determined by pressure
enhancements. At 6 cm the computations confirmed the fact that the
magnetic field is the principal factor that determines the structure
of sunspot-associated sources and showed that the effect of pressure
variations was small. Pressure variations were more important at 20 cm,
where the peak of the emission was associated with the sunspot and a
diffuse component was associated with the plage which had an average
pressure higher by a factor of 1.54 than the sunspot.

---------------------------------------------------------
Title: Radio and X-ray manifestations of a bright point flare
Authors: Gopalswamy, N.; Kundu, M. R.; Hanaoka, Y.; Enome, S.; Lemen,
J. R.
1996AIPC..374..408G Altcode: 1996hesp.conf..408G
We have found remarkably different manifestations of a bright point
flare in X-ray and radio (microwave) wavelengths, unlike previous
observations. In X-rays, the BP flare was relatively simple while
in radio, the bright point flare had a large scale component and
a transient moving component. The large scale structure may be the
radio counterpart of large scale structures sometimes seen during
X-ray BP flares. The transient component was also compact and moved
away from the location of the X-ray BP flare with a speed of ∼60
km s-1. The compact source also showed fast time structure
which suggests nonthermal emission mechanism for the transient sources.

---------------------------------------------------------
Title: Nonthermal radio emission from coronal X-ray structures
Authors: Kundu, Mukul R.; Raulin, Jean-Pierre; Nitta, Nariaki
1996AIPC..374..402K Altcode: 1996hesp.conf..402K
We have provided evidence that certain coronal X-ray structures such as
flaring X-ray bright points and X-ray jets give rise to nonthermal radio
emission in the form of metric type III bursts. We have shown an example
of a metric type IV/flare continuum being associated with the rupture
of a flaring loop-top and the ejection of X-ray emitting material.

---------------------------------------------------------
Title: Tracking Type III and Type II Solar Radio Bursts from Metric
to Hectometric Wavelengths using Ground-based and Space-borne
Observations
Authors: Gopalswamy, N.; Kundu, M. R.; Kaiser, M. L.; Kahler, S. W.;
Kondo, T.; Isobe, T.; Akioka, M.
1996AAS...188.1908G Altcode: 1996BAAS...28..851G
There exists a controversy regarding the origin of coronal and
interplanetary (IP) shocks. Present observations shows that coronal
shocks are associated with flares while the IP shocks are associated
with coronal mass ejections (CMEs). An important question in this
connection is whether the IP shocks are extensions of the coronal
shocks or they are independently driven by CMEs. The coronal shocks
have traditionally been inferred from metric type II radio bursts. The
ionospheric cut-off around 20 MHz had been a hurdle in arriving at
a firm conclusion regarding the continuation of type II bursts to
frequencies lower than the ionospheric cut off. The WAVES experiment on
board the WIND spacecraft has essentially removed this hurdle so that
we are able to track metric radio bursts to hectometric wavelengths. We
have identified about two dozen type II bursts observed by the Hiraiso
Radio Spectrograph (HiRAS) after the launch of the WIND satellite. Most
of these type II bursts were accompanied by type III bursts. We
have positively identified the solar flares associated with all the
events. When we examined the WIND Radio and Plasma waves (WAVES) data,
we found the following: (i) Most of the metric (Hiraiso) type III bursts
have counterparts in the WAVES data; (ii) None of the metric type II
bursts have counterparts in the WAVES data. This result suggest that
coronal shocks responsible for metric type II bursts are blast waves
which decay rapidly within the inner corona while the electron beams
producing type III bursts continue to propagate to the IP medium.

---------------------------------------------------------
Title: Millimeter Observations of a B5.6 Flare
Authors: Raulin, J. -P.; White, S. M.; Kundu, M. R.; Silva, A. V. R.;
Shibasaki, K.
1996AAS...188.4503R Altcode: 1996BAAS...28..894R
We present millimeter imaging observations of a B5.6 flare which occured
on 1994 August 16 in the active region AR 7765. The BIMA interferometer
and the Nobeyama radioheliograph observed both the impulsive phase
and the thermal phase of the flare emission. The 3.5 mm maps obtained
with BIMA allowed us to determine the location of the radio source
and its properties at different phases of the flare evolution. In
X-ray wavelengths the impulsive phase was detected by the first two
channels of BATSE (25-50 keV, 50-100 keV); although YOHKOH/SXT did not
observe the impulsive phase, it was possible to image the post-flare
loop in soft X-rays. We compare the images of the flare at different
wavelengths and discuss the relevance of millimeter emission in the
context of flare models.

---------------------------------------------------------
Title: Large Scale Features of the Radio Sun
Authors: White, S. M.; Gary, D. E.; Kundu, M. R.
1996AAS...188.7907W Altcode: 1996BAAS...28Q.956W
We present full-disk images of the Sun at 5 GHz made by observing 26
different fields with the Very Large Array and combining them using
mosaicking techniques. The resulting image combines sensitivity to
large-scale structures with good resolution. Full-disk images at 0.33,
1.4 and 17 GHz, a high-resolution magnetogram and a soft X-ray image
are compared with the 5 GHz image to investigate the physical properties
of large-scale features.

---------------------------------------------------------
Title: Coronal X-Ray Structures and Metric Radio Type III and
IV Bursts
Authors: Kundu, M. R.; Raulin, J. -P.; Nitta, N.; Raoult, A.
1996AAS...188.8609K Altcode: 1996BAAS...28R.964K
Over the past several years Yohkoh/SXT experiments have led to
the discovery of many new and interesting dynamic phenomena. Of
particular interest are the flaring X-ray bright points (XBPs),
X-ray jets, and flare associated plasmoids and other ejecta. We have
looked for evidence of nonthermal processes occurring in these X-ray
events, using radio bursts of spectral types III and IV. We have used
positional information of metric radio bursts using the Nancay (France)
Radioheliograph in the frequency range 150-450 MHz simultaneously with
the Yohkoh experiments. We have evidence of nonthermal type III burst
emission in the meter wave range in association with flaring XBPs and
certain classes of X-ray jets. We have detected metric structures,
namely flaring loops (possibly plasmoids) and other ejecta. The
implications of these findings will be discussed in terms of our
understanding of radio bursts of different spectral types.

---------------------------------------------------------
Title: Polarization of Microwaves Emitted From A Bipolar Active Region
Authors: Lee, Jeongwoo; White, Stephen; Gopalswamy, N.; Kundu, M. R.
1996AAS...188.3603L Altcode: 1996BAAS...28R.873L
High resolution microwave maps of a complex bipolar active region,
AR6615, were obtained using the VLA on 1991 May 7 at three frequencies,
4.9 GHz, 8.4 GHz, and 15 GHz. Comparison of this microwave observation
with Big Bear magnetogram suggests that inversion and depolarization of
microwave emission must have occurred at different sites of the active
region depending on frequency. For quantitative interpretation of the
polarization data, we constructed the coronal magnetic fields above
the active region using the potential field extrapolation. In the
model, we identified the quasi-transverse (QT) surface across which
change of the polarization may occur. It is found that the required
topology of the QT surface to explain the observed polarization
is correctly predicted by the potential field model, although the
locations of the 15 GHz gyroresonance sources required a nonlinear
force-free field extrapolation in part. With the calculation of the mode
coupling coefficient along the QT surface, we were able to locate the
region of depolarization above a strong sunspot, consistent with the
observation. We also discuss the appropriate theoretical gyroresonant
opacity for waves propagating perpendicular to the magnetic fields,
as needed to understand the observed polarization across the magnetic
neutral line. Applicability of the present results to study of the
coronal magnetic structure above complex bipolar regions, in general,
is briefly discussed.

---------------------------------------------------------
Title: A Multi Wavelength Study of Active Region Development
Authors: Lara, A.; Gopalswamy, N.; Kundu, M. R.; Perez-Enriquez, R.;
Koshiishi, H.; Enome, S.
1996AAS...188.3601L Altcode: 1996BAAS...28Q.873L
We report on a study of the evolution of several active regions during
1993 April 17-28 using data obtained at multiple wavelengths that
probe various heights of the active region corona. We use simultaneous
microwave (1.5 and 17 GHz) and Soft X-ray images obtained by the
Very Large Array (VLA), the Nobeyama Radio Heliograph (NRH) and the
Soft X-ray Telescope (SXT) on board the Yohkoh spacecraft. We also
use photospheric magnetograms from Kitt Peak National Observatory
to study the development of Solar Active Regions. We have followed
the development of various observed parameters such as brightness
temperature and polarization using radio images. The X-ray data were
used to track the development of density and temperature of active
regions. Using the fact that the quiet active region radiation is
thermal and adopting proper emission mechanism at each frequency
domain, we construct a consistent picture for the three dimensional
structure of the active regions. Particular attention has been paid to
the mode coupling observed at 17 GHz while the active regions crossed
the solar disk.

---------------------------------------------------------
Title: A model of the atmosphere above a sunspot from radio
observations
Authors: Zlotnik, E. Ya.; Kundu, M. R.; White, S. M.
1996R&QE...39..255Z Altcode:
The results of VLA observations of an unusual source of microwave
radiation, associated with the sunspot NOAA 7789 on October, 15,
1994, are presented. The fine structure of the source, which is a
ring structure in intensity and polarization at frequencies 4.5 and
8.0 GHz, is discussed. It is shown that the features observed can
be explained by a thermal cyclotron mechanism if the magnetic field
is approximated by a vertical dipole buried under the photosphere,
but the spatial distributions of kinetic temperature and electron
density in the atmosphere above the sunspot differ considerably from
the standard model. A two-dimensional source model (the dependences
of the parameters on the height and distance from the center of the
sunspot), which fits the observations at the above frequencies, is
evolved. The principal physical result is that the data observed are
explainable by the presence of an unexpectedly dense cool plasma in
the atmosphere over the center of the umbra.

---------------------------------------------------------
Title: Coronal Transients in Radio and X-rays
Authors: Kundu, Mukul R.
1996Ap&SS.243...15K Altcode: 1996IAUCo.154...15K
We present a summary of several studies of transient coronal phenomena
based upon high spatial resolution radio imaging data along with
Yohkoh SXT and HXT observations. In addition to normal flares the
studies also involve such exotic events as active region transient
brightenings (ARTB) and coronal jets and bright points. We provide
evidence of nonthermal processes in flaring X-ray bright points from
spatially resolved meter-wave data, existence and propagation of type II
burst emitting electrons in coronal jets, radio signatures of ARTB's,
and beaming of electrons producing microwave and hard X-rays. The
implications of these observations are discussed.

---------------------------------------------------------
Title: Metric Type III bursts associated with soft X-ray jets.
Authors: Raulin, J. P.; Kundu, M. R.; Hudson, H. S.; Nitta, N.;
Raoult, A.
1996A&A...306..299R Altcode:
From soft X-ray and metric radio observations with high temporal and
spatial resolution, we show that electron acceleration in the form of
Type III bursts occurs in association with coronal jets observed by the
Yohkoh soft X-ray telescope. The excellent correspondence between the
positions of the radio sources observed at different frequencies and
the X-ray jets strongly suggests that electron beams propagate along
the relatively dense paths formed by the jets. Assuming a constant
temperature for the jets, one can estimate the electron density from
the soft X-ray measurements. These computed electron densities agree
well with the values derived from Type III bursts produced by the
plasma emission process. The observations are consistent with the idea
that strong particle acceleration accompanies magnetic reconnection
in these events as well as in solar flares.

---------------------------------------------------------
Title: Detection of Large-Scale Radio Structure and Plasma Flow
during a Solar Bright Point Flare
Authors: Gopalswamy, N.; Kundu, M. R.; Hanaoka, Y.; Enome, S.; Lemen,
J. R.
1996ApJ...457L.117G Altcode:
We report on the detection of a large-scale radio structure and
plasma flow associated with a bright point flare observed on 1993
July 11. The bright point (BP) flare was simultaneously imaged by the
Nobeyama radioheliograph at 17 GHz and the Soft X-Ray Telescope on board
the Yohkoh mission. The microwave emission consists of a large-scale
structure and a compact moving source. The large-scale component seems
to be the radio counterpart of large-scale loop structures sometimes
observed in association with BP flares in X-rays. The compact source
moved from the location of the X-ray BP flare with a speed of about 60
km s-1, which suggests a plasma flow. Spatial comparison between X-ray
and radio data shows that the BP flare had different manifestations in
the two wavelength domains. The emission peaks in the two wavelength
domains did not coincide, which suggests cool plasma flow along the
large-scale radio structure. We were able to determine the temperature
and emission measure of the BP flare plasma from the X-ray data,
and thus we computed the expected radio flux from the X-ray--emitting
plasma. We found that the computed radio flux was much smaller than
the total observed radio flux.

---------------------------------------------------------
Title: First Images of a Solar Flare at Millimeter Wavelengths
Authors: Silva, Adriana V. R.; White, Stephen M.; Lin, Robert P.;
de Pater, Imke; Shibasaki, K.; Hudson, Hugh S.; Kundu, Mukul R.
1996ApJ...458L..49S Altcode:
We present the first high spatial resolution images of a solar flare
at millimeter wavelengths. On 1994 August 17, a GOES soft X-ray class
M1 flare was observed by the Berkeley-Illinois-Maryland Array at 86
GHz by the Nobeyama 17 GHz array and by the Yohkoh spacecraft. The
flare displayed both a prominent impulsive phase in microwaves and a
gradual phase that lasted over 30 minutes. The millimeter data were
taken only during the gradual phase. The millimeter images show a
source with a size of ~8", a peak brightness temperature of ~106 K,
and maximum optical depth of 0.09. At both X-ray and radio wavelengths,
the emitting region appeared to be compact (&lt;~20"). In soft X-ray,
the images are resolved into two sources: one located at a footpoint
and the other at the top of the flaring loop. The millimeter emission
is consistent with the predicted free-free flux from an isothermal
temperature (~14 MK) loop-top source, a multitemperature footpoint
source with a hot (~22 MK), and a cold (~12 MK) component. Most (80%)
of the millimeter flux density originates from the top of the magnetic
loop, and the footpoint contribution is only 20%.

---------------------------------------------------------
Title: VLA Observations of a Solar Active Region at 6.2 and 3.5 CM
Wavelength Compared with Model Calculations
Authors: Hildebrandt, J.; Kruger, A.; Gopalswamy, N.; Raulin, J. -P.;
Kundu, M. R.
1996ASPC...93..369H Altcode: 1996ress.conf..369H
No abstract at ADS

---------------------------------------------------------
Title: Three Part Structure of a CME Revealed by X-Ray and Microwave
Observations
Authors: Gopalswamy, N.; Kundu, M. R.; Lara, A.; Hanaoka, Y.; Enome,
S.; Lemen, J. R.; Akioka, M.
1996ASPC..111..393G Altcode: 1997ASPC..111..393G
The authors present X-ray (Yohkoh/SXT) and microwave (17 GHz Nobeyama)
observations of the 1993 July 10 - 11 CME. During this event, all the
substructures of a classical CME are revealed: frontal loop in X-rays,
prominence core in microwaves, dark cavity between prominence and
frontal loop in X-rays, and arcade structure beneath the prominence
in X-rays.

---------------------------------------------------------
Title: The Radio Outburst of eta Carinae
Authors: White, S. M.; Duncan, R. A.; Lim, J.; Drake, S. A.; Kundu,
M. R.
1996ASPC...93...59W Altcode: 1996ress.conf...59W
No abstract at ADS

---------------------------------------------------------
Title: Nonthermal Radio Emission from Coronal X-ray Jets
Authors: Kundu, M. R.; Raulin, J. P.; Nitta, N.; Hudson, H. S.;
Raoult, A.
1996ASPC...93..375K Altcode: 1996ress.conf..375K
No abstract at ADS

---------------------------------------------------------
Title: Detection of Nonthermal Radio Emission from Coronal X-ray Jets
Authors: Kundu, M. R.; Raulin, J. P.; Nitta, N.; Hudson, H. S.;
Raoult, A.; Shibata, K.; Shimojo, M.
1996mpsa.conf..445K Altcode: 1996IAUCo.153..445K
No abstract at ADS

---------------------------------------------------------
Title: A Search for Rotational Modulation in the EUV Emission from
AB Doradus
Authors: White, S. M.; Lim, J.; Rucinski, S. M.; Roberts, C.; Kilkenny,
D.; Ryan, S. G.; Prado, P.; Kundu, M. R.
1996aeu..conf..165W Altcode: 1996IAUCo.152..165W
No abstract at ADS

---------------------------------------------------------
Title: First Images of a Solar Flare at Millimeter Wavelengths
Authors: Silva, Adriana V. R.; White, Stephen M.; Lin, Robert P.;
de Pater, Imke; Shibasaku, K.; Hudson, Hugh S.; Kundu, Mukul R.
1996ADIL...AS...01S Altcode:
We present the first high-spatial-resolution images of a solar flare at
millimeter wavelengths. On 1994 August 17, a GOES soft X--ray class M1
flare was observed by the Berkeley--Illinois--Maryland Array (BIMA) at
86 GHz, by the Nobeyama 17 GHz array, and by the Yohkoh spacecraft. The
flare displayed both a prominent impulsive phase in microwaves and a
gradual phase which lasted over 30 minutes. The millimeter data were
taken only during the gradual phase. The millimeter images show a
source with a size of $\sim$8\arcsec, a peak brightness temperature
of ~ 10^6 K, and maximum optical depth of 0.09. At both X--ray and
radio wavelengths the emitting region appeared to be compact (&lt; 20
arcseconds). In soft X--ray the images are resolved into two sources:
one located at a footpoint and the other at the top of the flaring
loop. The millimeter emission is consistent with the predicted free-free
flux from an isothermal temperature (~ 14 MK) looptop source and a
multi--temperature footpoint source with a hot (~ 22 MK) and a cold (~
12 MK) component. Most (80%) of the millimeter flux density originates
from the top of the magnetic loop, and the footpoint contribution is
only 20%.

---------------------------------------------------------
Title: VLA and YOHKOH Observations of an M1.5 Flare
Authors: Gopalswamy, N.; Raulin, J. -P.; Kundu, M. R.; Nitta, N.;
Lemen, J. R.; Herrmann, R.; Zarro, D.; Kosugi, T.
1995ApJ...455..715G Altcode:
A major solar flare (X-ray importance M1.5 and optical importance SB)
was fully observed by the Very Large Array and the Yohkoh mission on
1993 April 22. Both thermal and nonthermal emissions were observed
in radio. In soft X-rays, the flare was confined to a compact region
in an arcade. In hard X-rays, there were two prominent footpoints,
coincident in projection with the soft X-ray footpoints and located
on either side of the magnetic neutral line inferred from photospheric
magnetograms The Yohkoh Bent Crystal Spectrometer (B CS) data provided
important context information which was helpful in cross-checking the
quantitative agreement between the radio and X-ray data. The microwave
spectrum peaked around 10 GHz and showed Razin suppression in the
beginning. Later on, the low-frequency spectral index dropped to a
value of 2, suggesting thermal emission. The VLA images of the flare at
1.5 GHz show that the flare emission started as a single source above
one footpoint; later on, the emission centroid moved toward the soft
X-ray structure to finally become cospatial with the latter. The two
locations of the 20 cm source corresponded to nonthermal (footpoint
source) and thermal (source cospatial with the soft X-ray structure)
emissions. We performed temperature and emission measure analysis of
the X-ray data (SXT, BCS, and HXT) and used them as input to determine
the expected radio emission. While there is morphological agreement
between the radio and soft X-ray structures in the thermal phase,
the 20 cm brightness temperature shows quantitative agreement with
temperature derived from the BCS data. We were able to identify
three emission mechanisms contributing to the 20 cm radio emission
at different times without any ad hoc assumption regarding emission
mechanisms. Razin-suppressed nonthermal gyroresonance emission,
plasma emission, and thermal free-free emission seem to be operating
and are found to be consistent with the plasma parameters derived
from the X-ray data. The magnetic field structure in the flaring
region showed differences before and after the flare as traced b soft
X-ray structures in the flaring region and confirmed by 20 cm radio
images. The superhot component with a temperature of 32 MK was observed
in hard X-ray images and in light curves during the impulsive phase of
the flare with possible radio signatures at 20 cm wavelength. We derived
the physical parameters of the flaring plasma, the magnetic field,
and the characteristics of nonthermal particles in the flaring region.

---------------------------------------------------------
Title: Microwave and Hard X-Ray Observations of Footpoint Emission
from Solar Flares
Authors: Kundu, M. R.; Nitta, N.; White, S. M.; Shibasaki, K.; Enome,
S.; Sakao, T.; Kosugi, T.; Sakurai, T.
1995ApJ...454..522K Altcode:
We investigate radio and X-ray imaging data for two solar flares in
order to test the idea that asymmetric precipitation of nonthermal
electrons at the two ends of a magnetic loop is consistent with the
magnetic mirroring explanation. The events we present were observed in
1993 May by the HXT and SXT X-ray telescopes on the Yohkoh spacecraft
and by the Nobeyama 17 GHz radioheliograph. The hard X-ray images in
one case show two well-separated sources; the radio images indicate
circularly polarized, nonthermal radio emission with opposite polarities
from these two sources, indicating oppositely directed fields and
consistent with a single-loop model. In the second event there are
several sources in the HXT images which appear to be connected by
soft X-ray loops. The strongest hard X-ray source has unpolarized
radio emission, whereas the strongest radio emission lies over strong
magnetic fields and is polarized. In both events the strongest radio
emission is highly polarized and not coincident with the strongest
hard X-ray emission. This is consistent with asymmetric loops in
which the bulk of the precipitation (and hence the X-ray emission)
occurs at the weaker field footpoint.

---------------------------------------------------------
Title: Microwave proxies for sunspot blocking and total irradiance
Authors: Schmahl, E. J.; Kundu, M. R.
1995JGR...10019851S Altcode:
The microwave flux of the Sun is responsive to the same conditions
that produce magnetically structured radiation at visible and X ray
wavelengths, and so the solar flux at high radio frequencies such
as 2800 MHz (10.7 cm) has been used as a proxy for solar optical
variations. We have previously found that the microwave flux time
series show spectral variations that provide useful proxy information
for total irradiance, and we have extended our analysis of the
daily solar fluxes from Toyokawa Observatory at 1000, 2000, 3750,
and 9400 MHz, in addition to the Ottawa 2800-MHz flux, for the years
1980-1989. An essential ingredient in our analysis is the extraction
of the rotationally-modulated microwave component, which differs
from the “S component” as recently defined in the literature. The
rotationally-modulated fraction of the emission contains a significant,
often dominant, contribution from gyroresonance emission, whereas the
S component, as defined by the excess above the cycle minimum level,
usually does not. This allows us to distinguish plage-associated
emission from spot-associated emission in the time series of microwave
flux. We show that in combination, the microwave fluxes for 1000-9400
MHz, which span the spectral peak of spot-associated emission,
provide a very good proxy both the active cavity radiometer irradiance
monitor (ACRIM) total irradiance and the sunspot-blocked component
of the irradiance, even without optical sunspot observations. Over
the 1984-1989 period, this proxy has a weighted correlation with
ACRIM of 95%, and an RMS deviation from the total irradiance of
0.27 w/m2, slightly better than the deviation (0.35
w/m2) found using optical data.

---------------------------------------------------------
Title: The Radio Properties of Solar Active Region Soft X-Ray
Transient Brightenings
Authors: White, S. M.; Kundu, M. R.; Shimizu, T.; Shibasaki, K.;
Enome, S.
1995ApJ...450..435W Altcode:
We present the results of a search for radio emission from active-region
transient brightenings identified in Yohkoh soft X-ray telescope
observations of active region AR 7260. We present detailed observations
of four events in which 17 GHz radio emission is clearly detected in
observations by the Nobeyama radioheliograph. The time profiles of
the 17 GHz data are very similar to those of the soft X-ray fluxes,
and the 17 GHz flux is very close to that expected from plasma with
the temperature and emission measure derived for the soft X-ray
emitting material from filter ratios. No impulsive nonthermal radio
emission was detected from any of the four events, although each was
at least GOES class B 1 in soft X-rays. Weak hard X-rays may have been
detected by GRO/BATSE from the strongest of the events, but not from
two others. These negative results leave open the possibility that
there is a difference between active region transient brightenings
and solar flares, in that the former do not convert a significant
amount of the released energy into accelerated electrons. However,
confirmation of this hypothesis will require a larger sample of events.

---------------------------------------------------------
Title: Detection of Nonthermal Radio Emission from Coronal X-Ray Jets
Authors: Kundu, M. R.; Raulin, J. P.; Nitta, N.; Hudson, H. S.;
Shimojo, M.; Shibata, K.; Raoult, A.
1995ApJ...447L.135K Altcode:
We report the detection of a type III burst in association with a
dynamic X-ray coronal jet observed by Yohkoh/SXT. The type III burst
observed with the Nancay (France) multifrequency radioheliograph is
spatially and temporally coincident with the X-ray jet. The radio
locations at different frequencies (236.6 and 164 MHz) are aligned
along the length of the jet. The observation of the type III burst in
association with the X-ray jet implies the acceleration of electrons
to several tens of keV, along with the heating responsible for the
production of soft X-rays. This association implies the existence of
open field lines in dense coronal structures identified on the Sun's
disk. This is the first observation of dense coronal structures on the
disk, along which type III emitting nonthermal electrons propagate. We
find that this structure begins to form before the type III emission. At
the time of the type III burst we estimate a density of 6--10 x 108
cm-3 for a temperature of ~5--6 MK at an altitude of 20,000 km.

---------------------------------------------------------
Title: Observations of Continuum and - Emission from Eta Carinae at
a Wavelength of 3 CM
Authors: Duncan, R. A.; White, S. M.; Lim, J.; Nelson, G. J.; Drake,
S. A.; Kundu, M. R.
1995RMxAC...2...23D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Metric Type III Bursts from a Flaring X-Ray Bright Point near
an Active Region
Authors: Kundu, M. R.; Raulin, J. P.; Pick, M.; Strong, K. T.
1995ApJ...444..922K Altcode:
X-ray bright points (XBPs) are known to show variability on a
number of timescales, including impulsive X-ray brightenings. The
relationship between these XBP 'flares' and normal flares is poorly
known. A fundamental question is whether nonthermal acceleration of
particles takes place in XBP flares. We address this issue by seravhing
for nonthermal radio emission at metric wavelengths from flaring XBPs
identified in Yohkoh/SXT data. Unequivocal evidence for type III-like
radio bursts usually attributed to beams of nonthermal electrons on open
field lines was found recently by Kundu et al. This suggests that XBP
flares are similar to normal flares and can indeed accelerate nonthermal
populations of energetic particles. Here we provide further evidence
of metric type III bursts from flaring XBPs located near active regions.

---------------------------------------------------------
Title: The Magnetic Field Over an Isolated Symmetric Sunspot
Authors: White, S. M.; Kundu, M. R.; Zlotnik, E. Ya.; Zheleznyakov,
V. V.; Nitta, N.
1995SPD....26..718W Altcode: 1995BAAS...27..970W
No abstract at ADS

---------------------------------------------------------
Title: Intense Radio Outburst from the Supermassive Star eta Carinae
Authors: Duncan, R. A.; White, S. M.; Lim, J.; Nelson, G. J.; Drake,
S. A.; Kundu, M. R.
1995ApJ...441L..73D Altcode:
On five occasions between 1992 June 29 and 1994 May 3, we have used
the Australia Telescope Compact Array (ATCA) to image Eta Carinae at
a wavelength of 3 cm and a resolution of 1 arcsec. These observations
have revealed remarkable activity. Since 1992 June, the total flux
density has increase from 0.8 to 2.2 Jy, and the original single compact
source has grown to a complex of sources spread over an area of about
16 sq arcsec. Strong hydrogen recombination-line spectral emission
has appeared at the site of the strongest of these new sources. This
recombination emission has the largest spectral width ever observed
from a star, +/- 250 km/s, and reveals gas with turbulent velocities
as great as 250 km/s approaching us at an average velocity of about
200 km/s. We believe that this radio outburst has been caused by a
more than threefold increase of ultraviolet luminosity, and consequent
ionization of previously neutral gas clouds.

---------------------------------------------------------
Title: Radio Counterpart of an X-ray Bright Point Flare
Authors: Gopalswamy, N.; Kundu, M. R.; Hanaoka, Y.; Enome, S.; Lemen,
J. R.
1995SPD....26.1317G Altcode: 1995BAAS...27Q.991G
No abstract at ADS

---------------------------------------------------------
Title: Spatially resolved Millimeter (86 GHz), Microwave (17 GHz)
and X-Ray Observations of the 17 August 94 flare
Authors: Silva, A. V. R.; Lin, R. P.; de Pater, I.; White, S. M.;
Kundu, M. R.
1995SPD....26..804S Altcode: 1995BAAS...27..972S
No abstract at ADS

---------------------------------------------------------
Title: Nouthermal Radio Emission From Coronal X-Ray Jets
Authors: Raulin, J. P.; Kundu, M. R.; Hudson, H. S.; Nitta, N.;
Raoult, A.
1995SPD....26.1318R Altcode: 1995BAAS...27..991R
No abstract at ADS

---------------------------------------------------------
Title: Book Review: Solar Magnetic Fields
Authors: Kundu, Mukul R.; Schüssler, M.; Schmidt, W.
1995ComAp..18...36K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Characteristics of Two Simple Microwave Bursts
Authors: Kundu, M. R.; White, S. M.; Nitta, N.; Shibasaki, K.;
Enome, S.
1995LNP...444...75K Altcode: 1995cmer.conf...75K
We present simultaneous microwave and X-ray data for two microwave
bursts with simple impulsive time profiles. The 17 GHz images show
compact sources, and in the one case for which we have simultaneous
soft and hard X-ray images, they also show compact sources coincident
with the radio source. One of the bursts is barely detected in soft
X-rays, yet has a moderate 17 GHz flux,.

---------------------------------------------------------
Title: Surprises in the Radio Signatures of CMEs
Authors: Gopalswamy, N.; Kundu, M. R.
1995LNP...444..223G Altcode: 1995cmer.conf..223G
We discuss several results regarding the relationship between coronal
mass ejections (CMEs) and metric radio emissions which have changed our
understanding of these phenomena considerably. Imaging observations
of metric radio emissions along with coronagraph observations have
been used to obtain these results. We consider the following: (i) Why
slow CMEs are associated with metric type IV radio emission contrary
to the earlier belief, (ii) Why shocks piston driven by the CMEs are
not seen in the solar corona, (iii) Thermal radio emission from the
CMEs and their implications to CME-flare relationship and (iv) Radio
signatures of coronas disconnection events.

---------------------------------------------------------
Title: Nobeyama Radio Observatory report, no. 361: The radio
properties of solar active region soft x-ray transient brightenings
Authors: White, S. M.; Kundu, M. R.; Shimizu, T.; Shibasaki, K.;
Enome, S.
1995STIN...9529098W Altcode:
We present the results of a search for radio emission from active-region
transient brightenings identified in Yohkoh Soft X-ray Telescope
observations of active region AR 7260. We present detailed observations
of four events in which 17 GHz radio emission is clearly detected in
observations by the Nobeyama Radioheliograph. The time profiles of
the 17 GHz data are very similar to those of the soft X-ray fluxes,
and the 17 GHz flux is very close to that expected from plasma with the
temperature and emission measure derived for the soft X-ray-emitting
material from filter ratios. No impulsive nonthermal radio emission
was detected from any of the 4 events, although each was at least
GOES class B1 in soft X-rays. Weak hard X-rays may have been detected
by GRO/BATSE from the strongest of the events, but not from two
others. These negative results leave open the possibility that there
is a difference between active region transient brightenings and solar
flares, in that the former do not convert a significant amount of the
released energy into accelerated electrons. However, confirmation of
this hypothesis will require a larger sample of events.

---------------------------------------------------------
Title: Polarization Features of Solar Radio Emission and Possible
Existence of Current Sheets in Active Regions
Authors: Gopalswamy, N.; Zheleznyakov, V. V.; White, S. M.; Kundu,
M. R.
1994SoPh..155..339G Altcode:
We show that it is possible to account for the polarization features
of solar radio emission provided the linear mode coupling theory is
properly applied and the presence of current sheets in the corona
is taken into account. We present a schematic model, including a
current sheet that can explain the polarization features of both the
low frequency slowly varying component and the bipolar noise storm
radiation; the two radiations face similar propagation conditions
through a current sheet and hence display similar polarization
behavior. We discuss the applications of the linear mode coupling
theory to the following types of solar radio emission: the slowly
varying component, the microwave radio bursts, metric type U bursts,
and bipolar noise storms.

---------------------------------------------------------
Title: Transient Microwave Brightenings in Solar Active Regions:
Comparison between VLA and YOHKOH Observations
Authors: Gopalswamy, N.; Payne, T. E. W.; Schmahl, E. J.; Kundu, M. R.;
Lemen, J. R.; Strong, K. T.; Canfield, R. C.; de La Beaujardiere, J.
1994ApJ...437..522G Altcode:
We report observations of transient microwave (2 cm) brightenings
and their relationship with brightenings in soft X-rays. The peak
flux of the microwave brightenings observed by the Very Large Array
(VLA) is smaller than the previously reported fluxes by two orders
of magnitude. The microwave sources were highly polarized (up to
100%) and were situated on the periphery of a sunspot umbra. Among
the many transients observed in X-rays by Yohkoh, two were observed
simultaneously in microwaves. The microwave sources were found to
be closer to the umbra of the sunspot than were the X-ray loops. It
seems that the microwave sources are located at the footpoints of
the looplike X-ray transients. Using the combined VLA, Yohkoh, and
Mees data set, we determine the physical parameters of the loop in
which the brightenings occur. We find that an increase in emission
measure accompanied by small-scale heating can account for the X-ray
brightening. The microwave emission can be interpreted as thermal
gyroresonance or nonthermal gyrosynchrotron processes during the X-ray
brightening. The magnetic field in the microwave-source region is
found to be 1200-1800 G. The observations also provide evidence for
temperature gradient in the coronal loops.

---------------------------------------------------------
Title: Detection of 17 GHz Radio Emission from X-Ray--bright Points
Authors: Kundu, M. R.; Shibasaki, K.; Enome, S.; Nitta, N.
1994ApJ...431L.155K Altcode:
Using observations made with the Nobeyama radio heliograph (NRH) at 17
GHz and the Yohkoh/SXT experiment, we report the first detection of 17
GHz signatures of coronal X-ray-bright points (XBPs). This is also the
first reported detection of flaring bright points in microwaves. We
have detected four BPs at 17 GHz out of eight identified in SXT data
on 1992 July 31, for which we looked for 17 GHz emission. For one
XBP located in a quiet mixed-polarity region, the peak times at 17
GHz and X-rays are very similar, and both are long-lasting-about 2
hr in duration. There is a second BP (located near an active region)
which is most likely flaring also, but the time profiles in the two
spectral domains are not similar. The other two 17 GHz BPs are quiescent
with fluctuations superposed upon them. For the quiet region XBP, the
gradual, long-lasting, and unpolarized emission suggests that the 17
GHz emission is thermal.

---------------------------------------------------------
Title: Metric Type III Bursts from Flaring X-ray Bright Points
Authors: Kundu, M. R.; Strong, K. T.; Pick, M.; Harvey, K. T.; Kane,
S. R.; White, S. M.; Hudson, H. S.
1994kofu.symp..343K Altcode:
X-ray bright points (XBP's) are known to show variability on a number
of timescales, including impulsive X-ray brightenings. The relationship
between these XBP “flares” and normal solar flares is poorly known. A
fundamental question is whether nonthermal acceleration of particles
takes place in XBP flares. We address this issue by searching for
nonthermal radio emission at metric wavelengths from flaring XBPs
identified in Yohkoh/SXT data. Unequivocal evidence for type-III-like
radio bursts, usually attributed to beams of nonthermal electrons on
open field lines, is found. This suggests that XBP flares are similar
to normal flares and can indeed accelerate nonthermal populations of
energetic particles.

---------------------------------------------------------
Title: Evolution of an Active Region and Flare Productivity
Authors: Kundu, M. R.; Shibasaki, K.; Enome, S.; Nitta, N.; Bruner,
M.; Sakao, T.; Kosugi, T.
1994kofu.symp..353K Altcode:
We have studied the evolution of an active region (AR 7515) in terms
of flare productivity. This region appears at the east limb on May 23,
1993 and then continues its onward march across the disk. We follow
its evolution until June 2. This region produces many small flares. We
study the topology, both magnetic and structural of the neighboring
regions as observed at 17 GHz by the Nobeyama Radio Heliograph (NRH)
and the Yohkoh/SXT to find their effects on the flare-producing AR. We
investigate the spatial structure of the flaring region from 17 GHz
and SXT maps during various times of the impulsive and decay phase,
to understand the difference in the flaring region spatial structure
during the preflare, impulsive and decay phases. In general, the maps
made during these phases show several loops. We try to relate these
flaring loops with the preflare active region structure.

---------------------------------------------------------
Title: Study of Active Region Magnetic Field Structures Using VLA
Radio, YOHKOH X-ray and MEES Optical Observations
Authors: Gopalswamy, N.; Schmahl, E. J.; Kundu, M. R.; Lemen, J. R.;
Strong, K. T.; Canfield, R. C.; de La Beaujardiere, J.
1994kofu.symp..347G Altcode:
We report on the observation of compact magnetic flux tubes from the
boundary between the umbra and penumbra of a large sunspot in AR 7135
on April 24, 1992. The structure and geometry of one such flux tube
was determined using the coordinated observations obtained by the
Very Large Array, the Yohkoh Soft X-ray Telescope and the Mees Solar
Observatory. From radio observations we infer that the magnetic field
of the flux tube at the spot-side footpoint is ~ 1300-1800 G.

---------------------------------------------------------
Title: Observation of 17 GHz Radio Emission from X-ray Bright Points
Authors: Kundu, M. R.; Shibasaki, K.; Enome, S.; Nitta, N.
1994kofu.symp...79K Altcode:
Using observations made with the Nobeyama radio heliograph (NRH) at 17
GHz and the Yohkoh/SXT experiment, we report the first detection of 17
GHz signatures of coronal X-ray bright points (XBP's). This is also the
first reported detection of flaring bright points in microwaves. We
have detected four BP's at 17 GHz out of eight observed by SXT on
July 31, 1992, for which we looked for 17 GHz emission. For one XBP
located in a quiet mixed-polarity-region, the peak times at 17 GHz
and X-rays are very similar, and both are long lasting -- at least
6 hours in duration. There is a second BP (located near an active
region) which is most likely flaring also, but the time profiles in
the two spectral domains are not similar. The other two 17 GHz BPs
are quiescent with fluctuations superposed upon them. For the quiet
region XBP, we believe that the 17 GHz emission is thermal.

---------------------------------------------------------
Title: Multiwavelength Observations of a Solar Flare
Authors: White, S. M.; Silva, A.; de Pater, I.; Lin, R. P.; Gary,
D. E.; Hudson, H. S.; Doyle, J. G.; Hagyard, M. J.; Kundu, M. R.
1994kofu.symp..203W Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Radio Source around eta Carinae
Authors: White, S. M.; Duncan, R. A.; Lim, J.; Nelson, G. J.; Drake,
S. A.; Kundu, M. R.
1994ApJ...429..380W Altcode:
We present high spatial resolution radio observations of the peculiar
southern star Eta Carinae, made with the Australian Telescope. The
images, at 8 and 9 GHz with a resolution of 1.0 arcsec show a source
of dimension 10 arcsec and total flux of 0.7 Jy dominated by a strong
central peak. The radio emission is unpolarized and offers no support to
models which invoke degenerate stars or more exotic objects within the
core of Eta Car. In these data we find no evidence for more than one
energy source in the core with arcsecond separations as some infrared
observations have suggested. Several levels of structure are evident in
the radio image, which shows symmetry on the larger scales. Conventional
formulae for stellar wind radio sources give a mass loss rate of order 3
x 10-4 Solar Mass/yr based on the radio flux in the central
peak, which yields a wind momentum flux of order 20% of the momentum
flux available from the star's radiation field. The radio emission at
these frequencies is consistent with thermal emission from gas flowing
away from a 'luminous blue variable' star (LBV) Eta Car is probably
the brightest thermal stellar wind radio source in the sky.

---------------------------------------------------------
Title: Solar Cycle Variation of the Microwave Spectrum and Total
Irradiance
Authors: Schmahl, E. J.; Kundu, M. R.
1994SoPh..152..167S Altcode: 1994svs..coll..167S; 1994IAUCo.143..167S
We have extended the proxy relationship between irradiance and
microwaves by using the daily solar fluxes from Toyokawa Observatory
at 1000, 2000, 3750 and 9400 MHz in addition to the Ottawa 2800 MHz
flux for the years 1980-1989. It turns out that the flux at 1000 MHz is
better correlated with irradiance than the flux at higher frequencies-an
unexpected result. We have also found that the spectrum of the flux
shows shape changes that are related to the number and type of active
regions. Because of this the five-frequency spectral measurements of
microwave flux allow one to separate the sunspot and coronal features,
providing an improved proxy of solar variability.

---------------------------------------------------------
Title: Nonthermal Processes in Flaring X-Ray--bright Points
Authors: Kundu, M. R.; Strong, K. T.; Pick, M.; White, S. M.; Hudson,
H. S.; Harvey, K. L.; Kane, S. R.
1994ApJ...427L..59K Altcode:
X-ray-bright point (XBPs) are known to show variability on a number of
timescales, including impulsive X-ray brightenings. The relationship
between these XBP 'flares' and normal solar flares is poorly known. A
fundamental question is whether nonthermal acceleration of particles
takes place in XBP flares. We address this issue by searching for
nonthermal radio emission at metric wavelengths from flaring XBPs
identified in Yohkoh soft x-ray telescope (SXT) data. Unequivocal
evidence for type III-like radio bursts, usually attributed to beams
of nonthermal electrons on open field lines, is found. This suggests
that XBP flares are similar to normal flares and can indeed accelerate
nonthermal populations of energetic particles.

---------------------------------------------------------
Title: Nonthermal Radio Emission Associated with a Coronal
Disconnection Event
Authors: Gopalswamy, N.; Kundu, M. R.; St. Cyr, O. C.
1994ApJ...424L.135G Altcode:
We have found possible radio signatures of a coronal disconnection event
observed by the Solar Maximum Mission Coronagraph/Polarimeter. The
radio emission seems to be produced by charged particles accelerated
during the same reconnection process which is responsible for the
disconnection event. We discuss the implications of the radio emission
characteristics to the reconnection process.

---------------------------------------------------------
Title: Three dimensional coronal structures using clark lake
observations
Authors: Schmahl, E. J.; Gopalswamy, N.; Kundu, M. R.
1994AdSpR..14d..65S Altcode: 1994AdSpR..14...65S
Throughout the quiet-Sun years 1982-1987, the Clark Lake Radioheliograph
mapped the solar corona on a daily basis at frequencies from 30 to
100 MHz. The Clark Lake maps show a variety of features which we have
analyzed quantitatively. Among the features are coronal streamers,
which appear to cross the solar disk during a solar rotation. We have
modeled the streamers with various geometrics and density profiles,
and computed ray-tracing images for comparison with the CLRO maps. These
models produced estimates of density and spatial scales in 3 dimensions
for the streamers. We discuss the significance of these estimates and
compare them with inferences made from optical observations. One of
the possible conclusions we draw from these comparisons is that there
are unresolved structures in stremers, not observable optically in
the limb data.

---------------------------------------------------------
Title: Three Dimensional Coronal Structures Using Clark-Lake
Observations
Authors: Schmahl, E. J.; Gopalswamy, N.; Kundu, M. R.
1994SoPh..150..325S Altcode:
We have undertaken a study of coronal features observed at
meter-decameter wavelengths using the Clark Lake radioheliograph. Among
the coronal structures we have studied are the radio manifestations of
coronal streamers on the solar disk and above the solar limb. We have
analyzed the radio data quantitatively, using ray-tracing models for
comparison with the maps. Our study provides information about the
streamers' three-dimensional shapes, scales, and density profiles,
for comparison with related observations using white-light coronagraphs.

---------------------------------------------------------
Title: Non-radial magnetic field structures in the solar corona
Authors: Gopalswamy, N.; Kundu, M. R.; Raoult, A.; Pick, M.
1994SoPh..150..317G Altcode:
We report on the structure and geometry of coronal magnetic fields
inferred from the observations of meter-decimeter type III and moving
type IV radio bursts, associated with a Hα flare. This is the first
report of type III radio bursts from the Nançay radioheliograph after
it acquired the two-dimensional multifrequency capability. Dispersion of
the radio source positions with frequency suggests that open and closed
field lines are considerably inclined to the radial direction which is
consistent with the connectivity observed in the magnetogram. We suggest
that multiple arch systems are involved in the type IV emission. From
the polarization and dispersion characteristics of the type IV source,
we infer that the emission is due to fundamental plasma emission.

---------------------------------------------------------
Title: Pulsed Acceleration in Solar Flares
Authors: Aschwanden, Markus J.; Benz, Arnold O.; Dennis, Brian R.;
Kundu, Mukul R.
1994ApJS...90..631A Altcode: 1994IAUCo.142..631A
We study the nonlinear dynamics of particle acceleration in solar flares
by analyzing the time series of various quasi-periodic radio signatures
during flares. In particular we present the radio and hard X-ray data
of three flares which suppport the following tentative conclusions:
(1) Particle acceleration and injection into magnetic structures
occurs intrinsically in a pulsed mode (with a typical period of
1-2 s), produced by a single, spatially coherent, nonlinear system,
rather than by a stochastic system with many spatially independent
components ('statistical flare' produced by a fragmented primary energy
release). (2) The nonlinear (quasi-periodic) mode of pulsed particle
acceleration and injection into a coronal loop can be stabilized by
phase locking with an MHD wave (oscillation) mode, if both periods
are close to each other. (3) Pulsed injection of electron beams into
a coronal loop may trigger nonlinear relaxational oscillations of
wave-particle interactions. This is particularly likely when the limit
cycles of both systems are similar.

---------------------------------------------------------
Title: Eta Carinae
Authors: White, S.; Duncan, R.; Drake, S.; Lim, J.; Kundu, M.
1994IAUC.5932....2W Altcode: 1994IAUC.5932....1W
S. White, University of Maryland; R. Duncan, Australia Telescope;
S. Drake, Goddard Space Flight Center; J. Lim, California Institute of
Technology; and M. Kundu, University of Maryland, report: "Australia
Telescope observations of the luminous blue variable eta Car show
that it is undergoing a radio outburst, with the flux having doubled
in the last 7 months and apparently still increasing. It is currently
a 2-Jy radio source at 9 GHz. The rise in flux is associated with the
appearance of a new feature in the radio images, about 1".1 northwest
of the radio source attributed to the stellar wind and almost as
bright. Assuming that this feature is due to a gas clump ejected
asymmetrically by the star and radiating thermal free-free emission,
the minimum mass involved is 0.005 solar mass. Infrared observations
to follow the history of dust formation in this gas clump would be
valuable."

---------------------------------------------------------
Title: Observing Stellar Coronae with the Goddard High Resolution
Spectrograph. I. The dMe Star AU Microscopii
Authors: Maran, S. P.; Robinson, R. D.; Shore, S. N.; Brosius, J. W.;
Carpenter, K. G.; Woodgate, B. E.; Linsky, J. L.; Brown, A.; Byrne,
P. B.; Kundu, M. R.; White, S.; Brandt, J. C.; Shine, R. A.; Walter,
F. M.
1994ApJ...421..800M Altcode:
We report on an observation of AU Mic taken with the Goddard High
Resolution Spectrograph (GHRS) aboard the Hubble Space Telescope. The
data consist of a rapid sequence of spectra covering the wavelength
range 1345-1375 A with a spectral resolution of 10,000. The observations
were originally intended to search for spectral variations during
flares. No flares were detected during the 3.5 hr of monitoring. A
method of reducing the noise while combining the individual spectra
in the time series is described which resulted in the elimination of
half of the noise while rejecting only a small fraction of the stellar
signal. The resultant spectrum was of sufficient quality to allow the
detection of emission lines with an integrated flux of 10-15
ergs/sq cm(sec) or greater. Lines of C I, O I, O V, Cl I, and Fe XXI
were detected. This is the first indisputable detection of the 1354
A Fe XXI line, formed at T approximately = 107 K, on a
star other than the Sun. The line was well resolved and displayed
no significant bulk motions or profile asymmetry. From the upper
limit on the observed line width, we derive an upper limit of 38 km/s
for the turbulent velocity in the 107 K plasma. An upper
limit is derived for the flux of the 1349 A Fe XII line, formed at T
approximately = 1.3 x 106 K. These data are combined with
contemporaneous GHRS and International Ultraviolet Explorer (IUE) data
to derive the volume emission measure distribution of AU Mic over the
temperature range 104-107 K. Models of coronal
loops in hydrostatic equilibrium are consistent with the observed
volume emission measures of the coronal lines. The fraction of the
stellar surface covered by the footprints of the loops depends upon the
loop length and is less than 14% for lengths smaller than the stellar
radius. From the upper limit to the estimated width of the Fe XXI line
profile we find that the we cannot rule out Alfven wave dissipation
as a possible contributor to the required quiescent loop heating rate.

---------------------------------------------------------
Title: Millimeter, Microwave, Hard X-Ray, and Soft X-Ray Observations
of Energetic Electron Populations in Solar Flares
Authors: Kundu, M. R.; White, S. M.; Gopalswamy, N.; Lim, J.
1994ApJS...90..599K Altcode: 1994IAUCo.142..599K
We present comparisons of multiwavelength data for a number of solar
flares observed during the major campaign of 1991 June. The different
wavelengths are diagnostics of energetic electrons in different energy
ranges: soft X-rays are produced by electrons with energies typically
below 10 keV, hard X-rays by electrons with energies in the range
10-200 keV, microwaves by electrons in the range 100 keV-1 MeV, and
millimeter-wavelength emission by electrons with energies of 0.5 MeV
and above. The flares in the 1991 June active period were remarkable in
two ways: all have very high turnover frequencies in their microwave
spectra, and very soft hard X-ray spectra. The sensitivity of the
microwave and millimeter data permit us to study the more energetic
(greater than 0.3 MeV) electrons even in small flares, where their
high-energy bremsstrahlung is too weak for present detectors. The
millimeter data show delays in the onset of emission with respect to
the emissions associated with lower energy electrons and differences in
time profiles, energy spectral indices incompatible with those implied
by the hard X-ray data, and a range of variability of the peak flux in
the impulsive phase when compared with the peak hard X-ray flux which
is two orders of magnitude larger than the corresponding variability
in the peak microwave flux. All these results suggest that the hard
X-ray-emitting electrons and those at higher energies which produce
millimeter emission must be regarded as separate populations. This has
implications for the well-known 'number problem' found previously when
comparing the numbers of non thermal electrons required to produce
the hard X-ray and radio emissions.

---------------------------------------------------------
Title: Radio Constraints on Coronal Models for dMe Stars
Authors: White, S. M.; Lim, J.; Kundu, M. R.
1994ApJ...422..293W Altcode:
Radio data are used to test coronal models for dMe stars. Specifically,
we show that photospheric magnetic field observations imply that the
low corona of a dMe star should be saturated by magnetic fields with an
average strength in excess of 1 kG. In such fields the hot component
of the corona detected in X-ray observations (temperature of order 2
x 107 K) would be optically thick at least up to 15 GHz due
to thermal gyroresonance opacity. The resulting emission would easily
be detectable by radio observations and should have a radio spectrum
rising in the microwave range. We have carried out observations
to test this prediction, and in the majority of cases find that
the observed fluxes at 15 GHz are too low to be consistent with the
assumptions. In the few cases where the stars were detected at 15 GHz,
the evidence indicates that the observed emission is nonthermal. These
results imply that the hot component of the X-ray-emitting plasma in
the corona is not coincident with the strong magnetic fields in the
lower corona. Because the hot plasma must still be confined by closed
magnetic field lines, it is likely to be restricted to heights of the
order of a stellar radius above the photosphere. The results seem to
imply a different genesis for the two components of the X-ray-emitting
corona of flare stars: the hot component may be cooling flare plasma,
while the cooler component (temperature of order 3 x 106
K) is associated with a more conventional coronal heating mechanism.

---------------------------------------------------------
Title: Observations of the 1991 Eclipse at 3.5 MM Wavelength
Authors: White, S. M.; Kundu, M. R.
1994IAUS..154..167W Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Interferometry of Solar Flares at 3-mm Wavelength
Authors: Kundu, M. R.; White, S. M.; Gopalswamy, N.; Lim, J.
1994IAUS..154..131K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Effects of Largescale and Smallscale Density Structures
on the Radio Emission from Coronal Streamers
Authors: Thejappa, G.; Kundu, M. R.
1994SoPh..149...31T Altcode:
The radio observations of the coronal streamers obtained using Clark
Lake radioheliograph at 73.8, 50.0, and 38.5 MHz during a period of
minimum activity in September 1986 are presented. Streamers appear to
correlate with two prominent disk sources whose intensities fluctuated
randomly. The variations in half-power diameter of the radio Sun are
found to correspond with the variations in the white-light extents of
the coronal streamers. It appears that the shape of the radio Sun is
not a function of the phase of the solar cycle; instead it depends on
the relative positions of the streamers in the corona. The observed
peak brightness temperatures,TB, of the streamers are found
to be very low, being ≃6 × 104 K.

---------------------------------------------------------
Title: A Search for gamma-Ray Emission from Active Stars
Authors: White, S. M.; Harmon, B. A.; Lim, J.; Kundu, M. R.
1994ASPC...64..498W Altcode: 1994csss....8..498W
No abstract at ADS

---------------------------------------------------------
Title: VLA Observations of a High Coronal Flare
Authors: Raulin, J. P.; Gopalswamy, N.; Kundu, M. R.; Nitta, N.
1993AAS...183.0706R Altcode: 1993BAAS...25.1300R
We present radio observations of a coronal flare which occurrred on 1993
April 22, in a weak magnetic field region to the west of AR 7477. The
observations were made by the Very Large Array (VLA) at 20 and 90
cm. The event consists of bright (brightness temperature of 10(10) K)
unpolarized bursts, followed by a longlasting unpolarized continuum with
moderately high brightness temperature (2-3 10(9) K) in the high corona
(90 cm observations). The low coronal counterpart of this flare is a
weak and moderatly polarized 20 cm radio emission. Full disk Yohkoh
images show that the corresponding radio emission is located in or
above magnetic loops connecting AR 7477 and its neighborhood. The
presence of permanent and non-varying noise storm associated with
AR 7477 seems to indicate that the overall magnetic field structure
of the active region is unaffected by the flare. The coronal radio
source which is indicative of acceleration of electrons to nonthermal
energies, is not associated with major Hα emissio n nor with bright
X ray emission. The absence of any detectable circular polarization,
as well as the high brightness temperature, seems to indicate that
the 90 cm emission is second harmonic plasma emission.

---------------------------------------------------------
Title: Variability in Sunspot Associated Microwave Emission: Umbral
Oscillations?
Authors: Gopalswamy, N.; Schmahl, E. J.; Kundu, M. R.
1993AAS...183.6808G Altcode: 1993BAAS...25.1396G
We report on microwave observations of sunspot associated emission
that shows variability over a time scale of minutes. To our knowledge,
this is the first time such rapid variability has been observed in
microwave radiation from a sunspot. These observations were obtained
by the Very Large Array (VLA) on April 24, 1992 at 2cm. The radio
emission from the sunspot umbra was in the form of several compact
sources with a size less than 4 arcsec. The time evolution of the peak
flux of these sources showed significant time variations which were
sometimes periodic. The period of these ocillations was approximately
3 min, similar to that of intensity and Doppler shift oscillations
observed in optically thin, transition region lines such as C IV
(1548.19 Angstroms) in sunspot umbrae. There were also morphological
changes in the extended sunspot emission over which the compact sources
were superposed. We also observed the appearance of new compact sources
within the umbra where there was reduced emission before. The brightness
temperatures of these compact sources were in the range (1-5)times 10(5)
K. We explore possible interpretations of the time variability.

---------------------------------------------------------
Title: Evolution of a Solar Active Region and Flare Productivity
Authors: Kundu, M. R.; Shibasaki, K.; Enome, S.; Nitta, N.; Bruner, M.
1993AAS...183.6807K Altcode: 1993BAAS...25.1396K
We have studied the evolution of an active region (AR 7515) in terms of
flare productivity. This region appeared on the east limb on May 23,
1993 and continued its onward march across the disk. We followed its
evolution until June 2. This region produced many small flares. We
studied the topology, both magnetic and structural of the flaring
region as observed at 17 GHz by the Nobeyama radio Heliograph (NRH)
with a spatial resolution of 10 arcsec and the Yohkoh SXT which has
a spatial resolution of 2.5 arcsec. Among other things, we find: (i)
Frequently a flare starts with the appearance of a new region/loop
which interacts with a pre-existing loop; this interaction acta as a
flare trigger. (ii) There appear to exist multiple sets of interacting
loops in the same active region. Different bursts on the same day
seem to come from diffrent sets of interacting loops. (iii) Sometimes
two or more sets of interacting loops can activate at the same time,
giving rise to different peaks in the same burst. In the decay phase
of some bursts there may appear a new or reactivated region/loop which
becomes the source of new burst emission. (iv) A simple spiky burst
in general originates from a narrow region and by implication from a
compact set of interacting loops.

---------------------------------------------------------
Title: Evidence for Ordinary Mode Emission from Microwave Bursts
Authors: Alissandrakis, C. E.; Nindos, A.; Kundu, M. R.
1993SoPh..147..343A Altcode:
We analyze high-resolution, one-dimensional observations of simple
microwave bursts, obtained at 4.9 GHz with the Westerbork Synthesis
Radio Telescope in 1980, together with Hα photographs of the associated
flares from the Observatories of Athens and Meudon. In most cases the
polarization structure can be interpreted in terms of extraordinary mode
emission, taking into account the polarity of the underlying magnetic
field and propagation effects, which may lead to inversion of the sense
of polarization in the limbward part of the flaring loop. We found
evidence for ordinary mode emission in two classes of events. In one
class theo-mode comes from regions overlying strong magnetic field,
which we interpret in terms of thermal gyroresonance absorption of
the extraordinary mode at the third harmonic of the gyrofrequency. In
the other class the entire burst emits in theo-mode, which may be
attributed to high gyrosynchrotron optical depth.

---------------------------------------------------------
Title: Structure of a fast coronal mass ejection from radio
observations.
Authors: Gopalswamy, N.; Kundu, M. R.
1993AdSpR..13i..75G Altcode: 1993AdSpR..13R..75G
The authors investigate the thermal structure of a coronal mass ejection
(CME) in meter-dekameter wavelengths and compare it with the optical
evidence. The multifrequency observations enable us to infer the three
dimensional structure of the CME. The authors estimated the mass of
the CME and found to be in reasonable agreement with the range of
values obtained from white light observations.

---------------------------------------------------------
Title: Interferometric observations of solar flares at 3 mm wavelength
Authors: Kundu, M. R.; White, S. M.; Gopalswamy, N.; Lim, J.
1993AdSpR..13i.289K Altcode: 1993AdSpR..13..289K
We report on the observations of a number of flares at a wavelength of
3.5 mm during the 1991 June solar campaign. Many flares, including
small ones, show an impulsive phase at milllimeter wavelengths
which indicates the presence of MeV electrons, and the millimeter
observations are far more sensitive to such electrons than are current
γ-ray detectors. However, these energetic electrons do not always show
a good correlation with the lower-energy electrons which produce hard
X-rays below 100 keV. The production efficiency of MeV electrons seems
to vary considerably from flare to flare. An extended phase similar to
the soft X-ray behaviour is also seen at millimeter wavelengths, which
we attribute to dense hot material radiating thermal bremsstrahlung. In
the impulsive onset the millimeter emission seems to be consistently
delayed with respect to the hard X-rays.

---------------------------------------------------------
Title: Simultaneous Observations of Solar Plage with the Solar
Extreme Ultraviolet Rocket Telescope and Spectrograph (SERTS),
the VLA, and the Kitt Peak Magnetograph
Authors: Brosius, Jeffrey W.; Davila, Joseph M.; Thompson, William T.;
Thomas, Roger J.; Holman, Gordon D.; Gopalswamy, N.; White, Stephen
M.; Kundu, Mukul R.; Jones, Harrison P.
1993ApJ...411..410B Altcode:
We obtained simultaneous images of solar plage on 1991, May 7
with SERTS, the VLA,4 and the NASA/National Solar Observatory
spectromagnetograph at the NSO/Kitt Peak Vacuum Telescope. Using
intensity ratios of Fe XVI to Fe XV emission lines, we find that the
coronal plasma temperature is (2.3-2.9) x 10 exp 6 K throughout the
region. The column emission measure ranges from 2.5 x 10 exp 27 to
l.3 x 10 exp 28 cm exp -5. The calculated structure and intensity
of the 20 cm wavelength thermal bremsstrahlung emission from the hot
plasma observed by SERTS is quite similar to the observed structure and
intensity of the 20 cm microwave emission observed by the VLA. Using
the Meyer (1991, 1992) revised coronal iron abundance, we find no
evidence either for cool absorbing plasma or for contributions from
thermal gyroemission. Using the observed microwave polarization and the
SERTS plasma parameters, we calculate a map of the coronal longitudinal
magnetic field. The resulting values, about 30-60 G, are comparable
to extrapolated values of the potential field at heights of 5000 and
10,000 km.

---------------------------------------------------------
Title: Meter-Wave Radio Emission from Flaring X-ray Bright Points
Authors: Kundu, M. R.; Strong, K. T.; Pick, M.; Kane, S. R.; Harvey,
K.; White, S. M.
1993BAAS...25.1180K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A Study of the Solar Active Regions Using Simultaneous VLA
and Yohkoh Soft X-ray Imaging: CoMStOC `92
Authors: Gopalswamy, N.; White, S. M.; Kundu, M. R.; Lemen, J. R.;
Strong, K. T.; Schmelz, J. T.
1993BAAS...25R1213G Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Hard X-ray and Radio Spectra for Solar Flares from AR 6659
Authors: White, S. M.; Murphy, R.; Schwartz, R. A.; Kundu, M. R.;
Gopalswamy, N.; Lim, J.
1993BAAS...25Q1222W Altcode:
No abstract at ADS

---------------------------------------------------------
Title: VLA and Yohkoh Observations of an M1.5 Flare
Authors: Gopalswamy, N.; Kundu, M. R.; Lemen, J. R.; Nitta, N.;
Strong, K. T.
1993BAAS...25.1186G Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Millimeter, Microwave and X-Ray Morphology and Spectra of
the 07Jan92 Flare
Authors: Silva, A. V.; Lin, R. P.; de Pater, I.; White, S. M.; Kundu,
M. R.; Gary, D. E.; Hudson, H. S.
1993BAAS...25Q1223S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: VLA, OVRO, Yohkoh and Optical Observations During CoMStOC
Authors: Schmahl, E. J.; Gopalswamy, N.; Kundu, M. R.; Lemen, J.;
Strong, K. T.; de La Beaujardiere, J.
1993BAAS...25.1213S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Solar Coronal Plasma and Magnetic Field Diagnostics Using
SERTS and Coordinated VLA Observations
Authors: Brosius, J. W.; Davila, J. M.; Thompson, W. T.; Thomas, R. J.;
Holman, G. D.; Gopalswamy, N.; White, S. M.; Kundu, M. R.; Jones, H. P.
1993BAAS...25.1224B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A Multiwavelength Portrait of a Solar Active Region
Authors: White, S. M.; Kundu, M. R.; Gopalswamy, N.
1993BAAS...25.1183W Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Radio Source Around eta Carinae
Authors: White, S. M.; Duncan, R. A.; Lim, J.; Nelson, G. J.; Drake,
S. A.; Kundu, M. R.
1993AAS...182.3906W Altcode: 1993BAAS...25..858W
The first high--spatial--resolution (1{(”) }) radio image of the
source surrounding the famous massive southern star eta Carinae has
been obtained with the Australia Telescope. The image shows a number of
interesting features: a strong central peak; ridges of emission close
to the peak and extending away from it in the directions of putative
“jets” seen in the HST image of the region, and also other ridges in
the directions of the lobes of the Homunculus; a box--like extended
feature of dimension 7{(”) } \ times 5{(”) }, with its major axis
orthogonal to the major axis of the Homunculus; and two fainter lobes
extending to 5{(”) } \ from the star in the directions of both lobes
of the Homunculus. The radio image bears a strong resemblance to the
high--resolution infra--red images of the region around the star. No
radio emission associated with the more extended X-ray--emitting nebula
is detected. The current rate of mass loss from the star is estimated,
and physical conditions within the nebula are discussed.

---------------------------------------------------------
Title: Spectral observations of active region sources with RATAN-600
and WSRT
Authors: Alissandrakis, C. E.; Gel'Frejkh, G. B.; Borovik, V. N.;
Korzhavin, A. N.; Bogod, V. M.; Nindos, A.; Kundu, M. R.
1993A&A...270..509A Altcode:
We present spectral observations of neutral line and sunspot associated
sources obtained with the RATAN-600 radio telescope and the WSRT
in the wavelength range of 2 to 6 cm. Sources associated with large
sunspots have flat spectra, while neutral line sources have very steep
spectra. In the case of a large spot we estimated the magnetic field
to be at least 2700 G at the base of the transition region and 1800 G
in the low corona. We consider possible interpretations of the radio
emission above the neutral lines. Gyroresonance emission at the fourth
harmonic is inadequate, whereas emission from a small population of
nonthermal electrons (total number 10 exp 30 to 10 exp 31) with a
delta = 3 power law distribution seems to be sufficient.

---------------------------------------------------------
Title: Thermal and nonthermal emissions during a coronal mass ejection
Authors: Gopalswamy, N.; Kundu, M. R.
1993SoPh..143..327G Altcode:
We report on the thermal and nonthermal radio emissions from a coronal
mass ejection (CME) observed at meter-decameter wavelengths using the
Clark Lake multifrequency radioheliograph. From white-light observations
of the Solar Maximum Mission Coronagraph/Polarimeter instrument the CME
was found to have a speed of ∼ 450 km s−1. Since there
was no nonthermal radio emission in the beginning of the event and the
one which occurred later was quite weak, we were able to observe the
thermal structure of the CME in radio. Type III bursts and a nonthermal
continuum started several minutes after the CME onset. We use the radio
and optical observations to show that the CME was not driven by the
flare. We investigate the thermal structure and geometry of the mass
ejection in radio and compare it with the optical evidence. Finally
we develop a schematic model of the event and point out that particle
acceleration high in the corona is possible.

---------------------------------------------------------
Title: A 1.5 GHz Radio Survey of the Hyades Open Stellar Cluster
Authors: White, S. M.; Jackson, P. D.; Kundu, M. R.
1993AJ....105..563W Altcode:
Results of a radio survey of the Hyades open stellar cluster carried out
with the VLA at 1.5 GHz are reported. Seventeen fields containing over
150 cataloged stars were mapped down to a limiting sensitivity ranging
from 0.3 mJy at the centers of the fields to 0.9 mJy at a distance of 20
arcmin from field centers. Two stars were detected as radio sources:
the evolved spectroscopic binary V471 Tau, consisting of a white
dwarf and a red dwarf; and the apparently premain-sequence G+K star
spectroscopic binary HD 27130. The failure to detect any single stars as
radio sources is generally consistent with the age-rotation-activity
paradigm, according to which stellar activity is due to magnetic
fields produced by dynamo action in rapidly rotating stars and should
decrease with age as a star spins down due to magnetic braking. It
is concluded that the Hyades M dwarf population is not more active at
radio wavelengths than the nearby flare star population, or else the
number of flare stars in the Hyades is much less than presently assumed.

---------------------------------------------------------
Title: Analysis of EUV, Microwave and Magnetic Field Observations
of Solar Plage
Authors: Brosius, J. W.; Davila, J. M.; Jones, H. P.; Thompson, W. T.;
Thomas, R. J.; Holman, G. D.; White, S. W.; Gopalswamy, N.; Kundu,
M. R.
1993ASPC...46..291B Altcode: 1993mvfs.conf..291B; 1993IAUCo.141..291B
No abstract at ADS

---------------------------------------------------------
Title: Radio observations of coronal streamers.
Authors: Kundu, Mukul R.
1992ESASP.348...87K Altcode: 1992cscl.work...87K
The author presents some radio observations of coronal streamers,
obtained at meter-decameter wavelengths, using the Clark Lake
multifrequency radioheliograph. Using daily imaging observations he
has generated synoptic charts similar to white light coronagraph
synoptic charts, and compared radio brightness enhancements with
bright coronal streamers. By using several frequencies simultaneously,
it has been possible to construct three-dimensional structures of
coronal streamers. The author shows that type III producing electrons
propagate in coronal streamers. He also compares the relative positions
of type III burst sources and coronal streamers as observed by HAO C/P
experiment aboard SMM; infers the paths of type III-emitting electrons
in dense coronal streamers, and from multi-frequency observations
derives electron density distributions above active regions near
the limb.

---------------------------------------------------------
Title: Observations of stationary radio sources: coronal polar plumes?
Authors: Gopalswamy, Natchimuthkonar; Schmahl, Edward J.; Kundu,
Mukul R.
1992ESASP.348..113G Altcode: 1992cscl.work..113G
Weak stationary radio sources are often observed near the poles of
the Sun during solar minimum in the two dimensional radio images at
meter-decameter wavelengths. The authors present observations from the
Clark Lake multifrequency radioheliograph obtained during Carrington
rotation 1771 (Jan 14 to Feb 10, 1986) and 1785 (Jan 31 to Feb 25,
1987). They explore various possibilities to interpret these stationary
sources involving thermal and nonthermal emissions from polar plumes.

---------------------------------------------------------
Title: Models of coronal streamers at meter-decameter wavelengths.
Authors: Schmahl, Edward J.; Gopalswamy, Natchimuthkonar; Kundu,
Mukul R.
1992ESASP.348..145S Altcode: 1992cscl.work..145S
Throughout the quiet Sun years 1982 - 1987, the Clark Lake
radioheliograph routinely mapped the solar corona on a daily basis at
frequencies from 30 to 100 MHz. The Clark Lake maps show a variety
of features which are analyzed quantitatively. Among the features
are coronal streamers, which appear to cross the solar disk during a
solar rotation. The authors have modeled the streamers with various
geometries and computed ray-tracing images for comparison with the
CLRO maps. The best fitting streamer models have a density profile
≍5 times Saito (1970) with a background ≍0.1 times Saito. The
required low background value may be explained by either scattering on
"microstructure" or unresolved "macrostructure".

---------------------------------------------------------
Title: Solar Observations with a Millimeter Wavelength Array
Authors: White, S. M.; Kundu, M. R.
1992SoPh..141..347W Altcode:
Rapid developments in the techniques of interferometry at millimeter
wavelengths now permit the use of telescope arrays similar to the
Very Large Array at microwave wavelengths. These new arrays represent
improvements of orders of magnitude in the spatial resolution and
sensitivity of millimeter observations of the Sun, and will allow us
to map the solar chromosphere at high spatial resolution and to study
solar radio burst sources at millimeter wavelengths with high spatial
and temporal resolution. Here we discuss the emission mechanisms at
millimeter wavelengths and the phenomena which we expect will be the
focus of such studies. We show that the flare observations study the
most energetic electrons produced in solar flares, and can be used to
constrain models for electron acceleration. We discuss the advantages
and disadvantages of millimeter interferometry, and in particular focus
on the use of and techniques for arrays of small numbers of telescopes.

---------------------------------------------------------
Title: Are coronal type II shocks piston driven?
Authors: Gopalswamy, N.; Kundu, M. R.
1992AIPC..264..257G Altcode: 1992pacp.work..257G
Flare blast waves and shocks piston driven by coronal mass ejections
(CMEs) have been proposed to be responsible for generating type II
radio bursts in the solar corona. The idea for piston-driven shocks
came primarily from temporal association of shocks and CMEs. Our
compilation of CME events with simultaneous radio observations with
positional information supports idea of flare blast waves.

---------------------------------------------------------
Title: The High-Frequency Characteristics of Solar Radio Bursts
Authors: Lim, J.; White, S. M.; Kundu, M. R.; Gary, D. E.
1992SoPh..140..343L Altcode:
We compare the millimeter, microwave, and soft X-ray emission from
a number of solar flares in order to determine the properties of the
high-frequency radio emission of flares. The millimeter observations
use a sensitive interferometer at 86 GHz which offers much better
sensitivity and spatial resolution than most previous high-frequency
observations. We find a number of important results for these
flares: (i) the 86 GHz emission onset appears often to be delayed
with respect to the microwave onset; (ii) even in large flares the
millimeter-wavelength emission can arise in sources of only a few
arc sec dimension; (iii) the millimeter emission in the impulsive
phase does not correlate with the soft X-ray emission, and thus is
unlikely to contain any significant thermal bremsstrahlung component;
and (iv) the electron energy distributions implied by the millimeter
observations are much flatter (spectral indices of 2.5 to 3.6) than
is usual for microwave or hard X-ray observations.

---------------------------------------------------------
Title: Unusually Low Coronal Radio Emission at the Solar Minimum
Authors: Thejappa, G.; Kundu, M. R.
1992SoPh..140...19T Altcode:
We present two-dimensional observations of the quiet Sun at 73.8, 50.0,
and 38.5 MHz obtained with the Clark Lake Radioheliograph during the
sunspot minimum period of September 1986. The observed peak brightness
temperatures during the entire period of sunspot minimum are found
to be extremely low, lying in the range (0.6 × 105 K −
2.5 × 105 K). It is shown that these low values cannot
be explained by the generally adopted models for Ne and
Te in a homogeneous corona. The effect of scattering by
random density fluctuations is introduced in order to decrease the
values of predicted Tb. The value of peak Tb
is computed as a function of relative r.m.s. density fluctuations ε =
&lt;ΔNe&gt;/Ne; and it is found that ɛ should
be in the range from 0.07 to 0.19, 0.1 to 0.25, and 0.15 to 0.35,
respectively, at 38.5, 50.0, and 73.8 MHz, respectively, to explain
the observed low brightness temperatures.

---------------------------------------------------------
Title: Radio flares and magnetic fields on weak-line T Tauri stars.
Authors: White, S. M.; Pallavicini, R.; Kundu, M. R.
1992A&A...259..149W Altcode:
We report the first detection of circular polarization in the radio
emission of two weak-line T Tauri stars. This is direct confirmation
of the presence of magnetic fields in the coronae of these stars. The
degree of polarization at 5 GHz is small, consistent with previous
observations which did not find measurable polarization. We have also
observed a radio flare on one of the two stars. The rising spectrum
of the radio emission together with the low degree of polarization
are strong evidence that radio outbursts on this class of stars are
due to nonthermal gyrosynchrotron emission which is optically thick
in the microwave range. One of the two stars shows no evidence for
circumstellar material, and thus can be classified as 'naked'. However
the other apparently has a dust disk, and the evidence of flaring on
this star indicates that the mechanism involved does not require an
empty circumstellar environment.

---------------------------------------------------------
Title: Analysis of EUV, Microwave, and Magnetic Field Observations
of a Solar Active Region
Authors: Brosius, J. W.; Davila, J. M.; Jones, H. P.; Thompson, W. T.;
White, S. M.; Gopalswamy, N.; Kundu, M. R.
1992AAS...180.4002B Altcode: 1992BAAS...24R.792B
No abstract at ADS

---------------------------------------------------------
Title: Simultaneous Hard X-ray, Soft X-ray, Millimeter and Microwave
Observations of a Solar Flare
Authors: White, S. M.; Kundu, M. R.; Lim, J.; Gopalswamy, N.
1992AAS...180.4504W Altcode: 1992BAAS...24..802W
We present non-imaging data across a wide range of wavelengths for a
solar flare which occurred on 1991 June 13. This flare is of interest
because it shows a spike in hard X-rays at the beginning of the event
which had a relatively hard X-ray spectrum, and was followed by a much
softer impulsive phase. We present the BATSE and OSSE observations
(from the Gamma Ray Observatory): the former have good time resolution,
while the latter provide well-resolved spectral information. These are
contrasted with the GOES soft-X-ray data on the hot thermal component in
the corona, and radio observations up to 86 GHz which are sensitive to
both the nonthermal and thermal components of the flare. The 86 GHz data
from the BIMA millimeter interferometer show a spike in the impulsive
phase coincident with the hard X-ray spike above 100 keV, as well as
a long-duration thermal phase which appears to be consistent with an
origin in the same material seen by GOES. We discuss the implications
of the observations for particle acceleration in this flare.

---------------------------------------------------------
Title: Estimation of the Mass of a Coronal Mass Ejection from Radio
Observations
Authors: Gopalswamy, N.; Kundu, M. R.
1992ApJ...390L..37G Altcode:
The mass of a coronal mass ejection (CME) is estimated using
meter-decametric observations obtained with the Clark Lake
multifrequency radioheliograph. Mass estimates in the past were made
using coronagraph and white-light photometer observations. Since
the radiation at radio and optical wavelength regimes has different
physical origins, the radio method can provide an independent check
on the mass estimates. The estimate of the 1986 February 16 CME using
the radio method is close to the average value of CME masses reported
in the literature.

---------------------------------------------------------
Title: Millimeter Observations of Solar Flares
Authors: Silva, A. V.; Lin, R. P.; de Pater, I.; White, S. M.; Kundu,
M. R.
1992AAS...180.4510S Altcode: 1992BAAS...24..803S
No abstract at ADS

---------------------------------------------------------
Title: Radio Observations During the 1991 June Campaign of Max'91
in Conjunction with Compton GRO Experiments
Authors: Kundu, M. R.
1992AAS...180.3403K Altcode: 1992BAAS...24R.783K
A summary of all available radio observations made during the 1991
June campaign of the MAX '91/Flare 22 program will be presented. The
presentation will be concerned primarily with millimeter wavelength
(BIMA and Nobeyama) and centimeter wavelengths (Owens Valley and
Nobeyama) observations. Emphasis will be given to the question of
millimeter observations as a diagnostic for Mev electrons in solar
flares (gamma ray flares --- BATSE and OSSE data), millimeter emission
occurring at the steep rise phase of hard X-ray emitting electrons
(BATSE data) and delay of millimeter emission onset and 25-100 Kev
X-rays (BATSE data). Implications of these results for generation
of millimeter emission and particle acceleration process will be
discussed. The Nobeyama data consist of non-imaging patrol observations
at several frequencies in the frequency range 1--80 GHz, and Owens
Valley data were obtained using the frequency agile interferometer in
the frequency range 1--18 GHz. Light curves and spectral information
of the most energetic flares will be presented.

---------------------------------------------------------
Title: 2-cm Observations of Quiescent and Flaring Emission from a
Solar Active Region
Authors: Lim, J.; White, S. M.; Kundu, M. R.
1992AAS...180.1102L Altcode: 1992BAAS...24..746L
We present 2-cm images of a solar active region comprising a large
leading spot and several smaller trailing spots, observed with the VLA
on 1989 Dec 14 and 16. On both days, slowly-varying quiescent emission
and impulsive flaring emission were detected. Comparisons of the radio
images with white-light pictures and magnetograms obtained on Dec 13
and 17 revealed that the quiescent emission originated almost entirely
from above the penumbra of large spots, whereas the flaring emission
originated from regions of complex magnetic field topology near but
not necessarily above magnetic neutral lines. The most intense source
of quiescent emission had a relatively low brightness-temperature (
~ 10(5) K), was highly circularly polarized (ranging from about 30\
trailing edge (i.e., limbward side) of the large leading spot. We
discuss models for this emission, constrained by the low brightness
temperature but high polarization. The weaker flare of Dec 14 showed
a single resolved source, and was weakly circularly-polarized. The
stronger flare of Dec 16 comprised a strong source with multiple peaks
and several weaker compact sources, all with low degrees of circular
polarization. Snapshot images of this flare showed an elongated feature
moving rapidly away from the main region of emission and joining with
the compact sources. We discuss likely mechanisms for this feature,
and emission process(es) responsible for the flares.

---------------------------------------------------------
Title: The Structure of the Corona of dMe Flare Stars
Authors: White, S. M.; Lim, J.; Kundu, M. R.
1992AAS...180.6005W Altcode: 1992BAAS...24..826W
There is now considerable information on both the surface magnetic
fields of dMe flare stars and on the thermal (X-ray emitting)
populations in their coronae. We show that the simplest picture of the
corona of a dMe flare star based on the measured photospheric magnetic
field strengths, the measured filling factors of these fields, and
the X-ray emission from their coronae, are inconsistent with radio
observations of the coronae. We discuss possible resolutions of this
dilemma.

---------------------------------------------------------
Title: A 5GHz radio survey of selected POST T Tauri and naked T
Tauri stars.
Authors: White, S. M.; Pallavicini, R.; Kundu, M. R.
1992A&A...257..557W Altcode:
Results of a radio survey of weak-lined T Tauri (variably
classified as either post T Tauri or naked T Tauri) stars at 5
GHz are reported. Thirty-two targets, chosen on the basis of known
high-activity levels or youth indications, were observed, and 15,
including eight previously unknown radio sources, were detected. It
is suggested that most weak-lined T Tauris with high activity levels,
e.g., as indicated by a high X-ray flux, are likely to be detectable
radio sources at some time, but the radio emission goes through high
and low phases. For the subsample of 14 stars observed in Taurus-Auriga
which were thoroughly studied at IR, optical, and X-ray wavelengths,
a clear association is found between radio activity and youth.

---------------------------------------------------------
Title: Observations on Mode Coupling in the Solar Corona and Bipolar
Noise Storms
Authors: White, S. M.; Thejappa, G.; Kundu, M. R.
1992SoPh..138..163W Altcode:
We review high-spatial-resolution observations of the Sun which reflect
on the role of mode coupling in the solar corona, and present a number
of new observations. We show that typically polarization inversion
is seen at 5 GHz in active region sources near the solar limb, but
not at 1.5 GHz. Although this is apparently in contradiction to the
simplest form of mode coupling theory, in fact it remains consistent
with current models for the active region emission. Microwave bursts
show no strong evidence for polarization inversion. We discuss bipolar
noise storm continuum emission in some detail, utilizing recent VLA
observations at 327 MHz. We show that bipolar sources are common at
327 MHz. Further, the trailing component of the bipole is frequently
stronger than the leading component, in apparent conflict with the
`leading-spot' hypothesis. The observations indicate that at 327 MHz
mode coupling is apparently strong at all mode-coupling layers in the
solar corona. The 327 MHz observations require a much weaker magnetic
field strength in the solar corona to explain this result than did
earlier lower-frequency observations: maximum fields are 0.2 G. This
is a much weaker field than is consistent with current coronal models.

---------------------------------------------------------
Title: High Dynamic Range Multifrequency Radio Observations of a
Solar Active Region
Authors: White, S. M.; Kundu, M. R.; Gopalswamy, N.
1992ApJS...78..599W Altcode:
High-dynamic-range multifrequency radio observations of a solar active
region are presented. The evolution of the region is followed at 5
GHz as it rotates from the limb to disk center, and when it is at
disk center, observations at 0.33, 1.5, 5, 8.4, and 15 GHz are used
to analyze the distribution of density and magnetic field within
the active region. A dynamic range of up to 1500 (at 8.4 GHz) was
achieved because these data were well suited to the self-calibration
technique. The signatures of both optically thick gyroresonance emission
are unambiguously identified, and magnetic fields and optically thin
thermal free-free emission are outlined. Images are compared at 5
and 8.4 GHz in order to identify regions in the trailing part of
the active region where optically thin four-harmonic gyroresonance
emission is contributing to the observed brightness temperatures at
5 GHz, indicating the presence of 450 G fields.

---------------------------------------------------------
Title: Millimeter and hard X-ray/γ-ray observations of solar flares
during the June 91 GRO campaign.
Authors: Kundu, M. R.; White, S. M.; Gopalswamy, N.; Lim, J.
1992NASCP3137..502K Altcode: 1992como.work..502K
We have carried out high-spatial-resolution millimeter observations
of solar flares using the Berkeley-Illinois-Maryland Array (BIMA). At
the present time, BIMA consists of only three elements, which is
not adequate for mapping highly variable solar phenomena, but is
excellent for studies of the temporal structure of flares at millimeter
wavelengths at several different spatial scales. We present BIMA
observations made during the Gamma Ray Observatories (GRO)/Solar Max
1991 campaign in Jun. 1991 when solar activity was unusually high. Our
observations covered the period 8-9 Jun. 1991; this period overlapped
the period 4-15 Jun. when the Compton Telescope made the Sun a target
of opportunity because of the high level of solar activity.

---------------------------------------------------------
Title: Meter-decameter radio emission associated with a coronal
mass ejection
Authors: Kundu, M. R.; Gopalswamy, N.
1992LNP...399..268K Altcode: 1992esf..coll..268K; 1992LNP...399..268G; 1992IAUCo.133..268K
A study of meter-dekameter radio emission associated with the 1986
Feb 10 coronal Mass ejection event is presented here. The event
was accompanied by a major flare (optical importance 1B and X-ray
importance C9.6), preceded by a filament disappearance. Changes in
the intensity of a pre-existing noise storm was observed during the
onset of the flare. A flare continuum, a moving type IV, and a type
II occurred during the event. The event was also associated with a
strong hard X-ray burst. The speeds of moving type IV burst and CME
were of the same order of 1600 kms -1, while the type II shock speed
was 1900 kms -1. The positional data indicate that the moving type IV
burst and the inferred type II shock had different trajectories. The
moving type IV burst was confined to one leg of the CME while the
type II shock was far ahead of the CME leading edge. We discuss the
inferred relation among different entities such as the CME, type II
shock, type IV plasmoid and the erupting filament.

---------------------------------------------------------
Title: A 5 GHz Survey of Weak-Lined T Tauri Stars
Authors: White, S. M.; Pallavicini, R.; Kundu, M. R.
1992ASPC...26..334W Altcode: 1992csss....7..334W
No abstract at ADS

---------------------------------------------------------
Title: Multifrequency Observations of a Remarkable Solar Radio Burst
Authors: White, S. M.; Kundu, M. R.; Bastian, T. S.; Gary, D. E.;
Hurford, G. J.; Kucera, T.; Bieging, J. H.
1992ApJ...384..656W Altcode:
Observations of an impulsive solar-radio burst from three observatories
are presented. The striking observational aspects of this flare are
that the time profile was identical throughout at 8.6, 15, and 86
GHz, that the spectrum was apparently flat from 15 to 86 GHz, and
that there was a sharp cutoff in the spectrum between 5.0 and 8.6
GHz. The simplest interpretation of the cutoff, namely as a plasma
frequency effect, leads to the conclusion that there was exceptionally
high-density material in the solar corona (of about 5 x 10 exp 11/cu
cm). Very Large Array images at 15 GHz show a single-loop structure
which brightened uniformly and showed little change in size during the
whole impulsive phase. The flat spectrum is consistent with optically
thin thermal bremsstrahlung emission, but the lack of observed soft
X-ray emission and other properties of the flare cannot easily be
accommodated by this mechanism. The possibility is explored that the
emission is optically thick due to thermal absorption of nonthermal
gyrosynchrotron emission, or optically thin gyrosynchrotron emission
absorbed by high-density material intervening along the line of
sight. Both of these explanations also face difficulties.

---------------------------------------------------------
Title: Radio observations of weak-lined T Tauri stars.
Authors: White, S. M.; Pallavicini, R.; Kundu, M. R.
1992MmSAI..63..751W Altcode:
We report the results of a search for radio-continuum emission from
weak-lined T Tauri stars selected on the basis of a range of criteria. A
correlation is found with strong X-ray emission and with youth. All the
stars in the survey older than about 20 million years were not detected
as radio sources. A flare was seen on one of the survey targets, with
a rise time of several hours. Circular polarization was also seen in
two of the targets, providing the first direct confirmation of the
presence of magnetic fields on these stars.

---------------------------------------------------------
Title: Radio observations of solar and stellar coronae
Authors: Kundu, M. R.; White, S. M.
1992MmSAI..63..715K Altcode:
Recent results of radio observations of the solar and stellar coronae
are reviewed. Attention is given to the results obtained on quiet-sun
fine structures; the active region observations, with particular
consideration given to the soft X-ray and radio comparisons of
observations made during the Coronal Magnetic Structures Observing
Campaign and the strength of the magnetic fields in the corona; the
radio observations of solar flares; and the radio observations of
stellar coronae of the RS Canum Venaticorum binaries, M dwarf stars,
pre-main-sequence stars, and chemically-peculiar B stars. Also discussed
are current issues in stellar radiophysics and perspectives in solar
radio physics.

---------------------------------------------------------
Title: HST Observations of the Flare Star AU MIC
Authors: Robinson, R. D.; Shore, S. N.; Carpenter, K. G.; Woodgate,
B. E.; Maran, S. P.; Brandt, J. C.; Kundu, M. R.; White, S. M.;
Linsky, J. L.; Walter, F. M.
1992ASPC...26...31R Altcode: 1992csss....7...31R
No abstract at ADS

---------------------------------------------------------
Title: Largescale Structures Associated with Eruptive Flares and
Radio Waves
Authors: Gopalswamy, N.; Kundu, M. R.
1992LNP...399..207G Altcode: 1992esf..coll..207G; 1992IAUCo.133..207G
We review some recent results obtained from 2-dimensional imaging
observations of the Sun using the Clark Lake multifrequency
radioheliograph. The radioheliograph produced images of the Sun's
corona on a daily basis at several frequencies within the range
20-125 MHz during the period 1982-87. Using these images both large
scale structures as well as transient phenomena such as bursts have
been studied. In this paper we discuss the nature of radio emission
associated with eruptive filaments and CMEs. It is possible to
trace the structure of magnetic fields in the corona based on the
multifrequency observations of moving type IV bursts at meter and
decameter wavelengths. We illustrate this by discussing specific
events. We discuss a rare case of the detection of thermal radio
emission in association with a fast CME. We estimate the CME mass
using spatially resolved radio data.

---------------------------------------------------------
Title: VLA observations of solar active regions at 6 and 20 CM
Authors: Alissandrakis, C. E.; Kundu, M. R.; Shevgaonkar, K. R.
1991A&A...251..276A Altcode:
High-resolution observations are presented of two active regions
at 6 and 20 cm over a period of 5 days, together with H-alpha and
photospheric magnetic fields. The large-scale emission at 20 cm is
associated with the H-alpha plage. In one region the strongest source
was over the neutral line, near the tip of an active-region filament,
which indicates that the emission probably originated in small-scale
coronal loops. In the second region the peak of the emission was near
a well-developed sunspot. Neither region showed evidence of large-scale
loops joining their preceding and following parts. Several other sources
were observed at 20 cm; a source associated with an H-alpha plage
region crossed by a filament and one associated with a small bipolar
region are briefly discussed. The 6-cm emission from a well-developed
spot showed clearly the characteristics expected from gyroresonance
model computations.

---------------------------------------------------------
Title: An Investigation of the Flare Star AU Mic with the Goddard
High Resolution Spectrograph on the Hubble Space Telescope
Authors: Maran, S. P.; Woodgate, B. E.; Carpenter, K. G.; Robinson,
R. D.; Shore, S. N.; Linsky, J. L.; Brown, A.; Byrne, P. B.; Kundu,
M. R.; White, S.; Brandt, J. C.; Shine, R. A.; Walter, F. M.
1991BAAS...23.1382M Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Large-Scale Features of the Sun at 20 Centimeter Wavelength
Authors: Gopalswamy, N.; White, S. M.; Kundu, M. R.
1991ApJ...379..366G Altcode:
Results are reported from an experimental study of the characteristics
of large-scale coronal structures such as active regions, plages,
filaments, and coronal holes using data obtained with the VLA
at 1.5 GHz during the period September 11-17, 1988. The radio
data were supplemented with He 10830- A, H-alpha, and Calcium-K
spectroheliograms. A statistical analysis of some of the characteristics
of the active regions is performed. Most of the active region sources
were found to be about 100 arcsec in size, with bridges between regions
common; lower brightness temperature regions showed a higher degree of
polarization in general. The maximum polarization was found at the edge
of active regions but well within the associated plages. The degree of
polarization from bright active regions was small (not more than 20
percent), in agreement with previous results. Evidence was found for
compression of preexisting flux by the emerging flux from a new region,
which took place in the apparent absence of magnetic reconnection.

---------------------------------------------------------
Title: Time Resolved Observations of the Lyman-Alpha Region in AU
Mic with the Goddard High Resolution Spectrograph
Authors: Woodgate, B. E.; Maran, S. P.; Carpenter, K. G.; Robinson,
R. D.; Shore, S. N.; Linsky, J. L.; Byrne, P. B.; Kundu, M. R.
1991BAAS...23.1383W Altcode:
No abstract at ADS

---------------------------------------------------------
Title: VLA Observations of Interacting Flaring Loops
Authors: Kundu, M. R.; White, S. M.; McConnell, D. M.
1991SoPh..134..315K Altcode:
We present 4.9 GHz observations of an impulsive radio burst observed
at the Very Large Array on 1981 May 16. The flare occurred in a
complex active region containing several spots. The radio burst lay
at the edge of an active-region microwave source, close to a neutral
line. The compact burst showed morphological evidence for the presence
of two loops in the rise phase, with the subsequent burst peak lying
between these loops. This suggests that interaction between the loops
played some role in the initiation of the flare. The flare spectrum is
consistent with thermal gyrosynchrotron emission. The main microwave
peak was displaced from the nearest Hα kernels by about 10″, but
there is strong evidence for post-flare loops coincident with the Hα
kernels during the later stages of the event.

---------------------------------------------------------
Title: Coronal Magnetic Structures Observing Campaign. I. Simultaneous
Microwave and Soft X-Ray Observations of Active Regions at the
Solar Limb
Authors: Nitta, N.; White, S. M.; Kundu, M. R.; Gopalswamy, N.; Holman,
G. D.; Brosius, J. W.; Schmelz, J. T.; Saba, J. L. R.; Strong, K. T.
1991ApJ...374..374N Altcode:
Using simultaneous microwave and soft X-ray measurements made with
the Very Large Array (VLA) at 6 and 20 cm and the X-ray Polychromator
(XRP) aboard the Solar Maximum Mission (SMM), we have studied two
active regions near the solar limb. These observations were taken as
part of the Coronal Magnetic Structures Observing Campaign (CoMStOC),
a collaboration designed to study the magnetic field in the solar
corona. The images in soft X-rays and at 20 cm wavelength are similar:
both show peaks above the active regions and extended bridge of
emission 200,000 km long connecting the two regions. The brightness
temperature of the 20 cm emission is lower than that predicted from the
X-ray emitting material, however; it can be attributed to free-free
emission in cooler (&lt;106 K) plasma not visible to XRP,
with an optical depth ∼1. The 6 cm emission is concentrated at lower
altitudes and in a ∼160,000 km long bundle of loops in the northern
active region. Comparison of the 6 cm map with the potential magnetic
field lines computed from photospheric magnetic fields (measured 2 days
earlier) indicates that the 6 cm emission is associated with fields
of less than ∼200 G. Such fields would be too weak to attribute the
observed 6 cm emission to gyroresonance radiation. Analysis of the
6 cm loop bundle indicates that it is strongly asymmetric, with the
magnetic field in the northern leg ∼2 times stronger than in the
southern leg; the 6 cm emission most likely arises from a combination
of hot ( ≥ 2 × 106 K) and cool plasmas, while the 20 cm
emission becomes optically thick in the cooler (∼9 × 103
K) plasma. We estimate an Alfvén speed ∼7000 km s-1
and ratio of electron gyrofrequency to plasma frequency ∼1.0 in the
northern leg of the 6 cm loop.

---------------------------------------------------------
Title: A Search for Solar Oscillations in the Solar Chromosphere
Using Millimeter Interferometric Observations
Authors: Kundu, M. R.; White, S. M.
1991BAAS...23R1033K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Global Streamer Evolution
Authors: Thejappa, G.; Kundu, M. R.; Gopalswamy, N.
1991BAAS...23.1045T Altcode:
No abstract at ADS

---------------------------------------------------------
Title: On the Reconciliation of Simultaneous Microwave Imaging and
Hard X-Ray Observations of a Solar Flare
Authors: Nitta, N.; White, S. M.; Schmahl, E. J.; Kundu, M. R.
1991SoPh..132..125N Altcode:
We have compared microwave imaging data for a small flare with
simultaneous hard X-ray spectral observations. The X-ray data suggest
that the power-law index δ of the energy distribution of the radiating
electrons is 5.3 (thick-target) which differs significantly from the
estimate (δ = 1.4) from a homogeneous optically-thin gyrosynchrotron
model which fits the radio observations well. In order to reconcile
these results, we explore a number of options. We investigate a double
power-law energy spectrum for the energetic electrons in the flare,
as assumed by other authors: the power law is steep at low energies
and much flatter at the higher energies which produce the bulk of the
microwaves. The deduced break energy is about 230 keV if we tentatively
ignore the X-ray emission from the radio-emitting electrons: however,
the emission of soft photons by the flat tail strongly contributes to
the observed hard X-ray range and would flatten the spectrum there. A
thin-target model for the X-ray emission is also inconsistent with
radio data. An inhomogeneous gyrosynchrotron model with a number of
free parameters and containing an electron distribution given by the
thick-target X-ray model could be made to fit the radio data.

---------------------------------------------------------
Title: VLA Observations of Radio Filaments
Authors: Gopalswamy, N.; White, S. M.; Kundu, M. R.
1991BAAS...23.1045G Altcode:
No abstract at ADS

---------------------------------------------------------
Title: New Observations of Solar Noise Storm Radiation at Decameter
Wavelengths
Authors: Thejappa, G.; Kundu, M. R.
1991SoPh..132..155T Altcode:
We report multifrequency observations of storm continuum and other radio
bursts. Based on their positional study and their correlation with other
coronal and photospheric features, we deduce that the storm source is
located in the magnetic field lines lying above a single bipolar active
region. Energetic electrons trapped in the magnetic structures above
the spots must be responsible for the storm radiation. We show that
spontaneous emission of Langmuir waves by anisotropic distributions can
explain both storm continuum and bursts self-consistently. Whenever
the collisional damping (νc) is more than the growth
(- υA), there is a steady emission responsible for the
continuum, and whenever νc = -υA (which may
be satisfied randomly) there is a sudden jump in Tb giving
rise to bursts. The number density of energetic particles required
to explain the storm continuum at 73.8, 50, and 30.9 MHz frequencies
is estimated to lie in the limits nb/ne ∼
10−10−10−9 in the context of the present
observations. The brightness spectrum of the storm continuum is computed
and compared with observations.

---------------------------------------------------------
Title: Millimeter Imaging of Energetic Electrons in Solar Flares in
Conjunction with GRO Experiments
Authors: Kundu, M. R.; White, S. M.
1991BAAS...23Q1073K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Millimeter Interferometric Observations of Solar Flares During
the SOLAR-A Mission
Authors: Kundu, M. R.; White, S. M.
1991LNP...387..338K Altcode: 1991fpsa.conf..338K
We present the results of the first high-spatial-resolution
interferometric observations of solar flares at millimeter wavelengths,
carried out with the Berkeley-Illinois-Maryland Array (BIMA). The
observations represent an improvement of an order of magnitude in
both sensitivity and spatial resolution compared with previous solar
observations at these wavelengths. Most of the flares occurring within
the field of view during the observations have been detected by BIMA,
including both very impulsive and longer-duration events. It appears
that millimeter burst sources are not much smaller than microwave
sources. If the emission in the flash phase is predominantly due to
gyrosynchrotron emission, we can rule out thermal gyrosynchrotron models
for the radio emission because the flux at millimeter wavelengths is
too high. During the Solar-A mission we plan to obtain both imaging
data as well as dedicated patrol observations of flare time profiles
at millimeter wavelengths.

---------------------------------------------------------
Title: Strong Magnetic Fields and Inhomogeneity in the Solar Corona
Authors: White, S. M.; Kundu, M. R.; Gopalswamy, N.
1991ApJ...366L..43W Altcode:
It is shown that fields of 1800 G can exist in the corona based
on observations of gyroresonance emission at 15 GHz at coronal
temperatures. The strong fields occur in a small source radiating
in the extraordinary (x) mode over the penumbra of a large symmetric
sunspot. The optically-thin ordinary mode emission from the region shows
a nearby peak at only 36,000 K which may be due to a sunspot plume,
and a hole over the umbra consistent with the expected low-density
material there. The x-mode source is highly asymmetric, despite the
apparent symmetry of the sunspot, and its appearance and location
imply that the strongest magnetic fields in the corona are localized
in a compact flux tube.

---------------------------------------------------------
Title: High spatial resolution observations of solar flares at 3.3
mm wavelength
Authors: Kundu, M. R.; White, S. M.; Welch, W. J.; Bieging, J. H.
1991AdSpR..11e..91K Altcode: 1991AdSpR..11...91K
We present the first high-spatial-resolution interferometric
observations of solar flares at millimeter wavelengths, carried out
with the Berkeley-Illinois-Maryland Array (BIMA). The observations
represent an improvement of an order of magnitude in both sensitivity
and spatial resolution compared with previous solar observations at
these wavelengths. Most of the flares occurring within the field of
view during the observations were detected by BIMA, including both very
impulsive and longer-duration events. It appears that millimeter burst
sources are not much smaller than microwave sources. If the emission in
the flash phase is predominantly due to gyrosynchrotron emission, we can
rule out thermal gyrosynchrotron models for the radio emission because
the flux at millimeter wavelengths is too high. During the Flares 22
campaign we will collect both imaging data as well as dedicated patrol
observations of flare time profiles at millimeter wavelengths.

---------------------------------------------------------
Title: Millimeter Solar Observing with BIMA
Authors: Kundu, M. R.; White, S. M.; Welch, W. J.
1991max..conf...11K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: VLA Observations of Active Region 5555 During the 1st Max'91
Campaign
Authors: Schmahl, E. J.; Gopalswamy, N.; Kundu, M. R.
1991max..conf...23S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Association of a Type IV Burst with a Slow CME
Authors: Gopalswamy, N.; Kundu, M. R.
1991max..conf..139G Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Triennial Report of IAU Commission 40 (Radio Astronomy)
1988-1991
Authors: Altenhoff, Wilhelm J.; Andernach, Heinz; Baars, Jaap; Chini,
Rolf; Cohen, R. J.; Condon, J. J.; Fukui, Y.; Güsten, R.; van der
Hulst, J. M.; Henkel, C.; Huchtmeier, W.; Ishiguro, M.; Krichbaum, T.;
Kundu, M.; Lasenby, A.; Reich, W.; Roelfsema, P.; Thorsett, S. E.;
Tuffs, R.; Walmsley, C. M.; Wendker, H.; Wielebinski, R.; Wilson,
T. L.; Witzel, A.
1991IAUTA..21..449A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Meter-Decameter Observations of Dme Flare Stars with the
Clark-Lake Radio Telescope
Authors: Jackson, P. D.; Kundu, M. R.; Kassim, N.
1990SoPh..130..391J Altcode:
The now-closed Clark Radio Observatory was used in 1984 and 1985 to
search for flaring emission from a number of dMe flare stars in the
30.9 to 110.6 MHz frequency range. No emission was found to greatly
exceed detection limits which range from about 1 Jy for 1 hr averaging,
to about 50 Jy for 1 s averaging, even though flares were often seen
to tens of mJy at 20 cm using the VLA for those times when VLA-CLRO
observations were coordinated. There are marginal detections of flaring
from AD Leo over two periods on December 15, 1985 which mark the
beginning and the end of along-lasting, narrow-band flare at 1415 MHz.

---------------------------------------------------------
Title: Coronal mass ejections and solar radio bursts
Authors: Kundu, Mukul R.
1990IJRSP..19..506K Altcode:
The radio signatures and properties of coronal mass ejection (CME)
events are discussed. The signatures are mostly in the form of type
2 and type 4 burst emissions. Although type 2 bursts are temporally
associated with CMEs, it is shown that there is no spatial relationship
between them. It is shown that moving type 4 and type 2 bursts can be
associated with slow CMEs with speeds as low as 200 km/s, contrary to
the previous belief that only CMEs with speeds greater than 400 km/s
are associated with radio bursts. A specific event is discussed in
which the CME and type 4 burst had nearly the same speed and direction,
but the type 2 burst location was behind the CME and its motion was
transverse. The speed and motion of the type 2 burst strongly suggest
that the type 2 shock was decoupled from the CME and probably due to
a flare behind the limb. Therefore only the type 4 source could be
directly associated with the slow CME.

---------------------------------------------------------
Title: The Observation of an Unusually Fast Type IV Plasmoid
Authors: Gopalswamy, N.; Kundu, M. R.
1990ApJ...365L..31G Altcode:
A moving type IV burst of the 'isolated source' type has been detected
whose out-of-plane speed, at 1600 km/sec, becomes about 2800 km/sec
upon assumption of radial motion; this is twice as high as previously
reported speeds for bursts of this type. While shock waves are known
to have such high speeds, and a shock wave is likely to form ahead
of a high-speed plasmoid, no radio signature has been observed for
such a shock. This lack of shock detection may, however, be primarily
due to poor observing conditions. Energetic electrons, trapped in an
about 1.4 G magnetic field of the plasmoid, can adequately account
for the emission.

---------------------------------------------------------
Title: Book-Review - Energetic Phenomena on the Sun
Authors: Kundu, M. R.; Woodgate, B.; Schmahl, E. J.; Staude, J.
1990AN....311..416K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: UVSP and VLA observations of the 24 June 1980 flare: Asymmetric
or isotropic beaming?
Authors: Kundu, M. R.; Cheng, C. C.; Schmahl, E. J.
1990SoPh..129..343K Altcode:
Observations of the 15:22 UT flare of 24 June 1980 were made using the
Very Large Array (VLA) at 6 cm wavelength simultaneously with the Hard
X-ray Imaging Spectrometer (HXIS) aboard the Solar Maximum Mission. It
was found that at the peak of the impulsive phase, the brightest
microwave point appeared to lie between the soft (3.6-8.0 keV) and hard
(22-30 keV) X-ray maxima, which were themselves separated by ∼ 20″
(Kundu et al., 1984). Since the publication of these results, we have
analyzed the imaging data from the Ultraviolet Spectrometer Polarimeter
(UVSP) with the goal of narrowing the possible interpretations of the
event. Like the VLA and HXIS, the UVSP observations provide information
about the location of the primary electrons; the observations taken
together suggest that the fast electrons were symmetrically distributed
within the flare loop.

---------------------------------------------------------
Title: Filament Eruption and Storm Radiation at Meter / Decameter
Wavelengths
Authors: Kundu, M. R.; Gopalswamy, N.
1990SoPh..129..133K Altcode:
We report the study of a weak noise storm observed by the Clark Lake
multifrequency radioheliograph at four frequencies. The noise storm
onset was associated with a filament eruption and a gradual rise and
fall in soft X-rays. We compare the noise storm emission with related
emissions in other wavelengths to develop a composite scenario of
the event. Using the properties of the quiet corona inferred from the
simultaneously observed quiet-Sun radiation, we estimate the brightness
temperature of the storm continuum, which seems to be consistent with
the observations reported in Solar Geophysical Data. Superthermal
particles with a temperature that is ten times the coronal electron
temperature and a density of ∼ 10−3 times the coronal
density are adequate to explain the observed radiation. Since the noise
storm observations were made at four frequencies, we were able to obtain
a brightness temperature spectrum of the storm radiation. If the storm
radiation is affected in the same way as the quiet-Sun emission by
inhomogeneities, the observed spectrum can be interpreted as due to
propagation effects. Since the Clark Lake instrument can observe both
quiet Sun and weak bursts simultaneously, we were able to estimate
the propagation effects from the quiet-Sun observations and use it to
correct the brightness temperature of storm radiation.

---------------------------------------------------------
Title: Multiple Moving Magnetic Structures in the Solar Corona
Authors: Gopalswamy, N.; Kundu, M. R.
1990SoPh..128..377G Altcode: 1990IAUCo.121P.377G
We report the study of moving magnetic structures inferred from the
observations of a moving type IV event with multiple sources. The
ejection contains at least two moving radio emitting loops with
different relative inclinations. The radio loops are located above
multiple Hα flare loops in an active region near the limb. We
investigate the relationship between the two systems of loops. The
spatial, temporal and geometrical associations between the radio
emission and near surface activities suggest a scenario similar to
coronal mass ejection (CME) events, although no CME observations exist
for the present event. From the observed characteristics, we find that
the radio emission can be interpreted as Razin suppressed optically thin
gyrosynchrotron emission from nonthermal particles of energy ∼ 100,
keV and density ∼ 102-105 cm−3
in a magnetic field ≤ 2 G.

---------------------------------------------------------
Title: Microwave and X-Ray Observations of a Major Confined Solar
Flare
Authors: Schmahl, E. J.; Schmelz, J. T.; Saba, J. L. R.; Strong,
K. T.; Kundu, M. R.
1990ApJ...358..654S Altcode:
Observations of an X4 flare of May 19, 1984 using the VLA and the
SMM X-ray Polychromator are discussed. The 6 cm radio source remained
stationary throughout the decay phase. Combined with other evidence,
this indicates that the flare was magnetically confined and did not
disrupt the complex structure of its region. The observed structures
may be associated with a neutral sheet connecting the two bipoles.

---------------------------------------------------------
Title: First High Spatial Resolution Interferometric Observations
of Solar Flares at Millimeter Wavelengths
Authors: Kundu, M. R.; White, S. M.; Gopalswamy, N.; Bieging, J. H.;
Hurford, G. J.
1990ApJ...358L..69K Altcode:
The first high spatial resolution interferometric observations
of solar flares at millimeter wavelengths, carried out with the
Berkeley-Illinois-Maryland Array are presented. The observations were
made at 3.3 mm wavelength during the very active periods of March 1989,
using one or three baselines with fringe spacings of 2-5 arcsec. The
observations represent an improvement of an order of magnitude in
both sensitivity and spatial resolution compared with previous solar
observations at these wavelengths. It appears that millimeter burst
sources are not much smaller than microwave sources. The most intense
bursts imply brightness temperatures of over 10 to the 6th K and are due
to nonthermal gyrosynchrotron emission or possibly thermal free-free
emission. If the emission in the flash phase is predominantly due to
gyrosynchrotron emission, thermal gyrosynchrotron models can be ruled
out for the radio emission because the flux at millimeter wavelengths
is too high.

---------------------------------------------------------
Title: Microbursts at Meter-Decameter Wavelengths
Authors: Thejappa, G.; Gopalswamy, N.; Kundu, M. R.
1990SoPh..127..165T Altcode:
We study the characteristics of microbursts using a large data base
obtained with the multifrequency radioheliograph of the Clark Lake Radio
Observatory. Most of the new observations were made during July 29,
1985 to August 2, 1985; we also include for statistical studies the
microburst data used in our earlier studies. We perform a statistical
analysis of many characteristics such as frequency drift, source size
and brightness temperature and compare them with the properties of
normal type III bursts. We investigate the coronal structures and
surface activities associated with some of the events. We find that
(i) the brightness temperature is in the range 6 × 105
K to 6 × 107 K; (ii) the drift rate of the microbursts is
slightly smaller than that of normal type III bursts, implying electron
beams with speeds ∼0.2c.

---------------------------------------------------------
Title: CoMStOCI: Physical Properties of an Active Region Loop Observed
at the Solar Limb
Authors: Holman, G. D.; Brosius, J. W.; Nitta, N.; White, S. M.; Kundu,
M. R.; Gopalswamy, N.; Schmelz, J. T.; Saba, J. L. R.; Strong, K. T.
1990BAAS...22..899H Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Evolution of Active Regions at 20 cm
Authors: Gopalswamy, N.; White, S. M.; Kundu, M. R.
1990BAAS...22..795G Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Magnetic Field Strengths in Post-Flare Loop Systems
Authors: Schmahl, E. J.; Kundu, M. R.
1990BAAS...22Q.827S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The solar probe mission
Authors: Feldman, W. C.; Anderson, J.; Bohlin, J. D.; Burlaga, L. F.;
Farquhar, R.; Gloeckler, G.; Goldstein, B. E.; Harvey, J. W.; Holzer,
T. E.; Jones, W. V.; Kellogg, P. J.; Krimigis, S. M.; Kundu, M. R.;
Lazarus, A. J.; Mellott, M. M.; Parker, E. N.; Rosner, R.; Rottman,
G. J.; Slavin, J. A.; Suess, S. T.; Tsurutani, B. T.; Woo, R. T.;
Zwickl, R. D.
1990AIPC..203..101F Altcode: 1990pacr.rept..101F
The Solar Probe will deliver a 133.5 kg science payload into a 4 Rs
perihelion solar polar orbit (with the first perihelion passage in 2004)
to explore in situ one of the last frontiers in the solar system-the
solar corona. This mission is both affordable and technologically
feasible. Using a payload of 12 (predominantly particles and
fields) scientific experiments, it will be possible to answer many
long-standing, fundamental problems concerning the structure and
dynamics of the outer solar atmosphere, including the acceleration,
storage, and transport of energetic particles near the Sun and in the
inner (&lt;65 Rs) heliosphere.

---------------------------------------------------------
Title: High-Dynamic-Range Multifrequency Radio Observations of a
Solar Active Region
Authors: White, S. M.; Kundu, M. R.; Gopalswamy, N.
1990BAAS...22R.794W Altcode:
No abstract at ADS

---------------------------------------------------------
Title: VLA Observations of Solar Active Regions at 6 and 20 cm During
the Spacelab 2 Mission
Authors: Alissandrakis, C. E.; Kundu, M. R.; Shevgaonkar, R. K.
1990BAAS...22..795A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Millimeter-Interferometer Observations of Solar Flares
Authors: Kundu, M. R.; White, S. M.; Gopalswamy, N.; Bieging, J. H.;
Hurford, G. J.
1990BAAS...22..823K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: New Observations of Storm Radiation at Decameter Wavelengths
and Their Interpretation
Authors: Thejappa, G.; Gopalswamy, N.; Kundu, M. R.
1990BAAS...22..794T Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Kilometric Shock-Associated Events and Microwave Bursts
Authors: Kundu, M. R.; MacDowall, R. J.; Stone, R. G.
1990Ap&SS.165..101K Altcode:
The peak times of impulsive microwave bursts are compared with those
of shock-associated (SA) kilometric radio events. The first peaks in
these two frequency regimes are usually well-correlated in time, but
the last peaks of the SA events observed at 1 MHz occur an average of
20 min after the last impulsive microwave peaks. In some cases, the
SA events overlap in time with the post-burst increases of microwave
bursts; sometimes there is general correspondence in their intensity
time profiles. These observations suggest that the earlier components
of the SA events are usually caused by electrons accelerated in or
near the microwave source region. We discuss the possibility that the
later components of some SA events could be associated with nonthermal
electrons responsible for microwave post-burst increases, although
they have traditionally been attributed to electrons accelerated at
type II burst producing shocks in the upper corona.

---------------------------------------------------------
Title: Magnetic field reconnection in solar and stellar flares
Authors: Kundu, M. R.; White, S. M.
1990AdSpR..10i..85K Altcode: 1990AdSpR..10...85K
Radio observations are sensitive to energetic electrons, and thus are an
important tool for studying the properties of solar flares. High spatial
resolution multifrequency observations at centimeter wavelengths can
provide important information on the region of energy release during
flares and, therefore, on their triggering mechanisms. The changes in
polarization and its structure during the preflare and impulsive phase
have led to inferences about magnetic field topology in the flaring
region /1/. We have learnt that evolving magnetic field structures
often trigger the flare /2/. In this paper, we discuss evidence for
magnetic reconnection in both solar and stellar flares derived from
radio observations. We present two cases of solar flares well-observed
by the VLA which show interacting magnetic structures leading to a
flare. Both cases are strongly suggestive of reconnection. In the
second part of the paper we discuss more indirect evidence based on
flares in the coronae of red dwarf stars.

---------------------------------------------------------
Title: Some Problems in Low Frequency Solar Radio Physics
Authors: Gopalswamy, N.; Kundu, M. R.
1990LNP...362...97G Altcode: 1990lfas.work...97G
Several important problems in solar radio physics can be attacked using
the high spatial resolution observations from a low frequency space
array, as the problem of ionospheric refraction does not exist. Noise
storms are believed to occur in closed magnetic loops due to trapped
superthermal particles. Recent radioheliograph observations suggest such
a magnetic field topology up to altitudes of about 40 MHz emission. The
problem of relative locations and sources of the storm continuum and
bursts can be effectively studied by imaging them with higher spatial
resolution. Interplanetary type II bursts are observed from heights
above ~ 10 R while coronal type II bursts are observed from heights less
than ~ 3 R. Observations filling this gap have important implications
for the understanding of solar-terrestrial relations through shocks
and mass ejections.

---------------------------------------------------------
Title: Millimeter and Microwave Activity of the Sun
Authors: Kundu, M. R.; White, S. M.
1990IAUS..142..457K Altcode:
Preliminary results of high-spatial-resolution millimeter observations
of recent solar flares carried out with the Berkeley-Illinois-Maryland
Array are presented. Findings obtained from multifrequency observations
using the VLA are reported. The time profiles of several bursts
during March 1989 are presented. Most of the bursts were impulsive and
short-lived, and a number of longer-duration bursts were observed as
well. All the bursts were fairly weak, with none exceeding 1 sfu of
correlated amplitude. A number had rise times less than the available
resolution of 10 sec. VLA observations in September 1988 showed that
there is exceptionally good correspondence between the 1.5-GHz radio
sources and the regions which are dark in He 10830 images and bright
in Ca images.

---------------------------------------------------------
Title: The Radio Spectra of Rs-Canum Stars
Authors: White, S. M.; Kundu, M. R.; Uchida, Y.; Nitta, N.
1990ASPC....9..239W Altcode: 1990csss....6..239W
The results of observations of several systems are presented for the
0.327-90 GHz range to study the radio coronae and outbursts associated
with the RS CVn stars, as well as their visibility at millimeter
wavelengths. The radio spectra are observed with the VLA and the
Nobeyama 45-m millimeter-wavelength telescope. The three stars observed
with the Nobeyama and VLA telescopes are UX Ari, AR Lac, and HR 5110,
and the frequencies and conditions of the nonsimultaneous observations
are set forth. Observations of the RS CVn systems at mm wavelengths
is possible, and it is theorized that important information regarding
flares and energy release can be derived from these data. A simple model
is presented for the radio-coronae source related to outbursts of up
to 5 GHz, and the onset of outbursts are predicted to be accompanied
by low frequency type-II plasma emission.

---------------------------------------------------------
Title: The Sun at the Vla's Metric and Decimetric Wavelengths
Authors: White, S. M.; Kundu, M. R.; Gopalswamy, N.; Schmahl, E. J.
1990IAUS..142..523W Altcode:
Preliminary results of solar observations at 0.333 and 1.5 GHz
made with the VLA during the September 11-17, 1988 period are
presented. Generally, there are few structural changes in the active
region sources from one day to the next, suggesting that structural
evolution is relatively slow. Contour maps at 1.5 GHz are presented
for each of the four days. Two noise storms were present at 0.33 GHz
all week and were highly polarized.

---------------------------------------------------------
Title: Measurement of solar magnetic fields from radio observations
Authors: Kundu, M. R.
1990MmSAI..61..431K Altcode:
Measurements of magnetic fields in the sun's atmosphere using radio
observations are discussed. Radio measurements of magnetic fields in
the chromosphere and the corona are indirect. In the chromosphere,
these are based upon the measurement of polarization of active regions
at millimeter wavelengths. In the transition region and the corona, the
properties of gyroresonance radiation of active regions at centimeter
wavelengths are used. Total intensity and polarization maps and modeling
are used to determine which harmonic (second or third) is predominant
in the active region emission. A direct method of measuring coronal
magnetic fields using cyclotron line emission is discussed, and the
relevant data as presently available are presented.

---------------------------------------------------------
Title: Dual Frequency Variability Study of an Active Region
Authors: Shevgaonkar, R. K.; Kundu, M. R.
1990IAUS..142..489S Altcode:
The VLA is used to investigate a short-time variability of a solar
region at 6 and 2 cm wavelengths simultaneously. The observed low
brightness temperatures indicate that the emission is mainly originating
from the chromosphere-corona transition region. It is shown that an
independent variation of a few percent in the magnetic field (900 +/-
45 G) and a factor-of-two variation in the density (2 to 4 x 10 exp
10/cu cm) over a time scale of a few hours is required to explain the
uncorrelated brightness temperature at the two wavelengths.

---------------------------------------------------------
Title: The Radio Signatures of a Slow Coronal Mass Ejection: Electron
Acceleration at Slow-Mode Shocks?
Authors: Kundu, M.; Gopalswamy, N.; White, S.; Cargill, P.; Schmahl,
E. J.; Hildner, E.
1989ApJ...347..505K Altcode:
The evolution of a coronal mass ejection (CME) event observed on
February 17, 1985 is studied using two-dimensional radio imaging
observations along with simultaneously obtained coronagraph
observations. This event shows that a slow CME can be associated
with type II and type IV radio bursts. The implications of the spatial
association of the radio bursts with the CME are discussed. It is argued
that the CME is due to an instability of the large-scale magnetic
field in a helmet streamer and that the radio bursts are some of the
responses to this instability. The new feature of this event is the
clear association of the moving type IV burst with a CME traveling
slower than the coronal Alfven speed. The structure of slow shocks
driven by such a CME is discussed, and it is shown that shock drift
and diffusive acceleration are ineffective. An acceleration mechanism
involving current-driven lower hybrid waves is proposed.

---------------------------------------------------------
Title: A VLA Survey of Nearby Flare Stars
Authors: White, Stephen M.; Jackson, Peter D.; Kundu, Mukul R.
1989ApJS...71..895W Altcode:
Results from a VLA survey of nearby flare stars are combined with
those of other surveys to compare the incidence of radio detection of
late-type dwarf stars with other stellar parameters. About 40 percent
of known nearby flare stars were detected in the survey. It is found
that there is a deficiency of radio detections for M dwarf stars later
than dM5.5, in agreement with the falloff in X-ray luminosity of these
stars. Evidence is found for a link between radio activity and rotation,
because most of the detected sources are stars which are believed to
be young disk stars and are still rapid rotators.

---------------------------------------------------------
Title: Simple non-thermal models for the quiescent radio emission
of dMe flare stars.
Authors: White, S. M.; Kundu, M. R.; Jackson, P. D.
1989A&A...225..112W Altcode:
Simple nonthermal gyrosynchrotron models were applied to the quiescent
emission of M dwarf stars. Evidence is presented which suggests that
these stars have a number of smaller active regions contributing
to the observed flux. The evidence includes an absence of Zeeman
polarization in optical observations and a lack of polarization in
quiescent emission.

---------------------------------------------------------
Title: Soft X-Ray, Microwave, and Hard X-Ray Emission from a Solar
Flare: Implications for Electron Heating and Acceleration in Current
Channels
Authors: Holman, Gordon D.; Kundu, Mukul R.; Kane, Sharad R.
1989ApJ...345.1050H Altcode:
The soft X-ray, microwave, and hard X-ray emissions from the solar
flare of May 14, 1980 are studied. The flare consists of a gradual
component in soft X-rays and microwaves and a superposed impulsive
burst accompanied by hard X-ray emission. The impulsive phase of the
flare appears in the soft X-ray emission as a temperature spike and
as an increased rate of energy dissipation into the plasma. A new,
spatially and spectrally distinct, microwave component appears during
the impulsive burst. The data are interpreted in terms of Joule heating
and the electric field acceleration of electrons in one or more current
sheets. It is found that all three emissions can be generated with
sub-Dreicer electric fields. The soft X-ray emitting plasma can be
heated by a single current sheet only if the resistivity in the sheet
is well above the classical, collisional resistivity. Conditions are
also given for the hard X-ray emission to be from nonthermal electrons
with classical resistivity.

---------------------------------------------------------
Title: Evidence for Noise Storm Emission by Superthermal Particles
During a Filament Eruption
Authors: Gopalswamy, N.; Kundu, M. R.
1989BAAS...21.1146G Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Radio Observations of Coronal Changes
Authors: Kundu, M. R.; Gopalswamy, N.
1989BAAS...21.1145K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Limb Passage of a Microwave Source
Authors: Schmahl, E. J.; Kundu, M. R.
1989BAAS...21R1145S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Microbursts at Meter-Decameter Wavelengths
Authors: Thejappa, G.; Gopalswamy, N.; Kundu, M. R.
1989BAAS...21.1145T Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Time Variability of Solar Active Regions at Centimeter
Wavelengths
Authors: Shevgaonkar, R. K.; Kundu, M. R.
1989ApJ...342..586S Altcode:
An analysis is presented of the variability of centimeter wavelength
emission originating from the solar transition region and lower
corona, and the variability is compared with the sun's quiescent
emission. Sequential dual wavelength observations are presented and
used to put constraints on a possible model of the variability of
active region emissions and to better understand the dynamics of
active regions. It is shown that gyroresonance emission contributes
significantly to the active region emission at 6 cm, whereas all the
quiet-sun emission can be attributed to free-free emission. From
comparison of the quiet-sun and active region models, it is shown
that the density at the base of the transition region is higher in
active regions.

---------------------------------------------------------
Title: Energetic Phenomena on the Sun
Authors: Kundu, Mukul R.; Woodgate, B.; Schmahl, E. J.
1989ASSL..153.....K Altcode: 1989eps..conf.....K
No abstract at ADS

---------------------------------------------------------
Title: The First Interferometric Observations with Arc-Second
Resolution of Solar Radio Bursts at Millimeter Wavelengths
Authors: Kundu, M. R.; White, S. M.; Gopalswamy, N.; Bieging, J. H.
1989BAAS...21..861K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: VLA Observations of a Small Impulsive Flare
Authors: White, S. M.; Kundu, M. R.; McConnell, D.
1989BAAS...21R.834W Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Meter Wave Radio Signatures of Slow CME's and Coronal Streamer
Evolution
Authors: Kundu, M. R.; Gopalswamy, N.
1989BAAS...21R.857K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Partially Occulted Microwave and X-ray Flares
Authors: Schmahl, E. J.; Kundu, M. R.; Tappin, J.; Simnett, G.
1989BAAS...21Q.834S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Radioheliograph and White-Light Coronagraph Studies of a
Coronal Mass Ejection Event
Authors: Gopalswamy, N.; Kundu, M. R.
1989SoPh..122..145G Altcode:
We analyze the radioheliograph and SMM-C/P observations of 1986 November
3 mass ejection event. The metric radio emissions are the only detected
activity associated with the mass ejection, but are adequate to study
the evolution of the event. The start time of the ejection seems to
precede a possible flare behind the limb indicated by the early type
III bursts. We discuss the physical relation between various types of
bursts and the CME. We interpret moving type IV bursts as a plasma
emission process. It is also shown using white-light coronagraph
data that the density in the source region of the moving type IV is
sufficient to support second harmonic plasma emission at the observed
frequency of 50 MHz.

---------------------------------------------------------
Title: Interpretation of Multiwavelength Observations of Solar Active
Regions Obtained During CoMStOC
Authors: Brosius, J. W.; Holman, G. D.; Nitta, N.; White, S. M.; Kundu,
M. R.; Gopalswamy, N.; Schmelz, J. T.; Saba, J. R. L.; Willson, R.
1989BAAS...21..838B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Radio and Optical Observations of Moving Magnetic Structures
in the Solar Corona
Authors: Gopalswamy, N.; Kundu, M. R.
1989BAAS...21..857G Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Simultaneous Microwave and Soft X-ray Observations of Active
Regions at the Solar Limb
Authors: Nitta, N.; White, S.; Kundu, M.; Gopalswamy, N.; Holman,
G.; Brosius, J.; Schmelz, J.; Saba, J.; Strong, K.
1989BAAS...21..828N Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Joule Heating and Runaway Electron Acceleration in a Solar
Flare
Authors: Holman, G. D.; Kundu, M. R.; Kane, S.
1989BAAS...21..864H Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Sun at the VLA's Meter and Decimeter Wavelengths
Authors: White, S. M.; Gopalswamy, N.; Kundu, M. R.
1989BAAS...21..861W Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Simultaneous Multi-Frequency Imaging Observations of Solar
Microwave Bursts
Authors: Kundu, M. R.; White, S. M.; Schmahl, E. J.
1989SoPh..121..153K Altcode: 1989IAUCo.104..153K
We review the results of simultaneous two-frequency imaging observations
of solar microwave bursts with the Very Large Array. Simultaneous 2 and
6 cm observations have been made of bursts which are optically thin at
both frequencies, or optically thick at the lower frequency. In the
latter case the source structure may differ at the two frequencies,
but the two sources usually seem to be related. However, this is not
always true of simultaneous 6 and 20 cm observations. The results have
implications for the analysis of non-imaging radio data of solar and
stellar flares.

---------------------------------------------------------
Title: A Slowly Moving Plasmoid Associated with a Filament Eruption
Authors: Gopalswamy, N.; Kundu, M. R.
1989SoPh..122...91G Altcode:
We report the imaging observations of a slowly moving type IV burst
associated with a filament eruption. This event was preceded by weak
type III burst activity and was accompanied by a quasi-stationary
continuum that persisted for several hours. The starting times and
speeds of moving type IV burst and the erupting filament are nearly
the same, implying a close physical relation between the two. The
moving type IV burst is interpreted as gyrosynchrotron emission from
a plasmoid containing a magnetic field of ∼1-2 G and nonthermal
electrons of density ∼105-106 cm−3
with a relatively low average energy of ∼50 keV.

---------------------------------------------------------
Title: Quiscent and flaring radio emission from the flare stars
AD Leonis, EQ Pegasi, UV Ceti, Wolf 630, YY Geminorum and YZ Canis
Minoris.
Authors: Jackson, P. D.; Kundu, M. R.; White, S. M.
1989A&A...210..284J Altcode:
Observations of the flare stars AD Leo, EQ Peg, UV Cet, Wolf 630,
YY Gem, and YZ CMi at 6 and 20 cm wavelengths are presented. These
observations display how a sample of the more active radio flare stars
behave over periods of several hours. An extensive time analysis
at five minute resolution, to investigate the typical variability
of these stars, is presented together with a ten-second-resolution
time analysis for periods of enhanced activity. Highlights are the
enhanced 6-cm activity from both components of the UV Ceti system,
quiescent emission from UV Ceti at 20 cm (which has a higher flux than
the quiescent emission at 6 cm), the possible detection of polarized
quiescent emission, a 20-cm flare from AD Leo in which the polarization
changes sign during the rise phase of the flare, and a relatively high
level of 6-cm emission from AD Leo.

---------------------------------------------------------
Title: Recent results of meter-decameter wave observations of
solar flares.
Authors: Gopalswamy, N.; Kundu, M. R.
1989sasf.confP.185G Altcode: 1989IAUCo.104P.185G; 1988sasf.conf..185G
The authors present recent results from meter-decameter imaging of
several classes of solar radio bursts: preflare activity in the form
of type III bursts, correlated type IIIs from distant sources, and
type II and moving type IV bursts associated with flares and CMEs.

---------------------------------------------------------
Title: Non-thermal electrons and stellar radio emission.
Authors: White, S. M.; Kundu, M. R.
1989sasf.confP..37W Altcode: 1989IAUCo.104P..37W
Radio emission from dMe flare stars has both a flaring and a quiescent
component. When one compares stellar radio emission with the Sun,
however, one finds that the apparent brightness temperature of the
quiescent component often exceeds the temperature of non-thermal solar
radio flares, and so it is likely that stellar quiescent emission also
comes from non-thermal electrons. Here the authors briefly review the
observations of quiescent emission, argue that the emitting regions
are small, show that such small regions can still account for the
observed fluxes, and discuss the source of electrons.

---------------------------------------------------------
Title: Joule heating and runaway electron acceleration in a solar
flare
Authors: Holman, Gordon D.; Kundu, Mukul R.; Kane, Sharad R.
1989dots.work..198H Altcode:
The hard and soft x ray and microwave emissions from a solar flare
(May 14, 1980) were analyzed and interpreted in terms of Joule heating
and runaway electron acceleration in one or more current sheets. It
is found that all three emissions can be generated with sub-Dreicer
electric fields. The soft x ray emitting plasma can only be heated
by a single current sheet if the resistivity in the sheet is well
above the classical, collisional resistivity of 107 K,
1011/cu cm plasma. If the hard x ray emission is from
thermal electrons, anomalous resistivity or densities exceeding 3
x 1012/cu cm are required. If the hard x ray emission is
from nonthermal electrons, the emissions can be produced with classical
resistivity in the current sheets if the heating rate is approximately 4
times greater than that deduced from the soft x ray data (with a density
of 1010/cu cm in the soft x ray emitting region), if there
are at least 104 current sheets, and if the plasma properties
in the sheets are characteristic of the superhot plasma observed in some
flares by Lin et al., and with Hinotori. Most of the released energy
goes directly into bulk heating, rather than accelerated particles.

---------------------------------------------------------
Title: Energetic phenomena on the Sun: Introduction.
Authors: Kundu, M. R.; Woodgate, B.
1989epos.conf.....K Altcode:
Contents: 1. Previous history. 2. The Solar Maximum Mission: objectives,
instruments, operations. 3. Summary of workshop results.

---------------------------------------------------------
Title: Particle acceleration.
Authors: Vlahos, L.; Machado, M. E.; Ramaty, R.; Murphy, R. J.;
Alissandrakis, C.; Bai, T.; Batchelor, D.; Benz, A. O.; Chupp, E.;
Ellison, D.; Evenson, P.; Forrest, D. J.; Holman, G.; Kane, S. R.;
Kaufmann, P.; Kundu, M. R.; Lin, R. P.; MacKinnon, A.; Nakajima,
H.; Pesses, M.; Pick, M.; Ryan, J.; Schwartz, R. A.; Smith, D. F.;
Trottet, G.; Tsuneta, S.; van Hoven, G.
1989epos.conf..127V Altcode:
Contents: 1. Introduction. 2. Phenomena associated with
mildly-relativistic electrons. 3. Phenomena associated with ions and
relativistic electrons in solar flares. 4. Theoretical studies of
particle acceleration. 5. Achievements - outstanding questions.

---------------------------------------------------------
Title: Energetic phenomena on the sun
Authors: Kundu, Mukul Ranjan; Woodgate, Bruce; Schmahl, E. J.
1989epos.book.....K Altcode: 1989QB526.F6E52....
No abstract at ADS

---------------------------------------------------------
Title: Three dimensional structures of coronal streamers, holes and
CME plasmoids from multifrequency imaging observations
Authors: Kundu, M. R.; Schmahl, E. J.; Gopalswamy, N.; White, S. M.
1989AdSpR...9d..41K Altcode: 1989AdSpR...9R..41K
Throughout the quiet Sun years 1982-1987, the Clark Lake Radioheliograph
routinely mapped the solar corona on a daily basis at frequencies from
30 to 100 MHz. The Clark Lake maps show a variety of features which
we have analyzed quantitatively, providing information about the three
dimensional nature of large scale structures of the solar corona.

---------------------------------------------------------
Title: First interferometric observations with arc-sec. resolution
of solar radio bursts at millimeter wavelengths
Authors: Kundu, Mukul R.; White, S. M.; Gopalswamy, N.; Bieging, J. H.
1989dots.work..119K Altcode:
The Berkeley-Maryland-Illinois Array (BIMA) is briefly described in
the context of solar observations. Specific areas of research that
could be performed using BIMA during the Solar Maximum Mission (SMM)
in 1991 are outlined. Some preliminary results of flare observations
during March 1989 are presented.

---------------------------------------------------------
Title: Largescale Magnetic Field Phenomena
Authors: Harrison, R. A.; Bentley, R. D.; Brosius, J.; Dwivedi,
B. N.; Jardine, M.; Klimchuk, J. A.; Kundu, M. R.; Pearce, G.; Saba,
J.; Sakurai, T.; Schmahl, E. J.; Schmelz, J.; Sime, D. G.; Steele,
C. D. C.; Sun, M. T.; Tappin, S. J.; Waljeski, K.; Wang, A. H.; Wu,
S. T.
1989tnti.conf....1H Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Microwave Evidence for Large-Scale Changes Associated with
a Filament Eruption
Authors: Kundu, M. R.; Schmahl, E. J.; Fu, Q. -J.
1989ApJ...336.1078K Altcode:
VLA observations at 6 and 20 cm wavelengths taken on August 3, 1985
are presented, showing an eruptive filament event in which microwave
emission originated in two widely separated regions during the
disintegration of the filament. The amount of heat required for the
enhancement is estimated. Near-simultaneous changes in intensity and
polarization were observed in the western components of the northern
and southern regions. It is suggested that large-scale magnetic
interconnections permitted the two regions to respond similarly to
an external energy or mass source involved in the disruption of the
filament.

---------------------------------------------------------
Title: Millimeter wavelength observations of solar flares for Max 1991
Authors: Kundu, M. R.; Gopalswamy, N.; Nitta, N.; Schmahl, E. J.;
White, S. M.; Welch, W. J.
1988fnsm.work..107K Altcode:
The Hat Creek millimeter-wave interferometer (to be known as the
Berkeley-Illinois-Maryland Array, BIMA) is being upgraded. The improved
array will become available during the coming solar maximum, and will
have guaranteed time for solar observing. The Hat Creek millimeter-wave
interferometer is described along with the improvements. The scientific
objectives are briefly discussed.

---------------------------------------------------------
Title: Detection of the dMe Flare Star YZ Canis Minoris Simultaneously
at 20 and 90 Centimeter Wavelengths
Authors: Kundu, M. R.; Shevgaonkar, R. K.
1988ApJ...334.1001K Altcode:
The first aperture synthesis detection of the flare star YZ CMi at
90 cm wavelength is presented here. The simultaneous observations
carried out at 20 and 90 cm wavelengths show that the emission at the
two wavelengths is unipolar in the same sense and is uncorrelated. The
high brightness temperature of ≡1013K at 90 cm wavelength
strongly supports the coherent nature of the emission. The authors
propose that the coherent emission is intrinsically unpolarized and the
polarization is introduced by absorption in the higher coronal levels
with large-scale magnetic fields, presumably the dipole magnetic field.

---------------------------------------------------------
Title: Modelling a C-type flare observed in microwaves and hard X-rays
Authors: Schmahl, E. J.; Kundu, M. R.; Dennis, Brian R.
1988fnsm.work..246S Altcode:
Using the very large array (VLA) at 6 and 20 cm wavelength and
the hard X-ray burst spectrometer on the Solar Maximum Mission,
a two-ribbon flare was observed from the onset phase through the
maximum and decline on November 14, 1981. Because of the extensive
size of the microwave source and the gradual variations in hard X-rays
whose spectrum becomes progressively flatter with time, the flare
is classified as a C-type flare. Considering the hardening of the
X-ray spectrum and its non-impulsive nature, a coronal trap model was
invoked for the energetic electrons. The microwave emission is easily
accounted for by gyrosynchronous radiation from mildly relativistic
electrons. It was found that the source must be optically thick at
20 cm during the maximum phase, but as the source evolved toward an
optically thin regime, the intensity decreased while the degree of
circular polarization increased. In an initial homogeneous model, we
found that the computed microwave spectrum was too narrow to match the
patrol spectrum from 606 to 15400 MHz. In the model, the magnetic field
consists of a dipolar arcade bridging the H alpha ribbons, and extending
to heights of order 40,000 to 50,000 km. The variation of the magnetic
field strength from footpoints to apex causes the gyrosynchrotron
spectrum to be broader. Preliminary conclusions regarding the electron
distributions producing the hard X-rays and the microwaves, and the
suitability of this model for C-type flares is presented.

---------------------------------------------------------
Title: Current Loop Coalescence Model of Solar Flares: Erratum
Authors: Tajima, T.; Sakai, J.; Nakajima, H.; Kosugi, T.; Brunel,
F.; Kundu, M. R.
1988ApJ...329..517T Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Variability of Metric Emission from the Sun
Authors: Shevgaonkar, R. K.; Kundu, M. R.; Jackson, P. D.
1988ApJ...329..982S Altcode:
Full-disk observations of the sun obtained with the VLA at 317 MHz have
been analyzed, with special attention being given to the short period
variability of the meter-wavelength sources. A reduction in brightness
is noted over coronal holes at 90 cm. Thermal emission models for the
slowly varying component are investigated, along with a nonthermal
emission mechanism for storm radiation at meter wavelengths. The
results indicate that the thermal model encounters difficulties in
accommodating short period changes over a few tens of minutes, and
that the nonthermal mechanism encounters difficulty in accounting for
the variability of low brightness temperatures of less than 10 to the
6th K. A gyrotron synchrotron emission mechanism has been ruled out.

---------------------------------------------------------
Title: High resolution microwave and X-ray observations of solar
flares
Authors: Alissandrakis, C. E.; Schadee, A.; Kundu, M. R.
1988A&A...195..290A Altcode:
This paper presents an analysis of high spatial resolution observations
of 18 weak flares, carried out during the Solar Maximum Year in the
microwave range, H-alpha, and soft X-rays, together with observations
of the associated hard X-ray emission and the photospheric magnetic
field. This combination of observations made it possible to obtain a
picture of the flare geometry and the relative position of the various
emissions, to study the change of the geometry during the flare, to
estimate the electron temperature and emission measure of the thermal
plasma, and to compute the contribution of the free-free process in
the microwave emission. Results are interpreted as evidence for the
presence of energetic electrons even in the post-burst phase of some
flares. There was also found a clear case of homologous radio and X-ray
bursts, one case of foot-point expansion with a relative velocity of
20 km/s at 6.16 cm, as well as some evidence of triggering of flares
by disturbances moving with a velocity of 5000-13,000 km/s.

---------------------------------------------------------
Title: Co-ordinated VLA and EXOSAT observations of the flrae stars
UV Ceti, EQ Pegasi, YZ Canis Minoris and AD Leonis.
Authors: Kundu, M. R.; Pallavicini, R.; White, S. M.; Jackson, P. D.
1988A&A...195..159K Altcode:
The authors have observed four flare stars (UV Cet, EQ Peg, YZ CMi
and AD Leo) simultaneously with the VLA and the EXOSAT satellite over
continuous periods of 7 - 10 h. This is the first time that flare stars
were observed simultaneously in X-rays and at microwave frequencies
with high sensitivity instrumentation. All stars were detected both at
the quiescent level and during flares. Although considerable activity
in both X-rays and in the radio was found, there was little correlation
between the two wavelength domains. The auhors discuss the significance
of these observations for coronal activity in red dwarf flare stars.

---------------------------------------------------------
Title: An Eruptive Prominence and Associated Cm-Mm Emission Outside
the Solar Limb
Authors: Zodi, A. M.; Correia, E.; Costa, J. E. R.; Kaufmann, P.;
Martin, S. F.; Kundu, M. R.
1988SoPh..116...83Z Altcode:
We present radio maps at 22 and 44 GHz which show the emission before
and after the eruption of a quiescent prominence located at the west
limb. The observed radiation following the eruption is not consistent
with thermal bremsstrahlung mechanism. It can be interpreted as due
to gyrosynchrotron emission of nonthermal electrons. Our observations
appear to be similar to the microwave radiation observed in post-flare
loops; this radiation is due to nonthermal electrons trapped in the
closed magnetic structures formed after the prominence eruption.

---------------------------------------------------------
Title: A Study of Coronal Bright Points at 20-CM Wavelength
Authors: Nitta, N.; Kundu, M. R.
1988SoPh..117...37N Altcode:
We present the results of a study of coronal bright points observed
at 20 cm with the VLA on a day when the Sun was exceptionally
quiet. Microwave maps of bright points were obtained using data for
the entire observing period of 5 hours, as well as for shorter periods
of a few minutes. Most bright points, especially those appearing
in the full-period maps appear to be associated with small bipolar
structures on the photospheric magnetogram. Overlays of bright point
(B.P.) maps on the Ca+K picture, show that the brightest
part of a B.P. tends to lie on the boundary of a supergranulation
network. In general, the bright points exhibit rapid variations in
intensity. There is no systematic correlation between the size of a
B.P. and its intensity; the apparently slow variation of B.P. emission
may have rapid fluctuations superimposed on it.

---------------------------------------------------------
Title: Modelling a C-Type Flare Observed in Microwaves and Hard X-rays
Authors: Schmahl, E. J.; Kundu, M. R.; Dennis, B. R.
1988BAAS...20R.748S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Millimeter Wavelength Observations of Solar Flares for Max'91
Authors: Kundu, M. R.; Gopalswamy, N.; Nitta, N.; Schmahl, E. J.;
White, S. M.
1988BAAS...20..746K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Moving Radio Loop Structure During a Fast CME
Authors: Gopalswamy, N.; Kundu, M. R.; Hundhausen, A.
1988BAAS...20Q.682G Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Slowly-Varying Observed with the Clark Lake Radioheliograph
Authors: Schmahl, E. J.; Kundu, M. R.; Gopalswamy, N.; Jackson, P. D.
1988BAAS...20..712S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A VLA Survey of dM Stars Covering a Broad Range in X-ray Fluxes
Authors: Kundu, M. R.; White, S. M.; Agrawal, P. C.
1988BAAS...20..696K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Coronal Bright Points at 6 and 20 Centimeter Wavelengths
Authors: Kundu, M. R.; Schmahl, E. J.; Fu, Q. -J.
1988ApJ...325..905K Altcode:
The paper presents the results of near-simultaneous observations
of bright points at 6 and 20 cm for a time interval of 10 hr
using the VLA. It is shown that, at both 6 and 20 cm, the radio
sources in the quiet sun have a very close association with bipolar
features seen in magnetograms and with dark features in He I 10830
A spectroheliograms. The paper discusses the associations and the
distributions of size, brightness, and temporal variation of the
microwave bright points. It is found that the brightness temperatures
of the 6 and 20 cm bright points are in the approximate ratio 0.09:1
expected from the emission mechanism being thermal bremsstrahlung.

---------------------------------------------------------
Title: Large scale structure of the Sun's corona.
Authors: Kundu, Mukul R.
1988sscd.conf..192K Altcode:
The author reviews some results concerning the large scale structure
of the Sun's corona, obtained with the imaging observations of the Sun
at meter-decameter wavelengths, using the Clark Lake multifrequency
radioheliograph.

---------------------------------------------------------
Title: Quasi-dedicated millimeter wave imaging observations of solar
flares during next solar maximum
Authors: Kundu, M. R.
1988AdSpR...8k..33K Altcode: 1988AdSpR...8...33K
A brief description of the Berkeley-Illinois-Maryland Millimeter Array
(BIMA) for synthesis mapping of the Sun and other sources is given
here. The array will be used in a quasi-dedicated mode to observe solar
flares. The main scientific objectives will be to obtain positional
and structural information of millimeter solar bursts and to study high
energy flare physics and the role of electron beams in producing Hα,
EUV and white light emission. Other studies will be concerned with
active regions, filaments and coronal holes at millimeter wavelengths.

---------------------------------------------------------
Title: Coronal bright points at 6cm wavelength
Authors: Fu, Qijun; Kundu, M. R.; Schmahl, E. J.
1988VA.....31..103F Altcode:
Results are presented from observations of bright points at a wavelength
of 6-cm using the VLA with a spatial resolution of 1.2 arcsec. During
two hours of observations, 44 sources were detected with brightness
temperatures between 2000 and 30,000 K. Of these sources, 27 are
associated with weak dark He 10830 A features at distances less than 40
arcsecs. Consideration is given to variations in the source parameters
and the relationship between ephemeral regions and bright points.

---------------------------------------------------------
Title: Coronal bright points in mircrowaves.
Authors: Kundu, M. R.; Nitta, N.
1988sscd.conf...89K Altcode:
An excellent map of the quiet Sun showing coronal bright points at
20 cm wavelength was produced using the VLA on February 13, 1987. The
authors studied the locations of bright points relative to features on
the photospheric magnetogram and Ca+K spectroheliogram. They
find that most bright points appearing in the full 5-hour synthesized
map are associated with small bipolar structures on the photospheric
magnetogram; and the brightest part of a B.P. tends to lie on the
boundary of a supergranulation network. The bright points exhibit rapid
variations in intensity superposed on an apparently slow variation.

---------------------------------------------------------
Title: Variability of meter wavelength solar radio emission.
Authors: Shevgaonkar, R. K.; Kundu, M. R.
1988sscd.conf..248S Altcode:
A study of the variability of solar radio emission at 90 cm wavelength
using the VLA is presented. The VLA observations have been supplemented
by meter and decameter wavelength observations obtained simultaneously
with the Clark Lake radioheliograph. 90 cm sources are well correlated
with Hα filaments; decameter sources are also correlated with coronal
holes. Various emission mechanisms have been examined to explain the
short period variability of the meter wavelength sources. The plasma
radiation at the fundamental plasma frequency, as has been proposed for
storm radiation appear to be the most acceptable emission mechanism,
provided the source filling factor is less than a few percent.

---------------------------------------------------------
Title: A two-zone model of coronal hole structure in the high corona.
Authors: Wang, Zhengzhi; Yoshimura, H.; Kundu, M. R.
1988sscd.conf..458W Altcode:
The authors propose a two-zone model of coronal hole structure in the
high corona at height around 1.5 to 1.7 solar radii, in which a central
zone and a boundary zone can be clearly distinguished. The model is
suggested by comparing the results of computation of potential magnetic
fields of the corona and meter-decameter radio observations. The
coronal magnetic fields were computed from the surface field observed
at the John M. Wilcox Solar Observatory at Stanford University. The
radio data were obtained at the Clark Lake Radio Observatory of the
University of Maryland. The location of a coronal hole at the base of
the corona is determined with the help of He I 10830 Å maps observed
at the National Solar Observatory at Kitt Peak.

---------------------------------------------------------
Title: Current Loop Coalescence Model of Solar Flares
Authors: Tajima, T.; Sakai, J.; Nakajima, H.; Kosugi, T.; Brunel,
F.; Kundu, M. R.
1987ApJ...321.1031T Altcode:
A computer simulation and theoretical study of the physical
characteristics of the explosive coalescence of current-carrying loops
is presented. Characteristics of the explosive coalescence include a
large impulsive increase of the kinetic energies of electrons and ions,
the simultaneous heating and acceleration of electrons and ions in high
and low energy ranges, and a break in the energy spectra of electrons
and ions. A characteristic double subpeak structure is found in the
quasi-periodic oscillations found in the time profiles of the solar
flares of June 7, 1980 and November 26, 1982 which can be explained
in terms of the coalescence instability of two current loops.

---------------------------------------------------------
Title: Simultaneous 2 and 6 Centimeter Wavelength Observations of
a Solar Flare Using the VLA
Authors: Kundu, M. R.; Velusamy, T.; White, S. M.
1987ApJ...321..593K Altcode:
VLA observations of a solar active region and a flare are discussed. The
event was observed at wavelengths of 2 and 6 cm simultaneously. Radio
maps prior to the flare delineate the most important magnetic structures
in the region. Interaction between these structures apparently led to
preheating of plasma above the active region some 30 minutes prior to
the flare. The 2 and 6 cm flare positions were coincident, and the time
profiles of the burst at the two wavelengths were almost identical,
implying that the same population of electrons was responsible for
emission at the two wavelengths. Emission was probably nonthermal
gyrosynchrotron radiation, and the physical conditions in the burst
source are derived using this assumption.

---------------------------------------------------------
Title: The Effect of a Large Flare on the Solar Corona
Authors: Schmelz, J. T.; Saba, J. L. R.; Strong, K. T.; Schmahl,
E. J.; Kundu, M. R.
1987BAAS...19S1122S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Imaging observations of the evolution of meter-decameter
burst emission during a major flare.
Authors: Gopalswamy, N.; Kundu, M. R.
1987SoPh..111..347G Altcode:
We present the results of a study of the evolution of 3 February,
1986 flare at meter-decameter wavelengths using the two dimensional
imaging observations made with the Clark Lake multifrequency
radioheliograph. The flare was complex and produced various types
of meter-decameter bursts. The preflare activity was observed in the
form of type III bursts some tens of minutes prior to the impulsive
onset. From the positional analysis of the preflare and impulsive
phase type III bursts and other measured characteristics we discuss
the characteristics of energy release and possible magnetic field
configurations in the vicinity of energy release region. From positional
and temporal studies of the flare continuum and type II burst in
relation to the microwave and hard X-ray emissions, we discuss the
possible magnetic field structures in which the accelerated particles
are confined or along which they propagate. We develop a schematic
model of the flaring region based upon our study.

---------------------------------------------------------
Title: Meterwave observations of a coronal hole.
Authors: Wang, Z.; Schmahl, E. J.; Kundu, M. R.
1987SoPh..111..419W Altcode:
We present meterwave maps showing a coronal hole at 30.9, 50.0, and
73.8 MHz using the Clark Lake Radioheliograph in October 1984. The
coronal hole seen against the disk at all three frequencies shows
interesting similarities to, and significant differences from its
optical signatures in He Iλl10830 spectroheliograms.

---------------------------------------------------------
Title: Coronal Bright Points in Microwaves: Their Optical Associations
and Emission Measures
Authors: Nitta, N.; Kundu, M. R.
1987BAAS...19.1122N Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Characteristics of shock-associated fast-drift kilometric
radio bursts.
Authors: MacDowall, R. J.; Stone, R. G.; Kundu, M. R.
1987SoPh..111..397M Altcode:
The existence of a class of fast-drift, shock-associated (SA),
kilometric radio bursts which occur at the time of metric type II
emission and which are not entirely the kilometric continuation
of metric type III bursts has been reported previously (Cane
et al., 1981). In this paper, we establish unambiguous SA event
criteria for the purpose of statistically comparing SA events with
conventional kilometric type III bursts. We apply these criteria to
all long-duration, fast-drift bursts observed by the ISEE-3 spacecraft
during a 28-month interval and find that more than 70% of the events
satisfying the criteria are associated with the radio signatures of
coronal shocks. If a given event in our sample is associated with a
metric type II or type IV burst, it is 13 times more likely to satisfy
the SA criteria than an event associated only with metric type III
activity. Compared with conventional kilometric type III bursts,
the characteristics of these SA events are longer duration, higher
maximum intensity, and a larger number of components. Differences in
these characteristics for the two classes of events are not sufficient
to distinguish all SA events from conventional type III bursts. The
consistent lack of reported metric type III activity during the latter
part of the candidate events suggests that some of the electrons are
accelerated high in the corona, at or near the altitude of the shock.

---------------------------------------------------------
Title: A Study of Solar Preflare Activity Using Two-Dimensional
Radio and Smm/xrp Observations
Authors: Kundu, M. R.; Gopalswamy, N.; Saba, J. L. R.; Schmelz,
J. T. S.; Strong, K. T.
1987SoPh..114..273K Altcode:
We present a study of type III activity at meter- decameter wavelengths
in the preflare phase of the 1986 February 3 flare using data obtained
with the Clark Lake Multifrequency Radioheliograph. We compare this
activity with similar type III burst activity during the impulsive
phase and find that there is a displacement of burst sources between the
onset and end times of the activity. A comparison of this displacement
at three frequencies suggests that the type III emitting electrons gain
access progressively to diverging and different field lines relative
to the initial field lines. The energetics of the type III emitting
electrons are inferred from observations and compared with those of
the associated hard X-ray emitting electrons. The soft X-ray data from
SMM-XRP shows enhanced emission measure, density and temperature in
the region associated with the preflare type III activity.

---------------------------------------------------------
Title: Simultaneous radio and white light observations of the 1984
June 27 coronal mass ejection event
Authors: Gopalswamy, N.; Kundu, M. R.
1987SoPh..114..347G Altcode:
We present the two-dimensional imaging observations of radio bursts in
the frequency range 25-50 MHz made with the Clark Lake multifrequency
radioheliograph during a coronal mass ejection event (CME) observed
on 1984, June 27 by the SMM Coronagraph/Polarimeter and Mauna Loa
K-coronameter. The event was spatially and temporally associated
with precursors in the form of meter-decameter type III bursts, soft
X-ray emission and a Hα flare spray. The observed type IV emission
in association with the CME (and the Hα spray) could be interpreted
as gyrosynchrotron emission from a plasmoid containing a magnetic
field of ∼2.5 G and nonthermal electrons with a number density of
∼ 105 cm−3 and energy ≳350 keV.

---------------------------------------------------------
Title: Quiet Sun and Slowly Varying Component at Meter and Decameter
Wavelengths
Authors: Lantos, P.; Alissandrakis, C. E.; Gergely, T.; Kundu, M. R.
1987SoPh..112..325L Altcode:
Comparison of maps of the Sun obtained over the period June 29 to July
8, 1982 at 169 MHz with the Nançay Radioheliograph and at 73.8, 50,
and 30.9 MHz with the Clark Lake Radioheliograph shows that the slowly
varying component at meter and decameter wavelengths is not always
thermal emission. During the period under study weak noise storm
continua were the most frequent sources of slowly varying component
at 169 and 73.8 MHz. Most filaments show no radio counterpart on the
disk. A streamer has been detected on the disk from 169 to 30.9 MHz with
an optimum observability at 50 MHz. The brightest source of the slowly
varying component from 73.8 to 30.9 MHz for most of the period was
located above an extended coronal hole in a region where a depression
was observed at 169 MHz. In favorable cases, electron densities can
be derived from the positions of noise storms and radio streamers;
these are in agreement with previous K-corona eclipse observations.

---------------------------------------------------------
Title: Two dimensional imaging observations of meter-decameter bursts
associated with the February 1986 flare activity
Authors: Gopalswamy, N.; Kundu, M. R.
1987sici.symp...16G Altcode:
An analysis is presented of the two dimensional imaging observations
of a flare observed on 3 Feb. l986 using the Clark Lake Multifrequency
Radioheliograph. The flare produced almost all types of Meter-decimeter
radio emission: enhanced storm radiation, type III/V bursts, II and
IV and flare continuum. The flare continuum had early (FCE) and late
(FC II) components and the type II occurred during the period between
these two components. Comparing the source positions of type III/V and
FCE it was found that these bursts must have occurred along adjacent
open and closed field lines, respectively. The positional analysis of
type II and FC II implies that the nonthermal electrons responsible for
FC II need not be accelerated by type II shock and this conclusion is
further supported by the close association of FC II with a microwave
peak. Using the positional and temporal analysis of all these bursts
and the associated hard X-ray and microwave emissions, a schematic
model is developed for the magnetic field configuration in the flaring
region in which the nonthermal particles responsible for these bursts
are confined or along which they propagate.

---------------------------------------------------------
Title: Microwave Observations of the X-Flare of May 19, 1984
Authors: Schmahl, E. J.; Kundu, M. R.; Schmelz, J. T.; Saba, J.;
Strong, K. T.
1987BAAS...19R1122S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Propagation of Electrons Emitting Weak Type-Iii Bursts in
Coronal Streamers
Authors: Gopalswamy, N.; Kundu, M. R.; Szabo, A.
1987SoPh..108..333G Altcode:
We report the observations of weak type III bursts at 73.8, 57.5, 50.0,
and 38.5 MHz from Clark Lake Radio Observatory on four days and discuss
their characteristics. In addition to Clark Lake data, the magnetogram
and sunspot/active region data and the coronal streamer data obtained
by HAO's Coronagraph/Polarimeter aboard SMM satellite are used to
study the location of the burst sources with respect to the coronal
streamers emanating from active regions. It is shown that the bursts
occur within or close to the edge of dense coronal streamers implying
that the coronal streamers contain open magnetic field lines along
which the electrons generating the bursts propagate. The positional
analysis of the bursts is used to estimate the variation of coronal
electron density with radial distance.

---------------------------------------------------------
Title: Meterwave observations of a coronal hole
Authors: Wang, Z.; Schmahl, E. J.; Kundu, M. R.
1987sici.symp...24W Altcode:
Meter-wave maps are presented showing a coronal hole at 30.9, 50.0,
and 73.8 MHz using the Clark Lake Radioheliograph in October 1984. The
coronal hole seen against the disk at all three frequencies shows
interesting similarities to, and significant differences from its
optical signatures in HeI lambda10830 spectroheliograms. The 73.8 MHz
coronal hole, when seen near disk center, appears to coincide with
the HeI footprint of the hole. At the lower frequencies, the emission
comes from higher levels of the corona, and the hole appears to be
displaced, probably due to the non-radial structure of the coronal
hole. The contrast of the hole relative to the quiet Sun is much greater
than reported previously for a coronal hole observed at 80 MHz. The
higher contrast is certainly real, due to the superior dynamic range,
sensitivity, and calibration of the Clark Lake instrument. Using
a coronal hole model, the electron density is derived from radio
observations of the brightness temperature. A very large discrepancy
is found between the derived density and that determined from Skylab
EUV observations of coronal holes. This discrepancy suggests that much
of the physics of coronal holes has yet to be elucidated.

---------------------------------------------------------
Title: Radio studies of large scale structures of the Sun's corona
and transient activity
Authors: Kundu, Mukul R.
1987sici.symp...22K Altcode:
The use of meter-decimeter wavelength imaging observations for four
different kinds of studies of solar coronal activity is discussed. (1)
Large scale structure of the upper corona; daily imaging observations
permit comparison of radio images with white light images from space
and ground observation, generation of synoptic charts similar to white
light coronagraph synoptic charts, and comparison of radio brightness
enhancements and deficiencies with bright coronal streamers and coronal
holes. (2) Relative positions of type III burst sources and coronal
streamers as observed by Solwind experiment on the P-78-1 satellite
and by the HAO C/P experiment aboard the SMM; infer the paths of
type III emitting electrons in dense coronal streamers, and from
multifrequency observations derive electron density distributions above
active regions near the limb. (3) Non-flare associated type II/type IV
bursts associated with coronal streamer disruption events; such type
IV sources have a rather slow velocity (approx = to or less than 100
km/s) CMEs. (4) Meter-decimeter microbursts; these are short duration
(2-10 sec) weak-type III-like bursts, produced at the fundamental plasma
frequency by plasma radiation processes which have important differences
from the standard mechanisms used to explain the strong type III bursts.

---------------------------------------------------------
Title: Simultaneous VLA Observations of a Flare at 6 and 20 Centimeter
Wavelengths
Authors: Velusamy, T.; Kundu, M. R.; Schmahl, E. J.; McCabe, M.
1987ApJ...319..984V Altcode:
Using the Very Large Array at 6 and 20 cm wavelengths, a May 15,
1980 solar flare was mapped. The 1B flare, as observed in H alpha
at Mees Solar Observatory, Maui, Hawaii, appeared as two sequential
flares occurring at different neutral lines. The peaks of the time
profile at 20 cm were delayed with respect to the 6 cm counterparts,
but they were related to each other and to the H alpha activity. At 20
cm, precursor activity occurred, and an oppositely polarized source an
arcminute away from the main burst may have triggered the flare. The
main 20 cm emission appeared to be displaced limbward from the 6 cm
burst. If both the 6 and 20 cm emission originated in the same system
of loops, it is inferred that the apparent lateral displacement was
caused by a height difference of 33,000 km in the sources of emission.

---------------------------------------------------------
Title: A study of hard X-ray associated meter-decameter bursts
observed on December 19, 1979
Authors: Kundu, M. R.; Gergely, T. E.; Kane, S. R.; Sawant, H. S.
1987STIN...8728486K Altcode:
The results of a study of the relationship of a complex meter-decameter
wavelength radio burst observed with the Clark Lake E-W and N-S
interferometers, with a hard X-ray burst observed with the X-ray
spectrometer aboard ISEE-3 are presented. The radio burst consisted
of several type III's, reverse drift type III's, a U burst, and type
II and type IV bursts. The X-ray emission was also complex. The radio
as well as hard X-ray emissions were observed before the flash phase
of the flare; they were not always associated and it is conjectured
that this may constitute evidence for acceleration of electrons high
in the corona. On the other hand, all components of the reverse drift
burst were associated with hard X-ray subpeaks, indicating multiple
injection of electron beams along field lines with different density
gradients. While the type II burst appeared to be related to the hard
X-ray burst, a detailed correspondence between individual features of
the radio and hard X-ray burst emissions could not be found. The type
IV burst started after all hard X-ray emissions ceased. Its source
appeared to be a magnetic arch, presumably containing energetic
electrons responsible for the gyrosynchrotron radiation of type IV.

---------------------------------------------------------
Title: Coronal Bright Points at 6 and 20 cm Wavelengths
Authors: Kundu, M. R.; Schmahl, E. J.; Jackson, P. D.; Fu, Q. -J.
1987BAAS...19..937K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Comparison of Large Scale Structures of the Corona in White
Light and Radio Wavelengths
Authors: Jackson, P. D.; Kundu, M. R.
1987BAAS...19..931J Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Soft X-Ray, Microwave and Delayed Hard X-Ray Emission From
Interacting Solar Flare Loops
Authors: Holman, Gordon D.; Kundu, Mukul R.
1987BAAS...19..925H Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Microwave Evidence for Large Scale Magnetic Rearrangements
Associated with a Filament Eruption
Authors: Schmahl, E. J.; Kundu, M. R.; Fu, Q. -J.
1987BAAS...19..925S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Dynamic Spectrum of a Radio Flare on UV Ceti
Authors: Jackson, Peter D.; Kundu, Mukul R.; White, Stephen M.
1987ApJ...316L..85J Altcode:
The dMe flare star UV Ceti (L726-8B) was observed at four frequencies
simultaneously in the 1385-1652 MHz band using the Very Large Array. A
flare lasting 10 minutes was observed with 6.67 s time resolution
'Dynamic spectrum'-type images in the Stokes parameters I and V show
considerable complexity in the frequency-time domain; some features show
a positive frequency drift with time, while others are more complex,
involving both positive and negative frequency drifts. The positive
drift features would be consistent with disturbances traveling downward
in the star's corona.

---------------------------------------------------------
Title: The Plasma and Magnetic Field Properties of Coronal Loops
Observed at High Spatial Resolution
Authors: Webb, D. F.; Holman, G. D.; Davis, J. M.; Kundu, M. R.;
Shevgaonkar, R. K.
1987ApJ...315..716W Altcode:
Two data sets are analyzed in order to improve understanding of
the plasma and magnetic field properties of active region coronal
loops. Each set consists of coaligned, high spatial resolution soft
X-ray, microwave, and magnetogram images that are used to compare
observations of coronal loops and their feet in the photosphere and
to constrain possible microwave emission mechanisms. The loops are
found to have plasma parameters typical of quiescent active region
loops. Each loop has a compact microwave source with peak brightness
temperature T(b) = 1-2.5 x 10 to the 6th K cospatial with or near
the loop apex. No complete loops are imaged in microwaves. The loop
emission observed at 4.9 GHz is best described by fourth harmonic
gyroresonance emission from a dipole loop model, but with less field
variation along the loop than in the models of Holman and Kundu (1985).

---------------------------------------------------------
Title: Very-large-array observations of a complex gradual solar
burst at 6 CM wavelength
Authors: Kundu, M. R.; McConnell, D.; White, S. M.; Shevgaonkar, R. K.
1987A&A...176..131K Altcode:
The authors present a 6 cm VLA observation of a burst from a solar
active region. The burst shows a normal impulsive rise-and-fall
superimposed on a gradual component. The peak brightness temperature
of the burst remains relatively constant, and the flux variations are
due to changes in the source structure. It appears as though an arcade
of loops is gradually heated or filled with hot plasma. The burst is
weakly polarized but unipolar; the authors investigate the possible
reasons for this structure. Depolarization of optically thin emission
due to twisted magnetic fields within the source can produce significant
depolarization, but is probably not active in this event. Instead,
it is suggested that the flare emission is optically thick and that
hot overlying material preferentially absorbs one polarization.

---------------------------------------------------------
Title: Large-scale structure of the sun's corona from radio
observations using the Clark Lake Radioheliograph
Authors: Kundu, M. R.; Gergely, T. E.; Schmahl, E. J.; Szabo, A.;
Loiacono, R.; Wang, Z.; Howard, R. A.
1987SoPh..108..113K Altcode:
We present meterwave maps of the solar corona made with the Clark Lake
Radioheliograph at 30.9, 50, and 73.8 MHz for one solar rotation. We
compare and contrast them with optical data: 10830 Å maps, white-light
coronagraph images (SOLWIND and Mauna Loa K coronameter) and forbidden
line scans. Most of the sources in the radio maps persist for two
days or more, and appear to rotate approximately with the solar
rate. A coronal hole seen against the disk at all three frequencies
shows interesting similarities and significant differences with
the optical signatures of the hole. Elongated features of the 50 MHz
corona correspond rather well to the azimuthal position of white light
streamers seen in SOLWIND images. Synoptic charts made from the radio
maps show overall similarities to synoptic charts constructed from
(limb) coronagraph data. Some of the differences may result from the
different weightings given by the radio and optical data to density
and temperature, or by the different sensitivities to non-radial
geometries. We show that the combined use of meter wave and optical
images provide considerable new insights into the three-dimensional
structure of the low to middle corona.

---------------------------------------------------------
Title: Correlated Type-Iii Burst Emission from Distant Sources on
the Sun
Authors: Kundu, M. R.; Gopalswamy, N.
1987SoPh..112..133K Altcode:
We report the observation and interpretation of a correlated type III
burst emitted from distant sources on the Sun. The angular separation
between the distant sources is as large as 26' or ∼ 106
km. There was an active region ∼ 30° behind the limb, and it is
believed that the type III burst emission originated from activity
in this region. The implications of the locations of the correlated
sources with regard to the geometry of the magnetic structures involved
in the flare process are discussed.

---------------------------------------------------------
Title: Coronal Bright Points at 6-CM Wavelengths
Authors: Fu, Q.; Kundu, M. R.; Schmahl, E. J.
1987SoPh..108...99F Altcode:
We report the results of the first observations of solar coronal bright
points at 6 cm wavelength using the Very Large Array (VLA), with a
spatial resolution of ∼ 1″.2. The maximum brightness temperature
of the sources observed is ≈ 3 × 104 K with a mean value
of ≈ 1 × 104 K (above the quiet Sun value). The lifetime
of most sources is between 5 and 20 min. The average diameter of the
sources is about 5-15″ arc. The sources are gaussian-like near the
footpoint of miniature loops and they appear in groups. The observations
indicate that significant fluctuations in the brightness temperature
(sometimes quasi-periodic) and in the spatial extents of these sources
can occur over periods of a few minutes.

---------------------------------------------------------
Title: A Type-Iv Burst Associated with a Coronal Streamer Disruption
Event
Authors: Kundu, M. R.
1987SoPh..111...53K Altcode:
A type IV burst was observed on February 17, 1985 with the Clark Lake
Radio Observatory multifrequency radioheliograph operating in the
frequency range 20-125 MHz. This burst was associated with a coronal
streamer disruption event. From two-dimensional images produced at 50
MHz, we show evidence of a type II burst and a slow moving type IV
burst. The observations of the moving type IV burst suggests that a
plasmoid containing energetic electrons can result from the disruption
of a coronal streamer.

---------------------------------------------------------
Title: The Sun's outer corona at radio wavelengths.
Authors: Kundu, Mukul R.
1987IJRSP..16..172K Altcode:
The use of meter-decameter wavelength imaging observations to
follow four different kinds of studies of solar coronal activity
is discussed. The Clark Lake Radio Observatory's multifrequency
radioheliograph which operates in the 20-125 MHz frequency range
is described. This paper emphasizes the differences observed in
coronal phenomena with instruments having a higher sensitivity
than the Culgoora instrument. New observations from the Clark Lake
radioheliograph which show details of the long-lived structure of the
corona are presented. These are then compared with features of the
optical corona as shown in the data obtained by satellite-borne and
ground-based coronagraphs.

---------------------------------------------------------
Title: 6 and 20 cm wavelength observations of coronal bright points
Authors: Kundu, M. R.; Schmahl, E. J.; Fu, Q. J.
1987SoPh..113..305K Altcode: 1982SoPh..113..305K
No abstract at ADS

---------------------------------------------------------
Title: Imaging observations of radio bursts at meter-decameter
wavelengths
Authors: Kundu, Mukul R.
1987SoPh..113...87K Altcode: 1982SoPh..113...87K
In this article, we review some of the recent results obtained with
imaging observations of the Sun at meter-decameter wavelengths, using
the Clark Lake multifrequency radioheliograph. We briefly discuss the
use of imaging observations to study the large scale structure of the
upper corona. We discuss non-flare associated type II/type IV bursts
associated with a coronal streamer disruption event associated with a
slow (≤100 Km/s) CME. We discuss meter-decameter microbursts, which
occur at coronal heights, often without any surface activity. Finally,
we discuss a correlated type III burst whose emission originates
almost simultaneously from two widely separated (≳ 105
Km) locations.

---------------------------------------------------------
Title: Microwave Observations of Red Dwarf Flare Stars
Authors: Kundu, M. R.; Jackson, P. D.; White, S. M.
1987LNP...291..100K Altcode: 1987LNP87.291..100K; 1987csss....5..100K
No abstract at ADS

---------------------------------------------------------
Title: A VLA Survey of dMe Flare Stars
Authors: Jackson, P. D.; Kundu, M. R.; White, S. M.
1987LNP...291..103J Altcode: 1987csss....5..103J; 1987LNP87.291..103J
A survey is underway, which uses the VLA at wavelengths of 6 and 20
cm, to search for radio emission from all dMe flare star. within about
10 parsecs of the Sun, and which have not yet been widely observed at
radio wavelengths. At 20 cm, two bands centered at 1415 and 1515 MHz
are observed and at 6 cm, two bands centered at 4535 and 4985 MHz are
observed. Results so far, based on a total observing time of about
one hour each during July 1986 have yielded detections from 9 of the
27 stellar systems in the program.

---------------------------------------------------------
Title: Multiwavelength Microwave Observations of Solar Active Regions
and Flares
Authors: Kundu, M. R.
1987sman.work...25K Altcode:
A preflare active region was studied using the Very Large Array (VLA)
at 2, 6 and 20 cm. The author also carried out simultaneous observations
of a microwave burst at 2 and 6 cm wavelengths with the VLA.

---------------------------------------------------------
Title: Microwave Observations of Flare Stars UV Ceti, AT Microscopii,
and AU Microscopii
Authors: Kundu, M. R.; Jackson, P. D.; White, S. M.; Melozzi, M.
1987ApJ...312..822K Altcode:
The results of observations of three red dwarf flare star systems,
UV Ceti, AT Mic, and AU Mic, made in February and March of 1985,
are reported. Flaring was detected from all three systems, and
quiescent emission from UV Cet and AU Mic. Models for the quiescent
microwave-emitting corona of UV Cet are discussed. The gravitational
scale height in current models is similar to or larger than the height
of the corona, which is a striking difference from the case of the
solar corona and confirms that magnetic structures are required to
confine the radio-emitting corona. The role of precipitation into the
chromosphere of the energetic particles in such a corona is explored,
and it is shown that for plausible parameters it may be the dominant
energy loss mechanism.

---------------------------------------------------------
Title: Impulsive Phase Observations and Their Interpretation
Authors: Canfield, R. C.; Bely-Dumau, E.; Brown, J. C.; Dulk, G. A.;
Emslie, A. G.; Enome, S.; Gabriel, A. H.; Kundu, M. R.; Melrose,
D.; Neidig, D. F.; Ohki, K.; Petrosian, V.; Poland, A.; Rieger, E.;
Tanaka, K.; Zirin, H.
1986epos.conf..3.4C Altcode: 1986epos.confC...4C
No abstract at ADS

---------------------------------------------------------
Title: Phenomena Associated with Ions and Relativistic Electrons
Authors: Vlahos, L.; Machado, M. E.; Ramaty, R.; Murphy, R. J.;
Allisandrakis, C.; Bai, T.; Batchelor, D.; Benz, A. O.; Chupp, E.;
Ellison, D.; Evenson, P.; Forrest, D. J.; Holman, G.; Kane, S. R.;
Kaufmann, P.; Kundu, M. R.; Lin, R. P.; MacKinnon, A.; Nakajima,
H.; Pesses, M.; Pick, M.; Ryan, J.; Schwartz, R. A.; Smith, D. F.;
Trottet, G.; Tsuneta, S.; van Hoven, G.
1986epos.conf.2.30V Altcode: 1986epos.confB..30V
No abstract at ADS

---------------------------------------------------------
Title: Theoretical Studies of Transport Processes
Authors: Canfield, R. C.; Bely-Dumau, E.; Brown, J. C.; Dulk, G. A.;
Emslie, A. G.; Enome, S.; Gabriel, A. H.; Kundu, M. R.; Melrose,
D.; Neidig, D. F.; Ohki, K.; Petrosian, V.; Poland, A.; Rieger, E.;
Tanaka, K.; Zirin, H.
1986epos.conf.3.34C Altcode: 1986epos.confBC.34C
No abstract at ADS

---------------------------------------------------------
Title: Impulsive phase transport
Authors: Canfield, Richard C.; Bely-Dubau, Francoise; Brown, John C.;
Dulk, George A.; Emslie, A. Gordon; Enome, Shinzo; Gabriel, Alan H.;
Kundu, Mukul R.; Melrose, Donald; Neidig, Donald F.
1986epos.conf..3.1C Altcode: 1986epos.confC...1C
The transport of nonthermal electrons is explored. The thick-target
electron beam model, in which electrons are presumed to be accelerated
in the corona and typically thermalized primarily in the chromosphere
and photosphere, is supported by observations throughout the
electromagnetic spectrum. At the highest energies, the anisotropy
of gamma-ray emission above 10 MeV clearly indicates that these
photons are emitted by anisotropically-directed particles. The timing
of this high-energy gamma-radiation with respect to lower-energy
hard X-radiation implies that the energetic particles have short
life-times. For collisional energy loss, this means that they are
stopped in the chromosphere or below. Stereoscopic (two-spacecraft)
observations at hard X-ray energies (up to 350 keV) imply that these
lower-energy (but certainly nonthermal) electrons are also stopped deep
in the chromosphere. Hard X-ray images show that, in spatially resolved
flares whose radiation consists of impulsive bursts, the impulsive
phase starts with X-radiation that comes mostly from the foot-points
of coronal loops whose coronal component is outlined by microwaves.

---------------------------------------------------------
Title: Mechanisms for Particle Accleration in Flares
Authors: Vlahos, L.; Machado, M. E.; Ramaty, R.; Murphy, R. J.;
Allisandrakis, C.; Bai, T.; Batchelor, D.; Benz, A. O.; Chupp, E.;
Ellison, D.; Evenson, P.; Forrest, D. J.; Holman, G.; Kane, S. R.;
Kaufmann, P.; Kundu, M. R.; Lin, R. P.; MacKinnon, A.; Nakajima,
H.; Pesses, M.; Pick, M.; Ryan, J.; Schwartz, R. A.; Smith, D. F.;
Trottet, G.; Tsuneta, S.; van Hoven, G.
1986epos.conf.2.42V Altcode: 1986epos.confB..42V
No abstract at ADS

---------------------------------------------------------
Title: Three-dimensional structures of solar active regions.
Authors: Kundu, M. R.
1986NASCP2442..291K Altcode: 1986copp.nasa..291K
Three dimensional structure of an active region is determined from
observations with the Very Large Array (VLA) at 2, 6, and 20 cm. This
region exhibits a single magnetic loop of length approx. 10 to the
10th power cm. The 2 cm radiation is mostly thermal bremsstrahlung and
originates from the footpoints of the loop. The 6 and 20 cm radiation
is dominated by the low harmonic gyroresonance radiation and originates
from the upper portion of the legs or the top of the loop. The loop
broadens toward the apex. The top of the loop is not found to be the
hottest point, but two temperature maxima on either side of the loop
apex are observed, which is consistent with the model proposed for
long loops. From 2 and 6 cm observations it can be concluded that
the electron density and temperature cannot be uniform in a plane
perpendicular to the axis of the loop; the density should decrease
away from the axis of the loop.

---------------------------------------------------------
Title: VLA observations of solar filaments at 6 and 20 cm wavelengths.
Authors: Kundu, M. R.
1986NASCP2442..117K Altcode: 1986copp.nasa..117K
Using the Very Large Array the author observed several solar filaments
at 1.5 and 5 GHz. The brightness temperatures of the filaments are
4 - 5×104K at 20 cm and 1.5 - 1.6×104K at
6 cm. The maximum temperature depressions appear to be associated
with Hα filaments. Comparison with He 10830 Å spectroheliogram
shows that 20 cm temperature depressions correspond to the regions
of reduced intensity in the He 10830 Å around filaments, which
correspond to coronal cavities. The author studied the temperature
and density structure of the transition sheath between the filament
and the surrounding corona assuming that the energy radiated away is
balanced by the energy conducted from the corona. He found that the
observations can be better explained by a model having a pressure
gradient in the transition sheath around the filament.

---------------------------------------------------------
Title: VLA observations of coronal bright points at 6 and 20 cm
wavelengths.
Authors: Kundu, M. R.
1986NASCP2442..349K Altcode: 1986copp.nasa..349K
Prior to and during the Spacelab-2 operation, observations were made
at 6 and 20 cm of solar coronal bright points, using the Very Large
Array (VLA) in the C-configuration. The ultraviolet coverage ranged
from 200 to 18,000 wavelengths. The maps were convolved with beams of
18 x 18 inches at 20 km and 4 x 4 inches at 6 cm. Only the preliminary
results from July 15 and July 31, 1985 observations.

---------------------------------------------------------
Title: Energetic Phenomena on the Sun: The Solar Maximum Mission
Flare Workshop. Proceedings
Authors: Kundu, Mukul; Woodgate, Bruce
1986epos.conf.....K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Large scale structure of the sun's radio corona.
Authors: Kundu, M. R.
1986NASCP2442..253K Altcode: 1986copp.nasa..253K
The author presents results of studies of large scale structures of
the corona at long radio wavelengths, using data obtained with the
multifrequency radioheliograph of the Clark Lake Radio Observatory. He
shows that features corresponding to coronal streamers and coronal
holes are readily apparent in the Clark Lake maps.

---------------------------------------------------------
Title: Narrow-Band Radio Flares from Red Dwarf Stars
Authors: White, Stephen M.; Kundu, Mukul R.; Jackson, Peter D.
1986ApJ...311..814W Altcode:
VLA observations of narrow-band behavior in 20 cm flares from two red
dwarf stars, L726 - 8A and AD Leo, are reported. The flare on L726
- 8A was observed at 1415 and 1515 MHz; the flux and the evolution
differed significantly at the two frequencies. The flare on AD Leo
lasted for 2 hr at 1415 MHz but did not appear at 1515 MHz. The AD Leo
flare appears to rule out a source drifting through the stellar corona
and is unlikely to be due to plasma emission. In the cyclotron maser
model the narrow-band behavior reflects the range of magnetic fields
present within the source. The apparent constancy of this field for 2
hr is difficult to understand if magnetic reconnection is the source of
energy for the flare. The consistent polarization exhibited by red dwarf
flares at 20 cm may be related to stellar activity cycles, and changes
in this polarization will permit measuring the length of these cycles.

---------------------------------------------------------
Title: Large scale structure of the corona.
Authors: Kundu, M. R.
1986NASCP2442..249K Altcode: 1986copp.nasa..249K
This is an introduction to this section of the proceedings. In this
section is a brief description of some radio results obtained with
meter-decameter radioheliograph. An optical study based upon synoptic
data of polarized brightness (pB), H alpha line filtergrams and large
scale B-fields is presented. This is followed by two papers on the
interpretation of coronal mass ejection (CME) and modeling of three
dimensional coronas.

---------------------------------------------------------
Title: Phenomena Associated with Mildly Relativistic Electrons
Authors: Vlahos, L.; Machado, M. E.; Ramaty, R.; Murphy, R. J.;
Allisandrakis, C.; Bai, T.; Batchelor, D.; Benz, A. O.; Chupp, E.;
Ellison, D.; Evenson, P.; Forrest, D. J.; Holman, G.; Kane, S. R.;
Kaufmann, P.; Kundu, M. R.; Lin, R. P.; MacKinnon, A.; Nakajima,
H.; Pesses, M.; Pick, M.; Ryan, J.; Schwartz, R. A.; Smith, D. F.;
Trottet, G.; Tsuneta, S.; van Hoven, G.
1986epos.conf..2.2V Altcode: 1986epos.confB...2V
No abstract at ADS

---------------------------------------------------------
Title: A study of solar filaments from high resolution microwave
observations
Authors: Kundu, M. R.; Melozzi, M.; Shevgaonkar, R. K.
1986A&A...167..166K Altcode:
Using the Very Large Array the authors have observed several solar
filaments at 1.5 and 5 GHz. The brightness temperatures of the filaments
are 4 - 5×104K at 20 cm and 1.5 - 1.6×104K at
6 cm. The maximum temperature depressions appear to be associated with
Hα filaments. Comparison with He 10830 Å spectroheliogram shows that
20 cm temperature depressions correspond to the region of reduced
intensity in the He 10830 Å around filaments, which correspond
to coronal cavities. The authors have studied the temperature and
density structure of the transition sheath between the filament and the
surrounding corona assuming that the energy radiated away is balanced by
the energy conducted from the corona. They find that the observations
can be better explained by a model having a pressure gradient in the
transition sheath around the filament.

---------------------------------------------------------
Title: Microwave Observations of Red Dwarf Flare Stars
Authors: Kundu, M. R.; Jackson, P. D.; White, S. M.
1986BAAS...18..984K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Simultaneous VLA and Hard X-Ray Observations of a Large Flare
on 1981 November 14
Authors: Dennis, B. R.; Kundu, M. R.; Melozzi, M.
1986BAAS...18..965D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Solar Microbursts at Meter-Dekameter Wavelengths
Authors: Kundu, M. R.; Gergely, T. E.; Szabo, A.; Loiacono, R.; White,
S. M.
1986ApJ...308..436K Altcode:
Microbursts are low-brightness-temperature bursts observed by the Clark
Lake radioheliograph. The bursts occur several times per hour during
quiet-sun periods and are seen at the observing frequencies from 30 to
70 MHz. They are stationary at a given frequency, have short rise times
and durations of 2-10 s. Here, observations of the bursts are presented
and interpretated in terms of plasma emission. The burst properties
suggest that they are weak type III bursts. The observations imply that
energy releases on the sun continue to be impulsive, with nonthermal
electron distributions, for small releases of energy. The relation of
the bursts to type III bursts and hard X-ray bursts is discussed.

---------------------------------------------------------
Title: Propagation of Weak Type III Burst Electrons in Dense Coronal
Streamers
Authors: Gopalswamy, N.; Kundu, M. R.; Szabo, A.
1986BAAS...18R.900G Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Book-Review - Solar Terrestrial Physics
Authors: Kundu, M. R.; Biswas, S.; Reddy, B. M.; Samadurai, S.; Somov,
B. V.
1986SSRv...44..403K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A VLA Survey of dMe Flare Stars
Authors: Jackson, P. D.; Kundu, M. R.; White, S. M.
1986BAAS...18..913J Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Coronal Activity at Meter-Decameter Wavelengths: Clark Lake
Observations
Authors: Schmahl, E. J.; Kundu, M. R.; Szabo, A.; Gergely, T. E.;
Howard, R.
1986BAAS...18R.900S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Solar Coronal Bright Points Observed with the VLA
Authors: Habbal, S. R.; Ronan, R. S.; Withbroe, G. L.; Shevgaonkar,
R. K.; Kundu, M. R.
1986ApJ...306..740H Altcode:
The first observations of solar coronal bright points made at 20-cm
wavelength with the VLA are reported. The brightness temperature of
the sources observed varies between 1 and 5 x 10 to the 5th K. The
observations indicate that significant fluctuations in the brightness
temperature as well as in the spatial extent of these sources can occur
over a few minutes. These fluctuations are shown to be due to density
and temperature fluctuations at transition region heights combined
with either plasma motions along magnetic field lines or changes in
magnetic field topology, or both.

---------------------------------------------------------
Title: Book-Review - Unstable Current Systems and Plasma Instabilities
in Astrophysics
Authors: Kundu, M. R.; Holman, G. C.; Somov, B. V.
1986SSRv...44..187K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A new microwave/X-ray diagnostic for the thermal phase of
solar flares
Authors: Schmahl, E. J.; Kundu, M. R.; Erskine, F. T.
1986SoPh..105...87S Altcode:
We have observed 10 solar bursts during the thermal phase using the
Haystack radio telescope at 22 GHz. We show that these high frequency
flux observations, when compared with soft X-ray band fluxes, give
useful information about the temperature profile in the flare loops. The
microwave and X-ray band fluxes provide determinations of the maximum
loop temperature, the total emission measure, and the index δ of the
differential emission measure (q(T)/T = cTδ−1). The
special case of an isothermal loop (δ = ∞) has been considered
previously by Thomas et al. (1985), and we confirm their diagnostic
calculations for the GOES X-ray bands, but find that the flare loops
we observed departed significantly from the isothermal regime. Our
results (δ = 1-3.5) imply that, during the late phases of flares,
condensation cooling (δ ≈ 3.5) competes with radiative cooling
(δ ≈ 1.5). Further, our results appear to be in good agreement with
previous deductions from XUV rocket spectra (δ ≈ 2-3).

---------------------------------------------------------
Title: High-Spatial-Resolution Microwave and Soft X-ray Observations
as Diagnostics of Solar Magnetic Loops
Authors: Holman, G. D.; Webb, D. F.; Davis, J. M.; Kundu, M. R.
1986BAAS...18..677H Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Clark Lake microbursts: on a lower limit to type III burst
brightnesstemperatures.
Authors: White, S. M.; Kundu, M. R.; Szabo, A.
1986SoPh..107..135W Altcode: 1987SoPh..107..135W
Further observations of solar microbursts by the Clark Lake
radioheliograph are reported. The microbursts have properties consistent
with weak type III bursts, with the implication that type III's can
have brightness temperatures as low as 106 K. We explore the
importance of this result. A single model to explain the stronger type
III bursts and the weaker microbursts is sought. We show that none of
the models for stabilizing the strongest type III electron streams
can explain the observed microbursts: these models have threshold
levels of Langmuir waves which imply emission (due to spontaneous
scattering off ions) with brightness temperatures in excess of those
observed. It appears that either some vital physics is still missing
from models for type III bursts, or that microbursts should have
properties significantly different from those of type III bursts. In
the latter case further observations should allow important tests of
type III models.

---------------------------------------------------------
Title: Decimeter Continuum Radio Emission from a Post-Flare Loop
Authors: Kundu, M. R.
1986SoPh..104..223K Altcode:
Radio observations offer an important means for providing estimates
of magnetic fields in post-flare loops.

---------------------------------------------------------
Title: A study of hard X-ray associated meter-decameter bursts
observed on December 19, 1979
Authors: Kundu, M. R.; Gergely, T. E.; Kane, S. R.; Sawant, H. S.
1986SoPh..103..153K Altcode:
We present the results of a study of the relationship of a complex
meter-decameter wavelength radio burst observed with the Clark Lake
E-W and N-S interferometers, with a hard X-ray burst observed with
the X-ray spectrometer aboard ISEE-3. The radio burst consisted of
several type III's, reverse drift type III's, a U burst, and type II
and type IV bursts. The X-ray emission was also complex. The radio
as well as hard X-ray emissions were observed before the flash phase
of the flare; they were not always associated and we conjecture that
this may constitute evidence for acceleration of electrons high in
the corona. On the other hand, all components of the reverse drift
burst were associated with hard X-ray subpeaks, indicating multiple
injection of electron beams along field lines with different density
gradients. While the type II burst appeared to be related to the hard
X-ray burst, a detailed correspondence between individual features of
the radio and hard X-ray burst emissions could not be found. The type
IV burst started after all hard X-ray emissions ceased. Its source
appeared to be a magnetic arch, presumably containing energetic
electrons responsible for the gyrosynchrotron radiation of type IV.

---------------------------------------------------------
Title: Microwave observations of red dwarf flare stars
Authors: Kundu, M. R.; White, S. M.; Jackson, P. D.
1986AdSpR...6h.117K Altcode: 1986AdSpR...6..117K
We discuss some recent observations of red dwarf flare stars. When
observed over periods of about 8 hours, each of 4 flare star systems
displayed at least one major flare at 20 cm. Quiescent emission at
6 cm was seen from UV Ceti and EQ Peg A, but flares were much less
frequent at 6 cm than at 20 cm. We also summarize earlier observations
of quiescent emission from UV Ceti. Observations of highly polarized
flares with brightness temperatures in excess of 1010 K
appear to be common on red dwarf stars. We have also found narrowband
flares which strengthen the argument that a coheren emission mechanism
is involved in these flares. One of those narrowband flares allows
us to place severe constraints on conditions in the flare source,
and if the flare is cyclotron maser emission it seems unlikely that
magnetic reconnection is involved in the flare.

---------------------------------------------------------
Title: Shock waves and coronal transients: The event of 1980 April 17
Authors: Gary, D. E.; Gergely, T. E.; Kundu, M. R.
1986AdSpR...6f.311G Altcode: 1986AdSpR...6..311G
The coronal mass ejection (CME) event of 1980 April 17 was observed
with the SMM coronagraph, and an accompanying Type II (shock wave
related) burst was observed simultaneously with the Culgoora and Clark
Lake radioheliographs. The method of analysis of the combined radio
observations is presented. Although the radio positions were affected
by severe ionospheric refraction, the combined radio observations allow
a useful reduction in the range of possible positions of the 80 MHz
source when the 43 MHz source is required to lie within the range of
position angles of the CME. The positions of the 80 MHz radio sources
under this assumption are compared with the positions of the CME loop.

---------------------------------------------------------
Title: Simultaneous imaging and spectral observations in microwaves
and hard X-rays of the impulsive phase of a solar limb flare
Authors: Schmahl, E. J.; Kundu, M. R.; Dennis, B. R.
1986AdSpR...6f.143S Altcode: 1986AdSpR...6..143S
We have observed the impulsive phase of a solar flare at microwave
wavelengths and in hard X-rays, and deduced the strength of the
magnetic field and the number of energetic electrons producing the
burst. The microwave observations, using the Very Large Array at 6 cm,
had spatial resolution of 8”×8”, close to the resolution of the Hard
X-ray Imaging Spectrometer on SMM which also imaged this flare. The Hard
X-ray Burst Spectrometer determined the spectrum of the burst in the
range 25-512 keV, and several patrol telescopes recorded the microwave
time profile at frequencies from 2.8 to 19.6 GHz. The combined data
show that the derived number of microwave emitting electrons is at
least three orders of magnitude fewer than the number of thick target
electrons producing the hard X-rays. We propose that the reason for
this discrepancy in numbers is that the fast electrons are highly
beamed, and radiate gyrosynchrotron emission less efficiently than
isotropically distributed electrons. However, we cannot rule out the
alternate explanation: that the electron energy spectrum steepens at
moderate energies (&gt; 150 keV), and then flattens at higher energies
(&gt; 200 keV) where gyrosynchrotron processes become important.

---------------------------------------------------------
Title: Impulsive phase transport.
Authors: Canfield, R. C.; Bely-Dubau, E.; Brown, J. C.; Dulk, G. A.;
Emslie, A. G.; Enome, S.; Gabriel, A. H.; Kundu, M. R.; Melrose,
D.; Neidig, D. F.; Ohki, K.; Petrosian, V.; Poland, A.; Rieger, E.;
Tanaka, K.; Zirin, H.
1986NASCP2439....3C Altcode:
Contents: 1. Introduction: motivation for transport studies, historical
perspective, overview of the chapter. 2. Impulsive phase observations
and their interpretation: gamma-ray emission above 10 MeV, hard
X-ray and microwave morphology, combined soft and hard X-ray spectra,
iron Kα emission, ultraviolet and hard X-ray emission, white light
emission, Hα emission. 3. Theoretical studies of transport processes:
electron beams and reverse currents, proton transport, radiative energy
transport by amplified decimetric waves. 4. Summary.

---------------------------------------------------------
Title: EXOSAT observations of quiescent and flaring emission from
active late-type stars
Authors: Pallavicini, R.; Monsignori-Fossi, B. C.; Landini, M.; Kundu,
M. R.; Lang, K. R.
1986AdSpR...6h.125P Altcode: 1986AdSpR...6Q.125P
The authors present the highlights of several guest investigator
programs carried out with the EXOSAT satellite. They discuss quiescent
as well as flaring emission from normal F to M dwarfs, from dMe flare
stars and from RS CVn binaries.

---------------------------------------------------------
Title: Solar-terrestrial physics. Proceedings of the second Indo-US
workshopon solar-terrestrial physics, held at New Delhi, India,
30 January - 3 February 1984.
Authors: Kundu, M. R.; Biswas, S.; Reddy, B. M.; Samadurai, S.
1986spps.book.....K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Possible evidence for beaming in flares from microwave and
hard X-rayimaging and spectra.
Authors: Schmahl, E. J.; Kundu, M. R.; Dennis, B. R.
1986lasf.conf..396S Altcode: 1986lasf.symp..396S
The authors have observed the impulsive phase of a solar flare at
microwave wavelengths and in hard X-rays, and deduced the strength of
the magnetic field and the number of energetic electrons producing the
burst. The combined data show that the derived number of microwave
emitting electrons is at least three orders of magnitude fewer than
the number of thick target electrons producing the hard X-rays. The
authors propose that the reason for this discrepancy in numbers is
that the fast electrons are highly beamed, and radiate gyrosynchrotron
emission less efficiently than isotropically distributed electrons.

---------------------------------------------------------
Title: A high spatial resolution study of microwave flare precursors
Authors: Kundu, M. R.
1986AdSpR...6f..93K Altcode: 1986AdSpR...6...93K
We provide several examples of preflare changes from VLA high resolution
microwave data, which show that in general the active region increases
in intensity and polarization over a period of several tens of minutes
prior to the onset of a flare in that region. However, this phenomenon
by itself does not appear to be sufficient to trigger a flare. We
show that a few minutes (&lt;~ 10 min) just before the flare onset
something else happens, usually in the form of one of the following
three features: (1) sudden change of polarization of the flaring region;
(2) change of orientation of the neutral plane separating one polarity
from another in a bipolar region; and (3) appearance of new sources in
the immediate vicinity of some pre-existing structure of the active
region. All three features are consistent with the emergence of new
flux, which interacts with a pre-existing region to form a neutral or
current sheet. The formation of the latter is ultimately responsible
for triggering the onset of a flare.

---------------------------------------------------------
Title: Coronal activity at radio wavelengths.
Authors: Kundu, M. R.
1986HiA.....7..725K Altcode:
The author describes the multifrequency radioheliograph of the Clark
Lake Radio Observatory. Its use for studies of large scale structures
of the corona at long radio wavelengths is discussed. The author shows
that features corresponding to coronal streamers and coronal holes
are readily apparent in the Clark Lake maps. The author also presents
results on studies of microbursts at meter-decameter wavelengths.

---------------------------------------------------------
Title: Microwave Observations of Flare Stars UV Ceti, AT Mic, and
AU Mic
Authors: Kundu, M. R.; Jackson, P. D.; Melozzi, M.; White, S. M.
1986LNP...254..284K Altcode: 1986csss....4..284K
No abstract at ADS

---------------------------------------------------------
Title: EXOSAT Detection of a Very Large Flare on EQ Peg
Authors: Pallavicini, R.; Kundu, M. R.; Jackson, P. D.
1986LNP...254..225P Altcode: 1986csss....4..225P
No abstract at ADS

---------------------------------------------------------
Title: Microbursts observed at Clark Lake
Authors: White, S. M.; Kundu, M. R.; Gergely, T. E.
1986AdSpR...6f.285W Altcode: 1986AdSpR...6Q.285W
Microbursts are low brightness temperature burst observed by the
Clark Lake radioheliograph. The bursts are seen at the observing
frequencies from 30 MHz to 70 MHz, are stationary at a given frequency,
and have short rise times and durations of 2 - 10 seconds. We present
observations of the bursts, and show that their properties imply that
they are weak type III bursts. However, we also show that none of the
theories invoked to explain strong type III bursts can accomodate such
weak bursts. We expect that important differences in the properties
of microbursts and the stronger type III's will be found, and will
be important in understanding the propagation of electron streams in
the corona.

---------------------------------------------------------
Title: Particle acceleration.
Authors: Vlahos, L.; Machado, M. E.; Ramaty, R.; Murphy, R. J.;
Allisandrakis, C.; Bai, T.; Batchelor, D.; Benz, A. O.; Chupp, E.;
Ellison, D.; Evenson, P.; Forrest, D. J.; Holman, G.; Kane, S. R.;
Kaufmann, P.; Kundu, M. R.; Lin, R. P.; MacKinnon, A.; Nakajima,
H.; Pesses, M.; Pick, M.; Ryan, J.; Schwartz, R. A.; Smith, D. F.;
Trottet, G.; Tsuneta, S.; van Hoven, G.
1986NASCP2439....2V Altcode:
Contents: 1. Introduction. 2. Phenomena associated with
mildly-relativistic electrons: soft and hard X-ray source structure,
location and development, microwave source structure, location and
development, time structures and time delays in radio and hard X-rays,
microwave rich flares, decimetric - metric observations and comparison
with X-ray observations, discussion of models for X-ray and microwave
emission. 3. Phenomena associated with ions and relativistic electrons:
gamma-ray observations, neutron observations, implications of gamma-ray
and neutron observations, interplanetary charged-particle observations,
acceleration mechanisms. 4. Mechanisms for particle acceleration
in flares: particle acceleration in reconnecting magnetic fields,
electron acceleration along the magnetic field with sub-Dreicer electric
fields, lower hybrid waves, Fermi acceleration and MHD turbulence,
shock acceleration, acceleration of electrons by intense radio waves,
preferential acceleration of heavy ions. 5. Achievements - outstanding
questions.

---------------------------------------------------------
Title: Impulsive energy release in solar flares: A summary
Authors: Kundu, M. R.
1986AdSpR...6f.207K Altcode: 1986AdSpR...6..207K
Discoveries in solar physics made during the SMM-SMY-SMA period are
highlighted, with special reference to impulsive energy release in
solar flares. Major discoveries include observational evidence for
magnetic reconnection and its theoretical interpretation, chromospheric
evaporation to explain the simultaneous blue shift of X-ray lines and
red shift of Hα, simultaneous production of high energy (Mev) electrons
and protons, and their acceleration by Fermi shock acceleration upto 100
Mev energies, and evidence for a new acceleration process to explain
the electron deficient very hard ion spectrum ( &gt; 1000 Mev) in the
extended emission phase of the large 1982 June 3 flare.

---------------------------------------------------------
Title: High Spatial Resolution Microwave Observations of Solar Flares
Authors: Kundu, M. R.
1986spps.book..159K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The proposed NRAO Millimeter Array and its use for solar
studies.
Authors: Kundu, Mukul R.
1986NASCP2449..471K Altcode: 1986rfsf.nasa..471K
The author gives a brief summary of the proposed NRAO Millimeter Array
discussed at a workshop held in Green Bank, W. Va., September 30 -
October 2, 1985. He also provides a brief description of the solar
studies that can be made with such an array.

---------------------------------------------------------
Title: Microwave imaging of a solar limb flare - Comparison of
spectra and spatial geometry with hard X-rays
Authors: Schmahl, E. J.; Kundu, M. R.; Dennis, B. R.
1985ApJ...299.1017S Altcode:
A solar limb flare was mapped using the Very Large Array (VLA) together
with hard X-ray (HXR) spectral and spatial observations of the Solar
Maximum Mission satellite. Microwave flux records from 2.8 to 19.6
GHz were instrumental in determining the burst spectrum, which has a
maximum at 10 GHz. The flux spectrum and area of the burst sources were
used to determine the number of electrons producing gyrosynchrotron
emission, magnetic field strength, and the energy distribution of
gyrosynchrotron-emitting electrons. Applying the thick target model
to the HXR spectrum, the number of high energy electrons responsible
for the X-ray bursts was found to be 10 to the 36th, and the electron
energy distribution was approximately E exp -5, significantly different
from the parameters derived from the microwave observations. The HXR
imaging observations exhibit some similiarities in size and structure
o the first two burst sources mapped with the VLA. However, during the
initial burst, the HXR source was single and lower in the corona than
the double 6 cm source. The observations are explained in terms of a
single loop with an isotropic high-energy electron distribution which
produced the microwaves, and a larger beamed component which produced
the HXR at the feet of the loop.

---------------------------------------------------------
Title: Book-Review - Unstable Current Systems and Plasma Instabilities
in Astrophysics - I.A.U. SYMP.107
Authors: Kundu, M. R.; Holman, G. D.; Roberts, B.
1985Obs...105..240K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Simultaneous observations of hard X-ray and microwave burst
sources in a limb flare
Authors: Takakura, T.; Kundu, M. R.; McConnell, D.; Ohki, K.
1985ApJ...298..431T Altcode:
Associated with a flare that occurred just behind the west solar limb on
1981 August 3, a hard X-ray source (20 - 30 keV) and a microwave source
at 5 GHz were observed simultaneously with the Hinotori spacecraft
and the VLA. Both sources were located in the corona. The height
of the centroid above the west limb was 15arcsec (104km)
for the hard X-ray source and 54arcsec (4×104km) for the
radio source. The sources are believed to be located near the tops of
two independent coronal arcades or loops, one low and the other high,
rather than at two different heights of a common arcade or loop.

---------------------------------------------------------
Title: Microwave emission from late-type dwarf stars UV Ceti and YZ
Canis Minoris.
Authors: Kundu, M. R.; Shevgaonkar, R. K.
1985ApJ...297..644K Altcode:
Simultaneous high-resolution observations of two late-type dwarf stars,
UV Cet and YZ CMi, at 6 and 20 cm are presented. These observations
put sufficient constraints on existing interpretations to conclude
that the quiescent microwave emission from these stars is due to
gyrosynchrotron radiation of nonthermal electrons having a power-law
energy distribution. From the lifetime of 1 hr of the nonthermal
particles against radiation and collision losses, a magnetic field of a
few thousand gauss on the photosphere of these stars is estimated. The
observations indicate that the ambient density in the coronae of YZ
CMi is an order of magnitude higher than that of UV Cet.

---------------------------------------------------------
Title: High Spatial Resolution Microwave Observations of the Sun
Authors: Kundu, M. R.
1985SoPh..100..491K Altcode:
Over the past decade two large arrays — the Westerbork Synthesis
Radio Telescope (WSRT) and the Very Large Array (VLA) built primarily
for sidereal radio astronomy have been used for solar radio astronomical
studies with spatial resolution of a few seconds of arc. In this review,
we discuss some results obtained at Maryland using these instruments.

---------------------------------------------------------
Title: The Diameter of the Sun at Decameter Wavelengths
Authors: Gergely, T. E.; Gross, B. D.; Kundu, M. R.
1985SoPh...99..323G Altcode:
Using observations obtained with the Clark Lake radioheliograph
we determined the diameter of the Sun in the decameter wavelength
range. Both equatorial and polar diameters increase with decreasing
frequency, as D=Afα. The eccentricity of the brightness
distribution appears to remain constant in the frequency range (30-74
MHz) in good agreement with the optical results in a corresponding
height range. The smaller size of the polar diameter is attributed to
coronal holes covering the poles during the period of our observations,
while streamers were observed at the equator most of the time.

---------------------------------------------------------
Title: Book-Review - Unstable Current Systems and Plasma Instabilities
in Astrophysics
Authors: Kundu, M. R.; Holman, G. D.; Kleczek, J.
1985Ap&SS.113..424K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: VLA Observations of a Radio Plage at Centimeter Wavelengths
Authors: Shevgaonkar, R. K.; Kundu, M. R.
1985SoPh...98..119S Altcode:
VLA observations of a solar plage region at 6 and 20 cm wavelengths are
presented. The high frequency 6 cm emission correlates well with the
associated sunspots, whereas 20 cm emission shows good correlation with
the Hα plage. Large temperature variations over a period of one day
are observed in the plage associated component without any significant
changes in the sunspots. The dominant emission mechanisms at 6 and
20 cm are found to be gyroresonance radiation and bremstrahlung
respectively. It is concluded that the coronal condensation above
the chromospheric Hα plage has an electron density of ∼5 ×
109 cm−3 and it extends to a height of ∼5
× 104 km.

---------------------------------------------------------
Title: Microwave Emission from Late Type Dwarf Stars UV Ceti and
YZ CMi
Authors: Kundu, M. R.; Shevgaonkar, R. K.
1985ASSL..116..229K Altcode: 1985rst..conf..229K
The authors present simultaneous VLA observations of two late type
dwarf stars UV Ceti and YZ CMi at 6 and 20 cm. Multiwavelength
observations put sufficient constraints on existing interpretations
of quiescent radio emission from these stars. They found that the
microwave emission is due to gyro-synchrotron radiation of nonthermal
electrons having a power law energy distribution. This emission
originates from a source whose size is 2 - 3 times larger than the
star. The authors estimate a magnetic field of ≡140 G and a density
of ⪉2×108cm-3 in the microwave source.

---------------------------------------------------------
Title: Summary of the Current and Future Problems in Radio Stars
Authors: Kundu, M. R.; Hjellming, R. M.
1985ASSL..116..397K Altcode: 1985rst..conf..397K
No abstract at ADS

---------------------------------------------------------
Title: Simultaneous Microwave Observations of Solar Flares at 6-CM
and 20-CM Wavelengths Using the VLA
Authors: Melozzi, M.; Kundu, M. R.; Shevgaonkar, R. K.
1985SoPh...97..345M Altcode:
Using the Very Large Array, solar burst observations have been carried
out simultaneously at 6 and 20 cm. Structural changes and preheating
have been observed in the flaring regions on time scales of minutes to
tens of minutes before the onset of the burst impulsive phase. The 6 cm
burst sources are located close to the neutral line, or near the legs
of a flaring loop. The 20 cm burst sources show complex and extended
structures spatially separated from both the preburst emission and the
gradual decay phase of the burst. We interpret the observations in terms
of a two-component flare model (bulk heating as well as acceleration
of particles) and derive the physical parameters of the burst sources.

---------------------------------------------------------
Title: Book-Review - Unstable Current Systems and Plasma Instabilities
in Astrophysics
Authors: Kundu, M. R.; Holman, G. D.; Achterberg, A.
1985SSRv...41..212K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Erratum - a Study of Flare Buildup from Simultaneous
Observations in Microwave Hα and Ultraviolet Wavelengths
Authors: Kundu, M. R.; Gaizauskas, V.; Woodgate, B. E.; Schmahl,
E. J.; Shine, R.; Jones, H. P.
1985ApJS...58..195K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The microwave structure of hot coronal loops
Authors: Holman, G. D.; Kundu, M. R.
1985ApJ...292..291H Altcode:
The thermal cyclotron emission from model dipole magnetic loops
is computed. It is shown that a simple, isothermal dipole loop can
show a great deal of spatial and polarization structure at microwave
frequencies. This structure is sensitive to the observation frequency
and angle of observation. Two qualitatively distinct microwave loop
structures can be distinguished: (1) 'thin loop,' observed as a
string of independent microwave peaks, corresponding to different
harmonics of the local electron gyrofrequency; and (2) 'thick loop,'
the harmonics are merged, so that a more continuous microwave structure
is observed. It is shown that the presence of an external plasma can
result in a change in the observed mode of polarization along one leg
of a loop, without a change in the sign of the line-of-sight magnetic
field. Models such as these, along with high-resolution microwave
and related observations, can provide an excellent diagnostic of the
magnetic and plasma properties of coronal loops.

---------------------------------------------------------
Title: Dual frequency observations of solar microwave bursts using
the VLA
Authors: Shevgaonkar, R. K.; Kundu, M. R.
1985ApJ...292..733S Altcode:
Simultaneous observations at 2 and 6 cm wavelengths of a solar active
region and of microwave bursts were carried out with the VLA. The
quiescent 6 cm emission is strongly associated with photospheric
sunspots and is dominated by gyroresonance radiation. The emission
at 2 cm, on the other hand, is due to free-free mechanism, and it
originates from the chromosphere-corona transition region. The bursts
observed have multiple peaks. Two-dimensional snapshot maps have been
produced at 6 and 2 cm. From the brightness temperature and the degree
of circular polarization, the magnetic field in the microwave burst
sources has been estimated. The generating mechanisms responsible
for 6 and 2 cm radiation are discussed; it is concluded that the 6 cm
radiation in the bursts studied here originates from the bulk heated
plasma, whereas the 2 cm radiation is due to the nonthermal particles
generated in the energy-release process.

---------------------------------------------------------
Title: Multiwavelength observations of a preflare solar active region
using the VLA
Authors: Kundu, M. R.; Shevgaonkar, R. K.
1985ApJ...291..860K Altcode:
A preflare active region was studied using the Very Large Array at 2,
6, and 20 cm. At 2 cm the region is composed of two components located
in regions of opposite polarity. Both components are preheated prior
to the impulsive onset of a flare. However, one component develops
new structures during preburst phase, and the burst occurs in this
location. It is believed that the new structures represent emerging
flux regions which interact with an overlying loop to produce a neutral
sheet, which ultimately is responsible for triggering the flare.

---------------------------------------------------------
Title: The Sun and nearby Stars: Microwave Observations at High
Resolution
Authors: Kundu, M. R.; Lang, K. R.
1985Sci...228....9K Altcode:
High-resolution microwave observations are providing new insights
into the nature of active regions and eruptions on the sun and nearby
stars. The strength, evolution, and structure of magnetic fields in
coronal loops can be determined by multiple-wavelength observations
with the Very Large Array. Flare models can be tested with Very Large
Array snapshot maps, which have angular resolutions of better than 1
second of arc in time periods as short as 10 seconds. Magnetic changes
that precede solar eruptions on time scales of tens of minutes involve
primarily emerging coronal loops and the interactions of two or more
loops. Magnetic reconnection at the interface of two closed loops may
accelerate electrons and trigger the release of microwave energy in
the coronal parts of the magnetic loops. Nearby main-sequence stars of
late spectral type emit slowly varying microwave radiation and stellar
microwave bursts that show striking similarities to those of the sun.

---------------------------------------------------------
Title: Observations of the Cygnus Loop at 40 MHz with the Clark Lake
Teepee Tee
Authors: Jackson, P. D.; Kassim, N. E.; Kundu, M. R.
1985BAAS...17..545J Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Observations of Flares at 6 and 20 cm Wavelengths From Late
Type Dwarf Stars UV Ceti and AT Mic
Authors: Kundu, M. R.; Jackson, P. D.; Melozzi, M.
1985BAAS...17..589K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A study of flare buildup from simultaneous observations in
microwave, H-alpha, and UV wavelengths
Authors: Kundu, M. R.; Gaizauskas, V.; Woodgate, B. E.; Schmahl,
E. J.; Shine, R.; Jones, H. P.
1985ApJS...57..621K Altcode:
The results of high-resolution observations of the solar preflare
activity of June 25, 1980 are analyzed. The observations were carried
out simultaneously in the UV microwave, and H-alpha wavelengths
using the VLA, the Ottawa River photoheliograph, and the Solar Max
spectrometer and polarimeter instruments. Increases were observed in the
intensitiy and polarization of compact sources at a wavelength of 6-cm
during the preflare hour. The increases were associated with rising and
twisting motions in the magnetic loops near the sight of the subsequent
flare. Consistent with this process, analysis of the transverse and
Doppler motions observed in the H-alpha filament before disruption
showed that the filament was activated internally by the motions of
evolving magnetic flux patterns. Ultraviolet data for C IV brightenings
and upflows at the first appearance of the H-alpha filament indicated
the presence of rising magnetic loops and material rising within the
loops. The complete VLA, microwave and H-alpha data sets are given.

---------------------------------------------------------
Title: The coalescence instability in solar flares
Authors: Tajima, T.; Brunel, F.; Sakai, J. -I.; Vlahos, L.; Kundu,
M. R.
1985IAUS..107..197T Altcode:
The nonlinear coalescence instability of current carrying solar loops
can explain many of the characteristics of the solar flares such as
their impulsive nature, heating and high energy particle acceleration,
amplitude oscillations of electromagnetic and emission as well as the
characteristics of two-dimensional microwave images obtained during
a flare. The plasma compressibility leads to the explosive phase of
loop coalescence and its overshoot results in amplitude oscillations
in temperatures by adiabatic compression and decompression. It is
noted that the presence of strong electric fields and super-Alfvenic
flows during the course of the instability play an important role in
the production of nonthermal particles. A qualitative explanation on
the physical processes taking place during the nonlinear stages of
the instability is given.

---------------------------------------------------------
Title: Unstable current sytems and plasma instabilities in
astrophysics
Authors: Kundu, M. R.; Holman, G. D.
1985IAUS..107.....K Altcode:
Among the topics discussed are: magnetic field reconnection in
cosmic plasmas; energy dissipation mechanisms in the solar corona;
and the acceleration of runaway electrons and Joule heating in solar
flares. Consideration is also given to: the nonlinear evolution of
the resistive tearing mode; anomalous transport in current sheets;
equilibrium and instability in extragalactic jets; and magnetic
field reconnection in differentially rotating accretion disks. Among
additional topics discussed are: the creation of high energy electron
tails by lower hybrid waves and its connection with type-II and type-III
bursts; beam current systems in solar flares; and the spatio-temporal
features of microwave emissions of active regions and flares.

---------------------------------------------------------
Title: Forty Years of Solar Radio Research
Authors: Kundu, M. R.
1985spit.conf...23K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Microwave Observations of Solar Active Regions and Flares
Using the Very Large Array
Authors: Kundu, M. R.
1985spit.conf..503K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: An interpretation of the millisecond time variation in hard
X-ray solar flares
Authors: Krishan, V.; Kundu, M. R.
1985IAUS..107..299K Altcode:
Recent observations of the fast time variability in the hard X-ray
emission from solar flares are interpreted. The fast spikes are assumed
to be superimposed on the thermal X-ray emission. The rise and fall of a
spike are caused by disruptions in the plasma. The rise time represents
the impulsive heating time and the decay or fall time represents a
quick cooling of the plasma due to the accelerating growth rate of
the m = 1 tearing mode. The estimated characteristic time durations
of the spike are found to be in good agreement with the observed ones.

---------------------------------------------------------
Title: Observational evidence for magnetic reconnection in microwave
solar bursts
Authors: Kundu, M. R.
1985IAUS..107..185K Altcode:
Observations of magnetic reconnection in the solar coronal magnetic
field are presented. The observations were carried out using the
NRAO VLA with a special resolution of 2 arcsec at 6-cm. The period of
observation corresponded to the onset of an impulsive burst observed on
May 14, 1980 at 19:57 UT. A second set of VLA observations of several
interconnecting coronal loops associated with the onset of an impulsive
burst on June 24, 1980, is also presented. The acceleration of electrons
emitting microwaves was observed during magnetic reconnection in both
events. Polarization maps for three selected phases in the evolution
of the burst events are provided.

---------------------------------------------------------
Title: Erratum - Microwave Soft and Hard X-Ray Imaging Observations
of Two Solar Flares
Authors: Kundu, M. R.; Machado, M. E.; Erskine, F. T.; Rovira, M. G.;
Schmahl, E. J.
1984A&A...140..476K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Center-to-limb variation of a sunspot-associated microwave
source
Authors: Alissandrakis, C. E.; Kundu, M. R.
1984A&A...139..271A Altcode:
Observations of the simple bipolar active region McMath 16862,
obtained with the Westerbork Synthesis Radio Telescope at 6.16 cm
over six consecutive days, indicate two bright sources associated
with the region's two main spots, as well as some weaker emission
that may be associated with loop structures. Application of a novel
analytical method has allowed the mapping of the vertical as well as
the horizontal component of the sunspot magnetic field at specific
locations in the low corona. While the vertical component decreases
away from the source's center, the horizontal component has both a
radial and an azimuthal part. These results are interpreted in terms
of a force-free magnetic field model, as well as in terms of a dipole
whose axis is inclined to the vertical.

---------------------------------------------------------
Title: Structure and Polarization of Active Region Microwave Emission
Authors: Kundu, M. R.; Alissandrakis, C. E.
1984SoPh...94..249K Altcode:
We present observations of active region radio emission at 6.16 cm
wavelength, obtained with an angular resolution of 3″ by 10″
arc using the Westerbork Synthesis Radio Telescope (WSRT) during the
action interval May 20-27, 1980 of the Solar Maximum Year (SMY). We
present maps in both total intensity (I) and circular polarization (V)
of three regions (Hale numbers 16850, 16863, and 16864) and provide a
detailed comparison of these maps with on- and off-band Hα pictures
and with magnetograms. The strongest sources were associated with
neutral lines and soft X-ray arcades. We present evidence that these
neutral lines were characterized by having their two opposite polarities
close to each other, implying a high magnetic field gradient, and by
their association with arch filament systems. The sunspot associated
radio sources had a relatively simple structure in region 16850;
however for the large spots of regions 16864 and 16863 the emission
had a patchy appearance with a tendency of the peaks to lie over the
penumbra. In the V maps we observed for the first time two `islands',
polarized in the sense of the ordinary mode, which were located inside
the sunspot associated sources and were associated with intrusions
of opposite polarity field into the penumbra. These structures can be
accounted for if the electron temperature along the line of sight is
not a monotonically increasing function of height, but has a maximum
near the second harmonic level. Finally we give a detailed analysis of
observations of the inversion of the sense of circular polarization in
region 16863. We find that the large scale structure of the magnetic
field can be approximated by a dipole with its axis inclined by 11°
with respect to the photosphere and with a dipole moment of about
2 × 1031 cgs units; the depolarization line is located
at a height of 0.16-0.19 R⊙ above the dipole, where the estimated
intensity of the magnetic field is 10-20 G.

---------------------------------------------------------
Title: Simultaneous Observations of Solar Flares at 6 and 20 cm
Wavelengths Using the VLA
Authors: Melozzi, M.; Shevgaonkar, R. K.; Kundu, M. R.
1984BAAS...16.1003M Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Microbursts at Meter-Decameter Wavelengths
Authors: Kundu, M. R.; Gergely, T. E.; Loiacono, R.
1984BAAS...16R.892K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Temporal and Spatial Variations of Solar Coronal Bright Points
Observed with the VLA
Authors: Habbal, S. R.; Cowell, A.; Ronan, R.; Withbroe, G. L.;
Shevgaonkar, R.; Kundu, M.
1984BAAS...16..929H Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Microwave and Hard X-ray Imaging of a Solar Limb Flare
Authors: Schmahl, E. J.; Kundu, M. R.
1984BAAS...16.1002S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Coronal extension of flaring region magnetic fields inferred
from high-resolution microwave and type III burst observations
Authors: Lantos, P.; Pick, M.; Kundu, M. R.
1984ApJ...283L..71L Altcode:
Observations of three solar radio bursts, obtained with the Very Large
Array of the National Radio Astronomy Observatory at 6 cm wavelength,
have been combined with meter observations from the Mark III Nancay
Radioheliograph. There is a good correlation between solar activity
observed at the two wavelength domains. A small change by about 10
sec in the centimetric burst location corresponds to a large change,
by about 0.5 solar radius, in the related metric type III burst
location. This indicates discrete injection/acceleration regions and
the presence of very divergent magnetic fields. The bursts come from
two distinct active regions. With two-dimensional spatial resolution,
it is shown that, in this sample, each active region possesses a coronal
extension that is separated from that of the neighboring active region.

---------------------------------------------------------
Title: Three-dimensional structures of two solar active regions from
VLA observations at 2, 6, and 20 centimeter wavelengths
Authors: Shevgaonkar, R. K.; Kundu, M. R.
1984ApJ...283..413S Altcode:
Three-dimensional structures of two active region groups are
determined from observations with the Very Large Array (VLA) at 2, 6,
and 20 cm. One of the groups exhibits a single magnetic loop of length
approximately 10 to the 10th cm. The 2 cm radiation is mostly thermal
bremsstrahlung and originates from the footprints of the loop. The
6 and 20 cm radiation is dominated by low-harmonic gyroresonance
radiation and originates from the upper portion of the legs or the top
of the loop. The loop broadens toward the apex. The top of the loop
is not found to be the hottest point, but two temperature maxima on
either side of the loop apex are observed, which is consistent with
the model proposed for long loops. From 2 and 6 cm observations it
can be concluded that the electron density and temperature cannot be
uniform in a plane perpendicular to the axis of the loop; the density
should decrease away from the axis of the loop.

---------------------------------------------------------
Title: Recent advances in solar radio physics
Authors: Kundu, M. R.
1984InEPS..93..201K Altcode:
High spatial resolution microwave observations of solar active regions,
coronal loops and flares are reviewed. Observations of preflare active
regions are presented; in particular the interpretations of reversal of
polarization at the flare site and the role of newly emerging flux in
triggering the onset of flares are considered. The spatial locations
of microwave burst emitting regions are discussed; loops or arcades
of loops appear to be the sites of flare energy release in microwave
bursts. Direct observational evidence of magnetic reconnection as
the primary cause of acceleration of electrons in microwave bursts
is provided.

---------------------------------------------------------
Title: Sharp Edges in Solar Microwave Spectra - Neutral Current
Sheets or Cyclotron Lines
Authors: Schmahl, E. J.; Shevgaonkar, R. K.; Kundu, M. R.; McConnell,
D.
1984SoPh...93..305S Altcode:
We have mapped two solar active regions using the VLA at three closely
spaced frequencies (4496, 4716, and 4996 MHz) in an attempt to determine
the origin of the steep spectra (indexγ ≈ −5 to −8) sometimes
observed with large single telescopes. One of the regions observed
indeed shows an anomalously large slope (γ ≈ −6) compared to the
usual (γ ≈ −2 to −2.5). The other region shows a similar slope
(γ ≈ −5) but with a larger range of statistical error. Two possible
explanations for such steep edges in solar spectra are (1) transmission
effects of neutral current sheets, and (2) the appearance of cyclotron
lines. The internal evidence of the microwave maps and simultaneous
optical observations favor an explanation in terms of cyclotron lines.

---------------------------------------------------------
Title: The Radio Sky from Clark Lake
Authors: Kundu, M. R.
1984S&T....67..519K Altcode:
The Clark Lake Radio Observatory's telescope is currently the most
sophisticated instrument for low frequency astronomical radio
research. Using this instrument, astronomers have identified an
association of bright X-ray point flares on the sun with the brief,
intense radio bursts, classified as 'Type III', that are generated by
the interaction of electron streams with ambient coronal plasma. Other
solar observations at Clark Lake are of coronal transient shock waves
and plasma cloud distributions. Radio galaxies such as 3C 129 are also
frequent objects of study.

---------------------------------------------------------
Title: The spatial distribution of 6 centimeter gyroresonance emission
from a flaring X-ray loop
Authors: Kahler, S. W.; Webb, D. F.; Davis, J. M.; Kundu, M. R.
1984SoPh...92..271K Altcode:
We compare simultaneous high resolution soft X-ray and 6 cm images
of the decay phase of an M3 X-ray flare in Hale Region 16413. The
photographic X-ray images were obtained on an AS &amp; E sounding
rocket flown 7 November, 1979, and the 6 cm observations were made with
the VLA. The X-ray images were converted to arrays of line-of-sight
emission integrals and average temperature throughout the region. The
X-ray flare structure consisted of a large loop system of length ∼
1.3 arc min and average temperature ∼8 × 106 K. The peak
6 cm emission appeared to come from a region below the X-ray loop. The
predicted 6 cm flux due to thermal bremsstrahlung calculated on the
basis of the X-ray parameters along the loop was about an order of
magnitude less than observed. We model the loop geometry to examine the
expected gyroresonance absorption along the loop. We find that thermal
gyroresonance emission requiring rather large azimuthal or radial field
components, or nonthermal gyrosynchrotron emission involving continual
acceleration of electrons can explain the observations. However,
we cannot choose between these possibilities because of our poor
knowledge of the loop magnetic field.

---------------------------------------------------------
Title: VLA observations of fine structures in a solar active region
at 6 centimeter wavelength.
Authors: McConnell, D.; Kundu, M. R.
1984ApJ...279..421M Altcode:
A complex solar active region at 6 cm has been observed with the
VLA. Radio images of the region have been constructed and compared
with simultaneous optical data from the region. It is found that all
radio sources are associated with either sunspots or regions of the
corona where strong transverse magnetic fields are likely, that the
transverse field sources are brighter than the sunspot sources, and
that some of the sunspot sources have a polarized ring structure. The
observations are interpreted in terms of thermal gyroresonance emission,
with the radiation from the transverse field sources being at the
third harmonic of the gyrofrequency and predominantly at the second
harmonic from the sunspot sources.

---------------------------------------------------------
Title: Sharp Edges in Solar Microwave Spectra: Neutral Current Sheets
or Cyclotron Lines?
Authors: Schmahl, E. J.; Shevgaonkar, R. K.; Kundu, M. R.
1984BAAS...16..534S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Simultaneous Observation of Hard X-ray and Microwave Burst
Sources in a Limb Flare
Authors: Kundu, M. R.; Takakura, T.
1984BAAS...16..524K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Microwave, soft and hard X-ray imaging observations of two
solar flares
Authors: Kundu, M. R.; Machado, M. E.; Erskine, F. T.; Rovira, M. G.;
Schmahl, E. J.
1984A&A...132..241K Altcode:
A set of microwave and hard X-ray observations of two flares observed
simultaneously with the Very Large Array (VLA) and the Solar Maximum
Mission Hard X-ray Imaging Spectrometer (SMM-HXIS) are presented. The
LVA was used at 6 cm to map the slowly varying and burst components
in three neighboring solar active regions (Boulder Nos. 2522, 2530,
and 2519) from approximately 14:00 UT until 01:00 UT on June 24-25,
1980. Six microwave bursts less than 30 sfu were observed, and for
the strongest of these, two-dimensional 'snapshot' (10 s) maps with
spatial resolution of 5 in. were synthesized. HXIS data show clear
interconnections between regions 2522 and 2530. The X-ray observations
present a global picture of flaring activity, while the VLA data show
the complexity of the small magnetic structures associated with the
impulsive phase phenomena. It is seen that energy release did not
occur in a single isolated magnetic structure, but over a large area
of intermingled loop structures.

---------------------------------------------------------
Title: The Microwave Structure of Hot Coronal Loops
Authors: Holman, G. D.; Kundu, M. R.; Yang, C.
1984BAAS...16R.534H Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Simultaneous Dual Wavelength Observations of an Impulsive
Microwave Burst Using the VLA
Authors: Shevgaonkar, R. K.; Kundu, M. R.
1984BAAS...16Q.524S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Interpretation of microwave active region structures using
SMM soft X-ray observations
Authors: Strong, K. T.; Alissandrakis, C. E.; Kundu, M. R.
1984ApJ...277..865S Altcode:
The purpose of this paper is to investigate the roles played
by the geometrical effect of gyroresonance absorption and by the
low-temperature (&lt;106K) flux tubes above sunspot regions
with microwave ring structures, by combining WSRT 6 cm observations
with the X-ray observations made with the X-ray Polychromator on the
SMM satellite. Some features associated with Hale regions 16863 and
16864 are analyzed from observations on 1980 May 25 and 26 combined
with model computations of the radio emission. The nature of a cool and
compact coronal feature seen in soft X-rays, which corresponded to some
interesting microwave and magnetic features, is also examined. Finally,
the origin of the X-ray and radio emission associated with neutral
lines of the magnetic field is considered.

---------------------------------------------------------
Title: A study of the evolution of energetic electrons in a solar
flare
Authors: Holman, G. D.; Kundu, M. R.; Dennis, B. R.
1984ApJ...276..761H Altcode:
A study of the impulsive microwave and hard X-ray emissions from the
June 25, 1980 solar flare notes that its light curves are consistent
with the flaring of the regions in unison rather than sequentially,
or in an uncorrelated manner. The maximum 6-cm flux, which occurs 1.4
min after the maximum in the integrated 28-498 keV X-ray emission,
and coincides with a secondary peak in the X-ray light curve, is
explained by the observation that the X-ray spectrum, and hence that
of the electrons, is harder at the time of the 6-cm flux maximum. The
results show a clear correlation between the X-ray flux greater than
100 keV and the microwave flux. The steep, low-frequency spectrum at
the time of the 6-cm maximum indicates that the emission at this time
is nonthermal. The spectral behavior of the hard X-ray emission is
not consistent with the betatron acceleration mechanism.

---------------------------------------------------------
Title: A multiple type-II burst associated with a coronal transient
and its MHD simulation
Authors: Gergely, T. E.; Kundu, M. R.; Wu, S. T.; Dryer, M.; Smith,
Z.; Stewart, R. T.
1984AdSpR...4g.283G Altcode: 1984AdSpR...4..283G
A large coronal transient took place on 8 May 1981. The transient
was related to an M7.7/2B flare and was associated with at least two
coronal type II bursts. The velocities of the type II bursts were
in the range 1100-1800 kms-1, in excess of the transient
velocity of 500-1000 kms-1. Two dimensional positions of
the type II radio sources are available from both the Clark Lake and
the Culgoora Radio Observatories. We carry out two dimensional MHD
simulations of the event, taking into account the observed velocity,
position, and size of the type II bursts. We simulate the multiple
shocks observed during the event and their interaction, and discuss
some results of the simulation.

---------------------------------------------------------
Title: Coronal transients and their interplanetary effects.
Authors: Hundhausen, A. J.; Burlaga, L. F.; Feldman, W. C.; Gosling,
J. T.; Hildner, E.; House, L. L.; Howard, R. A.; Krieger, A. S.;
Kundu, M. R.; Low, B. C.; Sheeley, N. R., Jr.; Steinolfson, R. S.;
Stewart, R. T.; Stone, R. G.; Wu, S. T.
1984NASRP1120....6H Altcode:
Contents: 1. Introduction. 2. Background material: Ancient history -
solar flares and geomagnetic storms. Modern history - interplanetary
shock waves. Coronal transients or mass ejections. 3. The present:
Theoretical models. New observations of coronal mass ejections. 4. The
future: Solar origins. Interplanetary effects.

---------------------------------------------------------
Title: Forty Years of Solar Radio Astronomy - a History of Major
Advances
Authors: Kundu, Mukul R.
1984sdra.conf..247K Altcode: 1983sdra.conf..247K
No abstract at ADS

---------------------------------------------------------
Title: Observations of solar radio bursts from meter to kilometer
wavelengths
Authors: Kundu, M. R.; Stone, R. G.
1984AdSpR...4g.261K Altcode: 1984AdSpR...4..261K
Using the Clark Lake Radioheliograph data we present direct
evidence that type III electron streams propagate in dense coronal
streamers. We also present imaging observations of meter-decameter
microbursts, which appear to be similar to those observed in hard
X-rays. At meter-decameter wavelengths, these microbursts appear to
be due to plasma radiation. From observations made with ISSE-3, we
discuss the characteristics of hectometer and kilometer wavelength
radio bursts. In particular, we show that from studies of type III
storms that the exciter electrons propagate along spiral structures,
where the density is enhanced and that there is an acceleration of
the solar wind. We discuss type II bursts at kilometer wavelengths,
compare them with meter type II bursts and discuss their association
with interplanetary shocks. We show that the interaction between type
III electron streams and shocks at kilometer wavelengths can provide
information on the interplanetary shock geometry. Finally, we discuss
the possibility that some shock associated (SA) events may be emissions
caused by electrons accelerated lower in the atmosphere rather than
high in the corona in type II shocks. Recent advances in solar
research have resulted from new work on plasma radiation theory, new
observations of active regions and flares across the electromagnetic
spectrum and the availability of spacecraft in situ measurements of
solar ejecta. In this paper, we review some results obtained with the
Clark Lake multifrequency radioheliograph at meter-decameter wavelengths
and from satellite multifrequency directive observations at hectometer
and kilometer wavelengths. We present evidence that type III electrons
propagate in dense coronal streamers, and that frequently observed
microbursts (presumably of type III) at meter-decameter wavelengths
are due to plasma radiation. We discuss observations of hectometer and
kilometer type III radio storms which reveal information about active
region structures, interplanetary magnetic field configuration, and
solar wind acceleration. We also discuss kilometer type II bursts,
interactions between type III electrons and interplanetary shocks,
and present some new results on shock associated (SA) events.

---------------------------------------------------------
Title: Relative positions of microwave and hard X-ray burst sources
Authors: Kundu, M. R.
1984AdSpR...4g.157K Altcode: 1984AdSpR...4Q.157K
Simultaneous microwave and hard X-ray imaging observations of 12 bursts
show that it is difficult to discern a general pattern between microwave
and hard X-ray burst locations. In general, the microwave source is
displaced from the hard X-ray source. The commonly believed behavior
of the microwave source being located near the top and hard X-ray
source near the footpoints of a loop appears to be true in some cases
but not all. If the burst source is simple, both may be located near
loop tops. Sometimes when the hard X-ray source has two components,
one weak and one strong, the microwave source is not located over
a neutral line (loop top) but close to a sunspot where the magnetic
field is strongest. It appears that more than one loop or arcade may
sometimes be involved in the microwave and hard X-ray emission. This
is particularly true when several interacting loops trigger the onset
of a flare.

---------------------------------------------------------
Title: Solar Terrestrial Physics
Authors: Kundu, M. R.; Biswas, B.; Reddy, B. M.; Ramadurai, S.
1984stp..conf.....K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Recent advances in solar radio physics.
Authors: Kundu, M. R.
1984PIASE..93..201K Altcode:
The author reviews high spatial resolution microwave observations of
solar active regions, coronal loops and flares. Observations of preflare
active regions are presented; in particular the author discusses the
interpretations of reversal of polarization at the flare site and
the role of newly emerging flux in triggering the onset of flares. He
discusses the spatial locations of microwave burst emitting regions;
loops or arcades of loops appear to be the sites of flare energy
release in microwave bursts.

---------------------------------------------------------
Title: Millisecond time structures in hard x-ray bursts from Sun
Authors: Krishan, V.; Kundu, M. R.
1984stp..conf..147K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Radio and Visible Light Observations of a Coronal Arcade
Transient
Authors: Gergely, T. E.; Kundu, M. R.; Erksine, F. T., III; Sawyer, C.;
Wagner, W. J.; Illing, R.; House, L. L.; McCabe, M. K.; Stewart, R. T.;
Nelson, G. J.; Koomen, M. J.; Michels, D.; Howard, R.; Sheeley, N.
1984SoPh...90..161G Altcode:
We discuss simultaneous visible-light and radio observations of
a coronal transient that occurred on 9 April, 1980. Visible-light
observations of the transient and the associated erupting prominence
were available from the Coronagraph/Polarimeter carried aboard SMM,
the P78-1 coronagraph, and from the Haleakala Observatory. Radio
observations of the related type III-II-IV bursts were available from
the Clark Lake and Culgoora Observatories. The transient was extremely
complex; we suggest that an entire coronal arcade rather than just a
single loop participated in the event. Type III burst sources observed
at the beginning of the event were located along a nearby streamer,
which was not disrupted, but was displaced by the outmoving loops. The
type II burst showed large tangential motion, but unlike such sources
usually do, it had no related herringbone structure. A moving type
IV burst source can be associated with the most dense feature of the
white-light transient.

---------------------------------------------------------
Title: Association Between X-Ray and Meter - Decameter Bursts (stip
Interval Viii)
Authors: Sawant, H. S.; Kane, S. R.; Kundu, M. R.; Gergely, T. E.
1984sii..conf..113S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Hydrologic appraisal of rivers plan-form at confluence zone -
A case study using Landsat MSS data
Authors: Shevgaonkar, R. K.; Kundu, M. R.
1984AdSpR...4g.247S Altcode: 1984AdSpR...4..247S
In river systems confluences and bifurcations are typical features
whose effects are largely dependent on the specific characteristics
of the rivers involved. The study makes an attempt to analyse the
planform configuration at the confluence zone of the Wainganga and
Khobragadi rivers in the central part of India. The data used are the
Landsat MSS CCT data of date 17.12.1972 for scene 154-046 and black
and white aerial photographs of November, 1969. Supervised method
of classification using maximum likelihood classification method is
employed. The study confirms that the discharge and sediment transport
in the individual rivers constitute the dominating factors in the
changes of planform geometry at a confluence. The usefulness of the
Landsat MSS data and digital analysis techniques. for generating the
necessary data inputs for the study is also validated.

---------------------------------------------------------
Title: High spatial resolution microwave observations of Solar Flares
Authors: Kundu, M. R.
1984stp..conf..159K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: VLA observations of "compact" sources in CTB 80.
Authors: Velusamy, T.; Kundu, M. R.
1983JApA....4..253V Altcode:
High resolution (3 arcsec-4 arcsec) maps of three compact sources in
CTB 80, observed with the Very Large Array at 6 and 20 cm wavelengths
are presented. The central core consists of a limb-brightened shell
(of diameter 30 arcsec) superimposed on a diffuse emission of size
75 arcsec x 45 arcsec. The compact sources 1949+324 and 1952+332
located near the tips of the southwest and northeast ridges are rather
remarkable and possibilities for these to be fragments ejected by the
SN are examined. 1949+324 is fully resolved by the 4 arcsec beam and
shows structure with multiple components oriented perpendicular to
the ridge. 1950+326 is a background radio source.

---------------------------------------------------------
Title: Optical, microwave and UV imagery of a solar flare.
Authors: Gaizauskas, V.; Kundu, M. R.; Schmahl, E. J.; Shine, R. A.;
Woodgate, B. E.
1983JRASC..77..261G Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Thermal Phase of Flares: A New Diagnostic Using Microwaves
&amp;GOES X-rays
Authors: Schmahl, E. J.; Kundu, M. R.; Erskine, F. E.
1983BAAS...15..972S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Three Dimensional Structures of Solar Active Regions and
Flare Buildup from VLA Observations
Authors: Kundu, M. R.; Shevgaonkar, R. K.
1983BAAS...15..972K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Spatial Characteristics of Microwave Bursts
Authors: Kundu, M. R.
1983SoPh...86..205K Altcode:
The spatial characteristics of microwave bursts are discussed
in relation to impulsive and post-burst phases. The existence of
two components - a gradual and another spiky - in the impulsive
phase is discussed from the WSRT high time and spatial resolution
observations. Using the WSRT data, evidence is presented for homologous
flares at 6 cm, from the similarity of their spatial structure and
their temporal evolution. Preflare changes in microwave active regions
are presented and their interpretations in terms of newly emerging flux
at the flare site are discussed. High spatial resolution observations
of the structure of microwave flaring loops and their interpretation
in terms of arcades of loops as the sites of primary energy release
are presented. Theoretical interpretation of the confinement of
microwave producing energetic electrons in the coronal part of loops is
discussed. The relative timing of the peaks of impulsive hard X-ray and
microwave burst is discussed. Possible diagnostics of impulsive phase
onsets from cm-λ polarization data are presented, and the role of the
emergence of new flux and of the current sheet formed between closed
loops in producing impulsive energy release at centimeter wavelengrths
are analyzed.

---------------------------------------------------------
Title: X-Ray and Microwave Observations of Active Regions
Authors: Webb, D. F.; Davis, J. M.; Kundu, M. R.; Velusamy, T.
1983SoPh...85..267W Altcode:
We compare coordinated, high spatial resolution (2-3 arc sec)
observations at 6 cm and in soft X-rays with photospheric magnetograms
and optical filtergrams of two active regions. The correspondence
of the brightest centimetric components in these regions with
coronal loops, sunspots and pores, chromospheric structures and the
photospheric magnetic field was determined. Our principal results are:
The association between the microwave components and coronal X-ray and
photospheric magnetic field structures is complex; in general X-ray
emission was not associated with the microwave components. A majority of
the components were not associated with sunspots, although the brightest
(Tb ≥ 4 × 106 K) components overlay regions
of strong photospheric field or high field gradients. Several of the
components coincided with the apparent bases of shorter coronal loops
and 4 with the tops of X-ray loops.

---------------------------------------------------------
Title: Direct evidence of type III electron streams propagating in
coronal streamers
Authors: Kundu, M. R.; Gergely, T. E.; Turner, P. J.; Howard, R. A.
1983ApJ...269L..67K Altcode:
Using two-dimensional solar images at 73.8 MHz, obtained with the
Clark Lake Multifrequency Radioheliograph, the authors present direct
evidence that type III electron streams propagate in dense coronal
streamers. This evidence is substantiated by the excellent coincidence
that is found in position angle between the densest parts of streamers
observed with the Solwind coronagraph on the P78-1 satellite and the
maximum brightness of type III burst sources.

---------------------------------------------------------
Title: VLA observations of a solar active region and coronal loops
Authors: McConnell, D.; Kundu, M. R.
1983ApJ...269..698M Altcode:
In May 1981, observations of a solar active region at 6 cm and 20 cm
were conducted with the aid of a Very Large Array (VLA). It was found
that the 6 cm emission was associated with sunspots and transverse
magnetic fields between spots. The 20 cm emission came from elongated
sources connecting regions of opposite magnetic polarity. The sources
of the emission at 20 cm could be identified as coronal loops. A model
for hydrostatic loops proposed by Rosner et al. (1978) was employed to
determine a likely mechanism for the emission at 20 cm. It was found
that a two-component model of bremsstrahlung emission from the feet
and gyroresonance emission from the top of the loops can satisfactorily
explain the observations.

---------------------------------------------------------
Title: Network to Cell Contrast at Microwaves
Authors: Chiuderi Drago, F.; Kundu, M. R.; Schmahl, E. J.
1983SoPh...85..237C Altcode:
Using different models deduced from EUV lines for the cell and
for various network components, the corresponding radio brightness
temperature in the millimetric and centimetric range of wavelengths
are computed. The contrast C = [Tb (network)]/[Tb
(cell)] and the difference ΔT = Tb (network) - Tb
(cell) are compared with the few available observations of the quiet
Sun inhomogeneities performed with sufficient angular resolution. The
comparison shows a satisfactory agreement with most of the observations.

---------------------------------------------------------
Title: A coronal transient associated with a high-speed type II burst
Authors: Gergely, T. E.; Kundu, M. R.; Hildner, E.
1983ApJ...268..403G Altcode:
Several characteristics of a white light transient observed by the ATM
Coronagraph experiment aboard Skylab are discussed. The transient was
associated with a very high speed type II radio burst. The observed
plane of the sky speed of the burst was 4900 km/s, 6-7 times higher
than the speed of the transient itself. Based on the relative speeds
of the transient and the radio burst, it is argued that the type II
disturbance must have propagated in a still undisturbed corona, at an
approximately 35-deg angle to the preexisting streamer and along an
essentially open field configuration. The electron density gradients
derived from the radio and the white light observations are compared,
and it is shown that they are in agreement within the limits of the
observations. The assumption that the type II was a weak MHD shock
leads to large values for the coronal magnetic field. The possibility
that the type II radition originated in a strong shock, with a magnetic
Mach number greater than 2, is considered.

---------------------------------------------------------
Title: Microwave, Soft and Hard X-ray Imaging Observations of Two
Solar Flares
Authors: Kundu, M. R.; Machado, M.; Erskine, F. T.; Rovira, M. G.;
Schmahl, E. J.
1983BAAS...15..714K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: First Results from the Clark-Lake Multifrequency
Radioheliograph
Authors: Kundu, M. R.; Erickson, W. C.; Gergely, T. E.; Mahoney,
M. J.; Turner, P. J.
1983SoPh...83..385K Altcode:
We give a brief description of the Clark Lake Multifrequency
Radioheliograph which is presently used for solar research in the
frequency range 20-125 MHz. We present two-dimensional images of the
Sun's corona at several frequencies within this range, obtained with
time resolution as good as 1.28 s. The shape of the Sun's outer corona
as observed at meter-decameter wavelengths appears to change in time
periods as short as a few seconds.

---------------------------------------------------------
Title: Decameter Wavelength Observations of the Quiet Sun
Authors: Gergely, T. E.; Gross, B. D.; Kundu, M. R.
1983BAAS...15Q.716G Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Ground based solar radio observations during solar maximum
mission
Authors: Kundu, M. R.
1983STIN...8320887K Altcode:
The Very Large Array (VLA) and the Westerbork Synthesis Radio Telescope
(WSRT) were used for making aperture synthesis maps of solar active
and flaring regions. Observations of the Flare buildup in the form
of increased intensity and polarization were made. Ring structure
associated with sunspots were interpreted as due to the existence of
cool material above the spot. Model computations were performed to
explain the total intensity and polarization structures of a continuous
set of active region maps.

---------------------------------------------------------
Title: Thermal and Nonthermal Phenomena in Solar Flare Loops at
20-CM Wavelength and in X-Rays
Authors: Schmahl, E. J.; Kundu, M. R.; Landecker, P. B.; McKenzie,
D. L.
1983SoPh...83....3S Altcode: 1983STIN...8424522S
We present X-ray images from the P78-1 satellite for a long-lasting
burst at 20 cm wavelength mapped with the Very Large Array on 19 May,
1979 by Velusamy and Kundu (1981). The decimeter wave observations
were originally interpreted in terms of two models, one invoking
thermal electrons radiating at low harmonics of the gyrofrequency,
and the other invoking mildly relativistic electrons emitting
gyrosynchrotron radiation. If indeed the 20 cm source is thermal,
it should also be visible in soft X-rays, while if it is nonthermal,
the soft X-ray emission should be weak or spatially or temporally
distinct from the 20 cm burst. We find that only one of the three 20
cm sources was approximately co-spatial with the soft X-ray source,
and that it was only partially thermal. The 20 cm burst is therefore
primarily decimeter type IV emission from mildly relativistic electrons
of the post-flare phase. The long lifetime (≳ 2h) and
smooth temporal variation of the burst belie its nonthermal nature
and suggest continuous acceleration as well as long term storage of
energetic electrons.

---------------------------------------------------------
Title: Observations of H-alpha and microwave brightening caused by
a distant solar flare
Authors: Kundu, M. R.; Rust, D. M.; Bobrowsky, M.
1983ApJ...265.1084K Altcode:
Three subflares were observed at 6 cm λ and at Hα (6563 Å) with
the VLA and the Solar Observing Optical Network high resolution
telescopes. Synthesized maps with integration times of 10 and 30 s
show that most of the 6 cm burst emission originated in ≡10arcsec
- 15arcsec features coincident with or adjacent to Hα flare
kernels. During the onset of one of the subflares 6 cm emission was
discovered in a loop stretching &gt;105 km from the primary
flare site; this emission was associated with faint Hα flarelike
brightness at the remote footpoint of the loop. Assuming that the
energy for the distant brightening originated at the primary flare
site, it is found that ≡4 × 1024 ergs s-1
propagated along the connecting magnetic loop at a velocity of ≥
6000 km s-1. Various possible mechanisms for the distant
activation are discussed.

---------------------------------------------------------
Title: Magnetic development of flaring regions at centimeter
wavelengths
Authors: Kundu, M. R.
1983ASSL..102..335K Altcode: 1983ards.proc..335K; 1983IAUCo..71..335K
A hard X-ray associated impulsive 6 cm burst observed by Kundu et
al. (1981) on June 25, 1980, is considered along with several preflare
6 cm maps related to this event. The maps show that the region is very
complex and consists of numerous components. Many of these components
are bipolar. The components have brightness temperatures in the range
from 6,000,000 to 9,000,000 K during the hour before the flare. Some of
the observed phenomena might imply the emergence of a flux of reverse
polarity at coronal levels. It is believed that the reverse polarity
may be caused by the expansion of a preexisting flux tube in which
twisting increases its coronal magnetic field.

---------------------------------------------------------
Title: REVIEW ARTICLE: Advances in solar radio astronomy
Authors: Kundu, M. R.
1982RPPh...45.1435K Altcode:
The status of the observations and interpretations of the sun's radio
emission covering the entire radio spectrum from millimeter wavelengths
to hectometer and kilometer wavelengths is reviewed. Emphasis is
given to the progress made in solar radio physics as a result
of recent advances in plasma and radiation theory. It is noted
that the capability now exists of observing the sun with a spatial
resolution of approximately a second of arc and a temporal resolution
of about a millisecond at centimeter wavelengths and of obtaining
fast multifrequency two-dimensional pictures of the sun at meter
and decameter wavelengths. A summary is given of the properties of
nonflaring active regions at millimeter, centimeter, and meter-decameter
wavelengths. The properties of centimeter wave bursts are discussed
in connection with the high spatial resolution observations. The
observations of the preflare build-up of an active region are
reviewed. High spatial resolution observations (a few seconds of arc
to approximately 1 arcsec) are discussed, with particular attention
given to the one- and two-dimensional maps of centimeter-wavelength
burst sources.

---------------------------------------------------------
Title: Solar microwave bursts — A review
Authors: Kundu, M. R.; Vlahos, L.
1982SSRv...32..405K Altcode:
We review the observational and theoretical results on the physics of
microwave bursts that occur in the solar atmosphere. We particularly
emphasize the advances made in burst physics over the last few
years with the great improvement in spatial and time resolution
especially with instruments like the NRAO three element interferometer,
Westerbork Synthesis Radio Telescope and more recently the Very Large
Array (VLA). We review the observations on pre-flare build-up of an
active region at centimeter wavelengths. In particular we discuss
the observations that in addition to the active region undergoing
brightness and polarization changes on time scales of the order
of an hour before a flare, there can be a change of the sense of
polarization of a component of the relevant active region situated
at the same location as the flare, implying the emergence of a flux
of reverse polarity at coronal levels. The intensity distribution
of cm-λ bursts is similar to that of soft X-ray and hard X-ray
bursts. Indeed, it appears that the flaring behavior of the Sun at cm
wavelengths is similar to that of some other cosmic transients such
as flare stars and X-ray bursters. We discuss three distinct phases
in the evolution of cm bursts, namely, impulsive phase, post-burst
phase, and gradual rise and fall. The radiation mechanism for the
impulsive phase of the microwave burst is gyrosynchrotron emission
from mildly relativistic electrons that are accelerated near the
energy release site and spiral in the strong magnetic field in the
low corona. The details of the velocity distribution function of the
energetic electrons and its time evolution are not known. We review
the spectral characteristics for two kinds of velocity distribution,
e.g., Maxwellian and Maxwellian with a power law tail for the energetic
electrons. In the post-burst phase the energetic electrons are gradually
thermalized. The thermal plasma released in the energy release region
as well as the expanded parts of the overheated upper chromosphere
may alter the emission mechanism. Thus, in the post-burst phase,
depending on the average density and temperature of the thermal plasma,
the emission mechanism may change from gyrosynchrotron to collisional
bremsstrahlung from a thermal plasma. The gradual rise and fall (GFR)
burst represents the heating of a flare plasma to temperatures of the
order of 106 K, in association with a flare or an X-ray
transient following a filament disruption. We discuss the flux density
spectra of centimeter bursts. The great majority of the bursts have a
single spectral maximum, commonly around 6 cm-λ The U-shaped signature
sometimes found in cm-dcm burst spectrum of large bursts is believed
to a be a reflection of only the fact that there are two different
sources of burst radiation, one for cm-λ and the other for dcm-λ,
with different electron energy distributions and different magnetic
fields. Observations of fine structures with temporal resolutionof 10
100 ms in the intensity profiles of cm-λ bursts are described. The
existence of such fine time structures imply brightness temperatures
in burst sources of order 1015 K; their interpretation
in terms of gyrosynchrotron measuring or the coherent interaction
of upper hybrid waves excited by percipitating electron beams in
a flaring loop is discussed. High spatial resolution observations
(a few seconds of arc to ∼ 1″ arc) are discussed, with special
reference to the one- and two-dimensional maps of cm burst sources. The
dominance of one sense of circular polarization in some weak 6 cm
bursts and its interpretation in terms of energetic electrons confined
in an asymmetric magnetic loop is discussed. Two-dimensional snapshot
maps obtained with the VLA show that multi-peak impulsive 6 cm burst
phase radiation originates from several arcades of loops and that the
burst source often occupies a substantial portion of the flaring loop,
and is not confined strictly to the top of the loop. This phenomenon
is interpreted in terms of the trapping of energetic electrons due
to anomalous doppler resonance instability and the characteristic
scale length of the magnetic field variation along the loop. The VLA
observations also indicate that the onset of the impulsive phase of a
6 cm burst can be associated with the appearance of a new system of
loops. The presence of two loop systems with opposite polarities or
a quadrupole field configuration is reminiscent of flare models in
which a current sheet develops in the interface between two closed
loops. We provide an extensive review of the emission and absorption
processes in thermal and non-thermal velocity distributions. Unlike
the thermal plasma where absorption and emission are inter-related
through Kirchoff's law, the radiation emitted from a small population
of non-thermal electrons can be reabsorbed from the same electrons
(self-absorption) or from the background (thermal) electrons through
gyro-resonance absorption, and free-free absorption. We also suggest
that the non-thermal electrons can be unstable and these instabilities
can be the source of very high brightness temperature, fine structure
(∼ 10 ms) pulsations. Finally in the last part of this review we
present several microwave burst models-the magnetic trap model, the
two-component model, thermal model and the flaring loop model and give
a critical discussion of the strength and weakness of these models.

---------------------------------------------------------
Title: Active region magnetic fields inferred from simultaneous VLA
microwave maps, X-ray spectroheliograms, and magnetograms
Authors: Schmahl, E. J.; Kundu, M. R.; Strong, K. T.; Bentley, R. D.;
Smith, J. B., Jr.; Krall, K. R.
1982SoPh...80..233S Altcode:
A series of VLA maps at 6 cm wavelength have been generated from
observations of a solar active region (NOAA 2363) on 29 and 30 March,
1980. During the same period, X-ray spectroheliograms were acquired
for this region in the lines of O VIII, Ne IX, Mg XI, Si XIII, S
XV, and Fe XXV, with X-rayn Polychromator (XRP) aboard the Solar
Maximum Mission (SMM). Intervals of relative quiescence (i.e.,
when X-ray flares and centimeter wave bursts were not evident)
were selected for microwave mapping. The resulting VLA maps have
spatial resolution of 4″ × 4″, and generally show two or more
sources whose slowly evolving substructures have spatial scales
of 10″-30″. These maps were co-registered with Hα photographs
(courtesy of AF/AWS SOON, Holloman and Ramey AFB) to an accuracy of ±
8″. Similarly, the X-ray spectroheliograms have been co-registered
with white light photographs to about the same accuracy. Magnetograms
from KPNO and MSFC have also been co-aligned, and the magnetic X-ray,
and microwave features compared. In general we have found that (a)
the peaks of X-ray and 6 cm emission do not coincide, although (b) the
sources in the two wavelength domains tend to overlap. These facts in
themselves are evidence for the existence of opacity mechanisms other
than thermal bremsstrahlung. In order to quantify this assertion, we
have computed differential emission measures to derive densities and
temperatures. Using these and calculated force-free magnetic fields from
Kitt Peak magnetograms, we present an assessment of the mechanism of
gyroresonance absorption at low harmonics of the electron gyrofrequency
as the source of opacity responsible for the microwave features. We
conclude that large-scale currents must be present in the active region
loops to account for the bright 6 cm sources far from sunspots.

---------------------------------------------------------
Title: Correspondence Between 6 cm and Optical Images of a Solar
Active Region
Authors: McConnell, D.; Schmahl, E. J.; Kundu, M. R.
1982BAAS...14..921M Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Upflows Immediately Prior to the Impulsive Phase of Solar
Flares
Authors: Woodgate, B. E.; Shine, R. A.; Schmahl, E. J.; Kundu, M.;
Gaizauskas, V.
1982BAAS...14..898W Altcode:
No abstract at ADS

---------------------------------------------------------
Title: VLA Observations of Dramatic Changes in Fine Structure of
Solar Active Regions
Authors: Schmahl, E. J.; McConnell, D. M.; Kundu, M. R.
1982BAAS...14..924S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: VLA observations of the evolution of a solar burst source
structure at 6 centimeter wavelength
Authors: Velusamy, T.; Kundu, M. R.
1982ApJ...258..388V Altcode:
Evolutionary changes in the total intensity and polarization structure
of a 6 cm radio burst source have been observed with the VLA, over time
scales ranging from 10 s to several minutes. This burst was associated
with a 2B/M1 flare observed on 1980 May 14. The 6 cm burst consisted
of a gradual phase of 30 minutes duration and a strong impulsive phase
of duration less than two minutes. Synthesized maps of total intensity
and polarization were obtained with spatial resolution of 2 x 3 arcsec
and with temporal resolutions of five minutes during the gradual phase
and 10 s during the impulsive phase. The sequence of polarization
maps suggests a complex magnetic field structure undergoing rapid
changes. Most importantly, they show the development of two bipolar
regions or quadrupole structure just prior to the impulsive energy
release.

---------------------------------------------------------
Title: Positional Characteristics of Meter-Decameter Wavelength
Bursts Associated with Hard X-Ray Bursts
Authors: Kundu, M. R.; Gergely, T. E.; Kane, S. R.
1982SoPh...79..107K Altcode:
Several type III, type II, and type IV bursts were observed on April
25 and 26, 1979 with the Clark Lake Radio Observatory's E-W and
N-S swept frequency interferometers in the range 20-110 MHz. The
radio bursts were associated with hard X-ray bursts in the energy
range 26-154 keV, as observed by ISEE-3. The type III bursts, which
were associated with impulsive hard X-rays, were observed to great
heights (∼ 3.1R⊙ from disk center at 28 MHz) and their
location indicates that the electron streams responsible for them were
injected at the footpoints of magnetic field lines which diverge in the
corona. With one exception, all the type III bursts occurred in dense
coronal regions. Two gradual hard X-ray bursts were observed to occur
in association with a type IV without type II, and a type IV-type II
burst. For the gradual burst (observed on April 25) associated with
a type IV only, it is believed that part of the energetic electrons
responsible for meter-decameter type IV are trapped in a plasmoid behind
a weak shock, as evidenced by the absence of a type II, while another
part is located in low lying magnetic loops producing centimeter and
hard X-radiation. The type II burst associated with the other gradual
hard X-ray burst (observed on April 26) started approximately 9 min
after the impulsive hard X-ray burst peak. This rather long delay
between the type II onset and the impulsive maximum is believed to
represent the time interval over which the shock becomes strong enough
to produce a detectable type II higher in the corona.

---------------------------------------------------------
Title: Probing the Radio Sun
Authors: Kundu, M. R.
1982S&T....64....6K Altcode:
Radio studies of solar flares by the Very Large Array (VLA) of the
National Radio Astronomy Observatory are discussed along with the
results of cm and X-ray observations of flares. The synthesis of maps
of regions of the sun just prior to flares and the validation of solar
flare models using VLA are treated. Theories of the source of a flare's
energy, and of the processes that produce one, are summarized. One
unusual flare is cited as support for the flare model in which a
current sheet develops at the interface between two closed loops.

---------------------------------------------------------
Title: Electron pitch angle scattering and the impulsive phase
microwave and hard X-ray emission from solar flares
Authors: Holman, G. D.; Kundu, M. R.; Papadopoulos, K.
1982ApJ...257..354H Altcode:
Observations and theoretical considerations have led to a model for
impulsive phase flare emission involving the heating and acceleration
of thermal electrons in the coronal part of a magnetic loop. The bulk
of the heated gas is confined between conduction fronts, but particles
with velocities a few times greater than the thermal velocity can escape
into the lower part of the loop. It is shown that, when the electron
gyrofrequency exceeds the plasma frequency, the escaping electrons are
unstable to the generation of electrostatic plasma waves which scatter
the particles in pitch angle to a nearly isotropic distribution. It is
also shown that this scattering can (1) enhance the microwave emission
from the upper part of the loop, and (2) due to the Landau damping of
both low and high phase velocity waves, can lead to one or two breaks
in the impulsive-phase hard X-ray spectrum.

---------------------------------------------------------
Title: Positions of type II fundamental and harmonic sources in the
30 100 MHz range
Authors: Sawant, H. S.; Gergely, T. E.; Kundu, M. R.
1982SoPh...77..249S Altcode:
Observations of a type II burst with fundamental and harmonic structure
were made, with the Clark Lake Radio Observatory's E-W and N-S sweep
frequency interferometers operating in the range 120-20 MHz with time
and frequency resolution of 1 s and 100 kHz, respectively. The type II
burst was preceded by a type III-type V, and the associated flare of
importance SN was located at S 20 W 73. The interferometric data show
that the fundamental and harmonic were coincident in position. Further,
the type III positions as a function of frequency were practically the
same as those of the type II burst. The implications of these results
are discussed.

---------------------------------------------------------
Title: Radio imaging of solar flares using the very large array -
New insights into flare process
Authors: Kundu, M. R.; Schmahl, E. J.; Velusamy, T.; Vlahos, L.
1982A&A...108..188K Altcode:
An interpretation of VLA observations of microwave bursts is presented
in an attempt to distinguish between certain models of flares. The VLA
observations provide information about the pre-flare magnetic field
topology and the existence of mildly relativistic electrons accelerated
during flares. Examples are shown of changes in magnetic field topology
in the hour before flares. In one case, new bipolar loops appear to
emerge, which is an essential component of the model developed by
Heyvaerts et al. (1977). In another case, a quadrupole structure,
suggestive of two juxtaposed bipolar loops, appears to trigger the
flare. Because of the observed diversity of magnetic field topologies
in microwave bursts, it is believed that the magnetic energy must
be dissipated in more than one way. The VLA observations are clearly
providing means for sorting out the diverse flare models.

---------------------------------------------------------
Title: Time Variability and Structure of Quiet Sun Sources at 6-CM
Wavelength
Authors: Erskine, F. T.; Kundu, M. R.
1982SoPh...76..221E Altcode:
Using the Westerbork Synthesis Radio Telescope (WSRT) we produced a
synthesized map of a quiet Sun region on June 15, 1976, and studied
the structure and time variability of the quiet emitting regions at
6 cm wavelength with a spatial resolution of 6 arc sec. Comparison
of the 12hr synthesis map with Ca+ K filtergram shows
that bright and dark features on the 6 cm quiet Sun synthesized
map correspond to the chromospheric networks and cells observed
in Ca+ K. All 6 cm bright features lie over bright
Ca+ K network elements. The reverse correlation is not
true, that is, not all bright Ca+ K network features have
their 6 cm counterparts. Comparison with the photospheric magnetogram
shows that about 72% of the photospheric magnetic field enhancements
(¦B¦ ≥ 5 G) are coincident with 6 cm emissive regions. Only one
6 cm feature could be positively identified with a bipolar magnetic
structure. This implies that no more than 20-25% of the 6 cm emitting
features could be associated with X-ray bright points. Intercomparison
of our 12hr two-dimensional synthesis map, a 4hr two-dimensional
synthesis map (around meridian) and the one-dimensional fan beam
scans of the quiet Sun region at 6 cm, along with the Ca+
K filtergram and photospheric magnetogram shows that: (1) All of
the 15 time-varying elements at 6 cm were located on Ca+
K networks; (2) about 40% of the 15 time varying elements at 6 cm
are coincident with enhancements of the photospheric magnetogram;
(3) individual time-varying sources have minimum source size (FWHM) of
∼15 arc sec and maximum brightness temperature of ∼105 K;
(4) the life time of the time varying sources varies from a few minutes
to several tens of minutes; (5) the intensity of the sources varies by
factors of 2 to 7 over time periods of ∼1 min to tens of minutes;
and (6) the sources tend to disappear for periods of up to tens of
minutes and to reappear at the same locations.

---------------------------------------------------------
Title: Observations of ring structure in a sunspot associated source
at 6 centimeter wavelength
Authors: Alissandrakis, C. E.; Kundu, M. R.
1982ApJ...253L..49A Altcode:
The detection of a new kind of sunspot-associated source in which the
emission comes predominantly from a ring structure with size between
that of the umbra and the penumbra is reported. The absence of emission
from the center of the spot is interpreted in terms of the orientation
of the magnetic field and the presence of low temperature material
above the umbra.

---------------------------------------------------------
Title: Magnetic structure of a flaring region producing impulsive
microwave and hard X-ray bursts.
Authors: Kundu, M. R.; Schmahl, E. J.; Velusamy, T.
1982ApJ...253..963K Altcode:
Using VLA observations of the 1B/M1 flare of June 25, 1980, 6-cm
'snapshot' maps are synthesized. The spatial and temporal resolutions
during the 9 minutes of the impulsive phase were, respectively, 1
arcsec x 2 arcsec and 10 s. Some displacement is noted between the
locations of the burst source and the preflare loop structures seen
in the preflare map. The burst peak occurred on the neutral line of
the preflare polarization map, between the two oppositely polarized
microwave 'loop' structures approximately 40 arcsec long. Concurrent
hard X-ray observations were made of the burst, although these had
no spatial resolution. The 6-cm maps show the locations of a number
of the X-ray burst spikes. The 6-cm burst was fully resolved into at
least eight components, many of which were bipolar.

---------------------------------------------------------
Title: Simultaneous mapping of microwave burst sources with the VLA
at 2, 6 and 20 cm wavelengths.
Authors: Kundu, M. R.; Velusamy, T.; McConnell, D.
1982BAAS...14..572K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Centimeter Wavelength Observations of Active Regions and
Flares with a Few Arc-Second Resolution
Authors: Kundu, M. R.
1982coas.conf..119K Altcode: 1982cia..conf..119K
No abstract at ADS

---------------------------------------------------------
Title: Physics of the impulsive phase of solar flares
Authors: Kundu, M. R.
1982AdSpR...2k.159K Altcode: 1982AdSpR...2..159K
The physics of the impulsive phase of solar flares is discussed in
relation to high resolution microwave, hard X-ray and ultraviolet
observations. High spatial resolution observations of the structure of
microwave flaring loops and their interpretation in terms of arcades of
loops as the sites of primary energy release are presented. Theoretical
interpretation of the confinement of microwave producing energetic
electrons in the coronal part of loops is discussed. High temporal
and spatial resolution measurements in hard X-rays, as well as
observations of the spectral evolution of the hard X-ray emission are
presented. Observations of the relative locations of microwave and hard
X-ray emitting regions are presented and their significance with respect
to the energy release site and electron acceleration is discussed. The
relative timing of the peaks of impulsive hard X-ray and microwave burst
is discussed. The significance of ultraviolet measurements in obtaining
the density of flaring regions is discussed. Possible diagnostics of
impulsive phase onsets from cm-λ polarization data are presented, and
the role of the emergence of new flux and of the current sheet formed
between closed loops in producing impulsive energy release at centimeter
wavelengths are analyzed. Decimeter and meter wave manifestations of
preflash phase and millisecond pulsations at centimeter and decimeter
wavelengths and the relevant physical processes involved are discussed.

---------------------------------------------------------
Title: VLA observations of positions 42 6 centimeter burst peaks
associated with hard X-ray burst spikes
Authors: Kundu, M. R.; Bobrowsky, M.; Velusamy, T.
1981ApJ...251..342K Altcode:
Using the Very Large Array with a spatial resolution of 3 arcsec,
two-dimensional, 10-second synthesis maps are produced of four 6-cm
lambda bursts associated with multiply spiked hard X-ray bursts (20-300
keV). The positional, structural, and polarization characteristics
are investigated. It is noted that three of the four burst sources
are rather compact (less than approximately 10 arcsec). It is found
that the positions of the individual peaks or spikes within a single
burst are the same within plus or minus 2 arcsec. Interpreting these
different peaks as separate electron acceleration events, the results
suggest repeated acceleration of electrons within the same magnetic
trap. The trap situation is found to be consistent with the bipolar
nature of the burst sources except in one case.

---------------------------------------------------------
Title: New meter-wavelength observations of S 147
Authors: Angerhofer, P. E.; Kundu, M. R.
1981AJ.....86.1003A Altcode:
High-resolution 430-MHz (69.8 cm) continuum observations of the galactic
supernova remnant S 147 are presented. The presence of embedded numerous
small-diameter radio sources producing a well defined radio shell, and
a pronounced break in the flux density spectrum are suggested. Four
4C sources, several B2 sources and three anonymous sources are
included, and the mean spectral index of these sources is found to be
significantly less than that of typical extragalactic sources. Due
to the distribution of the angular diameters, it is also suggested
that the sources belong to the galactic sources, although the numbers
do not represent an excess over that expected from background source
counts. It is concluded that S 147 is in a relatively late stage of
remnant evolution, and the sources may be a result of ionization of
neutral material by the advancing shock.

---------------------------------------------------------
Title: Book-Review - Radio Physics of the Sun
Authors: Kundu, M. R.; Gergely, T. E.; Layzer, D.
1981Natur.291..518K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Observations of Solar Filaments at 8-GHZ 15-GHZ 22-GHZ
and 43-GHZ
Authors: Schmahl, E. J.; Bobrowsky, M.; Kundu, M. R.
1981SoPh...71..311S Altcode:
On April 3, 4, 6, and 8, 1978, solar observations were made using the
Haystack 120 ft telescope at 8, 15, 22, and 43 GHz. Hα filtergrams
obtained at the Sacramento Peak Observatory on the same days showed an
average of more than 30 filaments or filament fragments (per day) on the
disk. Most of these appeared as depressions in brightness temperature
at 15 and 22 GHz. Because of the relatively low spatial resolution at
8 GHz, only a few appeared at that frequency, and presumably because
of lower opacity in filaments at higher frequencies, few depressions
were visible at 43 GHz. At 15 and 22 GHz, more depressions appeared than
Hα filaments, but virtually all the radio depressions overlay magnetic
neutral lines. Taking the data sets for each day as independent samples,
we found that at 22 GHz, 46 of the 77 radio depressions were associated
with Hα filaments; at 15 GHz the correlation was smaller; only 27 out
of 48 being associated with the Hα filaments. The data imply that the
microwave depression features are the result of absorption by filaments
and perhaps also the result of other effects of the associated filament
channel, but not necessarily coronal depletion. The effects of filament
absorption are, statistically, about twice as effective as other
phenomena (such as absorption by material invisible in Hα, for example)
in creating the radio depression. A center-to-limb study of a single
large filament clearly showed that at 15 and 22 GHz the absorption
by cool hydrogen supported above the neutral line was the predominant
factor in producing the observed depression at radio frequencies.

---------------------------------------------------------
Title: Book-Review - Radio Physics of the Sun
Authors: Layzer, D.; Kundu, M. R.; Gergely, T. E.
1981Natur.291..517L Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Book-Review - Radio Physics of the Sun - I.A.U. SYMP.86
Authors: Kundu, M. R.; Gergeley, T. E.; Kruger, A.
1981SSRv...28..223K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Decameter studies of the 5 September 1973 flare
Authors: Gergely, T. E.; Kundu, M. R.
1981SoPh...71...65G Altcode:
We discuss the spectra and positions of the meter-decameter wavelength
radio sources associated with the 5 September 1973 flare. We discuss
the evolution of the size of the type II burst source and show that it
fluctuates by a factor of 10, or larger. Consequently, the potential
and kinetic energies associated with the shock are uncertain by the
same factor. By comparing the positions of the type II and type III
sources we conclude that while the shock wave associated with the type
II was guided along high loops, the type III electrons were injected
along open field lines which diverged within a short height in the
corona. The characteristics of a particularly interesting type III
burst with a low-frequency cut-off are discussed. We argue that nearby
loops were not disrupted by the shock and that the energetic electrons
produced during the event must have been injected at several sites
and guided along open field lines at large distances from the flare
to produce type III bursts.

---------------------------------------------------------
Title: VLA search for radio emission from stars with solar-type
structures
Authors: Bowers, P. F.; Kundu, M. R.
1981AJ.....86..569B Altcode:
Results are presented of a high-sensitivity search for 6-cm radio
emission from stars with evidence of active chromospheric or coronal
regions. The data indicate that many of these stars have radio
luminosities much less than those that have been found for known
radio stars.

---------------------------------------------------------
Title: Book-Review - Radio Physics of the Sun - IAU SYMP.86
Authors: Kundu, M. R.; Gergely, T. E.
1981Sci...212...90K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: VLA Observations of Solar Flares and Tests of Flare Models
Authors: Kundu, M. R.
1981BAAS...13..909K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A Search for Microwave Counterparts of Umbral Flashes
Authors: McConnell, D.; Kundu, M. R.; Schmahl, E. J.; Lites, B.
1981BAAS...13..858M Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Gyrosynchrotron Masering in Solar Flares
Authors: Morrison, P. J.; Holman, G. D.; Kundu, M. R.
1981BAAS...13..860M Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Flare Buildup at 6 cm Wavelength, in UV and Hα
Authors: Schmahl, E. J.; Kundu, M. R.; Woodgate, B.; Shine, R.
1981BAAS...13..846S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Two-Dimensional Radioheliographic Pictures of the Sun's Outer
Corona at 25.6-110.6 MHz
Authors: Kundu, M. R.; Erickson, W. C.; Turner, P. J.
1981BAAS...13Q.891K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Active Region Magnetic Fields
Authors: Smith, J. B., Jr.; Strong, K. T.; Schmahl, E. J.; Kundu,
M. R.; Krall, K. R.; Bentley, R. D.
1981BAAS...13..881S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: VLA Observations of Large Scale Microwave Brightening Following
a Flare
Authors: Bobrowsky, M.; Kundu, M. R.; Rust, D.
1981BAAS...13..846B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Interpretation of Microwave and X-Ray Bursts Observed with
the VLA and P78-1
Authors: Schmahl, E. J.; Kundu, M. R.; Landecker, P. B.; McKenzie,
D. L.
1981BAAS...13..553S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: MICROWAVE_ Solar Limb Brightening
Authors: Ahmad, I. A.; Kundu, M. R.
1981SoPh...69..273A Altcode:
Previous models of microwave limb brightening have omitted the
alignment of spicules along supergranule boundaries, have neglected
the high temperature sheath around spicules, and have assumed an
interspicular medium which was averaged over chromospheric network
and non-network regions. We present a model which includes these
factors. By constraining the model to conform to results from earlier UV
and optical studies we are effectively left with two free parameters:
the temperature at the core of the spicules, Tcore, and
(at solar minimum), the interspicular chromospheric network density
model of the lower transition zone. The absence of limb brightening
at the short millimeter wavelengths implies Tcore ≲ 6000
k. Differences between the model and certain deconvolved observations
near 9 mm are expected as a consequence of an extension of emission
beyond the optical limb, predicted by the model, which affects the
accuracy of the deconvolution technique. Unlike models which assume
homogeneous spicules in a random distribution, ours does not require
an abnormally high spicule area.

---------------------------------------------------------
Title: A multifrequency study of CTB 80 with the Westerbork synthesis
radio telescope.
Authors: Angerhofer, P. E.; Strom, R. G.; Velusamy, T.; Kundu, M. R.
1981A&A....94..313A Altcode:
We report observations of the galactic supernova remnant CTB 80 (W56,
G69.0 +2.7) with the Westerbork Synthesis Radio Telescope (WSRT) at 6,
2t, and 49 cm wavelengths. Maps of the brightness distribution and
linear polarization are presented for each wavelength, along with
discussion of the distributions of spectral index, magnetic field
direction and rotation measure over the central source and radio
ridges. The new data suggest that the bright central source
and the extended underlying emission are physically associated. The
spectrum over the central source is flat (α ∼ 0.0), steepening
uniformly away from the core in all directions. Linear polarization
is detected at all three observed wavelengths. The morphology, high
degree of polarization and flat spectral index of the core suggest that
`the central source may belong to the Crab Nebula type SNR class. Inspection of the PSS plates reveals the presence of considerable
optical nebulosity at the position of the radio continuum peak, adding
CTB 80 to the list of ∼30 optically visible supernova remnants.

---------------------------------------------------------
Title: Book-Review - Radio Physics of the Sun
Authors: Kundu, M. R.; Gergely, T. E.; Maxwell, A.
1981S&T....62..149K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Observing the Sun during Eclipses
Authors: Kundu, M. R.
1981Mercu..10..108K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: VLA observations of solar active regions at 6 CM wavelength
Authors: Kundu, M. R.; Schmahl, E. J.; Rao, A. P.
1981A&A....94...72K Altcode:
Synthesized maps of two solar active regions obtained from
observations with the Very Large Array (VLA) with 9-arcsec resolution
are presented. The most intense sources in these regions are found to
be associated with filamentary structures and magnetic neutral lines
as shown in H-alpha and photospheric magnetograms. These sources
are not located directly over sunspots in disagreement with earlier
observations. EUV and X-ray observations have suggested that similar
structures should be visible at cm wavelengths around but, outside of,
sunspots if the magnetic field is sufficiently strong. These results
are consistent with the locations of hot (greater than 1,000,000 K)
plasmas in active regions expected from generalization based on optical
photographs. Given the sizes of the radio sources, the volume emission
measures of soft X-rays observed from OSO-8 rule out the possibility
of thermal bremsstrahlung being of any significance, as far as the 6
cm emission is concerned. Therefore, gyroresonance absorption process
is the most likely cause of 6 cm emission from these sources, and its
likelihood is enhanced by the magnetic field geometry that is known
to exist over filaments and neutral lines.

---------------------------------------------------------
Title: VLA observations of postflare loops at 20 centimeter wavelength
Authors: Velusamy, T.; Kundu, M. R.
1981ApJ...243L.103V Altcode:
From observations with the VLA on May 19, 1979, the first spatially
resolved observations of 20 cm radio emission originating from postflare
loop systems are presented. The 20 cm burst was associated with an
H alpha flare and a soft X-ray burst, and most of the intense radio
emission occurred at the end of the H alpha flare and in the decay
phase of the X-ray burst. The 20 cm 'snapshot' maps of the burst
source obtained with a resolution of 12 arcsec x 24 arcsec show that
the radio emission occurred in structures that are similar in size
and shape to the systems of loops observed in X-rays. This postflare
radio emission is considered to be similar to the H alpha and X-ray
emissions originating in postflare loops. The radio observations of
postflare loops have the unique advantage that they offer an important
means of determining the average magnetic field strength in these
loops. Interpreting the radio emission in this particular event
as thermal gyroradiation or as nonthermal synchrotron radiation,
the magnetic field strength is estimated to lie in the range of
approximately 120-170 gauss.

---------------------------------------------------------
Title: Observations of the old supernova remnant S 147 at 11.1 and
18.2 cm wavelengths.
Authors: Kundu, M. R.; Angerhofer, P. E.; Fuerst, E.; Hirth, W.
1980A&A....92..225K Altcode:
New high resolution and high sensitivity radio observations of the
old galactic supernova remnant S 147, made at wavelengths of 11.1
and 18.2 cm, are reported. The data reveal the presence of a well
developed radio shell. The integrated flux density spectrum shows
a distinct break at 1 GHz, attributed to enhanced volume emissivity
of the swept-up interstellar material. The age of S 147 is likely to
be about 100,000 yr, making it one of the oldest optically visible
supernova remnants in the Galaxy. Derived physical parameters, based
on the new data, are also reported.

---------------------------------------------------------
Title: Erratum - MICROWAVE_ EUV and X-Ray Observations of Active
Region Loops - Evidence for Gyroresonance Absorption in the Corona
Authors: Kundu, M. R.; Schmahl, E. J.; Gerassimenko, M.
1980A&A....91..377K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Upper limits on the power in solar oscillations at 1.2 mm,
9 mm, 3.7 cm, and 11.1 CM wavelengths
Authors: Kundu, M. R.; Schmahl, E. J.
1980A&A....90..192K Altcode:
A search for solar oscillations has been made using the NRAO 36-ft
telescope at 1.2 mm, the NRL 85-ft telescope at 9 mm, and the NRAO
four-element interferometer at 3.7 and 11.1 cm wavelengths. After
corrections for the small coherence length of the optically observed
oscillations, for their known spectral bandwidth, and for the
visibility function of the interferometer, upper limits have been
placed on the fluctuating power at oscillation frequencies near 3
mHz. The interferometric observations at 3.7 cm and the single-dish
observations at 1.2 and 9 mm imply that less than 0.3, 0.04, and
0.1%, respectively, of the bremsstrahlung photons emitted from the
chromosphere show periodic fluctuations. This is 1 to 3 orders of
magnitude less than the fraction (approximately 1 to 2%) reported
at ultraviolet wavelengths. Simple arguments in terms of weak shock
theory suggest that the observable oscillations at centimeter and
millimeter wavelengths should be intrinsically weaker in the thermal
bremmstrahlung radiation than the optical, but the 3.7 cm wavelength
results are explained only by the absence of periodic fluctuations at
the level of formation.

---------------------------------------------------------
Title: VLA Observations of Two SMM Flares at 6 cm
Authors: Erskine, F. T.; Kundu, M. R.; Velusamy, T.
1980BAAS...12..901E Altcode:
No abstract at ADS

---------------------------------------------------------
Title: VLA Observations of a Centimeter Wavelength Burst Associated
With a Filament Eruption on May 14, 1980
Authors: Velusamy, T.; Kundu, M. R.
1980BAAS...12..901V Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Radio and Visible Light Observations of a Coronal Transient
Associated with a Prominence Eruption
Authors: Gergely, T. E.; Kundu, M. R.; Erskine, F. T.; Sawyer, C.;
Wagner, W. J.; Illing, R.; House, L. L.; McCabe, M. K.; Stewart,
R. T.; Nelson, G. J.
1980BAAS...12..900G Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Correlated Soft X-Ray and Microwave Observations of Active
Region Loops
Authors: Webb, D. F.; Davis, J. M.; Kundu, M. R.; Velusamy, T.
1980BAAS...12..916W Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Nonthermal Flare Emission and the Nonlinear Dynamics of High
Energy Electrons
Authors: Holman, G. D.; Papadopoulos, K.; Kundu, M. R.
1980BAAS...12..901H Altcode:
No abstract at ADS

---------------------------------------------------------
Title: VLA Observations of the Impulsive Phase of the June 25,
1980 Flare at 6 CM Wavelength
Authors: Kundu, M. R.; Velusamy, T.; Schmahl, E. J.
1980BAAS...12..901K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Comparison of VLA Microwave Maps of Active Regions with X-ray
Spectroheliograms
Authors: Schmahl, E. J.; Kundu, M. R.; Strong, K. T.
1980BAAS...12Q.907S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Observation with the VLA of a stationary loop structure on
the sun at 6 centimeter wavelength
Authors: Kundu, M. R.; Velusamy, T.
1980ApJ...240L..63K Altcode:
A looplike structure connecting two sunspots of opposite polarity in an
active region has been observed at 6 cm with a resolution of 3.5 arcsec,
using the Very Large Array. This loop structure is reminiscent of the
X-ray loops, as observed, for example, from Skylab. The brightness
temperature in the 'loop' is one-million K and five-million K near
its foot points. Most of the bright peaks in the 'loop' are well
aligned with a long neutral line. Several compact, highly circularly
polarized emission peaks were observed over emerging flux regions
near one of the spots. Some of these sources appear to be associated
with arch filament systems. The low brightness emission in the 'loop'
is attributed to optically thin thermal bremsstrahlung.

---------------------------------------------------------
Title: Synthesized map of a solar filament at 6 CM with approximately
15 arc SEC resolution
Authors: Rao, A. P.; Kundu, M. R.
1980A&A....86..373R Altcode:
Radio telescope observations have been used to provide the first
synthesized map of a filament at 6 cm with angular resolution of about
15 arcsec. The 'dirty' map of the north limb of the sun is shown along
with the dirty map of the residual after subtracting the three component
least squares model. There is very good correspondence between the
radio contours and the H alpha filament; the darkest feature of the
filament has a radio temperature depression of 7500 plus or minus 1500
K, and the corresponding brightness temperature of the filament is
12500 plus or minus 1500 K. It is concluded that for this particular
filament the radio size is not larger than the optical one.

---------------------------------------------------------
Title: Time Variability and Structure of Quiet Sun Sources at 6
cm Wavelength
Authors: Erskine, F. T.; Kundu, M. R.
1980BAAS...12..504E Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Observations of Solar Filaments at 8, 15, 22, and 43 Ghz
Authors: Schmahl, E. J.; Bobrowsky, M.; Kundu, M. R.
1980BAAS...12..507S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Nature of Meter-Decameter Bursts Associated with Hard X-ray
Bursts
Authors: Kundu, M. R.; Gergely, T. E.; Kane, S. R.
1980BAAS...12..478K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Two-Dimensional Snapshot Maps with the VLA of a Solar Burst
at 20 cm Wavelength
Authors: Velusamy, T.; Kundu, M. R.
1980BAAS...12..478V Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Observation with the VLA of a Stationary Loop Structure on
the Sun at 6 cm Wavelength
Authors: Kundu, M. R.; Velusamy, T.
1980BAAS...12..519K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Thermal Radio Emission from Solar Active Regions
Authors: Holman, G. D.; Kundu, M. R.
1980BAAS...12..517H Altcode:
No abstract at ADS

---------------------------------------------------------
Title: 6 CM observations of a solar active region and bursts with
approximately 6 arcsec resolution
Authors: Erskine, F. T.; Kundu, M. R.; Rao, A. P.
1980A&A....83..256E Altcode:
The paper examines the solar active region located near N04E49, that
was mapped at a 6 cm wavelength over a period of 12 hours, employing
the Westerbork synthesis radio telescope. Two impulsive radio bursts
were recorded during this time, one of which was associated with
a chromospheric flare. One-dimensional fan beam scans of the burst
sources were synthesized in order to display their time history with
regard to intensity, polarization, position and size.

---------------------------------------------------------
Title: Association of flaring X-ray bright points with type III bursts
Authors: Kundu, M. R.; Gergely, T. E.; Golub, L.
1980ApJ...236L..87K Altcode:
Using the swept-frequency radio observations obtained at the Clark
Lake Radio Observatory and the X-ray photographs taken by the S-054
experiment aboard Skylab, a search has been made for type III bursts
associated with X-ray bright point (XBP) flares. Using temporal as
well as spatial criteria for the association, four such events are
found over a period of 43 days. The time period was selected in such
a way that the level of flare and radio activity was low in order to
minimize the chance coincidences. The detection of type III bursts from
the flaring XBPs is of great interest, since it identifies them with the
flare process, of which XBP flares are thought to be the simplest form.

---------------------------------------------------------
Title: A model for sunspot associated emission at 6 CM wavelength
Authors: Alissandrakis, C. E.; Kundu, M. R.; Lantos, P.
1980A&A....82...30A Altcode:
Two-dimensional maps of total intensity and circular polarization of
a sunspot region at 6 cm have been calculated using a simple model
for the chromosphere-corona transition region and observations of
the longitudinal component of the photospheric magnetic field. The
calculations are in good agreement with the high resolution observations
of the same sunspot region at 6 cm, obtained with the Westerbork
Synthesis Radio Telescope. It is shown that the 6 cm radiation is
predominantly due to gyroresonance absorption process at the second
and third harmonics of the gyrofrequency (H = 900-600 G). Estimates of
the conductive flux and the electron density in the transition region
above the sunspot are also given.

---------------------------------------------------------
Title: Microwave, EUV, and X-ray observations of active region loops -
Evidence for gyroresonance absorption in the corona
Authors: Kundu, M. R.; Schmahl, E. J.; Gerassimenko, M.
1980A&A....82..265K Altcode:
The combined data from 3.7 and 11 cm radio maps, EUV spectroheliograms,
and X-ray photographs of an active region (McMath 12379) are
analyzed. The near equality of the radio brightness temperatures and
the electron temperature determined from the EUV and X-ray data implies
that the radio emission is thermal. Since the free-free absorption
is inadequate to account for this, the large optical depth must be
produced by gyroresonance absorption. It is inferred that the magnetic
scale height must be of the same order as the observed width of the
coronal loops (one-billion cm). The scale of emission in the radio,
and hence the scale of the absorbing region transverse to the line of
sight, is also of this order.

---------------------------------------------------------
Title: Solar burst observations at centimeter wavelengths
Authors: Kundu, M. R.
1980IAUS...86..157K Altcode:
Selected features of centimeter-wave solar radio burst are discussed
in relation to the generating mechanism of these bursts. Observations
are presented of active regions prior to the onset of a flare, the
intensity distributions of flares, the impulsive phase of a burst,
the post-burst phase, and gradual rise and fall burst. Analysis
of high-resolution impulsive bursts leads to a model of burst
emission in which impulsively accelerated plasma contained within
loop structures is responsible for the impulsive burst phase by the
ejection of high energy particles and for the post-burst phase by
the spread of slower particles, with emission in the centimeter wave
region primarily by bremsstrahlung. It is also pointed out that the
impulsive centimeter-wave bursts have been found to correspond with
hard X-ray bursts as well as soft X-ray kernels, indicating that the
centimeter wave region is no larger than the X-ray emitting region,
which would require either self-absorption or an asymmetrical bipolar
field structure to explain the greater X-ray intensities.

---------------------------------------------------------
Title: Maryland, University of
Authors: Kundu, M. R.
1980BAAS...12..226K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Observations of solar active regions at 2 and 6 CM wavelengths
with 3 arc second resolution
Authors: Velusamy, T.; Kundu, M. R.
1980IAUS...86..105V Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Observations of the quiet sun with 6 arcsec resolution
Authors: Kundu, M. R.; Rao, A. P.; Erskine, F. T.; Bregman, J. D.
1980IAUS...86...53K Altcode:
High-resolution observations of the quiet sun at 6 cm are reported. The
Westerbork Synthesis Radio Telescope was used to observe a central 10
x 10 arcmin disk region for 12 hours at a resolution of 6 arcsec in
the E-W direction and 15 arcsec in the N-S direction. The resulting
radio map reveals the presence of a supergranulation network with
network elements of 25,000 K and cells of 15,000 K, and which is of
the same scale as the Ca(+) network. Sequential observations of the
north, south, east and west limbs reveal a limb brightening of 40-60%
above the mean disk temperature, the peak of which is located 15 arcsec
outside the optical disk.

---------------------------------------------------------
Title: Impulsive phase of solar flares
Authors: Kane, S. R.; Crannell, C. J.; Datlowe, D.; Feldman, U.;
Gabriel, A.; Hudson, H. S.; Kundu, M. R.; Maetzler, C.; Neidig, D.;
Petrosian, V.
1980sfsl.work..187K Altcode: 1980sofl.symp..187K
The present understanding of the impulsive phase of a solar flare,
characterized by short-duration bursts of impulsive hard X-ray,
EUV, optical and radio emission indicating the release of energetic
electrons is reviewed. Observations of the spectral distribution
of impulsive hard X-ray bursts and of Type III and radio continuum
bursts are presented and interpreted in terms of energetic electron
distributions, and impulsive EUV, XUV, soft X-ray and optical
observations, which provide a lower limit to total energy release
during the impulsive phase, are discussed. The role of energetic
electrons in exciting the hard X-ray, EUV and microwave emissions is
considered, and thin-target, thick-target, partial-precipitation and
thermal models of impulsive phase electron acceleration are evaluated
in light of the observations. It is noted that available data do
not allow discrimination between a thermal or a nonthermal electron
distribution, on which depends the proportion of flare energy supplied
by the energetic electrons, and that data favors models which permit
at least partial electron precipitation. Future observational and
theoretical work is indicated.

---------------------------------------------------------
Title: Decametric radio bursts associated with coronal loop structures
Authors: Gergely, T. E.; Kundu, M. R.; Golub, L.; Webb, D.
1980IAUS...86..435G Altcode:
The association of X-ray loop structures with type III bursts
is examined using soft X-ray (2-54 A) pictures which were obtained
from the Skylab S-054 experiment. The properties of meter-decameter
wavelength radio bursts (type III) appear to be associated with two
different kinds of loop structures: (1) short lived small scale loops,
which are found to link magnetic fields of opposite polarity, called
X-ray bright points (XBP); and (2) long lasting loop systems which
connect opposite magnetic polarities of an active region as well as
active region complexes. It is judged that the presence of active region
loop complexes on the disk is a necessary yet insufficient condition for
the occurrence of a decametric storm and that conditions concerning the
geometry of the magnetic field must also be important in the process.

---------------------------------------------------------
Title: Radio physics of the sun: proceedings from IAU symposium
no. 86, held in College Park, Md. U.S.A., August 7-10, 1979.
Authors: Kundu, M. R.; Gergely, T. E.
1980IAUS...86.....K Altcode:
Papers are presented in the areas of the radio characteristics of the
quiet sun and active regions, the centimeter, meter and decameter
wavelength characteristics of solar bursts, space observations of
low-frequency bursts, theoretical interpretations of solar active
regions and bursts, joint radio, visual and X-ray observations of
active regions and bursts, and the similarities of stellar radio
characteristics to solar radio phenomena. Specific topics include
the centimeter and millimeter wave characteristics of the quiet sun,
radio fluctuations arising upon the transit of shock waves through the
transition region, microwave, EUV and X-ray observations of active
region loops and filaments, interferometric observations of 35-GHz
radio bursts, emission mechanisms for radio bursts, the spatial
structure of microwave bursts, observations of type III bursts, the
statistics of type I bursts, and the numerical simulation of type III
bursts. Attention is also given to the theory of type IV decimeter
bursts, Voyager observations of type II and III bursts at kilometric
wavelengths, radio and whitelight observations of coronal transients,
and the possibility of obtaining radio observations of current sheets
on the sun.

---------------------------------------------------------
Title: An interpretation of solar flare microwave spikes as
gyrosynchrotron masering
Authors: Holman, G. D.; Eichler, D.; Kundu, M. R.
1980IAUS...86..457H Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Book-Review - Radio Physics of the Sun IAU Symp 86
Authors: Kundu, M. R.; Gergely, T. E.
1980Natur.287..373K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Decameter radio and white light observations of the 21 August
1973 coronal transient
Authors: Gergely, T. E.; Kundu, M. R.
1980IAUS...91..245G Altcode:
The forces driving the ejecta of the coronal transient of August
21, 1973 are estimated using physical parameters derived by joint
radio and white light observations. The radio emission associated
with the transient was continuum in nature, and lasted for almost
5 hours. Simultaneous radio and white light measurements show that
the radio source was cospatial with one of the secondary white light
loops. Assuming a coronal temperature of 1,500,000 K, the results
yield an approximate equality of the gas and magnetic pressures at
2.0 solar radii. It is concluded that for this transient, the gas is
strongly influenced by changes in the magnetic field.

---------------------------------------------------------
Title: High-resolution observations of the quiet sun at 6 centimeters
using the Westerbork Synthesis Radio Telescope
Authors: Kundu, M. R.; Rao, A. P.; Erskine, F. T.; Bregman, J. D.
1979ApJ...234.1122K Altcode:
High-spatial-resolution (∼6") observations of the quiet Sun were
made at 6 cm with the Westerbork Synthesis Radio Telescope. A 10'
× 10' field of the central disk region observed on 1976 June 16
was synthesized. We show the first radio map of the supergranulation
network. Numerical autocorrelation of the radio map indicated a radio
"network" width ∼11,000 km and a radio "cell" spacing ∼32,000
km. The brightness temperature of typical network elements is ∼2.5
× l04 K, while that of the radio cells is ∼1.5 ×
l04 K. The contrast between the radio network and cells is
∼1.7:1 which is intermediate to that of the Ca+ K network
and Lα network. The radio map was compared with a Ca+ K
spectroheliogram of the same region on the same day. On 1976 June 17,
the four limbs of the Sun were also observed in an attempt to synthesize
the limb and study the extent and symmetry of limb brightening. The
results show that limb brightening is seen both in the north-south and
east-west directions, contrary to earlier low-resolution measurements
which showed limb brightening only in the east-west direction. The
peak of the limb brightening appears ∼15" outside the white-light
disk and the peak limb temperature is ∼40% greater than the mean
disk temperature.

---------------------------------------------------------
Title: Upper Limits on Solar Oscillation Power in Microwaves
Authors: Kundu, M. R.; Schmahl, E. J.
1979BAAS...11..641K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Centimeter Wavelength Observations of Solar Active Regions
With The Very Large Array
Authors: Kundu, M. R.; Schmahl, E. J.; Rao, A. P.
1979BAAS...11R.710K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Radio Interferometric Observations of Solar Bursts at 3.7-CM
and 11.1-CM Wavelengths
Authors: Kundu, M. R.; Angerhofer, P. E.
1979SoPh...64..159K Altcode:
Several solar active regions were observed during the 1976 vernal
equinox with the 3-element interferometer of the National Radio
Astronomy Observatory. The element spacings for these observations were
600, 2100, and 2700 m, resulting in maximum angular resolutions of about
3 arc sec at 3.7 cm and 8.5 arc sec at 11.1 cm. We fitted the fringe
visibility for each baseline pair as a function of projected baseline
with a single gaussian component, and calculated the extrapolated flux
at zero baseline, F0, the FWHM source size, a, and the peak
brightness temperature Tb. We present physical parameters
derived for the observed bursts.

---------------------------------------------------------
Title: An interpretation of the polarization structure of microwave
bursts.
Authors: Kundu, M. R.; Vlahos, L.
1979ApJ...232..595K Altcode:
High-spatial-resolution (a few seconds of arc) observations of
microwave bursts have demonstrated that only the impulsive phase of
the burst is polarized; one observes only one polarity in the burst
source if it is weak (Alissandrakis and Kundu) and both polarities if
it is intense (Enome et al.). These results are interpreted in terms
of an asymmetrical bipolar field structure of the loop in which the
energetic electrons responsible for the radiation are contained. The
role of unequal field strengths at the feet of the loop on the number of
electrons trapped and their pitch angle distribution are discussed in
a specific model. Computations of the polarized intensity originating
from each foot of the loop seem to be consistent with the observations
at present available.

---------------------------------------------------------
Title: Observations of alpha Orionis, R Aquilae, and R Aquarii at
14.9 GHz.
Authors: Bowers, P. F.; Kundu, M. R.
1979AJ.....84..791B Altcode:
The 14.9-GHz continuum flux densities of the M-type stars Alpha Ori,
R Aql, and R Aqr have been measured. For Alpha Ori and R Aql it is
suggested that the emission at this frequency is primarily due to
ionized gas associated with stellar chromospheres or coronae. For
R Aqr a model consistent with available data is proposed in which
the variable intensity of the radio emission depends on a variable
mass-loss rate for the Mira.

---------------------------------------------------------
Title: Radio and white-light observations of the 1973 August 21
coronal transient.
Authors: Gergely, T. E.; Kundu, M. R.; Munro, R. H.; Poland, A. I.
1979ApJ...230..575G Altcode:
A coronal transient, which occurred on August 21, 1973, has
been observed simultaneously in white light and at decameter
radio wavelengths. The radio observations were obtained with a
two-dimensional swept-frequency array (called the Teepee Tee). The
white-light observations consist of a series of photographs taken by
the High Altitude Observatory's coronagraph aboard Skylab. The radio
emission associated with the transient was continuum in nature and
lasted for almost 5 hours. The source of emission was observed to be
cospatial with the lower part of one of the secondary white-light
loops. A lower limit of 0.6 solar radius for the depth (extension
along the line of sight) of this part of the transient was derived
from considerations of radio-wave propagation in the corona. The radio
source showed no dispersion of height with frequency, and, therefore,
the emission is attributed to gyrosynchrotron radiation. Based on this
assumption, the magnetic-field strength in the lower part of the loop
is estimated to be in the 2.0-4.5-gauss range at a height of 2.1 solar
radii from the center of the sun.

---------------------------------------------------------
Title: Solar Atmospheric Inhomogeneities and Limb Brightening Models
Authors: Ahmad, I. A.; Kundu, M. R.
1979BAAS...11..410A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Radiobeobachtungen an S 147, ein Beitrag zur Diskussion alter
Supernovaüberreste
Authors: Fürst, E.; Hirth, W.; Angerhofer, P. E.; Kundu, M. R.;
Sofue, Y.
1979MitAG..45..103F Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Comparison of radio and EUV filaments: a two-component model.
Authors: Kundu, M. R.; Schmahl, E. J.
1979BAAS...11..393K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Discussion
Authors: Landi Degl'Innocenti, M.; Kundu, M. R.; Landman, D. A.;
Smartt, R. N.; Stenflo, J.
1979phsp.coll...85L Altcode: 1979IAUCo..44...85D; 1979phsp.coll...85D
No abstract at ADS

---------------------------------------------------------
Title: Discussion
Authors: Acton, L. W.; Engvold, O.; Heasley, J. N.; Heyvaerts, J.;
Hirayama, T.; Kundu, M. R.; Leroy, J. L.; Malville, J.; Rust, D. M.;
Zirin, H.
1979phsp.coll...31A Altcode: 1979IAUCo..44...31A
No abstract at ADS

---------------------------------------------------------
Title: Discussion
Authors: Kundu, M. R.; Schmahl, E. J.
1979phsp.coll..129K Altcode: 1979IAUCo..44..129K
No abstract at ADS

---------------------------------------------------------
Title: A broad look at solar physics adapted from the solar physics
study of August 1975
Authors: Parker, E.; Timothy, A.; Beckers, J.; Hundhausen, A.; Kundu,
M. R.; Leith, C. E.; Lin, R.; Linsky, J.; MacDonald, F. B.; Noyes, R.
1979sswp.book....3P Altcode: 1979sswp.book....3B
The current status of our knowledge of the basic mechanisms involved
in fundamental solar phenomena is reviewed. These include mechanisms
responsible for heating the corona, the generation of the solar
wind, the particle acceleration in flares, and the dissipation of
magnetic energy in field reversal regions, known as current sheets. The
discussion covers solar flares and high-energy phenomena, solar active
regions; solar interior, convection, and activity; the structure and
energetics of the quiet solar atmosphere; the structure of the corona;
the solar composition; and solar terrestrial interactions. It also
covers a program of solar research, including the special observational
requirements for spectral and angular resolution, sensitivity, time
resolution, and duration of the techniques employed.

---------------------------------------------------------
Title: Discussion
Authors: Chiuderi-Drago, F.; Kundu, M. R.; Lantos, P.; Zirin, H.
1979phsp.coll..134C Altcode: 1979IAUCo..44..134C
No abstract at ADS

---------------------------------------------------------
Title: Observations of Filaments at Centimeter and Millimeter
Wavelengths.
Authors: Kundu, M. R.
1979phsp.coll..122K Altcode: 1979IAUCo..44..122K; 1979phsp.conf..122K
Observations of quiescent-prominence radio filaments at centimeter
and millimeter wavelengths are reviewed. The finding that a radio
filament appears cooler than the background quiet sun is interpreted
by postulating that the filament is cool and optically thick, in
which case the brightness temperature of the filament should be the
same as its kinetic temperature. Optical spectroscopic observations
are discussed which indicate that a typical filament has an electron
density of approximately 100 billion per cu cm, a temperature of
about 6000 K, and a length of approximately 1000 km, implying that
the optical thickness is much greater than unity for all frequencies
less than 600 GHz. Millimeter- and centimeter-wavelength observations
of filaments at the limb are shown also to support the view that the
filaments are optically thick at these wavelengths. Radio observations
of filament transition sheaths and cavities are also examined.

---------------------------------------------------------
Title: Discussion
Authors: Acton, L. W.; Kundu, M. R.; Maltby, P.; Malville, J.; Orrall,
F. Q.; Sheeley, N.; Spicer, D. S.
1979phsp.coll..225A Altcode: 1979IAUCo..44..225A
No abstract at ADS

---------------------------------------------------------
Title: Discussion
Authors: Anzer, U.; Chiuderi-Drago, F.; Kundu, M. R.; Leroy, J. L.;
Malville, J.; Rompolt, B.; Sheeley, N.; Stenflo, J.; Tandberg-Hanssen,
E.; Öhman, Y.
1979phsp.coll...77A Altcode: 1979IAUCo..44...77A
No abstract at ADS

---------------------------------------------------------
Title: Fine structure and time variation of the quiet sun at 1.3 cm.
Authors: Rao, A. P.; Kundu, M. R.
1978SoPh...59..345R Altcode:
The Hat Creek two-element interferometer has been used to study
the quiet Sun at 22 GHz. A statistical analysis of output of the
interferometer clearly shows the existence of time variations on the
quiet Sun with time scales ∼180 s. The observations suggest that
the fine structure on the quiet Sun might consist of two components -
one which varies with the time scales ∼3 min and the other being
relatively stable. The average visibility amplitude indicates that the
fine structure on the Sun has a typical angular size of ∼6″. The
observation that the variance and the mean of the visibility amplitudes
depend in the same way on the projected baseline suggests that the
transient sources have angular size similar to the average size of
the fine structure on the quiet Sun. Power spectra of the output of
the interferometer show no significant periodicity.

---------------------------------------------------------
Title: High Resolution Observations of the Quiet Sun at 6 cm Using
the Westerbork Synthesis Radio Telescope
Authors: Kundu, M. R.; Rao, A. P.; Erskine, F. T.; Bregman, J. D.
1978BAAS...10Q.686K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Decameter Radio Observations of the 5 September, 1973 Flare
Authors: Gergely, T. E.; Kundu, M. R.
1978BAAS...10R.672G Altcode:
No abstract at ADS

---------------------------------------------------------
Title: High resolution observations of CTB 80 at 6.21 and 50
centimetres.
Authors: Velusamy, T.; Angerhofer, P.; Kundu, M. R.; Storm, R.
1978BASI....6...53V Altcode:
No abstract at ADS

---------------------------------------------------------
Title: 6 centimeter observations of solar bursts with 6" resolution.
Authors: Alissandrakis, C. E.; Kundu, M. R.
1978ApJ...222..342A Altcode:
During May 1974 data were collected on nine 6-cm solar bursts
originating in two active regions. One-dimensional fan-beam scans
were obtained every 30 seconds in order to study burst structure
and evolution. Maximum burst flux was in the 0.34-12.0 sfu range. At
maximum intensity the estimated brightness temperatures were in the
10 to the 6th to 2 x 10 to the 7th K range. Angular sizes ranged from
7-23 arcsec. In most cases an expansion of the burst core after maximum
intensity was observed along with a drift in the position of the burst
core. Four bursts were associated important H-alpha flares, and in all
cases burst maximum occurred before flare maximum. The bursts were
circularly polarized in the extraordinary mode sense during maximum
intensity. Since the polarization was the same over the extent of the
burst source, it is suggested that if the burst is associated with
loop sources, the emission is associated with one leg of the loop.

---------------------------------------------------------
Title: The association of nonthermal electrons with nonflaring
coronal transients.
Authors: Webb, D. F.; Kundu, M. R.
1978SoPh...57..155W Altcode:
A close temporal and spatial association has been found between erupting
filaments/coronal transients and radio noise storm continua. The three
transients studied occurred away from active regions and are members
of a class not usually accompanied by chromospheric emission. The
data analyzed were from the S-054 soft X-ray telescope on Skylab and
from one- and two-dimensional interferometers at meter and decameter
wavelengths at Nançay and Clark Lake observatories. Calculations
confirmed that observed microwave radiation from the transients is
due to thermal bremsstrahlung. The results are consistent with an
interpretation of heating of an increased amount of coronal plasma
by nonthermal, 10-100 keV electrons. Three possibilities for the
source of the material are described: (1) The filament material;
(2) evaporation from the chromosphere or transition region; and (3)
via a long-lived reconnection process.

---------------------------------------------------------
Title: Radio and White Light Observations of the 21 August 1973
Coronal Transient.
Authors: Gergely, T. E.; Kundu, M. R.
1978BAAS...10..456G Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Fine Structure and Time Variation of the Quiet Sun at 1.3 cm.
Authors: Rao, A. P.; Kundu, M. R.
1978BAAS...10..431R Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Radio Interferometric Observations of the Bright Core of
CTB 80.
Authors: Angerhofer, P. E.; Kundu, M. R.
1978BAAS...10..427A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Possible Explanation for the turnovers in Two Solar Microwave
Burst Spectra.
Authors: Ahmad, I. W.; Kundu, M. R.
1978BAAS...10..455A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Multifrequency observations of solar filaments at centimeter
wavelengths.
Authors: Kundu, M. R.; Fuerst, E.; Hirth, W.; Butz, M.
1978A&A....62..431K Altcode:
Summary. On June t5 and t6, t976 we observed solar filaments at five
wavelenths in the centimeter range. At t.2, 2.8, 6 and t t cm the
tOO-m-dish of the Max-PlanckInstitut fur Radioastronomie was used for
almost simultaneous measurements. In addition, the t3.7-m-telescope
of the University of Helsinki was used at a wavelength of 0.4cm. We
found a filament with a much larger size at radio than at optical
wavelengths. While the diameter of the radio filament turned out to
be about 2'., the one of the Ha-filament was only 0'S. This large
difference is explained in terms of a filament-cavity model and
the observations were used to determine the ratio of the electron
densities in the cavity and in the quiet region. We found a ratio of
about 3:4. Key words: solar filaments and cavities

---------------------------------------------------------
Title: A study of filament transition sheath from radio observations.
Authors: Rao, A. P.; Kundu, M. R.
1977SoPh...55..161R Altcode:
We have observed an Hα dark filament at 8, 15, and 22 GHz and derived
the radio spectrum of the filament. We suggest that the filament
has to be optically thick at radio frequencies and that the observed
spectrum is due to the presence of a transition sheath surrounding the
filament. We examine a model for the transition sheath in which the
energy radiated away is balanced by the conduction of heat from the
corona, and show that the radio observations indicate that little or
no thermal energy is conducted into the main body of the filament. We
compare the model with ultraviolet observations of filaments and
discuss how the discrepancies can be removed.

---------------------------------------------------------
Title: 2.8 and 6 cm wavelength observations of NGC 7822.
Authors: Angerhofer, P. E.; Kundu, M. R.; Becker, R. H.; Velusamy, T.
1977A&A....61..285A Altcode:
Summary. We present observations of the galactic radio source W 1 (=
NGC 7822) at wavelengths of 2.8 and 6 Cm. No linear polarization has
been detected over this region. We conclude that the known exciting
stars can account for the observed radio flux density at 6 Cm, and
that W 1 is a thermal radio source. Key words: Supernova remnants -
flux densities NGC7822 W1

---------------------------------------------------------
Title: Determination of the decameter wavelength spectrum of the
quiet Sun.
Authors: Erickson, W. C.; Gergely, T. E.; Kundu, M. R.; Mahoney, M. J.
1977SoPh...54...57E Altcode:
The Teepee Tee array of the Clark Lake Radio Observatory has been used
to compare the flux of the Sun with that of the sidereal sources Tau A
and Vir A at several frequencies in the range 109.0-19.0 MHz. Only the
two central banks of the E-W arm of the array were used as elements of
a phase switched interferometer so that the Sun could be observed as a
point source and compared directly to the sidereal sources. The Sun was
still partially resolved however, and appropriate corrections for this
effect were made. The observations were taken at times when the Sun and
either Tau A or Vir A were at the same declination. We have therefore
been able to derive the values for the solar flux, without having
to resort to a gain vs zenith distance correction. The observations,
combined with those available in the literature, allow us to derive
an accurate meter and decameter wavelength spectrum of the quiet Sun.

---------------------------------------------------------
Title: Coordinated X-ray, optical, and radio observations of YZ
Canis Minoris.
Authors: Karpen, J. T.; Crannell, C. J.; Hobbs, R. W.; Maran, S. P.;
Moffett, T. J.; Bardas, D.; Clark, G. W.; Hearn, D. R.; Li, F. K.;
Markert, T. H.; McClintock, J. E.; Primini, F. A.; Richardson, J. A.;
Cristaldi, S.; Rodono, M.; Galasso, D. A.; Magun, A.; Nelson, G. J.;
Slee, O. B.; Chugajnov, P. F.; Chugainov, P. F.; Efimov, Yu. S.;
Shakhovskoj, N. M.; Shakhovskoy, N. M.; Viner, M. R.; Venugopal,
V. R.; Spangler, S. R.; Kundu, M. R.; Evans, D. S.
1977ApJ...216..479K Altcode:
We report coordinated X-ray, optical, and radio observations of the
flare star YZ CMi, including the first occasion on which such a star has
been monitored in all three spectral regions simultaneously. Thirty-one
minor optical flares and 11 radio events were recorded. No major
optical flares greater than 3 magnitudes were observed during the
program. Although no flare- related X-ray emission was observed, the
measured upper limits in this band enable meaningful comparisons with
published flare-star models. Three of the five models predicting the
relative X-ray to optical or radio flare luminosities are in serious
disagreement with the observations. For the largest optical flare with
coincident X-ray co1verage, the 3 a upper limit on X-ray emission in
the 0.15-0.8 keV band is about 9 x 1028 ergs 5 - , corresponding to a
ratio of X-ray to B-band luminosity of &lt;0.3. Based on the present
results, the fraction of the galactic component of the diffuse soft
X-ray background contributed by UV Ceti-type flare stars is &lt;9 x
H, where H is the mean density of interstellar hydrogen within a few
hundred parsecs of the Sun. Subject headings: radio sources: variable -
stars: flare - stars: individual - X-rays: bursts

---------------------------------------------------------
Title: Observations of the quiet Sun at meter and decameter
wavelengths.
Authors: Kundu, M. R.; Gergely, T. E.; Erickson, W. C.
1977SoPh...53..489K Altcode:
The new TeePee Tee array of the Clark Lake Radio Observatory has
been used to observe the quiet Sun at 121.5, 73.8 and 26.3 MHz. The
equatorial brightness distributions at all three frequencies, and
the polar brightness distributions at the two higher ones have been
measured. From the observed total fluxes and half-power diameters we
have derived the peak brightness temperatures of the solar disk as
well as of some sources of the slowly varying component.

---------------------------------------------------------
Title: 3.5mm Depression features associated with Hα `disparitions
brusques'
Authors: Kundu, M. R.; Lantos, P.
1977SoPh...52..393K Altcode:
The characteristics of 3.5 mm depression features associated with two
`disparition brusques' observed in Hα are discussed. The millimeter
depressions still exist, although reduced in strength, after the
disappearance of the Hα filament. The two depressions correspond to
temperatures of 600 and 450 K before and to 200 and 250 K after the
Hα filament disappearance.

---------------------------------------------------------
Title: 6 centimeter observations of solar active regions with 6"
resolution.
Authors: Kundu, M. R.; Alissandrakis, C. E.; Bregman, J. D.; Hin, A. C.
1977ApJ...213..278K Altcode:
We have used the Westerbork Synthesis Radio Telescope for observations
of solar active regions at 6 cm during 1974 May 8-10. The particular
problems of using a sidereal instrument for solar observations are
discussed. Maps of total intensity and circular polarization were
obtained for four active regions with sunspots and a plage region;
the linear polarization was below the noise limit. The brightest
components of the 6 cm emission are associated with sunspots, while
weaker components are associated with the plage magnetic fields, both
longitudinal and transverse. An inversion of the sense of circular
polarization was observed in the preceding part of a region with
bipolar magnetic-field structure, about two days after the region
passed through the central meridian. Nine bursts were also observed,
and their one-dimensional positions with respect to the associated
active regions are given.

---------------------------------------------------------
Title: Brightness distributions of the Sun at 33 and 37 GHz.
Authors: Kundu, M. R.; Liu, S. -Y.; McCullough, T. P.
1977SoPh...51..321K Altcode:
The brightness distributions of the Sun were observed at 33 and
37 GHz. Maximum limb brightening of about 10% was observed at both
frequencies.

---------------------------------------------------------
Title: Polarization Properties of Solar Bursts at 6 cm Wavelength.
Authors: Kundu, M. R.; Allisandrakis, C. E.
1977BAAS....9R.328K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Determination of the Decameter Wavelength Spectrum of the
Quiet Sun.
Authors: Erickson, W. C.; Gergely, T. E.; Kundu, M. R.; Mahoney, M. J.
1977BAAS....9..371E Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Decameter Observations of the White Light Coronal Transient
of October 27, 1973
Authors: Gergely, T. E.; Kundu, M. R.; Erickson, W. C.
1977BAAS....9Q.369G Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A Study of Filament Transition Sheath from Radio Observations.
Authors: Rao, A. P.; Kundu, M. R.
1977BAAS....9..314R Altcode:
No abstract at ADS

---------------------------------------------------------
Title: 5 GHz observations of galactic supernova remnants.
Authors: Angerhofer, P. E.; Becker, R. H.; Kundu, M. R.
1977A&A....55...11A Altcode:
Brightness and polarization distributions over several galactic
supernova remnants have been observed at a wavelength of 6 cm. These
observations have confirmed the nonthermal nature of most of
the observed sources. It is suggested, however, that the objects
G33.1-0.1 (KES 78), G35.6-0.0, G37.6-0.1, G37.7+0.1, and G37.9-0.4 are
thermal. The results of these observations are presented in the form
of total intensity contour maps with superimposed polarization vectors.

---------------------------------------------------------
Title: A comparison of positions and sizes of sources of centimeter
and X-ray bursts.
Authors: Kundu, M. R.; Alissandrakis, C. E.; Kahler, S. W.
1976SoPh...50..429K Altcode:
We have made a parallel study of three cm-λ radio bursts, observed
on 9 August, 1973 with the NRAO 1 three-element interferometer at 3.7
and 11.1 cm and the associated X-ray flares observed with the S-054
telescope aboard Skylab. Within the errors of our measurements (±
5″) the radio and X-ray events are cospatial. We find good agreement
between the size of the X-ray kernel and that of the core of the cm
burst, while there is evidence that much of the impulsive radio flux
was produced in a larger area.

---------------------------------------------------------
Title: Observations of Solar Bursts at 6 cm Wavelength with Angular
Resolution of 6" arc.
Authors: Alissandrakis, C. E.; Kundu, M. R.
1976BAAS....8Q.555A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Observations of Jupiter's Radio Emission at 327 MHz and 1410
MHz During the Pioneer 11 Fly
Authors: Kundu, M. R.; Sarma, N. V. G.; Gerard, E.
1976BAAS....8..504K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Observation of a coronal hole at 85 GHz.
Authors: Kundu, M. R.; Liu, S. -Y.
1976SoPh...49..267K Altcode:
A coronal hole was observed at 85 GHz(3.5 mm-λ) on November 24,
1970, when a spectacular coronal hole was observed in soft X-rays by
AS&amp;E. The millimeter counterpart of the hole is much weaker and
less widespread than in X-rays. The brightness temperature inside the
hole was in most places about 100-200 K lower than the mean brightness
temperature of the Sun at 85 GHz.

---------------------------------------------------------
Title: Observations of intensity and linear polarization of CTB 80
at 6 and 2.8 cm.
Authors: Velusamy, T.; Kundu, M. R.; Becker, R. H.
1976A&A....51...21V Altcode:
The paper presents observations of the distribution of intensity and
linear polarization over the radio source CTB 80 at 6 and 2.8 cm. The
physical nature of the source is examined, particularly the relation
between the strong central component and a ridgelike structure that
extends across the northern half in the E-W direction. The structure,
nonthermal spectrum, and polarization of the central component are found
to be very similar to those of a supernova remnant, but the ridge is
shown to be unlike any feature of any other SNR. It is suggested that
the ridge may have resulted from expansion of the remnant shell into
a dense interstellar cloud or, alternatively, that CTB 80 might be a
nearby extragalactic radio source similar to Centaurus A.

---------------------------------------------------------
Title: 3.7 and 11.1 centimeter observations of the radio galaxy
3C 386.
Authors: Becker, R. H.; Kundu, M. R.
1976ApJ...207...29B Altcode:
We present radio observations of the radio galaxy 3C 386 at 3.7 and 11.1
centimeter wavelengths. The observations show that 3C 386 is composed
of two extended components and a pointlike source midway between the
two extended components which is coincident with an optical galaxy. The
radio emission from the extended components is highly polarized. Subject
headings: galaxies: individual - polarization - radio sources: extended

---------------------------------------------------------
Title: A decameter type II burst associated with a behind-the-limb
flare.
Authors: Gergely, T. E.; Kundu, M. R.
1976SoPh...48..357G Altcode:
The characteristics of a decameter type II burst associated with a
possible behind-the-limb flare are discussed. The burst source had an
unusually high velocity. Assuming that the disturbance propagated as
an MHD wave, the magnetic field strength at the 40 MHz plasma level
is estimated to be 5.6 gauss.

---------------------------------------------------------
Title: High-resolution radio observations of three supernova remnants.
Authors: Becker, R. H.; Kundu, M. R.
1976ApJ...204..427B Altcode:
The paper presents and discusses radio observations of three supernova
remnants (G21.5-0.9, G29.7-0.3, and 3C 391) made at 3.7 and 11.1
centimeters. The supernova remnant G21.5-0.9 has an elliptical
brightness distribution and is similar to the Crab Nebula as well
as 3C 58 in appearance and spectrum. The two remnants G29.7-0.3 and
3C 391 both show a broken shell structure typical of most galactic
supernova remnants.

---------------------------------------------------------
Title: A Search for Radio Halos Around Pulsars
Authors: Velusamy, T.; Kundu, M. R.
1976ApL....17..177V Altcode:
Observations of regions around 24 pulsars at 11, 21, and 40 cm are
presented. Very extended sources have been observed close to the nearby
pulsars 1642-03 and 1706-16. Double source structure with the pulsar
on the line of separation has been found around four pulsars. The
proper motions of pulsars 0823 + 26, 0834 + 06, 1133 + 16, and 2016 +
28 seem to be consistent with their possible association with the nearby
continuum sources. The possibility that some of these sources may be
radio halos or ghost remnants associated with the pulsars is discussed.

---------------------------------------------------------
Title: Differential rotation of the solar atmosphere as determined
from millimeter data.
Authors: Liu, S. -Y.; Kundu, M. R.
1976SoPh...46...15L Altcode:
Radiospectroheliograms obtained at millimeter wavelengths were used
to determine the rotation of the solar atmosphere. Regions observed
in both emission as well as absorption (associated with Hα dark
filaments) were followed across the disk. The average sidereal
rotation rate deduced from emissive regions is given by ω (deg
day-1)=14.152(±0.270)-4.194(±3.017)sin2B,
where B is the heliographic latitude and the quoted errors
are the standard deviations of a least squares fit to the
data. The rate deduced from absorption regions is given by
ω=14.729(±0.286)-1.050(±1.611)sin2B. This rate is larger
than that of emissive regions at all latitudes and shows smaller
differential rotation. This apparent difference in the rotation rates
is probably due to the difference in the height of formation of the
emissive and absorption regions. This difference could be used to
estimate the difference in height between an emissive region and an
absorption feature in millimeter radiation.

---------------------------------------------------------
Title: Observations of Jupiter's Radio Emission at 327 MHz and 1410
MHz During the Pioneer 11 Fly-By"
Authors: Kundu, M. R.; Sarma, N. V. G.; Gerard, E.
1976ApL....18...41K Altcode:
During the 1974 fly-by of Jupiter by the Pioneer 11 spacecraft, radio
observations were carried out daily at 327 and 1410 MHz for a period
of 60 days centered on December 3, 1974, the day of closest approach to
Jupiter. The 1410-MHz data reveal two significant short-term variations
in the Jovian radio emission; the largest one is probably present also
at 327 MHz although Faraday rotation in earth's ionosphere could have
affected the data. The two radio bursts appear to be correlated with
two long-duration electron bursts observed in the energy ranges from
2 to 7 and 6 to 30 MeV.

---------------------------------------------------------
Title: On the Structure of Filaments from Centimeter and Millimeter
Observations
Authors: Butz, M.; Fuerst, E.; Hirth, W.; Kundu, M. R.
1975SoPh...45..125B Altcode:
From filament observations at centimeter and millimeter wavelengths it
is shown that the transition layer between the dense, cool filamentary
material and the ambient hot, rarified corona is rather thin, of the
order of some hundred kilometers. Hence, the difference in the sizes
of filaments in the radio and optical domains is of the order of 1000
km or 2″, thus not detectable by the instruments so far used for
observations of filaments.

---------------------------------------------------------
Title: A search for periodic variations of solar radio emission at
3.7- and 11.1-cm wavelengths.
Authors: Kundu, M. R.; Alissandrakis, C. E.
1975MNRAS.173...65K Altcode:
Periodic time variations in the emission of quiet solar regions were
sought with the NRAO three-element interferometer at 3.7 and 11.1
cm. The visibility function of a source as obtained with a tracking
interferometer is an implicit function of time, because of projected
baseline changes, and therefore only observations taken when the
baseline changes vary slowly with time were used. The visibility
function shows significant time variations, but a power-spectrum
analysis of the data revealed no unique periodicity.

---------------------------------------------------------
Title: Comments on the Quiet Sun Brightness Distribution at 1.2
mm Wavelength
Authors: Kundu, M. R.; Liu, S. -Y.
1975SoPh...44..361K Altcode:
A re-analysis of the brightness distribution of the quiet Sun at 1.2
mm wavelength is made. It is concluded that there is no evidence for
uniform or limb-brightened distribution at this wave-length.

---------------------------------------------------------
Title: Observations at 6 CM of the solar active region
Authors: Kundu, M. R.; Alissandrakis, C. E.
1975Natur.257..465K Altcode:
Preliminary results are reported for the synthesis of a solar active
region from observations with a synthesis radio telescope at a
wavelength of 6 cm. Several individual sources are observed in the
total-intensity and circular-polarization maps. These are shown to
correspond to two large sunspots, two groups of small sunspots, and a
plage. A magnetogram indicates that this active region had a bipolar
structure with positive polarity concentrated on the main sunspots
and negative polarity scattered over the plage and some of the small
sunspots. It is noted that several radio bursts were recorded during
the observation period and that one corresponded to a H-alpha flare
near one of the sunspot groups.

---------------------------------------------------------
Title: Observations of nine supernova remnants at 10.6 GHz.
Authors: Becker, R. H.; Kundu, M. R.
1975AJ.....80..679B Altcode:
Intensity contour and polarization observation maps of nine supernova
remnants at a microwave frequency are presented and discussed. The
data provided are the highest-frequency (10.6 GHz) measurements to
date for several of these sources and should therefore be useful in
determining their spectra. Polarization ranges from 2 or 3% to as high
as 40-50%. Integrated fluxes for the sources vary from about 3 to more
than 25.

---------------------------------------------------------
Title: Depolarization of five supernova remnants: internal and
external Faraday effects.
Authors: Velusamy, T.; Kundu, M. R.
1975A&A....41..307V Altcode:
Summary. Depolarization in five supernova remnants Kes 69, W44,
1C443, 3Ct0 and 3C58 has been investigated using the polarization
measured at 2.8, 6, t t and 2t cin with equivalent resolutions. The
polarization data for certain regions in Kes 69, W 44 and IC 443
would be best interpreted if it were assumed that the depolarization
is caused by an internal Faraday effect in the source. The physical
parameters such as the internal and external rotation measures and
the degree of inhomogeneity within the source have been derived
from source models for internal depolarization. The sources Kes 69,
W 44 and IC 443 seem to have large internal rotation measures and the
rotation of the plane of polarization suggests deviations from the
2-law at long wavelengths. 3 C to and 3 C 58 have very small internal
Faraday effects. A possibility of depolarization due to the observed
variations of the external rotation measure across the remnants is
also examined. In either case, the depolarization was found to be
negligible at 2.8 cm in all these sources. When internal Faraday
rotation effects are present, the frequently assumed 2-law for the
rotation of the plane of polarization is found to be valid only for
wavelengths shorter than a critical value which in turn depends on
the amount of internal Faraday rotation in the source. Key words:
supernova remnants linear polarization Faraday rotati6n depolarization

---------------------------------------------------------
Title: High Resolution Polarization Observations of a Solar Active
Region at 6 cm.
Authors: Alissandrakis, C. E.; Kundu, M. R.
1975BAAS....7..473A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: 6 cm Observations of A Solar Active Region with the Westerbork
Synthesis Radio Telescope.
Authors: Kundu, M. R.; Alissandrakis, C. E.; van Someren Greve, H. W.
1975BAAS....7..235K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Decameter Storm Radiation, II
Authors: Gergely, T. E.; Kundu, M. R.
1975SoPh...41..163G Altcode:
The physical properties of six decametric storms, observed at Clark
Lake Radio Observatory are studied. The height of the storm continuum
sources was determined from the rotation rate. Assuming that the
radiation originates at the plasma frequency we computed the gradient
of electron density for the regions where the storms originate. The
mean angular size of the decametric continuum sources is large; it
increases with decreasing frequency. The storm continuum is found to be
strongly directive toward the disk center. The east-west asymmetry, well
observed at meter wavelengths is also observed at decameter wavelengths.

---------------------------------------------------------
Title: A Possible Relation Between z-Distribution and Spectral Index
for Galactic Supernova Remnants.
Authors: Becker, R. H.; Kundu, M. R.
1975BAAS....7R.247B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: High Resolution Observations of Solar Bursts at 3.7 and 11.1
cm Wavelengths
Authors: Alissandrakis, C. E.; Kundu, M. R.
1975SoPh...41..119A Altcode:
Four bursts were observed on August 9, 1973 with the NRAO 1 3-element
interferometer at 3.7 and 11.1 cm. By using a simple source model we
have calculated the temperature, flux, size and position of the small
scale components of the bursts as a function of time. We obtained
peak temperatures around 107 K for the components with
size of about 10″ at 11.1 cm and 3″ at 3.7cm. The peak flux
of these components lies between 4 and 40 % of the total peak flux
of the bursts. Two of the bursts were found to be right circularly
polarized. There is evidence that the location of these two bursts does
not coincide with the location of the brightest point of the associated
active regions. The existence of burst structures with temperatures
of the order of 107K indicates that at least part of the
radiation in these bursts is generated by a non-thermal mechanism.

---------------------------------------------------------
Title: Highly polarized radio outburst from Cygnus X-3.
Authors: Seaquist, E. R.; Gregory, P. C.; Perley, R. A.; Becker,
R. H.; Carlson, J. B.; Kundu, M. R.; Bignell, R. C.; Dickel, J. R.
1975JRASC..69...42S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A possible relation between spectral index and z-distribution
for supernova remnants.
Authors: Becker, R. H.; Kundu, M. R.
1975A&A....38..149B Altcode:
A statistical relation has been found between spectral index and the
mean distance from the galactic plane for supernova remnants. Using
z-distances calculated from the Sigma-D relationship and the observed
spectral indices at radio frequencies for 93 galactic supernova
remnants, the mean z-distance is found to vary from 175 pc to 60 pc
for remnants with flat and steep spectra, respectively. A possible
correlation between flat-spectra supernova remnants and pulsars is
discussed.

---------------------------------------------------------
Title: Ghost remnants around pulsars.
Authors: Velusamy, T.; Kundu, M. R.
1975BASI....3R..35V Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Highly polarised radio outburst from Cygnus X-3
Authors: Seaquist, E. R.; Gregory, P. C.; Perley, R. A.; Becker,
R. H.; Carlson, J. B.; Kundu, M. R.; Bignell, R. C.; Dickel, John R.
1974Natur.251..394S Altcode:
WE report here the results of extensive observations of a new series
of outbursts from Cyg X-3 which we commenced following the recent
IAU telegram alert from Sir Martin Ryle. A high degree of linear
polarisation has been discovered in one of the recent outbursts. The
degree of polarisation changes over a period of 17 d and reaches a
maximum of 14%. The observations indicate a high degree of order in
the source magnetic field and that a thermal plasma coexists with the
radiating relativistic electrons. In addition, a new upper limit of
0.05” has been obtained for the angular size of Cyg X-3, together
with an improved position for the source.

---------------------------------------------------------
Title: Polarization of supernova remnants: internal Faraday effects
and derived magnetic fields.
Authors: Velusamy, T.; Kundu, M. R.
1974BASI....2...38V Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Observations of intensity and linear polarization in supernova
remnants at 11 cm wavelength.
Authors: Velusamy, T.; Kundu, M. R.
1974A&A....32..375V Altcode:
Summary. Distributions of intensity and linear polarization at 11 cm in
twenty-four galactic sources in the northern sky are presented. The
observations were made with angular resolution of 5' using the
300-ft. telescope of the National Radio Astronomy Observatory. Twenty
sources were mapped in both total and polarized intensities and four
were mapped in total intensity only The present maps at 11 cm have
the highest resolution yet attained on many of these sources. Our
results indicate that the galactic sources G 53.9+0.3, G 54.4-0.3,
G 69.0+2.7 and G 93.4+1.8 are possible supernova remnants which until
now are not listed as such in any of the catalogues. Observations of
linear polarization at 6 cm in two sources, 3 C 434.1 and G 93.4+ 1.8,
are also presented. The characteristics of the observed sources are
discussed. Key words: supernova remnants - linear polarization

---------------------------------------------------------
Title: High Resolution Observations of Five Possible Supernova
Remnants at Centimeter Wavelengths.
Authors: Becker, R. H.; Kundu, M. R.
1974BAAS....6..313B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Absence of Periodic Variation in Solar Radiation at 3.7 cm
and 11.1 cm Wavelengths.
Authors: Alissandrakis, C.; Kundu, M. R.; Becker, R. H.
1974BAAS....6..348A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Meter and decameter wavelength positions of solar bursts of
July 31 August 7, 1972
Authors: Kundu, M. R.; Erickson, W. C.
1974SoPh...36..179K Altcode:
The positional analysis of solar bursts at meter and decameter
wavelengths observed during the period July 31-August 7, 1972 is
presented. Most of the activity during this period was associated with
the active regions McMath 11976 and 11970. Except near the CMP of
region 11976, two regions of continuum emission were observed - one
a relatively smooth continuum and the other a continuum superimposed
with many type III's and other fine structure. It seems possible to
interpret these continua in terms of plasma waves originating from
two sources located at different heights or with different electron
density gradients. The angular size of type III sources seems to
increase with decreasing frequency. This implies that the open field
lines along which the type III electrons travel have larger angular
extent at greater heights.

---------------------------------------------------------
Title: Observations of Coronal Disturbances from 1 to 9
Rsun. II: Second Event of 1973, January 11
Authors: Stewart, R. T.; Howard, R. A.; Hansen, F.; Gergely, T.;
Kundu, M.
1974SoPh...36..219S Altcode:
Observations of a coronal disturbance on 1973 January 11 commencing at
18h01m UT are described. The event is homologous
with an earlier disturbance from the same region of the corona. The
observations suggest that a cloud of coronal gas containing ∼ 4 ×
1039 electrons propagated outwards to ⩾ 5 R⊙
behind a piston-driven shock wave travelling at a velocity of 800 to
1200 km s−1.

---------------------------------------------------------
Title: Polarization of supernova remnants KE 69, G 357.7-0.1, HC 26,
and gamma Cygni at 6- and 2.8-cm wavelengths.
Authors: Kundu, M. R.; Velusamy, T.; Hardee, P. E.
1974AJ.....79..132K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Decameter Type IV Bursts Associated with Coronal Transients
Authors: Gergely, T. E.; Kundu, M. R.
1974SoPh...34..433G Altcode:
The characteristics of four moving type IV bursts, observed with
the 65-20 MHz sweptfrequency interferometer of the Clark Lake
Radio Observatory are discussed. All four bursts were associated
with depletions in the electron content of the white light
corona. Characteristics of the bursts are not unique, i.e. they differ
in source size, structure, duration and their association with other
radio bursts. Following Smerd and Dulk (1971) we believe that a shock
wave, moving out from the flare site is responsible for the expansion
of a magnetic arch or the ejection of a plasmoid which is observed as
the usual type IV burst. Behind the shock wave, the compressed coronal
gas moves outward, and as it expands it causes a depletion of electrons
in the inner corona. After the passage of the shock wave, sometimes the
coronal magnetic field structure is restored to its initial situation,
as evidenced by the observation of homologous transients.

---------------------------------------------------------
Title: Meter and Decameter Wavelength Positions of Solar Radio Bursts
of July 31-AUGUST 7, 1972 (presented by W.C. Erickson)
Authors: Kundu, M. R.; Errickson, W. C.
1974IAUS...57..231K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Long Base Line Interferometry of the Sun at 3.7 and 11.1
cm Wavelengths.
Authors: Kundu, M. R.; Alissandrakis, C.; Becker, R. H.
1974BAAS....6..219K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Fine Structure of a Solar Flare Region at 3.7 and 11.1 cm
Wavelengths
Authors: Kundu, M. R.; Velusamy, T.; Becker, R. H.
1974SoPh...34..217K Altcode:
On June 9, 1973, a flare associated burst was observed with the NRAO
3-element interferometer at 3.7 and 11.1 cm wavelength. The burst was of
`gradual rise and fall' type. Comparing the fringe amplitudes at 3.7
cm to the visibility computed for model flare regions we found that
the precursor data are best fitted by a region of 3″ in size while at
the time of the peak, the flare appears to have a size of 2″. During
the post-maximum phase a size of 5″ is the best estimate. Similar
computations have been done for 11.1 cm data. The peak brightness
temperatures are 1.2 × 109 K and 1.65 × 108 K
at 3.7 and 11.1 cm respectively. Such high temperatures would imply that
a significant fraction of the burst radiation has a non-thermal origin.

---------------------------------------------------------
Title: Fine Structure of a Solar Active Region at 3.7 and 11.1
cm Wavelengths
Authors: Kundu, M. R.; Becker, R. H.; Velusamy, T.
1974SoPh...34..185K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Fine structure of the sun at centimeter wavelengths.
Authors: Kundu, M. R.; Velusamy, T.; Becker, R. H.
1974IAUS...56...65K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Long Base-Line Interferometry of the Sun at Centimeter
Wavelengths
Authors: Kundu, M. R.
1974cesra...4...21K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Fine Structure of the Sun at 1.3 cm Wavelength
Authors: Kundu, M. R.; Velusamy, T.
1974SoPh...34..125K Altcode:
The two-element interferometer at Hat Creek Observatory was used at
1.3 cm wavelength to study the fine structure of the radio emissive
regions on the Sun. Observations of the quiet Sun at 1.3 cm show sudden
changes in the fringe amplitude and phase, lasting for typically about
5-8 min. Assuming that these events are identical in nature, a plot
of peak amplitude vs the projected baseline at the time of the event
suggests emission from a region of angular size of about 10″. The
corresponding brightness temperature is 50000 K. It is possible that
these events may be related to the appearance and disappearance of
groups of spicules or mottles.

---------------------------------------------------------
Title: Decameter Type IV Bursts Associated with Coronal Transients.
Authors: Gergely, T. E.; Kundu, M. R.
1974BAAS....6..218G Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Polarization of Solar Active Regions at 3.5 Millimeter
Wavelength
Authors: Kuńdu, M. R.; Gergely, T.
1973SoPh...31..461K Altcode:
A study of the circular polarization structure of solar active regions
has been made from data obtained at 3.5 mm wavelength, using the 36 ft
diameter radio telescope of the National Radio Astronomy Observatory
at Kitt Peak, Arizona. The angular resolution of the telescope at
this wavelength is 1'.2. All important active regions observed at 3.5
mm are bipolar in nature; the degree of polarization ranges from 1
to about 2%. These oppositely polarized components correspond with
the Mt. Wilson magnetic regions of opposite polarity; the line of
zero polarization delineates the neutral line between the regions of
opposite polarity on magnetograms. The longitudinal magnetic fields at
the level of 3.5 mm emission computed from the degree of polarization
are found to be several hundred gauss.

---------------------------------------------------------
Title: Interferometric Measurements of the Compact Source 2048 + 31
Authors: Becker, R. H.; Kundu, M. R.
1973NPhS..244..138B Altcode: 1973Natur.244..138B
OUR observations at 6 cm with a pencil beam of 6 arc min (ref. 1)
and others at 11 and 3 cm with pencil beams of 4.8 and 1.2 arc min
respectively (N. J. Keen, private communication) revealed a compact
radio source several arc min north of the centre of the Cygnus Loop. The
3 cm observations failed to resolve the source, implying an angular
size of less than 1 arc min.

---------------------------------------------------------
Title: Solar Active Regions at 9 and 3.5 mm Wavelengths under
Disturbed Conditions
Authors: Kundu, M. R.; Liu, Sou-Yang
1973SoPh...29..409K Altcode:
Some properties of solar active regions at 9 and 3.5 mm wavelengths
under disturbed conditions are discussed. New regions develop or weak
regions intensify at millimeter wavelengths as a result of flares
at distant sites. The spectra of the peak flux density of moderately
strong bursts observed at 9 mm show a sharp drop toward the shorter
millimeter wavelengths. The weak bursts at 3.5 mm manifest mainly as
heating phenomena.

---------------------------------------------------------
Title: Polarization of the supernova remnant HB21 at 11-cm wavelength
Authors: Kundu, M. R.; Becker, R. H.; Velusarny, T.
1973AJ.....78..170K Altcode:
Linear polarization at 11-cm wavelength has been detected in the
supernova remnant HB2 1. The degree of polarization varies from about
2% to as much as 20% in some regions. Comparison between the 11-
and 6-cm wavelength polarization measurements yields the rotation
measure, depolarization, and magnetic field distribu- tions over HB2
1. Over most of the remnant, the field appears to be the compressed
interstellar field. The depolarization at 11 cm is primarily due to
the steep gradient of the rotation measure. Large rotation measure
appears to occur in regions of enhanced optical emission.

---------------------------------------------------------
Title: Observations of the HII region S101 in Cygnus
Authors: Velusamy, T.; Kundu, M. R.
1973AJ.....78...31V Altcode:
Observation of 5101 at 11- and 6-cm wavelengths with beams of 5 and
6 arcsec respectively, are presented. The physical parameters of the
H II region have been deduced from the radio data. The excitation
parameter of the central exciting star of spectral type O7 is 47 pc
cm-2.

---------------------------------------------------------
Title: Millimeter Wavelength Observations of Solar Active Regions
Authors: Kundu, M. R.
1973NASSP.342..104K Altcode: 1973heps.conf..104K
No abstract at ADS

---------------------------------------------------------
Title: Polarization Structure of a Solar Flare Region at 9.5 mm
Wavelength
Authors: Kundu, M. R.; McCullough, T. P.
1972SoPh...27..182K Altcode:
Polarization structure of an active region that produced a minor
flare around 1900 UT on September 28, 1971 was measured at 9.5 mm
wavelength using the 85-ft telescope of the Naval Research Laboratory
Maryland Point Observatory. The angular resolution of the telescope
at this wavelength is 1.6'. The flare region underwent changes both
in the degree of polarization as well as in its polarization structure
before and after the start of the flare. These changes in the degree of
polarization correspond to a decrease of longitudinal magnetic field
of about 200 G at the chromospheric levels where the 9.5 mm radiation
originates. Observations on the polarization structure of active regions
for several days before and after September, 1971 are also presented.

---------------------------------------------------------
Title: The Quiet Sun Brightness Distributions at Millimeter
Wavelengths and Chro mospheric Inhomogeneities
Authors: Lantos, P.; Kundu, M. R.
1972A&A....21..119L Altcode:
Summary. The quiet sun brightness distributions at 9 and 3.5 mm
wavelengths are presented. The distribution at 9 mm shows definite
limb brightening whereas the distribution at 3.5 mm shows slight
limb darkening. The distribution at 1.2 mm wavelength is known to
exhibit definite limb darkening (Kundu, 1971). These distributions are
interpreted in terms of a two-component chromospheric modeL Key words:
sun - radiomillimetric wavelength - chromosphere - inhomogeneities

---------------------------------------------------------
Title: Brightness and polarization structure of four supernova
remnants 3C 58, IC 443, W28, and W44 at 2.8 centimeter wavelength.
Authors: Kundu, M. R.; Velusamy, T.
1972A&A....20..237K Altcode:
Summary. Distributions of brightness and polarization over four
supernova remnants 3C58, IC443, W28 and W44 have been measured at 2.8
centimeter wavelength with a beam of 3'. Distributions of rotation
measure over these sources have been computed by comparing the
present data with the data at longer wavelengths. Significantly large
variations of rotation measure over all the four sources have been
observed. The rotation measure varies systematically over the sources
3C58 and W44. Possible origin of the Faraday rotation entirely in the
interstellar medium outside the remnants is discussed. The distributions
of the orientation of the projected magnetic field, derived from our
data indicate very uniform orientation for the magnetic fields over
both 3C58 and W44. There is no evidence for radial magnetic field
in IC443. In W28, the projected magnetic field is tangential to the
northern shell part of the remnant. The physical parameter for the
remnants resulting from this study are given. Key words: supernova
remnants - brightness - polarization

---------------------------------------------------------
Title: Observations of the Cygnus Loop at 6-cm Wavelength
Authors: Kundu, M. R.; Becker, R. H.
1972AJ.....77..459K Altcode:
Brightness and polarization distributions of the Cygnus Loop have been
measured at 6-cm wavelength. Strong polarization of up to 25% has
been observed throughout the source south of b =31 OO . Significant
polarization has been detected in the northeastern shell region
(NGC 6992-95). The derived magnetic-field distribution is found to be
tangential to the southern boundary of the source, in agreement with
previously published results.

---------------------------------------------------------
Title: Observations of Prominences at 3.5 Millimeter Wavelength
Authors: Kundu, M. R.
1972SoPh...25..108K Altcode:
At 3.5 mm wavelength absorption features are observed in correspondence
with Hα dark filaments on the disk; beyond the limb the prominences
correspond to emissive regions. The absorption features are larger
(2'-3' arc) than the corresponding Hα dark filaments; the emissive
regions at the limb have similar angular sizes. The emissive regions
at the limb have electron temperatures of 5500±500 K; the amount of
absorption observed on the disk leads to mean electron densities of
about 5 × 1010 per cm3.

---------------------------------------------------------
Title: Polarization of Solar Active Regions at 9.5 mm Wavelength
Authors: Kundu, M. R.; McCullough, T. P.
1972SoPh...24..133K Altcode:
A study of the circular polarization structure of solar active regions
has been made from data obtained at 9.5 mm wavelength, using the 85 ft
reflector and polarimeter at the Naval Research Laboratory Maryland
Point Observatory. The angular resolution of the telescope at this
wavelength is 1'.6. All important active regions observed at 9.5 mm
are bipolar in nature, the degree of polarization is about the same
for both right and left circular components and it ranges up to about
4%. These oppositely polarized components correspond with the Mt. Wilson
magnetic regions of opposite polarity; the line of zero polarization
delineates clearly the neutral line between the regions of opposite
polarity on magnetograms. Unipolar regions in magnetograms also show
up as unipolar regions at 9.5 mm. Magnetic fields as low as 5-10 G on
magnetograms manifest as distinctly polarized regions on 9.5 mm maps. A
line of zero polarization seems to delineate the extent of `absorption
features' observed at 9.5 mm in coincidence with Hα dark filaments.

---------------------------------------------------------
Title: Solar Radio Emission at 1.2 mm Wavelength
Authors: Kundu, M. R.
1971SoPh...21..130K Altcode:
Some properties of solar active regions at 1.2 mm wavelength are
discussed. Equatorial and polar brightness distributions of the quiet
Sun at 1.2 mm wavelength are also presented.

---------------------------------------------------------
Title: Structure of Non-thermal Radio Source G 55.7+3.4 in the
Direction of CP1919
Authors: Kundu, M. R.; Velusamy, T.
1971NPhS..234...54K Altcode: 1971Natur.234...54K
Caswell and Goss1 have reported the detection of an
extended radio source G55.7+3.4 at 2,700 and 178 MHz in the direction
of the pulsar CP 1919, and because of its non-thermal spectrum they
have proposed that it might be a galactic supernova remnant (SNR)
associated with the pulsar. They pointed out, however, that the
age (5 × 104 yr) and distance (7.5 kpc) of the assumed
supernova remnant G55.7+3.4, calculated from its observed parameters,
did not agree with those (age 107 yr and distance 300 to
1,800 pc) of the pulsar CP 1919 calculated from the observed period,
its rate of slowing down, 21 cm absorption studies and dispersion
measure. But1 these estimates are crude and consequently the
apparent association should not be discarded as a chance coincidence. To
investigate this apparent association further, we have mapped the region
G55.7+ 3.4 at 11 and 21 cm wavelengths, with the 300 foot resurfaced
telescope of the National Radio Astronomy Observatory.

---------------------------------------------------------
Title: Brightness and polarization structure of four supernova
remnants at 2.8 centimeter wavelength.
Authors: Kundu, M. R.; Velusamy, T.
1971BAAS....3..499K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Polarization of Solar Active Regions at 9 millimeter Wavelength
Authors: Kundu, M. R.; McCullough, T. P.
1971BAAS....3R.449K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Polarization of the Supernova Remnant HB 21 AT a Wavelength
of 6 Centi-Meters
Authors: Kundu, M. R.
1971ApJ...165L..55K Altcode:
Linear polarization at 6-cm wavelength has been detected in the
supernova remnant HB 21. The degree of polarization varies from about 10
percent to as much as 30 percent in some regions. A detailed comparison
between the map at 6-cm wavelength obtained with a resolution of 6'
of arc and the optical picture of the remnant shows that the general
shape and boundary of the optical nebula correspond roughly with the
outermost radio contours. Some bright radio spots within the remnant
have diffuse optical nebulosities associated with them.

---------------------------------------------------------
Title: Polarization of Tycho's Supernova Remnant at a Wavelength of
2.8 Centimeters
Authors: Kundu, M. R.; Velusamy, T.
1971ApJ...163..231K Altcode:
The polarized-brightness distribution for Tycho's supernova remnant
has been obtained at a wavelength of 2.8 cm. The degree of linear
polarization varies considerably over the source from 8 percent near
the outer boundary to nearly zero at the center; the orientation of the
electric vectors is circumferential. From a comparison of the 2.8-cm
map with similar maps obtained at other wavelengths, the distributions
of spectrum, rotation measure, and depolarization over the source have
been studied.

---------------------------------------------------------
Title: Active Regions at Millimeter Wavelength and the Measurement
of Magnetic Fields
Authors: Kundu, M. R.
1971IAUS...43..642K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Polarization of 3C10, 3C58 and several other radio sources
at 2.8 Centimeter Wavelength
Authors: Kundu, M. R.; Velusamy, T.
1971BAAS....3...21K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Solar Bursts at Decameter and Hectometer Wavelengths
Authors: Kundu, M. R.
1971ASSL...27..287K Altcode: 1971psc..conf..287K
No abstract at ADS

---------------------------------------------------------
Title: Positions and Motions of Solar Bursts at Decameter Wavelengths
Authors: Kundu, M. R.; Erickson, W. C.; Jackson, P. D.; Fainberg, J.
1970SoPh...14..394K Altcode:
The positions and motions of solar bursts in the range 20 to 60 MHz have
been measured by the means of a sweep-frequency grating interferometer
with angular resolution of 5' arc at 60 MHz decreasing to 15' arc at
20 MHz. The positional characteristics of the decameter wavelength
bursts are discussed in terms of the commonly accepted theories of
the origin of radio bursts from plasma and synchrotron radiations.

---------------------------------------------------------
Title: Brightness and Polarization Structure of Three Supernova
Remnants at 6-AND 11-centimeter Wavelengths
Authors: Kundu, M. R.
1970ApJ...162...17K Altcode:
Distributions of brightness and polarization of three known supernova
remnants Puppis A, W28, and PKS 1459-41 (S.N. 1006) have been measured
at 6- and 11-centimeter wavelengths. Significant polarization has been
detected in all three sources. The distribution of the derived magnetic
fields has a tendency to be tangential to the rim on the shell side
of the sources Pup A and W28, whereas it tends to be approximately
radial for the supernova remnant of A.D. 1006.

---------------------------------------------------------
Title: Solar Active Regions at Millimeter Wavelengths
Authors: Kundu, M. R.
1970SoPh...13..348K Altcode:
Some properties of solar active regions at 9, 3.5 and 1.2 mm wavelengths
are discussed. The regions have excess brightness temperatures of up to
1000, 700 and 150 K at 9, 3.5 and 1.2 mm wavelengths. The background
radiation at 3.5 mm is often seen to be `absorbed' in regions closely
coincident with Hα dark filaments on the disk. Interpretation of this
`absorption' as due to the large optical thickness of the overlying
filamentary material leads to an estimate of electron density in
the filaments. The 9 and 3.5 mm-λ regions show almost one-to-one
correspondence with the Ca-plage regions as well as with the regions
on magnetograms. The latter relationship suggests the possibility
of measuring chromospheric magnetic fields from the measurement of
polarization at millimeter wavelengths.

---------------------------------------------------------
Title: The Slowly Varying Component of the Sun's Radiation at
Millimeter Wavelengths
Authors: Kundu, M. R.
1970BAAS....2T.203K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Polarization of the Cygnus Loop at 11-CENTIMETER Wavelength
Authors: Kundu, M. R.
1969ApJ...158L.103K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Polarized Brightness Distributions of Supernova Remnants IC
443 and W44 at 6-CM Wavelength
Authors: Kundu, M. R.; Velusamy, T.
1969ApJ...155..807K Altcode:
Polarized brightness distributions of two supernova remnants, IC 443
and W44, have been deter- mined at 6-cm wavelength, from observations
made with a resolution of 6', by using the 140-foot reflector of the
National Radio Astronomy Observatory. Both IC 443 and W44 are partially
linearly polarized at 6-cm wavelength. The degree of polarization and
orientation of electric vectors are different at different parts of IC
443. Over its southeastern rim, the degree of polarization is large,
about 4.5 per cent, and the orientation of electric field is largely
tangential. Over its northeastern peak, the degree of polarization is
low, and the field orientation is random. The distribution of polarized
brightness in W44 is broadly similar to that of total intensity. The
peak of linearly polarized radiation roughly coincides with the peak of
total intensity, and the electric field has a systematic alignment with
a position angle of 400 over the main peak as well as over the eastern
region. The degree of polarization is negligibly small over the peak
of the isolated source situated to the west of W44 around a = 18h50m528
and ô = O1°11'30", which indicates that it is thermal in nature

---------------------------------------------------------
Title: Polarized Brightness Distributions of Supernova Remnants IC
443 W44, and the Cygnus Loop at 6- and 11-cm Wavelengths
Authors: Kundu, M. R.
1969BAAS....1R.197K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Possible Interpretation of Pulses from a Radio Source
Authors: Kundu, M. R.; Chitre, S. M.
1968Natur.218.1037K Altcode:
THE Cambridge group1 recently announced the recording of
pulses from a local object, lasting for about 0.016 s and repeating
with extreme regularity with a period of 1.337 s, the accuracy being
one part in 107. There have been further observations from
Cambridge2 and from Jodrell Bank3. The amplitude
of the pulses varies randomly, the pulses appearing and disappearing
for periods of a few minutes. There is also a fine structure
superimposed on the main pulse. Despite the regularity of the pulses,
the power emitted varies significantly over all periods. Furthermore,
observations indicate a frequency drift of -5 MHz s-1. The
absence of any proper motion of the source, and the interpretation of
the frequency drift in terms of dispersion through the interstellar
plasma, limit the distance of the source to the range 103
A.U. &lt;d&lt;65 pc. An eighteenth magnitude blue stellar object has
been found near the object, although there seems to be uncertainty
about the nature of the object. From the pulse width and the rate of
frequency drift the source is smaller than 5 × 108 cm.

---------------------------------------------------------
Title: Lunar Occupation of a Solar Active Region at 4 cm Wavelength
Authors: Kundu, M. R.; Velusamy, T.
1968Natur.217.1132K Altcode:
THE solar eclipse of July 20, 1963, was observed from Ann Arbor,
Michigan, using the 85 ft. paraboloid telescope of the University of
Michigan. As observed from Michigan the solar eclipse was partial;
however, the Moon completely occulted two discrete regions on the
Sun-one near the east limb and the other near the west limb. We
observed the lunar occultation of the eastern region. At the 4 cm
wavelength at which this occultation was observed, the pencil beam
of the radio telescope had a half-power width of 5'.95 of arc. Drift
scans were taken across the region before the occultation in order to
find the position of the peak. These scans indicated an angular size
of about 3' of arc and a position which was in agreement with the
position indicated by Stanford λ 9.1 cm maps. Thus the beam almost
completely covered the discrete region, and the observations consisted
in tracking the region throughout the period of occultation with the
beam pointed on the peak of the region. The occultation was observed
in both immersion and emersion.

---------------------------------------------------------
Title: Solar Radio Astronomy
Authors: Kundu, Mukul R.
1968SvA....11..733K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Radio spectra of the nebula IC443
Authors: Kundu, M. R.; Velusamy, T.
1968MNRAS.140..173K Altcode:
Combining our observations at 430 and 195 MHz with pencil beams of 17'
and 35' arc respectively with other high resolution observations at
750, 1400, 3000 and 5000 MIIz, the flux density spectrum over different
regions of the shell source IC443 has been computed. It appears that
the north-east bright rim or shell has a curved spectrum with spectral
index of and below and above 750 MHz. The other regions exhibit a
straight line spectrum with spectral index of about .

---------------------------------------------------------
Title: Some Properties of the Sources of Slowly Varying Component
and of Bursts at 612 MC S
Authors: Swarup, G.; Kundu, M. R.; Kapahi, V. K.; Isloor, J. D.
1968IAUS...35..581S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A study of the Cygnus loop at 430, 195 and 41 MHz
Authors: Kundu, M. R.; Velusamy, T.
1967AnAp...30..723K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A study of galactic sources W 51 and W 44
Authors: Kundu, M. R.; Velusamy, T.
1967AnAp...30...59K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Solar Radio Astronomy
Authors: Kundu, Mukul R.
1967AZh....44..910K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Buchbesprechungen über: Solar Radio
Astronomy. (Ref. A. UNSÖLD)
Authors: Kundu, M. R.
1967ZA.....66..339K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Review of Publications- Solar Radio Astronomy
Authors: Kundu, Mukul R.
1966JRASC..60..296K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Solar Radio Astronomy
Authors: Kundu, Mukul R.
1966AmJPh..34..829K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Lunar Occultation of the Radio Sources 0938 + 18 and 1101 + 11
Authors: Cohen, M. H.; Kundu, M. R.
1966ApJ...143..621C Altcode:
The radio sources 0938 + 18 and 1101 + 11 have been observed at 430 MHz
during the immersion phase of a lunar occultation. The source 0938 +
18 is a single source of diameter 4"; 1101 + 11 is a double source
with approximately equal components separated by 9'.'4. The Palomar
8ky 8urvey pnnts show a faint bk object near 0938 + 18, and show no
optical object at the position of 1101 + 11.

---------------------------------------------------------
Title: Occultation of Taurus-A by the Solar Corona at 430 Mc/s in
June 1964
Authors: Kundu, M. R.
1965Natur.205..683K Altcode:
DURING June of every year, the radio source Taurus-A passes within a
small angular distance of the Sun. This particular situation, commonly
referred to as the occultation of Taurus-A by the Sun, permits an
investigation of the Sun's outer corona as the radio source is viewed
through it. The measurements made over the past several years have
demonstrated that the radiation from the source is scattered at the
electron density irregularities in the corona; as a result one observes
an apparent broadening of the source accompanied by a decrease of its
intensity. The effect becomes larger with decreasing angular separation
of the source from the Sun. This phenomenon has been observed in the
range of frequencies 26-178 Mc/s1-5. At wave-lengths of 6
and 18 cm the effect has been reported to be negative6,7,
except that a positive result has been reported on 10- and 25-cm
wave-lengths8. The results on all metre and decametre
wave-lengths are consistent and are in accordance with the theory
of small-angle multiple scattering, in which the angular size of
the scattered distribution is proportional to the square of the
wave-length. However, the increase of intensity on 169 Mc/s at 7
R0 (R0 is the photospheric radius) from the
centre of the Sun is not consistent with the theoretical prediction
based on the lower frequency data5. In order to investigate
if the coronal scattering is still effective at frequencies higher
than 169 Mc/s, and in particular to see if the increase of intensity
is also observed on 430 Mc/s, we undertook to observe at 430 Mc/s the
occultation of Taurus-A by the solar corona in June 1964, using the
1,000-ft. dish of the Arecibo Ionospheric Observatory.

---------------------------------------------------------
Title: Some Aspects of the Type-IV Continuum Radiation on Decimeter
Wave-lengths
Authors: Kundu, M. R.
1965ASSL....1..408K Altcode: 1965sosp.conf..408K
No abstract at ADS

---------------------------------------------------------
Title: Solar radio astronomy
Authors: Kundu, Mukul R.
1965sra..book.....K Altcode: 1965QB521.K9.......
No abstract at ADS

---------------------------------------------------------
Title: A Survey of the Interpretations of Radio and X-Ray Bursts
Authors: Kundu, M. R.
1964NASSP..50..335K Altcode: 1964psf..conf..335K
No abstract at ADS

---------------------------------------------------------
Title: Centimeter-Wave Radio and X-Ray Emission from the Sun
Authors: Kundu, M. R.
1963SSRv....2..438K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Spectral Characteristics of Solar Continuum Radiation in the
500-1000 Mc/s Range.
Authors: Kundu, M. R.; Spencer, C. L.
1963ApJ...137..572K Altcode:
The spectral characteristics of flare-associated continuum radiation
in the S()(} 1O()() Mc/s range are described. The continuum radiation
in this frequency range consists of a smooth background continuum
and different variabilities superimposed upon it. The superimposing
variabilities are mostly in the form of fine structure fast-drift
bursts; however, occasionally they appear in the form of "sprays" or
patchiness. The meter-X type IV continuum radiation is always associated
with a dcm-X burst of continuum radiation. The dcm-X continuum starts
almost simultaneously as the concurrent cm-X continuum; also, its
maxima sometimes correspond to the cm-X maxima. From these and other
characteristics (such as source sixe, height, motion, etc.) of dcm-X
continuum, it is suggested that the dcm-X continuum, like the concurrent
cm-X continuum, represents the first phase of type IV radiation as
a whole. Only a small fraction of meter- bursts of spectral types II
and V are associated with dcm-X bursts. The type II associated dcm-X
bursts are mostly of continuum type, although fast-drift elements
may sometimes be superim,posed "generalixed fast-drift' type. on the
continuum. The type V associated dcm-X bursts are mostly of

---------------------------------------------------------
Title: A Note on Bursts of Radio Emission and High Energy (&gt;20 keV)
X-Rays from Solar Flares
Authors: De Jager, C.; Kundu, M. R.
1963spre.conf..836D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Association of Centimeter-Wave Bursts with Different Spectral
Types of Meter-Wave Burst of Solar Radio Emission
Authors: Kundu, M. R.
1962JGR....67.2695K Altcode:
It is shown that about 40 per cent of 10.7 cm-λ bursts with
peak intensities greater than 5×10-22 wm-2
(c/s)-1 are accompanied by bursts on meter waves. The
percentage association increases with the peak intensity of 10.7 cm-λ
bursts and attains a value of about 90 per cent when the peak intensity
exceeds 1000×10-22 wm-2 (c/s)-1. The
reverse association, that is, the association of a meter-λ burst
with a burst on centimeter waves, is dependent on the spectral
type of the meter-λ burst. The association is about 15, 40, 70,
and 100 per cent for types III, V, II, and IV, respectively. The
type III and type V bursts usually occur within about 1 minute and
½ minute, respectively, of the associated cm-λ burst maxima. The
type II bursts occur after about 2 to 6 minutes of the associated
cm-λ burst maxima. The type IV bursts in the 250 to 580 Mc/s range
occur within about 4 minutes of the start of the associated cm-λ
bursts. From simultaneous dynamic spectral observations in the 25 to
580 Mc/s range and single-frequency observations on 9400, 3750, 2000,
and 1000 Mc/s, the average spectra of cm-λ bursts associated with
different spectral types of meter-λ bursts have been studied. It is
shown that cm-λ bursts associated with meter-λ type IV and type II
bursts have brightness temperatures of the order of 108
and 107 deg K, respectively, and can probably be explained
by synchrotron radiation of high-energy electrons. The cm-λ bursts
associated with type V and type III bursts have brightness temperatures
of 106 to 107 deg K in the 2000 to 9400 Mc/s
range and have probably a thermal plus synchrotron origin; the 1000
Mc/s bursts have brightness temperatures higher than 107
deg K and have a nonthermal origin, probably due to plasma oscillation
corresponding to type III bursts. The cm-λ bursts unaccompanied by any
meter-λ burst have brightness temperatures less than 106
deg K and are believed to have a thermal origin.

---------------------------------------------------------
Title: Some Relations between Centimeter-Wave Radio Bursts and Solar
Cosmic Rays and X-Rays
Authors: Kundu, M. R.
1962JPSJS..17B.259K Altcode: 1962ICRC....7B.259K; 1962PSJaP..17B.259K; 1962JPSJ...17B.259K
No abstract at ADS

---------------------------------------------------------
Title: The Nature of Type IV Solar Radio Bursts
Authors: Kundu, M. R.
1962JPSJS..17B.215K Altcode: 1962ICRC....7B.215K; 1962PSJaP..17B.215K; 1962JPSJ...17B.215K
No abstract at ADS

---------------------------------------------------------
Title: Bursts of Centimeter-Wave Emission and the Region of Origin
of X Rays from Solar Flares
Authors: Kundu, M. R.
1961JGR....66.4308K Altcode:
High energy (&gt;20 kev) solar X-ray emission during flares has been
measured with the help of rockets and balloons by various workers
[Chubb, Friedman, and Kreplin, 1960; Winckler, May, and Masley, 1961;
Peterson and Winckler, 1959; Vette and Casal, 1961]. The observation
of X rays in the quantum energy range 20 to 70 kev during three flares
accompanied by SID's led Friedman to suggest that the presence of such
X rays was characteristic of the flare process. The 20 to 70 kev X
rays appeared as an extension of the high intensity flux of 2 to 10
A X rays, which are the main components responsible for flare time
enhanced D-layer ionization (SID). It has been shown statistically by
Dodson, Hedeman, and Covington [1954], Hachenberg and Krüger [1960],
and Kawabata [1961] that centimeter-wave bursts are closely associated
with SID's.

---------------------------------------------------------
Title: Interferometric Studies of Type IV Solar Bursts of Continuum
Radiation on 340 and 87 Mc/s.
Authors: Kundu, M. R.; Firor, J. W.
1961ApJ...134..389K Altcode:
Interferometric observations made on 340 and 87 Mc/s show the following
properties of Type IV continuum bursts: (1) Type IV emission on 340 Mc/s
occurs at a height of less than 40000 km in the solar atmosphere. Its
source has a small angular diameter (usually less than 4'), and it shows
practically no motion within +2 minutes of arc. (2) Type IV emission
on 87 Mc/s occurs high in the corona (more than 200000 km above the
photosphere). Its source has a large angular diameter (of the order of
10' or larger) and a large movement. These distinctive properties of
Type IV emission as observed on 340 and 87 Mc/s support the suggestion
that Type IV emission occurs in two distinct phases-one characteristic
of centimeter-wave continuum emission extending up to frequencies as
low as 250 Mc/s, and the other, characteristic of meter-wave continuum
emission occurring at frequencies lower than about 250 Mc/s.

---------------------------------------------------------
Title: Some Studies on the Occurrence of Type IV Solar Bursts of
Continuum Radiation.
Authors: Kundu, M. R.
1961AJ.....66..289K Altcode:
It is shown that type IV emission in the range of frequencies 25-580 Mc
occurs in two distinct phases: (a) the first phase, usually observed
at frequencies higher than about 250 Mc, appears to be an extension
of the associated centimeter-wave burst which is also a broad-band
continuum emission. This emission occurs earlier than the associated
type II burst and can even occur independent of any type II burst. The
source of this emission is situated low in the chromosphere, has
no significant movement and has a small angular size, usually less
than 4'. The observed properties of this phase of continuum emission
are consistent with the suggestion that it it is caused low in the
chromosphere by synchrotron radiation of electrons generated during
the flare. (b) The second phase, usually observed at frequencies
lower than about 250 Mc, is closely associated with a type II burst
preceding it. The source of this continuum emission is situated high in
the corona and moves with velocities of more than 1000 km/sec. It has
a large angular size, usually 10' or larger. This second phase of type
IV emission was previously explained as due to synchrotron radiation of
electrons higher in the corona, when a cloud of gas with a shock front
(which excites the type II burst) moving at high velocities carries
a frozen-in magnetic field to the appropriate heights in the corona.

---------------------------------------------------------
Title: Some Studies on the Occurrence of Type IV Solar Bursts of
Continuum Radiation.
Authors: Kundu, M. R.
1961ApJ...134...96K Altcode:
It is shown that type IV emission in the range of frequencies 25-580
Mc/s occurs in two distinct phases: (a) The first phase, usually
observed at frequencies higher than about 250 Mc/s, appears to be
an extension of the associated centimeter-wave burst which is also
a broad-band continuum emission. This emission occurs earlier than
the associated type II burst and can even occur independent of any
type II burst. The source of this emission is situated low in the
chromosphere, has no significant movement, and has a small angular
size, usually less than 4'. The observed properties of this phase of
continuum emission are consistent with the suggestion that it is caused
low in the chromosphere by synchrotron radiation of electrons generated
during the flare. (b) The second phase, usually observed at frequencies
lower than about 250 Mc/s, is closely associated with a type II burst
preceding it. The source of this continuum emission is situated high in
the corona and moves with velocities of more than 1000 km/sec. It has
a large angular size, usually 10' or larger. This second phase of type
IV emission was previously explained as due to synchrotron radiation of
electrons higher in the corona, when a cloud of gas with a shock front
(which excites the type II burst) moving at high velocities carries
a frozen-in magnetic field to the appropriate heights in the corona.

---------------------------------------------------------
Title: A Comparison of the Dynamic Spectra of Solar Radio Bursts in
the Decimeterand Meter-Wave Ranges.
Authors: Kundu, M. R.; Roberts, J. A.; Spencer, C. L.; Kuiper, J. W.
1961ApJ...133..255K Altcode:
The existence of two classes of fast-drift (Type III) bursts is
recognized from a comparison of the dynainic spectra of solar radio
bursts observed at the University of Michigan in the 100-580 Mc/s range
and, in some cases, in the 20004000 Mc/s range and at Convair-Caltech in
the 500-950 Mc/s range One class corresponds to the meter-wave-length
bursts and predominantly extend to the low-frequency edge of the
records at 100 Mc/s a nd the other to the decimeter-t ype bursts which
are observed to terminate mainly above 400 Mc/s and typically between
400 and 550 Mc/s An example is given of an event in which the 500-950
Mc/s range shows a short continuum increase in time coincidence with
a group of meter-wave-length Type III bursts preceding a Type II
burst. Another example of a similar event shows that the continuum
increase exists at higher frequencies f &lt;2000 to &gt;4000 Mc/s)

---------------------------------------------------------
Title: Solar Radio Emission on Centimeter Waves and Ionization of
the E Layer of the Ionosphere
Authors: Kundu, M. R.
1960JGR....65.3903K Altcode:
It is shown that solar radio emission on any wavelength shorter than 30
cm is good as a solar index for ionospheric studies. The coefficient
of correlation between E-layer ionization index and solar radiation
decreases to a low value for wavelengths greater than about 30 cm,
indicating that a major part of solar X radiation responsible for
E-layer ionization originates in the solar atmosphere below the height
of origin of 30-cm solar radio emission.

---------------------------------------------------------
Title: A Relation Between Solar Radio Emission and Polar Cap
Absorption of Cosmic Noise
Authors: Kundu, M. R.; Haddock, F. T.
1960Natur.186..610K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Structures et propriétés des sources d'activit&amp;eacute
solaire sur ondes centimétriques
Authors: Kundu, M. R.
1959AnAp...22....1K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Etude interférométrique des sources d'activité solaire
sur 3 CM de longueur d'onde
Authors: Kundu, M. R.
1959IAUS....9..222K Altcode:
No abstract at ADS