white-stephen

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Author name code: white-stephen
ADS astronomy entries on 2022-09-14
=author:"White, S.M." OR =author:"White, Stephen M."

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Title: A Genetic Algorithm to Model Solar Radio Active Regions From
3D Magnetic Field Extrapolations
Authors: de Oliveira e Silva, Alexandre José; Selhorst, Caius Lucius;
Costa, Joaquim E. R.; Simões, Paulo J. A.; Giménez de Castro,
Carlos Guillermo; Wedemeyer, Sven; White, Stephen M.; Brajša, Roman;
Valio, Adriana
2022FrASS...9.1118D Altcode: 2022arXiv220503385S; 2022arXiv220503385J
In recent decades our understanding of solar active regions (ARs)
has improved substantially due to observations made with better
angular resolution and wider spectral coverage. While prior AR
observations have shown that these structures were always brighter
than the quiet Sun at centimeter wavelengths, recent observations
at millimeter and submillimeter wavelengths have shown ARs with well
defined dark umbrae. Given this new information, it is now necessary to
update our understanding and models of the solar atmosphere in active
regions. In this work, we present a data-constrained model of the AR
solar atmosphere, in which we use brightness temperature measurements
of NOAA 12470 at three radio frequencies: 17, 100 and 230 GHz. The
observations at 17 GHz were made by the Nobeyama Radioheliograph (NoRH),
while the observations at 100 and 230 GHz were obtained by the Atacama
Large Millimeter/submillimeter Array (ALMA). Based on our model, which
assumes that the radio emission originates from thermal free-free and
gyroresonance processes, we calculate radio brightness temperature
maps that can be compared with the observations. The magnetic field at
distinct atmospheric heights was determined in our modelling process by
force-free field extrapolation using photospheric magnetograms taken by
the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics
Observatory (SDO). In order to determine the best plasma temperature
and density height profiles necessary to match the observations,
the model uses a genetic algorithm that modifies a standard quiet Sun
atmospheric model. Our results show that the height of the transition
region (TR) of the modelled atmosphere varies with the type of region
being modelled: for umbrae the TR is located at 1080 ± 20 km above
the solar surface; for penumbrae, the TR is located at 1800 ± 50 km;
and for bright regions outside sunspots, the TR is located at 2000 ±
100 km. With these results, we find good agreement with the observed
AR brightness temperature maps. Our modelled AR can be used to estimate
the emission at frequencies without observational coverage.

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Title: Heating of the solar chromosphere through current dissipation
Authors: da Silva Santos, J. M.; Danilovic, S.; Leenaarts, J.; de
la Cruz Rodríguez, J.; Zhu, X.; White, S. M.; Vissers, G. J. M.;
Rempel, M.
2022A&A...661A..59D Altcode: 2022arXiv220203955D
Context. The solar chromosphere is heated to temperatures higher than
predicted by radiative equilibrium. This excess heating is greater
in active regions where the magnetic field is stronger. 
Aims: We aim to investigate the magnetic topology associated with an
area of enhanced millimeter (mm) brightness temperatures in a solar
active region mapped by the Atacama Large Millimeter/submillimeter
Array (ALMA) using spectropolarimetric co-observations with the 1-m
Swedish Solar Telescope (SST). Methods: We used Milne-Eddington
inversions, nonlocal thermodynamic equilibrium (non-LTE) inversions,
and a magnetohydrostatic extrapolation to obtain constraints on the
three-dimensional (3D) stratification of temperature, magnetic field,
and radiative energy losses. We compared the observations to a snapshot
of a magnetohydrodynamics simulation and investigate the formation
of the thermal continuum at 3 mm using contribution functions. 
Results: We find enhanced heating rates in the upper chromosphere of up
to ∼5 kW m−2, where small-scale emerging loops interact
with the overlying magnetic canopy leading to current sheets as shown
by the magnetic field extrapolation. Our estimates are about a factor
of two higher than canonical values, but they are limited by the ALMA
spatial resolution (∼1.2″). Band 3 brightness temperatures reach
about ∼104 K in the region, and the transverse magnetic
field strength inferred from the non-LTE inversions is on the order
of ∼500 G in the chromosphere. Conclusions: We are able to
quantitatively reproduce many of the observed features including the
integrated radiative losses in our numerical simulation. We conclude
that the heating is caused by dissipation in current sheets. However,
the simulation shows a complex stratification in the flux emergence
region where distinct layers may contribute significantly to the
emission in the mm continuum. The movie is available at <A
href="https://www.aanda.org/10.1051/0004-6361/202243191/olm">https://www.aanda.org</A>

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Title: Subarcsecond Imaging of a Solar Active Region Filament With
ALMA and IRIS
Authors: da Silva Santos, J. M.; White, S. M.; Reardon, K.; Cauzzi,
G.; Gunár, S.; Heinzel, P.; Leenaarts, J.
2022FrASS...9.8115D Altcode: 2022arXiv220413178D
Quiescent filaments appear as absorption features on the solar disk
when observed in chromospheric lines and at continuum wavelengths
in the millimeter (mm) range. Active region (AR) filaments are their
small-scale, low-altitude analogues, but they could not be resolved
in previous mm observations. This spectral diagnostic can provide
insight into the details of the formation and physical properties of
their fine threads, which are still not fully understood. Here, we shed
light on the thermal structure of an AR filament using high-resolution
brightness temperature (Tb) maps taken with ALMA Band 6 complemented by
simultaneous IRIS near-UV spectra, Hinode/SOT photospheric magnetograms,
and SDO/AIA extreme-UV images. Some of the dark threads visible in the
AIA 304 Å passband and in the core of Mg ii resonance lines have dark
(Tb &lt; 5,000 K) counterparts in the 1.25 mm maps, but their visibility
significantly varies across the filament spine and in time. These
opacity changes are possibly related to variations in temperature and
electron density in filament fine structures. The coolest Tb values
(&lt; 5,000 K) coincide with regions of low integrated intensity in the
Mg ii h and k lines. ALMA Band 3 maps taken after the Band 6 ones do not
clearly show the filament structure, contrary to the expectation that
the contrast should increase at longer wavelengths based on previous
observations of quiescent filaments. The ALMA maps are not consistent
with isothermal conditions, but the temporal evolution of the filament
may partly account for this.

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Title: Pulsar observations at low frequencies: applications to pulsar
timing and solar wind models
Authors: Kumar, P.; White, S. M.; Stovall, K.; Dowell, J.; Taylor,
G. B.
2022MNRAS.511.3937K Altcode: 2022MNRAS.tmp..319K; 2022arXiv220201251K
Efforts are underway to use high-precision timing of pulsars in order
to detect low-frequency gravitational waves. A limit to this technique
is the timing noise generated by dispersion in the plasma along the
line of sight to the pulsar, including the solar wind. The effects
due to the solar wind vary with time, influenced by the change in
solar activity on different time-scales, ranging up to ~11 yr for a
solar cycle. The solar wind contribution depends strongly on the angle
between the pulsar line of sight and the solar disc, and is a dominant
effect at small separations. Although solar wind models to mitigate
these effects do exist, they do not account for all the effects of
the solar wind and its temporal changes. Since low-frequency pulsar
observations are most sensitive to these dispersive delays, they
are most suited to test the efficacy of these models and identify
alternative approaches. Here, we investigate the efficacy of some
solar wind models commonly used in pulsar timing using long-term,
high-cadence data on six pulsars taken with the Long Wavelength Array,
and compare them with an operational solar wind model. Our results show
that stationary models of the solar wind correction are insufficient
to achieve the timing noise desired by pulsar timing experiments,
and we need to use non-stationary models, which are informed by other
solar wind observations, to obtain accurate timing residuals.

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Title: NuSTAR observations of a repeatedly microflaring active region
Authors: Cooper, Kristopher; Hannah, Iain G.; Grefenstette, Brian W.;
Glesener, Lindsay; Krucker, Säm; Hudson, Hugh S.; White, Stephen M.;
Smith, David M.; Duncan, Jessie
2021MNRAS.507.3936C Altcode: 2021arXiv210900263C; 2021MNRAS.tmp.2159C
We investigate the spatial, temporal, and spectral properties of 10
microflares from AR12721 on 2018 September 9 and 10 observed in X-rays
using the Nuclear Spectroscopic Telescope ARray and the Solar Dynamic
Observatory's Atmospheric Imaging Assembly and Helioseismic and Magnetic
Imager. We find GOES sub-A class equivalent microflare energies of
1026-1028 erg reaching temperatures up to 10
MK with consistent quiescent or hot active region (AR) core plasma
temperatures of 3-4 MK. One microflare (SOL2018-09-09T10:33), with
an equivalent GOES class of A0.1, has non-thermal hard X-ray emission
during its impulsive phase (of non-thermal power ~7 × 1024
erg s-1) making it one of the faintest X-ray microflares
to have direct evidence for accelerated electrons. In 4 of the 10
microflares, we find that the X-ray time profile matches fainter and
more transient sources in the extreme-ultraviolet, highlighting the need
for observations sensitive to only the hottest material that reaches
temperatures higher than those of the AR core (&gt;5 MK). Evidence
for corresponding photospheric magnetic flux cancellation/emergence
present at the footpoints of eight microflares is also observed.

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Title: Reduced Microwave Brightness Temperature in a Sunspot
Atmosphere Due to Open Magnetic Fields
Authors: Vrublevskis, A.; Ryabov, B. I.; White, S. M.
2021SoPh..296..144V Altcode: 2021arXiv210205476V
Motivated by dark coronal lanes in 284 Å extreme-ultraviolet (EUV)
observations from the Extreme-ultraviolet Imaging Telescope on board
the Solar and Heliospheric Observatory (SOHO/EIT), we construct and
optimize an atmosphere model of the active region (AR) 8535 sunspot
by adding a cool and dense component in the volume of plasma along
open field lines determined using the potential-field source-surface
(PFSS) extrapolation. Our model qualitatively reproduces the observed
reduced microwave brightness temperature in the northern part of
the sunspot in Very Large Array (VLA) observations from 13 May 1999
and provides a physical explanation for the coronal dark lanes. We
propose the application of this method to other sunspots with such
observed dark regions in the EUV or soft X-rays and with concurrent
microwave observations to determine the significance of open field
regions. The connection between open fields and the resulting plasma
temperature and density change is of relevance for slow solar wind
source investigations.

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Title: Nonequilibrium Flux Rope Formation by Confined Flares Preceding
a Solar Coronal Mass Ejection
Authors: Kliem, Bernhard; Lee, Jeongwoo; Liu, Rui; White, Stephen M.;
Liu, Chang; Masuda, Satoshi
2021ApJ...909...91K Altcode: 2021arXiv210102181K
We present evidence that a magnetic flux rope was formed before
a coronal mass ejection (CME) and its associated long-duration
flare during a pair of preceding confined eruptions and
associated impulsive flares in a compound event in NOAA Active
Region 12371. Extreme-ultraviolet images and the extrapolated
nonlinear force-free field show that the first two (impulsive)
flares, SOL2015-06-21T01:42, result from the confined eruption
of highly sheared low-lying flux, presumably a seed flux rope. The
eruption spawns a vertical current sheet, where magnetic reconnection
creates flare ribbons and loops, a nonthermal microwave source, and a
sigmoidal hot channel that can only be interpreted as a magnetic flux
rope. Until the subsequent long-duration flare, SOL2015-06-21T02:36,
the sigmoid's elbows expand, while its center remains stationary,
suggesting nonequilibrium but not yet instability. The "flare
reconnection" during the confined eruptions acts like "tether-cutting
reconnection" whose flux feeding of the rope leads to instability. The
subsequent full eruption is seen as an accelerated rise of the entire
hot channel, seamlessly evolving into the fast halo CME. Both the
confined and ejective eruptions are consistent with the onset of
the torus instability in the dipped decay index profile that results
from the region's two-scale magnetic structure. We suggest that the
formation or enhancement of a nonequilibrium but stable flux rope by
confined eruptions is a generic process occurring prior to many CMEs.

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Title: An overall view of temperature oscillations in the solar
chromosphere with ALMA
Authors: Jafarzadeh, S.; Wedemeyer, S.; Fleck, B.; Stangalini, M.;
Jess, D. B.; Morton, R. J.; Szydlarski, M.; Henriques, V. M. J.; Zhu,
X.; Wiegelmann, T.; Guevara Gómez, J. C.; Grant, S. D. T.; Chen,
B.; Reardon, K.; White, S. M.
2021RSPTA.37900174J Altcode: 2021RSTPA.379..174J; 2020arXiv201001918J
By direct measurements of the gas temperature, the Atacama Large
Millimeter/submillimeter Array (ALMA) has yielded a new diagnostic
tool to study the solar chromosphere. Here, we present an overview
of the brightness-temperature fluctuations from several high-quality
and high-temporal-resolution (i.e. 1 and 2 s cadence) time series
of images obtained during the first 2 years of solar observations
with ALMA, in Band 3 and Band 6, centred at around 3 mm (100 GHz)
and 1.25 mm (239 GHz), respectively. The various datasets represent
solar regions with different levels of magnetic flux. We perform
fast Fourier and Lomb-Scargle transforms to measure both the spatial
structuring of dominant frequencies and the average global frequency
distributions of the oscillations (i.e. averaged over the entire field
of view). We find that the observed frequencies significantly vary from
one dataset to another, which is discussed in terms of the solar regions
captured by the observations (i.e. linked to their underlying magnetic
topology). While the presence of enhanced power within the frequency
range 3-5 mHz is found for the most magnetically quiescent datasets,
lower frequencies dominate when there is significant influence from
strong underlying magnetic field concentrations (present inside and/or
in the immediate vicinity of the observed field of view). We discuss
here a number of reasons which could possibly contribute to the power
suppression at around 5.5 mHz in the ALMA observations. However,
it remains unclear how other chromospheric diagnostics (with an
exception of Hα line-core intensity) are unaffected by similar
effects, i.e. they show very pronounced 3-min oscillations dominating
the dynamics of the chromosphere, whereas only a very small fraction
of all the pixels in the 10 ALMA datasets analysed here show peak power
near 5.5 mHz. This article is part of the Theo Murphy meeting issue
`High-resolution wave dynamics in the lower solar atmosphere'.

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Title: NuSTAR Observation of Energy Release in 11 Solar Microflares
Authors: Duncan, Jessie; Glesener, Lindsay; Grefenstette, Brian W.;
Vievering, Juliana; Hannah, Iain G.; Smith, David M.; Krucker, Säm;
White, Stephen M.; Hudson, Hugh
2021ApJ...908...29D Altcode: 2020arXiv201106651D
Solar flares are explosive releases of magnetic energy. Hard X-ray
(HXR) flare emission originates from both hot (millions of Kelvin)
plasma and nonthermal accelerated particles, giving insight into flare
energy release. The Nuclear Spectroscopic Telescope ARray (NuSTAR)
utilizes direct-focusing optics to attain much higher sensitivity
in the HXR range than that of previous indirect imagers. This paper
presents 11 NuSTAR microflares from two active regions (AR 12671 on
2017 August 21 and AR 12712 on 2018 May 29). The temporal, spatial, and
energetic properties of each are discussed in context with previously
published HXR brightenings. They are seen to display several "large
flare" properties, such as impulsive time profiles and earlier peak
times in higher-energy HXRs. For two events where the active region
background could be removed, microflare emission did not display
spatial complexity; differing NuSTAR energy ranges had equivalent
emission centroids. Finally, spectral fitting showed a high-energy
excess over a single thermal model in all events. This excess was
consistent with additional higher-temperature plasma volumes in 10/11
microflares and only with an accelerated particle distribution in the
last. Previous NuSTAR studies focused on one or a few microflares at a
time, making this the first to collectively examine a sizable number of
events. Additionally, this paper introduces an observed variation in
the NuSTAR gain unique to the extremely low livetime (&lt;1%) regime
and establishes a correction method to be used in future NuSTAR solar
spectral analysis.

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Title: Probing chromospheric heating with millimeter interferometry
Authors: da Silva Santos, J. M.; de la Cruz Rodriguez, J.; White,
S. M.; Leenaarts, J.; Vissers, G. J. M.; Hansteen, V. H.; Danilovic, S.
2020AGUFMSH0010001D Altcode:
Observations at visible and ultraviolet wavelengths have shown that
solar active regions host different kinds of small-scale, transient,
bright structures that are believed to be heating events resulting
from the release of magnetic energy in the low atmosphere of the Sun,
especially at the early stages of flux emergence. It is of great
scientific interest to be able to accurately infer temperatures and
formation heights of the most localized events, which are still
matter of debate, in the hope of learning about the evolution of
active regions where occasionally more energetic phenomena lead to
much larger outbursts that propagate across the Solar System. The
millimeter (mm) continuum is a new complementary diagnostic for
chromospheric heating that is now available thanks to the Atacama
Large Millimeter/submillimeter Array (ALMA). We report on the
first ALMA 3 mm observations of small-scale heating events in a
solar active region. In contrast with the low-amplitude brightness
temperature variations in the quiet-Sun, the interferometric maps show
that the active region consists of long, warm, fibril-like structures
that connect magnetic concentrations of opposite polarity and often
flare up along with compact, flickering mm-bursts -- reminiscent of
ultraviolet bursts -- with brightness temperatures of up to 14000 K at
1.2" scales. These events also show simultaneous EUV emission observed
by the Solar Dynamics Observatory (SDO). We find a weak correlation
between the photospheric bright patches and the 3 mm continuum
brightness and, in particular, we do not detect any mm counterpart of
Ellerman bombs which confirms that they are photospheric phenomena. Our observations and modelling highlight the diagnostic capabilities
of ALMA for local heating in solar active regions and emphasize the
need for coordinated observations with IRIS and DKIST in the future.

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Title: NuSTAR Observation of Eleven Solar Microflares
Authors: Duncan, J. M.; Glesener, L.; Grefenstette, B.; Vievering,
J. T.; Hannah, I. G.; Smith, D. M.; Krucker, S.; White, S. M.; Hudson,
H. S.
2020AGUFMSH045..07D Altcode:
This work presents eleven microflares observed by the Nuclear
Spectroscopic Telescope ARray (NuSTAR), representing the first
time that a sizable number of these events have been examined
collectively. NuSTAR's direct focusing optics give it a dramatic
increase in sensitivity over indirect imagers in the hard X-ray
(HXR) range. HXR emission in solar flares originates from both hot
(millions of Kelvin) plasma and nonthermal accelerated particles,
both of which are diagnostic of flare energy release. Therefore,
NuSTAR solar observation campaigns can give unique insight into the
energetics of faint microflares, including those that were unobservable
with previous-generation HXR instruments. We discuss the temporal,
spatial, and energetic properties of all eleven microflares in context
with previously published HXR brightenings. They are seen to display
several `large-flare' properties, such as impulsive time profiles
and earlier peaktimes in higher energy HXRs. For two events where
active region background could be removed, microflare emission did
not display spatial complexity: differing NuSTAR energy ranges had
equivalent emission centroids. Finally, spectral fitting showed a high
energy excess over a single thermal model in all events. This excess
was found to most likely originate from additional higher-temperature
plasma volumes in 10/11 microflares, and from an accelerated particle
distribution in the last. Finally, we introduce an observed variation
in the NuSTAR gain unique to the extremely low-livetime (&lt; 1%)
regime, and establish a correction method to be used in future NuSTAR
solar spectral analysis.

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Title: Next-Generation Solar Radio Imaging Spectroscopy
Authors: Gary, D. E.; Bastian, T.; Chen, B.; Saint-Hilaire, P.; White,
S. M.
2020AGUFMSH056..07G Altcode:
Recent progress using instruments such as the Expanded Owens Valley
Solar Array (EOVSA) and the Jansky Very Large Array (JVLA) have amply
demonstrated the power of radio imaging spectroscopy at centimeter and
decimeter wavelengths for quantitative diagnostics of both flaring
and non-flaring solar plasma. For example, the unique sensitivity
of radio emission to the flaring coronal magnetic field has been
dramatically shown in a series of recent EOVSA papers, along with
accelerated electron diagnostics in the same volume. JVLA observations
have been used to probe particle acceleration in a termination shock
during a flare. In addition, multi-frequency full-disk imaging of
the non-flaring Sun with EOVSA is showing promise for quantitative
diagnostics of electron-based emission measure and active region
magnetic field and temperature structure. But EOVSA and the JVLA are
mere demonstrators for a far more advanced solar radio instrument,
the Frequency Agile Solar Radiotelescope (FASR), that is designed to
address a much more comprehensive science program with much greater
precision than is possible with EOVSA or non-solar-dedicated instruments
like the JVLA. This includes direct imaging of Coronal Mass Ejections
(CMEs) and their associated energetic particles both on and off
the solar disk, routine coronal magnetic field measurements at high
cadence, and continuous sampling of the full-Sun coronal temperature
and emission measure. Here we use examples from EOVSA and the JVLA to
envision what FASR's advanced design will be capable of. When paired
with highly complementary new X-ray-based diagnostics from space,
the remote sensing of high-energy particles through radio imaging
spectroscopy from the ground provides a far more complete picture of
the broad range of energetic phenomena that occur on the Sun than
either alone. Scientists interested in high-energy solar phenomena
have ample incentive to coordinate their efforts to ensure that space-
and ground-based capabilities advance together.

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Title: An age uncertainty model for the Cairo Nile height record,
622 to 1898 CE
Authors: White, S. M.; Stine, A.; Ludlow, F.; Manning, J.
2020AGUFMPP033..06W Altcode:
The longest instrumental climate record humans possess is the annual
Nile high/low stand record from Cairo (622 C.E. - 1898 C.E.), with
climatically useful records ending with construction of the Aswan Low
Dam in 1899. This unique record reflects a balance between equatorial
precipitation and subtropical evaporation integrated over ~30 degrees
of latitude. The veracity of this record has been questioned by
ancient and modern sources, but its utility was recently illustrated
by demonstrating a strong association between the record of explosive
volcanic eruptions in Greenland ice cores and years of low Nile flood
height. High-frequency uncertainty in the age model remains because
of the inconsistency in how the Islamic lunar calendar was marked
in Egypt, as opposed to other regions of the Islamic world, during
this 1276 year period. This uncertainty arises, in part, because of
language in the Koran (Surah 9 : 37) which was interpreted to require
explicit declaration from the Caliph (or after Saladin's conquest,
from the Sultan) in order to rectify the lunar calendar to the solar
calendar, a duty that was neglected to a greater or lesser extent
during different political dynasties leading to uncertain drift
between the two calendars. Here we explicitly model the uncertainty
in the how the lunar calendar was historically rectified, producing a
model of the full structure of the uncertainty in the dating of the
Cairo Nilometer record. Uncertainty grows across lunar cycles where
no independent constraints on the calendar exist, and collapses when
documentary records exist that tie the calendars on a specific date. We
demonstrate that application of this age-uncertainty model increases the
power with which climate signals can be extracted from the Nile record.

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Title: Observations of Solar Spicules at Millimeter and Ultraviolet
Wavelengths
Authors: Bastian, T.; De Pontieu, B.; Shimojo, M.; Iwai, K.;
Alissandrakis, C.; Nindos, A.; Vial, J. C.; White, S. M.
2020AGUFMSH004..08B Altcode:
Solar spicules are a ubiquitous chromospheric phenomenon in which
multitudes of dynamic jets with temperatures of order 104
K extend thousands of kilometers into the solar atmosphere. Recent
progress has been made refining the observational characteristics
of spicules using the Hinode Solar Optical Telescope (SOT) and the
Interface Region Imaging Spectrograph (IRIS) observations at optical
and ultraviolet wavelengths, respectively. Two types of spicule
have been identified. Type I spicules, prevalent in solar active
regions, have upward speeds of order 25 km/s and lifetimes of 3-7
min. They may be the limb counterpart to shock-wave-driven fibrils
commonly seen against the solar disk in active regions. In contrast,
type II spicules, more common in quiet regions and coronal holes,
display upward speeds of 50-150 km/s, lifetimes of 30-110 s, and
appear to be partially heated to temperatures of 105 K and
higher. These observations have provoked intense interest in spicules
and have led to proposals that type II spicules play a central role
as a source of hot plasma in the corona. Nevertheless, their role in
mass and energy transport between the lower and upper layers of the
solar atmosphere remains an outstanding problem. Here, we report
imaging observations of solar spicules at millimeter wavelengths using
the Atacama Large Millimeter-submillimeter Array (ALMA) with arcsecond
angular resolution. Continuum millimeter wavelength radiation forms
under conditions of local thermodynamic equilibrium, thereby providing a
complementary tool to UV lines, which form under non-LTE conditions. The
observations were made on 2018 December 24-25 at λ=1.25 mm and λ=3
mm. The ALMA observations pose special challenges, particularly at
1.25 mm, where the limited field of view of the instrument motivated
us to use a novel mosaic imaging technique: multiple pointings were
assembled to form a single map with an angular resolution of 1" x 0.7"
on a cadence of roughly 2 min. In contrast, we were able to image at 3
mm continuously, with a map cadence of 2 s and an angular resolution of
2.3" x 1.3". We compare and contrast the morphology and dynamics
of mm-λ observations of spicules with those obtained by IRIS at UV
wavelengths and place constraints on spicule temperatures and masses
using the joint millimeter-wavelength observations.

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Title: Microwave Study of a Circular Ribbon Flare
Authors: Lee, J.; White, S. M.; Liu, C.
2020AGUFMSH0430010L Altcode:
We present a microwave study of a circular ribbon flare. Data obtained
are the 17/34 GHz maps from the Nobeyama Radioheliograph (NoRH) of
SOL2014-12-17T04:51 along with (E)UV and magnetic data from the Solar
Dynamics Observatory (SDO). Major results and interpretations are as
follows: (1) the first activation of the circular ribbons comes in the
form of a gradual increase of the 17 GHz flux without a counterpart at
34 GHz, about 13 min before the impulsive phase, which we interpret
as representing thermal preheating. (2) The first sign of nonthermal
activity occurs in the form of stepwise flux increases at both 17
and 34 GHz about 4 min before the impulsive phase, which is likely of
nonthermal activation. (3) The main impulsive flare produces a sign
flip of the 17 GHz polarization state, which implies a breakout type
magnetic eruption. (4) The 17 GHz flux shows quasi-periodic pulsations
with a period around 1.5 min before and during the flare. While the
preflare pulsation is more obvious in total intensity at one end of
the flare loop, the flare pulsation is more obvious in the polarized
intensity at the region near the inner spine. We interpret the latter
as evidence for torsional Alfven waves generated at the magnetic
reconnection. (5) The 17/34 GHz fluxes show a secondary maximum at 25
min after the impulsive phase maximum. These fluxes are more enhanced
in the flare looptop than in the footpoints, which has an implication
on the nature of the EUV late phase. Our results show that microwave
emission of a circular ribbon flare provides new information on the
activities in the fan-spine structure.

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Title: ALMA observations of transient heating in a solar active region
Authors: da Silva Santos, J. M.; de la Cruz Rodríguez, J.; White,
S. M.; Leenaarts, J.; Vissers, G. J. M.; Hansteen, V. H.
2020A&A...643A..41D Altcode: 2020arXiv200614564D
 Aims: We aim to investigate the temperature enhancements and
formation heights of solar active-region brightenings such as Ellerman
bombs (EBs), ultraviolet bursts (UVBs), and flaring active-region
fibrils (FAFs) using interferometric observations in the millimeter
(mm) continuum provided by the Atacama Large Millimeter/submillimeter
Array (ALMA). Methods: We examined 3 mm signatures of heating
events identified in Solar Dynamics Observatory observations of an
active region and compared the results with synthetic spectra from a 3D
radiative magnetohydrodynamic simulation. We estimated the contribution
from the corona to the mm brightness using differential emission measure
analysis. Results: We report the null detection of EBs in the 3
mm continuum at ∼1.2″ spatial resolution, which is evidence that
they are sub-canopy events that do not significantly contribute to
heating the upper chromosphere. In contrast, we find the active region
to be populated with multiple compact, bright, flickering mm-bursts -
reminiscent of UVBs. The high brightness temperatures of up to ∼14 200
K in some events have a contribution (up to ∼7%) from the corona. We
also detect FAF-like events in the 3 mm continuum. These events show
rapid motions of &gt; 10 kK plasma launched with high plane-of-sky
velocities (37 - 340 km s-1) from bright kernels. The mm FAFs
are the brightest class of warm canopy fibrils that connect magnetic
regions of opposite polarities. The simulation confirms that ALMA
should be able to detect the mm counterparts of UVBs and small flares
and thus provide a complementary diagnostic for localized heating in the
solar chromosphere. Movie associated to Fig. 5 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/202038755/olm">https://www.aanda.org</A>

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Title: Microwave Study of a Solar Circular Ribbon Flare
Authors: Lee, Jeongwoo; White, Stephen M.; Chen, Xingyao; Chen, Yao;
Ning, Hao; Li, Bo; Masuda, Satoshi
2020ApJ...901L..10L Altcode: 2020arXiv200911926L
A circular ribbon flare (CRF) SOL2014-12-17T04:51 is studied using
the 17/34 GHz maps from the Nobeyama Radioheliograph along with (E)UV
and magnetic data from the Solar Dynamics Observatory. We report the
following three findings as important features of the microwave CRF. (1)
The first preflare activation comes in the form of a gradual increase
of the 17 GHz flux without a counterpart at 34 GHz, which indicates
thermal preheating. The first sign of nonthermal activity occurs in
the form of stepwise flux increases at both 17 and 34 GHz about 4
minutes before the impulsive phase. (2) Until the impulsive phase,
the microwave emission over the entire active region is in a single
polarization state matching the magnetic polarity of the surrounding
fields. During and after the impulsive phase, the sign of the 17
GHz polarization state reverses in the core region, which implies a
magnetic breakout-type eruption in a fan-spine magnetic structure. (3)
The 17 GHz flux around the time of the eruption shows quasi-periodic
variations with periods of 1-2 minutes. The pre-eruption oscillation is
more obvious in total intensity at one end of the flare loop, and the
post-eruption oscillation, more obvious in the polarized intensity at a
region near the inner spine. We interpret this transition as transfer
of oscillatory power from kink mode oscillation to torsional Alfvén
waves propagating along the spine field after the eruption. We argue
that these three processes are interrelated and indicate a breakout
process in a fan-spine structure.

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Title: Microwave and Hard X-Ray Flare Observations by NoRH/NoRP and
RHESSI: Peak-flux Correlations
Authors: Krucker, Säm; Masuda, Satoshi; White, Stephen M.
2020ApJ...894..158K Altcode:
This paper presents initial results from a statistical study of solar
microwave and hard X-ray flares jointly observed over the past two
solar cycles by the Nobeyama Radio Polarimeters, the Nobeyama Radio
Heliograph, and the Reuven Ramaty High Energy Solar Spectroscopic
Imager. As has been previously demonstrated, the microwave (17 GHz and
34 GHz) peak flux shows a linear correlation with the nonthermal hard
X-ray bremsstrahlung peak emission seen above 50 keV. The correlation
holds for the entire rise phase of each individual burst, while the
decay phases tend to show more extended emission at microwaves than
is generally attributed to particle trapping. While the correlation
is highly significant (coefficient of 0.92) and holds over more than
four orders of magnitude, individual flares can be above or below
the fitted line by an average factor of about 2. By restricting the
flare selection to source morphologies with the radio emission from
the top of the flare loop, the correlation tightens significantly,
with a correlation coefficient increasing to 0.99 and the scatter
reduced to a factor of 1.3. These findings corroborate the assumption
that gyrosynchrotron microwave and hard X-ray bremsstrahlung emissions
are produced by the same flare-accelerated electron population. The
extent of the linear correlation over four orders of magnitude suggests
that magnetic field strengths within nonthermal 17 GHz sources are
surprisingly similar over a wide range of flare sizes.

---------------------------------------------------------
Title: NuSTAR Observation of a Minuscule Microflare in a Solar
Active Region
Authors: Cooper, Kristopher; Hannah, Iain G.; Grefenstette, Brian W.;
Glesener, Lindsay; Krucker, Säm; Hudson, Hugh S.; White, Stephen M.;
Smith, David M.
2020ApJ...893L..40C Altcode: 2020arXiv200411176C
We present X-ray imaging spectroscopy of one of the weakest active
region (AR) microflares ever studied. The microflare occurred
at ∼11:04 UT on 2018 September 9 and we studied it using the
Nuclear Spectroscopic Telescope ARray (NuSTAR) and the Solar Dynamic
Observatory's Atmospheric Imaging Assembly (SDO/AIA). The microflare
is observed clearly in 2.5-7 keV with NuSTAR and in Fe XVIII emission
derived from the hotter component of the 94 Å SDO/AIA channel. We
estimate the event to be three orders of magnitude lower than a GOES
A class microflare with an energy of 1.1 × 1026 erg. It
reaches temperatures of 6.7 MK with an emission measure of 8.0 ×
1043 cm-3. Non-thermal emission is not detected
but we instead determine upper limits to such emission. We present the
lowest thermal energy estimate for an AR microflare in literature, which
is at the lower limits of what is still considered an X-ray microflare.

---------------------------------------------------------
Title: Accelerated Electrons Observed Down to &lt;7 keV in a NuSTAR
Solar Microflare
Authors: Glesener, Lindsay; Krucker, Säm; Duncan, Jessie; Hannah,
Iain G.; Grefenstette, Brian W.; Chen, Bin; Smith, David M.; White,
Stephen M.; Hudson, Hugh
2020ApJ...891L..34G Altcode: 2020arXiv200312864G
We report the detection of emission from a nonthermal electron
distribution in a small solar microflare (GOES class A5.7) observed
by the Nuclear Spectroscopic Telescope Array, with supporting
observation by the Reuven Ramaty High Energy Solar Spectroscopic Imager
(RHESSI). The flaring plasma is well accounted for by a thick-target
model of accelerated electrons collisionally thermalizing within the
loop, akin to the "coronal thick-target" behavior occasionally observed
in larger flares. This is the first positive detection of nonthermal
hard X-rays from the Sun using a direct imager (as opposed to indirectly
imaging instruments). The accelerated electron distribution has a
spectral index of 6.3 ± 0.7, extends down to at least 6.5 keV, and
deposits energy at a rate of ∼2 × 1027 erg s-1,
heating the flare loop to at least 10 MK. The existence of dominant
nonthermal emission in X-rays down to &lt;5 keV means that RHESSI
emission is almost entirely nonthermal, contrary to what is usually
assumed in RHESSI spectroscopy. The ratio of nonthermal to thermal
energies is similar to that of large flares, in contrast to what has
been found in previous studies of small RHESSI flares. We suggest
that a coronal thick target may be a common property of many small
microflares based on the average electron energy and collisional mean
free path. Future observations of this kind will enable understanding
of how flare particle acceleration changes across energy scales,
and will aid the push toward the observational regime of nanoflares,
which are a possible source of significant coronal heating.

---------------------------------------------------------
Title: Dampened El Niño in the Early Pliocene Warm Period
Authors: White, S. M.; Ravelo, A. C.
2020GeoRL..4785504W Altcode:
El Niño-Southern Oscillation (ENSO) is the strongest mode of
interannual climate variability, and its predicted response to
anthropogenic climate change remains unclear. Determining ENSO's
sensitivity to climatic mean state and the strength of positive
and negative feedbacks, notably the thermocline feedback, will help
constrain its future behavior. To this end, we collected ENSO proxy
data from the early and mid-Pliocene, a time during which tropical
Pacific zonal and vertical temperature gradients were much lower
than today. We found that El Niño events had a reduced amplitude
throughout the early Pliocene, compared to the late Holocene. By the
mid-Pliocene, El Niño amplitude was variable, sometimes reduced and
sometimes similar to the late Holocene. This trend in Pliocene ENSO
amplitude mirrors the long-term strengthening of zonal and vertical
temperature gradients and verifies model results showing dampened ENSO
under reduced gradients due to a weaker thermocline feedback.

---------------------------------------------------------
Title: NuSTAR observations of the quietest Sun
Authors: Hannah, I. G.; Cooper, K.; Grefenstette, B.; Glesener, L.;
Krucker, S.; Smith, D. M.; Hudson, H. S.; White, S. M.; Kuhar, M.
2019AGUFMSH41F3335H Altcode:
Observing X-rays (above a few keV) from the Sun provides a
direct insight into energy release (heating and/or particle
acceleration) in the solar atmosphere. Targeting the faintest
X-ray emission allows the study of the smallest flares and
eruption, and crucially their contribution to heating the solar
atmosphere. NuSTAR is an astrophysics telescope that uses directly
focusing X-rays optics to detect weak X-rays from the Sun. We have
observed the Sun many times since the start of solar pointings
in Sep 2014 through to our latest observations in 2019. See <A
href="http://ianan.github.io/nsovr/">http://ianan.github.io/nsovr/</A>
for an overview. During the current solar minimum, when the Sun is
devoid of active regions and presenting the very quietest levels of
activity, NuSTAR has targeted the Sun several times. We have detected
X-rays from a variety of sources: large diffuse sources, steady compact
sources, brief flares/brightenings and small eruptions. The NuSTAR
X-ray images of these weak sources are related to features seen at
other wavelengths, such as in softer X-rays with Hinode/XRT and EUV
with SDO/AIA. Crucially, NuSTAR's imaging spectroscopy allows us to
obtain and fit the X-ray spectrum from these small events determining
their thermal (and potentially non-thermal) properties. We will present
some of the latest solar observations with NuSTAR as we go through
the current solar minimum.

---------------------------------------------------------
Title: The Slowly Varying Corona. II. The Components of F
10.7 and Their Use in EUV Proxies
Authors: Schonfeld, S. J.; White, S. M.; Henney, C. J.; Hock-Mysliwiec,
R. A.; McAteer, R. T. J.
2019ApJ...884..141S Altcode: 2019arXiv191012964S
Using four years of full-disk-integrated coronal differential emission
measures calculated in Schonfeld et al. (2017), we investigate the
relative contribution of bremsstrahlung and gyroresonance emission
in observations of F 10.7, the 10.7 cm (2.8 GHz) solar
microwave spectral flux density and commonly used activity proxy. We
determine that the majority of coronal F 10.7 is produced
by the bremsstrahlung mechanism, but the variability observed over
individual solar rotations is often driven by gyroresonance sources
rotating across the disk. Our analysis suggests that the chromosphere
may contribute significantly to F 10.7 variability and
that coronal bremsstrahlung emission accounts for 14.2 ± 2.1 sfu
(∼20%) of the observed solar minimum level. The bremsstrahlung
emission has a power-law relationship to the total F 10.7
at high activity levels, and this combined with the observed linearity
during low activity yields a continuously differentiable piecewise fit
for the bremsstrahlung component as a function of F 10.7. We
find that the bremsstrahlung component fit, along with the Mg II index,
correlates better with the observed 5-37 nm spectrum than the common
81 day averaged F 10.7 proxy. The bremsstrahlung component
of F 10.7 is also well approximated by the moderate-strength
photospheric magnetic field parameterization from Henney et al. (2012),
suggesting that it could be forecast for use in both atmospheric
research and operational models.

---------------------------------------------------------
Title: Joint X-Ray, EUV, and UV Observations of a Small Microflare
Authors: Hannah, Iain G.; Kleint, Lucia; Krucker, Säm; Grefenstette,
Brian W.; Glesener, Lindsay; Hudson, Hugh S.; White, Stephen M.;
Smith, David M.
2019ApJ...881..109H Altcode: 2018arXiv181209214H
We present the first joint observation of a small microflare in X-rays
with the Nuclear Spectroscopic Telescope ARray (NuSTAR), in UV with the
Interface Region Imaging Spectrograph (IRIS), and in EUV with the Solar
Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA). These
combined observations allow us to study the hot coronal and cooler
chromospheric/transition region emission from the microflare. This small
microflare peaks from 2016 July 26 23:35 to 23:36 UT, in both NuSTAR,
SDO/AIA, and IRIS. Spatially, this corresponds to a small loop visible
in the SDO/AIA Fe XVIII emission, which matches a similar structure
lower in the solar atmosphere seen by IRIS in SJI1330 and 1400 Å. The
NuSTAR emission in both 2.5-4 and 4-6 keV is located in a source at
this loop location. The IRIS slit was over the microflaring loop,
and fits show little change in Mg II but do show intensity increases,
slight width enhancements, and redshifts in Si IV and O IV, indicating
that this microflare had most significance in and above the upper
chromosphere. The NuSTAR microflare spectrum is well fitted by a
thermal component of 5.1 MK and 6.2 × 1044 cm-3,
which corresponds to a thermal energy of 1.5 × 1026 erg,
making it considerably smaller than previously studied active region
microflares. No non-thermal emission was detected but this could be
due to the limited effective exposure time of the observation. This
observation shows that even ordinary features seen in UV can remarkably
have a higher-energy component that is clear in X-rays.

---------------------------------------------------------
Title: The Low-Frequency Solar Corona in Circular Polarization
Authors: McCauley, Patrick I.; Cairns, Iver H.; White, Stephen M.;
Mondal, Surajit; Lenc, Emil; Morgan, John; Oberoi, Divya
2019SoPh..294..106M Altcode: 2019arXiv190710878M
We present spectropolarimetric imaging observations of the solar corona
at low frequencies (80 - 240 MHz) using the Murchison Widefield Array
(MWA). These images are the first of their kind, and we introduce
an algorithm to mitigate an instrumental artifact by which the total
intensity signal contaminates the polarimetric images due to calibration
errors. We then survey the range of circular polarization (Stokes V )
features detected in over 100 observing runs near solar maximum during
quiescent periods. First, we detect around 700 compact polarized sources
across our dataset with polarization fractions ranging from less than
0.5% to nearly 100%. These sources exhibit a positive correlation
between polarization fraction and total intensity, and we interpret
them as a continuum of plasma emission noise storm (Type I burst)
continua sources associated with active regions. Second, we report
a characteristic "bullseye" structure observed for many low-latitude
coronal holes in which a central polarized component is surrounded by
a ring of the opposite sense. The central component does not match the
sign expected from thermal bremsstrahlung emission, and we speculate
that propagation effects or an alternative emission mechanism may
be responsible. Third, we show that the large-scale polarimetric
structure at our lowest frequencies is reasonably well-correlated
with the line-of-sight (LOS) magnetic field component inferred from
a global potential field source surface (PFSS) model. The boundaries
between opposite circular polarization signs are generally aligned with
polarity inversion lines in the model at a height roughly corresponding
to that of the radio limb. This is not true at our highest frequencies,
however, where the LOS magnetic field direction and polarization sign
are often not straightforwardly correlated.

---------------------------------------------------------
Title: ALMA detection of dark chromospheric holes
Authors: White, Stephen M.; Loukitcheva, Maria A.; Solanki, Sami K.
2019AAS...23421704W Altcode:
Atacama Large Millimeter/submillimeter Array (ALMA) observations of a
quiet-Sun region at a wavelength of 3 mm are compared with available
chromospheric observations in the UV and visible as well as with
photospheric magnetograms. The ALMA images clearly reveal the presence
of distinctive cold areas in the millimeter maps having temperatures of
around 60% of the normal quiet Sun at 3 mm, which are not seen in the
other data. We speculate that ALMA is sensing cool chromospheric gas,
whose presence had earlier been inferred from infrared CO spectra.

---------------------------------------------------------
Title: The Focusing Optics X-ray Solar Imager (FOXSI)
Authors: Christe, Steven; Shih, Albert Y.; Krucker, Sam; Glesener,
Lindsay; Saint-Hilaire, Pascal; Caspi, Amir; Gburek, Szymon;
Steslicki, Marek; Allred, Joel C.; Battaglia, Marina; Baumgartner,
Wayne H.; Drake, James; Goetz, Keith; Grefenstette, Brian; Hannah,
Iain; Holman, Gordon D.; Inglis, Andrew; Ireland, Jack; Klimchuk,
James A.; Ishikawa, Shin-Nosuke; Kontar, Eduard; Massone, Anna-maria;
Piana, Michele; Ramsey, Brian; Schwartz, Richard A.; Woods, Thomas N.;
Chen, Bin; Gary, Dale E.; Hudson, Hugh S.; Kowalski, Adam; Warmuth,
Alexander; White, Stephen M.; Veronig, Astrid; Vilmer, Nicole
2019AAS...23422501C Altcode:
The Focusing Optics X-ray Solar Imager (FOXSI), a SMEX mission concept
in Phase A, is the first-ever solar-dedicated, direct-imaging, hard
X-ray telescope. FOXSI provides a revolutionary new approach to
viewing explosive magnetic-energy release on the Sun by detecting
signatures of accelerated electrons and hot plasma directly in
and near the energy-release sites of solar eruptive events (e.g.,
solar flares). FOXSI's primary science objective is to understand the
mystery of how impulsive energy release leads to solar eruptions, the
primary drivers of space weather at Earth, and how those eruptions are
energized and evolve. FOXSI addresses three important science questions:
(1) How are particles accelerated at the Sun? (2) How do solar plasmas
get heated to high temperatures? (3) How does magnetic energy released
on the Sun lead to flares and eruptions? These fundamental physics
questions are key to our understanding of phenomena throughout
the Universe from planetary magnetospheres to black hole accretion
disks. FOXSI measures the energy distributions and spatial structure of
accelerated electrons throughout solar eruptive events for the first
time by directly focusing hard X-rays from the Sun. This naturally
enables high imaging dynamic range, while previous instruments have
typically been blinded by bright emission. FOXSI provides 20-100 times
more sensitivity as well as 20 times faster imaging spectroscopy
than previously available, probing physically relevant timescales
(&lt;1 second) never before accessible. FOXSI's launch in July 2022
is aligned with the peak of the 11-year solar cycle, enabling FOXSI
to observe the many large solar eruptions that are expected to take
place throughout its two-year mission.

---------------------------------------------------------
Title: ALMA Detection of Dark Chromospheric Holes in the Quiet Sun
Authors: Loukitcheva, Maria A.; White, Stephen M.; Solanki, Sami K.
2019ApJ...877L..26L Altcode: 2019arXiv190506763L
We present Atacama Large Millimeter/submillimeter Array (ALMA)
observations of a quiet-Sun region at a wavelength of 3 mm, obtained
during the first solar ALMA cycle on 2017 April 27, and compare them
with available chromospheric observations in the UV and visible as
well as with photospheric magnetograms. ALMA images clearly reveal the
presence of distinct particularly dark/cool areas in the millimeter
maps with temperatures as low as 60% of the normal quiet Sun at 3 mm,
which are not seen in the other data. We speculate that ALMA is sensing
cool chromospheric gas, whose presence had earlier been inferred from
infrared CO spectra.

---------------------------------------------------------
Title: Thermal and Nonthermal Evolutions of a Circular Ribbon Flare
Authors: Lee, Jeongwoo; Liu, Chang; White, Stephen M.; Wang, Haimin
2019AAS...23431003L Altcode:
We studied the activation and the extended activity of a circular-ribbon
flare, SOL2014-12-17T04:51 by performing the Differential Emission
Measure (DEM) inversion analysis of the extreme ultraviolet (EUV)
images of the Atmospheric Imaging Assembly (AIA) instrument onboard
the Solar Dynamics Observatory (SDO) and analysis of the microwave data
from the Nobeyama Radioheliograph (NoRH). We will present the following
results. 1. The circular ribbon as an indicator of the dome-shaped
separatrix is better visible in the preflare phase in the form of very
narrow channel of enhance temperature. It is activated much earlier
(10-15 min before the impulsive phase at 04:33 UT), and its temporal
correlation with the outer spine temperature suggests the initial
activation of the circular ribbon by magnetic reconnection in the
outer spine. 2. The flare ribbons are active only within a limited
section of the entire circular ribbon, suggesting the hyperbolic
flux tube reconnection rather than null point reconnection. They are
activated 4 min before the impulsive phase together with the inner
spine, and involve nonthermal electrons as evidenced by the NoRH 34
GHz emission. 3. The temperature-high region and the DEM-high region
coincide each other in the impulsive phase, and then separate from each
other, implying that the rising magnetic fields carry hot plasma away
while the high-density cooler plasma stays on the fan surface. 4. An
unusually extended decay phase in this event can be understood as the
maximum DEM in the impulsive phase occurs at a higher temperature and
then gradually shifts to lower temperatures where EUV emission is more
efficient. Namely, the extended EUV activity is due to slow cooling
of the hot plasma within the confined magnetic structure.

---------------------------------------------------------
Title: First detection of non-thermal emission in a NuSTAR solar
microflare
Authors: Glesener, Lindsay; Krucker, Sam; Duncan, Jessie McBrayer;
Hannah, Iain; Grefenstette, Brian; Chen, Bin; Smith, David M.; White,
Stephen M.; Hudson, Hugh S.
2019AAS...23422503G Altcode:
We report the detection of emission from a non-thermal electron
distribution in a small solar microflare observed by the Nuclear
Spectroscopic Telescope Array (NuSTAR). On 2017 August 21, NuSTAR
observed a solar active region for approximately an hour before the
region was eclipsed by the Moon. The active region emitted several
small microflares of GOES class A and smaller. In this work, we present
spectroscopy demonstrating evidence of electron acceleration in one of
these microflares (GOES class A5.7) and we compare energetic aspects
of the accelerated distribution to commonly studied larger flares. The
flaring plasma observed by NuSTAR, with supporting observation by
the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), is
well accounted for by a thick-target model of accelerated electrons
collisionally thermalizing within the loop, akin to the "coronal
thick target" behavior occasionally observed in larger flares. Future
observations of this kind will enable understanding of how flare
particle acceleration changes across energy scales, and will aid
the push toward the observational regime of nanoflares, which are a
possible source of significant coronal heating.

---------------------------------------------------------
Title: Resolving the Radio Photospheres of Main Sequence Stars
Authors: Carilli, Christopher; Butler, B.; Golap, K.; Carilli, M. T.;
White, S. M.
2019BAAS...51c.243C Altcode: 2019astro2020T.243C
We discuss the need for spatially resolved observations of the radio
photospheres of main sequence stars. Such studies are fundamental to
determining the structure of stars in the key transition region from
the cooler optical photosphere to the hot chromosphere — the regions
powering exo- space weather phenomena.

---------------------------------------------------------
Title: Particle Acceleration and Transport, New Perspectives from
Radio, X-ray, and Gamma-Ray Observations
Authors: Gary, Dale; Bastian, Timothy S.; Chen, Bin; Drake, James F.;
Fleishman, Gregory; Glesener, Lindsay; Saint-Hilaire, Pascal; White,
Stephen M.
2019BAAS...51c.371G Altcode: 2019astro2020T.371G
Particle acceleration and particle transport are ubiquitous in
astrophysics. The Sun offers an astrophysical laboratory to study these
in minute detail, using radio dynamic imaging spectroscopy to measure
coronal magnetic fields, time and space evolution of the electron
distribution function.

---------------------------------------------------------
Title: Diagnostics of Space Weather Drivers Enabled by Radio
Observations
Authors: Bastian, Tim; Bain, Hazel; Chen, Bin; Gary, Dale E.;
Fleishman, Gregory D.; Glesener, Lindsay; Saint-Hilaire, Pascal;
Lonsdale, Colin; White, Stephen M.
2019BAAS...51c.323B Altcode: 2019astro2020T.323B; 2019arXiv190405817B
The Sun is an active star that can impact the Earth, its magnetosphere,
and the technological infrastructure on which modern society
depends. Radio emission from space weather drivers offers unique
diagnostics that complement those available at other wavelengths. We
discuss the requirements for an instrument to enable such diagnostics.

---------------------------------------------------------
Title: Radio, Millimeter, Submillimeter Observations of the Quiet Sun
Authors: Bastian, Tim; Chen, Bin; Gary, Dale E.; Fleishman, Gregory
D.; Glesener, Lindsay; Lonsdale, Colin; Saint-Hilaire, Pascal; White,
Stephen M.
2019BAAS...51c.493B Altcode: 2019arXiv190405826B; 2019astro2020T.493B
We point out the lack of suitable radio observations of the quiet Sun
chromosphere and corona and outline requirements for next generation
instrumentation to address the gap.

---------------------------------------------------------
Title: Probing Magnetic Reconnection in Solar Flares: New Perspectives
from Radio Dynamic Imaging Spectroscopy
Authors: Chen, Bin; Bastian, Tim; Dahlin, Joel; Drake, James F.;
Fleishman, Gregory; Gary, Dale; Glesener, Lindsay; Guo, Fan; Ji,
Hantao; Saint-Hilaire, Pascal; Shen, Chengcai; White, Stephen M.
2019BAAS...51c.507C Altcode: 2019astro2020T.507C; 2019arXiv190311192C
Magnetic reconnection is a fundamental physical process in many
laboratory, space, and astrophysical plasma contexts. In this white
paper we emphasize the unique power of remote-sensing observations
of solar flares at radio wavelengths in probing fundamental physical
processes in magnetic reconnection.

---------------------------------------------------------
Title: Solar Coronal Magnetic Fields: Quantitative Measurements at
Radio Wavelengths
Authors: Fleishman, Gregory; Bastian, Timothy S.; Chen, Bin; Gary,
Dale E.; Glesener, Lindsay; Nita, Gelu; Saint-Hilaire, Pascal; White,
Stephen M.
2019BAAS...51c.426F Altcode: 2019astro2020T.426F
Quantitative measurements of coronal and chromospheric magnetic field is
currently in its infancy. We describe a foundation of such observations,
which is a key input for MHD numerical models of the solar atmosphere
and eruptive processes, and a key link between lower layers of the
solar atmosphere and the heliosphere.

---------------------------------------------------------
Title: ngVLA Observations of Coronal Magnetic Fields
Authors: Fleishman, G. D.; Nita, G. M.; White, S. M.; Gary, D. E.;
Bastian, T. S.
2018ASPC..517..125F Altcode:
Energy stored in the magnetic field in the solar atmosphere above
active regions is a key driver of all solar activity (e.g., solar
flares and coronal mass ejections), some of which can affect life
on Earth. Radio observations provide a unique diagnostic of the
coronal magnetic fields that make them a critical tool for the
study of these phenomena, using the technique of broadband radio
imaging spectropolarimetry. Observations with the ngVLA will provide
unique observations of coronal magnetic fields and their evolution,
key inputs and constraints for MHD numerical models of the solar
atmosphere and eruptive processes, and a key link between lower layers
of the solar atmosphere and the heliosphere. In doing so they will
also provide practical "research to operations" guidance for space
weather forecasting.

---------------------------------------------------------
Title: Imaging Stellar Radio Photospheres with the Next Generation
Very Large Array
Authors: Carilli, C. L.; Butler, B.; Golap, K.; Carilli, M. T.; White,
S. M.
2018ASPC..517..369C Altcode: 2018arXiv181005055C
We perform simulations of the capabilities of the next generation Very
Large Array to image stellar radio photospheres. For very large (in
angle) stars, such as red supergiants within a few hundred parsecs,
good imaging fidelity results can be obtained on radio photospheric
structures at 38 GHz employing standard techniques, such as disk model
fitting and subtraction, with hundreds of resolution elements over the
star, even with just the ngVLA-classic baselines to 1000 km. Using the
ngVLA Rev B plus long baseline configuration (with baselines out to
9000 km, August 2018), we find for main sequence stars within ∼ 10
pc, the photospheres can be easily resolved at 85 GHz, with accurate
measures of the mean brightness and size, and possibly imaging large
surface structures, as might occur on e.g., active M dwarf stars. For
more distant main sequence stars, we find that measurements of sizes and
brightnesses can be made using disk model fitting to the (u,v)-data down
to stellar diameters ∼ 0.4 mas in a few hours. This size would include
M0 V stars to a distance of 15 pc, A0 V stars to 60 pc, and Red Giants
to 2.4 kpc. Based on the Hipparcos catalog, we estimate that there are
at least 10,000 stars that will be resolved by the ngVLA. While the
vast majority of these (95%) are giants or supergiants, there are still
over 500 main sequence stars that can be resolved, with ∼ 50 to 150 in
each spectral type (besides O stars). Note that these are lower limits,
since radio photospheres can be larger than optical, and the Hipparcos
catalog might not be complete. Our initial look into the Gaia catalog
suggests these numbers might be pessimistic by a factor few.

---------------------------------------------------------
Title: Characteristics of Late-phase &gt;100 MeV Gamma-Ray Emission
in Solar Eruptive Events
Authors: Share, G. H.; Murphy, R. J.; White, S. M.; Tolbert, A. K.;
Dennis, B. R.; Schwartz, R. A.; Smart, D. F.; Shea, M. A.
2018ApJ...869..182S Altcode:
We characterize and catalog 30 solar eruptive events observed by the
Fermi Large Area Telescope (LAT) having late-phase &gt;100 MeV γ-ray
emission (LPGRE), identified 30 yr ago in what were called long-duration
gamma-ray flares. We show that LPGRE is temporally and spectrally
distinct from impulsive phase emission in these events. The spectra
are consistent with the decay of pions produced by &gt;300 MeV protons
and are not consistent with primary electron bremsstrahlung. Impulsive
&gt;100 keV X-ray emission was observed in all 27 LPGRE events where
observations were made. All but two of the LPGRE events were accompanied
by a fast and broad coronal mass ejection (CME). The LPGRE start times
range from CME onset to 2 hr later. Their durations range from ∼0.1 to
20 hr and appear to be correlated with durations of &gt;100 MeV solar
energetic particle (SEP) proton events. The power-law spectral indices
of the &gt;300 MeV protons producing LPGRE range from ∼2.5 to 6.5
and vary during some events. Combined γ-ray line and LAT measurements
indicate that LPGRE proton spectra are steeper above 300 MeV than they
are below 300 MeV. The number of LPGRE protons &gt;500 MeV is typically
about 10× the number in the impulsive phase of the solar eruptive
event and ranges in nine events from ∼0.01× to 0.5× the number in
the accompanying SEP event, with large systematic uncertainty. What
appears to be late-phase electron bremsstrahlung with energies up
to ∼10 MeV was observed in one LPGRE event. We discuss how current
models of LPGRE may explain these characteristics.

---------------------------------------------------------
Title: Science with an ngVLA: ngVLA Observations of Coronal Magnetic
Fields
Authors: Fleishman, Gregory D.; Nita, Gelu M.; White, Stephen M.;
Gary, Dale E.; Bastian, Tim S.
2018arXiv181006622F Altcode:
Energy stored in the magnetic field in the solar atmosphere above
active regions is a key driver of all solar activity (e.g., solar
flares and coronal mass ejections), some of which can affect life
on Earth. Radio observations provide a unique diagnostic of the
coronal magnetic fields that make them a critical tool for the
study of these phenomena, using the technique of broadband radio
imaging spectropolarimetry. Observations with the ngVLA will provide
unique observations of coronal magnetic fields and their evolution,
key inputs and constraints for MHD numerical models of the solar
atmosphere and eruptive processes, and a key link between lower layers
of the solar atmosphere and the heliosphere. In doing so they will
also provide practical "research to operations" guidance for space
weather forecasting.

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Title: Microwave and Hard X-Ray Observations of the 2017 September
10 Solar Limb Flare
Authors: Gary, Dale E.; Chen, Bin; Dennis, Brian R.; Fleishman,
Gregory D.; Hurford, Gordon J.; Krucker, Säm; McTiernan, James M.;
Nita, Gelu M.; Shih, Albert Y.; White, Stephen M.; Yu, Sijie
2018ApJ...863...83G Altcode: 2018arXiv180702498G
We report the first science results from the newly completed Expanded
Owens Valley Solar Array (EOVSA), which obtained excellent microwave
(MW) imaging spectroscopy observations of SOL2017-09-10, a classic
partially occulted solar limb flare associated with an erupting flux
rope. This event is also well-covered by the Reuven Ramaty High Energy
Solar Spectroscopic Imager (RHESSI) in hard X-rays (HXRs). We present
an overview of this event focusing on MW and HXR data, both associated
with high-energy nonthermal electrons, and we discuss them within
the context of the flare geometry and evolution revealed by extreme
ultraviolet observations from the Atmospheric Imaging Assembly (AIA)
aboard the Solar Dynamics Observatory. The EOVSA and RHESSI data reveal
the evolving spatial and energy distribution of high-energy electrons
throughout the entire flaring region. The results suggest that the
MW and HXR sources largely arise from a common nonthermal electron
population, although the MW imaging spectroscopy provides information
over a much larger volume of the corona.

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Title: Observations of the solar chromosphere with ALMA and comparison
with theoretical models
Authors: Brajsa, Roman; Sudar, Davor; Skokic, Ivica; Benz, Arnold O.;
Kuhar, Matej; Kobelski, Adam; Wedemeyer, Sven; White, Stephen M.;
Ludwig, Hans-G.; Temmer, Manuela; Saar, Steven H.; Selhorst, Caius L.
2018csss.confE..37B Altcode: 2018arXiv181207293B
In this work we use solar observations with the ALMA radio telescope
at the wavelength of 1.21 mm. The aim of the analysisis to improve
understanding of the solar chromosphere, a dynamic layer in the
solar atmosphere between the photosphere andcorona. The study has
an observational and a modeling part. In the observational part
full-disc solar images are analyzed.Based on a modied FAL atmospheric
model, radiation models for various observed solar structures are
developed. Finally, theobservational and modeling results are compared
and discussed.

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Title: Modeling the Ionosphere with GPS and Rotation Measure
Observations
Authors: Malins, J. B.; White, S. M.; Taylor, G. B.; Stovall, K.;
Dowell, J.
2018RaSc...53..724M Altcode: 2018arXiv180602802M
The ionosphere contributes time-varying Faraday rotation (FR)
to radio signals passing through it. Correction for the effect of
the ionosphere is important for deriving magnetic field information
from FR observations of polarized cosmic radio sources, as well as
providing valuable diagnostics of the structure of the ionosphere. In
this paper, we evaluate the accuracy of models commonly used to correct
for its effects using new observations of pulsars at low frequencies,
which provide total rotation measures (RMs) at better precision
than previously available. We evaluate models of the ionosphere
derived from modern digital ionosondes that provide electron density
information as a function of height, as well as GPS-derived total
electron content (TEC) measurements. We combine these density models
with reference global magnetic field models to derive ionospheric RM
contributions. We find that the models disagree substantially with
each other and seek corrections that may explain the differences in
RM prediction. Additionally, we compare these models to global TEC
models and find that local high-cadence TEC measurements are superior
to global models for ionospheric RM correction.

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Title: The Reported Durations of GOES Soft X-Ray Flares in Different
Solar Cycles
Authors: Swalwell, Bill; Dalla, Silvia; Kahler, Stephen; White,
Stephen M.; Ling, Alan; Viereck, Rodney; Veronig, Astrid
2018SpWea..16..660S Altcode: 2018arXiv180510246S
The Geostationary Orbital Environmental Satellites (GOES) Soft X-ray
(SXR) sensors have provided data relating to, inter alia, the time,
intensity, and duration of solar flares since the 1970s. The GOES
SXR Flare List has become the standard reference catalogue for
solar flares and is widely used in solar physics research and space
weather. We report here that in the current version of the list there
are significant differences between the mean duration of flares which
occurred before May 1997 and the mean duration of flares thereafter. Our
analysis shows that the reported flare timings for the pre-May 1997
data were not based on the same criteria as is currently the case. This
finding has serious implications for all those who used flare duration
(or fluence, which depends on the chosen start and end times) as part
of their analysis of pre-May 1997 solar events or statistical analyses
of large samples of flares, for example, as part of the assessment of
a solar energetic particle forecasting algorithm.

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Title: Daily Coronal DEMs from AIA
Authors: White, Stephen M.; henry, Timothy; Schonfeld, Samuel;
Hock-Mysliwiec, Rachel
2018tess.conf22404W Altcode:
Daily solar full-disk coronal differential emission measure (DEM)

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Title: The Focusing Optics X-ray Solar Imager (FOXSI)
Authors: Christe, Steven; Shih, Albert Y.; Krucker, Sam; Glesener,
Lindsay; Saint-Hilaire, Pascal; Caspi, Amir; Allred, Joel C.; Chen,
Bin; Battaglia, Marina; Drake, James Frederick; Gary, Dale E.; Goetz,
Keith; Gburek, Szymon; Grefenstette, Brian; Hannah, Iain G.; Holman,
Gordon; Hudson, Hugh S.; Inglis, Andrew R.; Ireland, Jack; Ishikawa,
Shin-nosuke; Klimchuk, James A.; Kontar, Eduard; Kowalski, Adam F.;
Massone, Anna Maria; Piana, Michele; Ramsey, Brian; Schwartz, Richard;
Steslicki, Marek; Ryan, Daniel; Warmuth, Alexander; Veronig, Astrid;
Vilmer, Nicole; White, Stephen M.; Woods, Thomas N.
2018tess.conf40444C Altcode:
We present FOXSI (Focusing Optics X-ray Solar Imager), a Small Explorer
(SMEX) Heliophysics mission that is currently undergoing a Phase A
concept study. FOXSI will provide a revolutionary new perspective on
energy release and particle acceleration on the Sun. FOXSI's primary
instrument, the Direct Spectroscopic Imager (DSI), is a direct imaging
X-ray spectrometer with higher dynamic range and better than 10x the
sensitivity of previous instruments. Flown on a 3-axis-stabilized
spacecraft in low-Earth orbit, DSI uses high-angular-resolution
grazing-incidence focusing optics combined with state-of-the-art
pixelated solid-state detectors to provide direct imaging of solar hard
X-rays for the first time. DSI is composed of a pair of X-ray telescopes
with a 14-meter focal length enabled by a deployable boom. DSI has a
field of view of 9 arcminutes and an angular resolution of better than 8
arcsec FWHM; it will cover the energy range from 3 up to 50-70 keV with
a spectral resolution of better than 1 keV. DSI will measure each photon
individually and will be able to create useful images at a sub-second
temporal resolution. FOXSI will also measure soft x-ray emission down
to 0.8 keV with a 0.25 keV resolution with its secondary instrument,
the Spectrometer for Temperature and Composition (STC) provided by
the Polish Academy of Sciences. Making use of an attenuator-wheel and
high-rate-capable detectors, FOXSI will be able to observe the largest
flares without saturation while still maintaining the sensitivity to
detect X-ray emission from weak flares, escaping electrons, and hot
active regions. This presentation will cover the data products and
software that can be expected from FOXSI and how they could be used
by the community.

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Title: Microwave Imaging of Flares and Active Regions with the
Expanded Owens Valley Solar Array
Authors: Gary, Dale E.; Chen, Bin; Fleishman, Gregory D.; Kuroda,
Natsuha; Nita, Gelu M.; White, Stephen M.; Yu, Sijie
2018tess.conf21058G Altcode:
The Expanded Owens Valley Solar Array (EOVSA), operating in the
microwave range (2.5-18 GHz), is the first solar-dedicated radio
instrument to achieve true multi-frequency imaging of the Sun. As of
the time of this Triennial Earth-Sun Summit meeting, EOVSA will have
completed its first year of full operation. We present some highlights
of both active region and flare observations that demonstrate the
exciting new capabilities of the instrument, including excellent
coverage of several large flares that occurred in the 2017 September
period. We also provide information for public access to the data, and
for getting started with analysis. We are developing tools to simplify
working with the data, as well as modeling tools for interpreting
the results in the context of complementary multi-wavelength data
from space- and ground-based instruments. The progress and current
status of these efforts is given in this and a number of companion
presentations at the meeting.

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Title: DoD Space Weather S&amp;T Challenges
Authors: Hock-Mysliwiec, Rachel; Starks, Michael J.; White, Stephen M.
2018tess.conf41204H Altcode:
AFRL is a key player for transitioning space environment research into
DoD operations, and feeding operational needs back to the research
community

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Title: EUV Irradiance from the EVE MEGS-A Dataset and its Implications
for F10.7
Authors: Schonfeld, Samuel; White, Stephen M.; Hock-Mysliwiec, Rachel;
Henney, Carl J.; Mcateer, R. T. James
2018tess.conf40906S Altcode:
We present analysis of the complete spectral dataset from the
Extreme-ultraviolet (EUV) Variability Experiment (EVE) MEGS-A
instrument. Using these data, we construct daily differential emission
measures (DEMs) and use them to analyze the long-term variability
of the global corona and the irradiance it produces. We identify a
discontinuity in the EUV irradiance and DEMs separating solar minimum
and maximum conditions. Using the DEMs we also study the relationship
between EUV and F10.7, the 10.7 cm (2.8 GHz) solar activity
proxy. We compare predictions of the geoeffective F10.7
from the DEMs and photospheric magnetic field observations with the
commonly used 81-day averaged F10.7 to investigate their
uses in parameterizing the solar EUV irradiance. We demonstrate a
fundamental variability in the relationship between F10.7
and EUV associated with the two coronal sources of F10.7
emission.

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Title: Hunting for Hydrothermal Vents at the Local-Scale Using AUV's
and Machine-Learning Classification in the Earth's Oceans
Authors: White, S. M.
2018LPICo2085.6026W Altcode:
New AUV-based mapping technology coupled with machine-learning methods
for detecting individual vents and vent fields at the local-scale
raise the possibility of understanding the geologic controls on
hydrothermal venting.

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Title: NuSTAR Detection of X-Ray Heating Events in the Quiet Sun
Authors: Kuhar, Matej; Krucker, Säm; Glesener, Lindsay; Hannah,
Iain G.; Grefenstette, Brian W.; Smith, David M.; Hudson, Hugh S.;
White, Stephen M.
2018ApJ...856L..32K Altcode: 2018arXiv180308365K
The explanation of the coronal heating problem potentially lies in
the existence of nanoflares, numerous small-scale heating events
occurring across the whole solar disk. In this Letter, we present
the first imaging spectroscopy X-ray observations of three quiet
Sun flares during the Nuclear Spectroscopic Telescope ARray (NuSTAR)
solar campaigns on 2016 July 26 and 2017 March 21, concurrent with
the Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA)
observations. Two of the three events showed time lags of a few minutes
between peak X-ray and extreme ultraviolet emissions. Isothermal fits
with rather low temperatures in the range 3.2-4.1 MK and emission
measures of (0.6-15) × 1044 cm-3 describe
their spectra well, resulting in thermal energies in the range (2-6)
× 1026 erg. NuSTAR spectra did not show any signs of a
nonthermal or higher temperature component. However, as the estimated
upper limits of (hidden) nonthermal energy are comparable to the thermal
energy estimates, the lack of a nonthermal component in the observed
spectra is not a constraining result. The estimated Geostationary
Operational Environmental Satellite (GOES) classes from the fitted
values of temperature and emission measure fall between 1/1000 and
1/100 A class level, making them eight orders of magnitude fainter in
soft X-ray flux than the largest solar flares.

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Title: Magnetic Structure of a Composite Solar Microwave Burst
Authors: Lee, Jeongwoo; White, Stephen M.; Liu, Chang; Kliem, Bernhard;
Masuda, Satoshi
2018ApJ...856...70L Altcode:
A composite flare consisting of an impulsive flare SOL2015-06-21T01:42
(GOES class M2.0) and a more gradual, long-duration flare
SOL2015-06-21T02:36 (M2.6) from NOAA Active Region 12371, is studied
using observations with the Nobeyama Radioheliograph (NoRH) and the
Solar Dynamics Observatory (SDO). While composite flares are defined
by their characteristic time profiles, in this paper we present
imaging observations that demonstrate the spatial relationship of
the two flares and allow us to address the nature of the evolution
of a composite event. The NoRH maps show that the first flare is
confined not only in time, but also in space, as evidenced by the
stagnation of ribbon separation and the stationarity of the microwave
source. The NoRH also detected another microwave source during the
second flare, emerging from a different location where thermal plasma
is so depleted that accelerated electrons could survive longer against
Coulomb collisional loss. The AIA 131 Å images show that a sigmoidal
EUV hot channel developed after the first flare and erupted before the
second flare. We suggest that this eruption removed the high-lying flux
to let the separatrix dome underneath reconnect with neighboring flux
and the second microwave burst follow. This scenario explains how the
first microwave burst is related to the much-delayed second microwave
burst in this composite event.

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Title: Exploring the Sun with ALMA
Authors: Bastian, T. S.; Bárta, M.; Brajša, R.; Chen, B.; Pontieu,
B. D.; Gary, D. E.; Fleishman, G. D.; Hales, A. S.; Iwai, K.; Hudson,
H.; Kim, S.; Kobelski, A.; Loukitcheva, M.; Shimojo, M.; Skokić,
I.; Wedemeyer, S.; White, S. M.; Yan, Y.
2018Msngr.171...25B Altcode:
The Atacama Large Millimeter/submillimeter Array (ALMA) Observatory
opens a new window onto the Universe. The ability to perform continuum
imaging and spectroscopy of astrophysical phenomena at millimetre and
submillimetre wavelengths with unprecedented sensitivity opens up new
avenues for the study of cosmology and the evolution of galaxies, the
formation of stars and planets, and astrochemistry. ALMA also allows
fundamentally new observations to be made of objects much closer
to home, including the Sun. The Sun has long served as a touchstone
for our understanding of astrophysical processes, from the nature of
stellar interiors, to magnetic dynamos, non-radiative heating, stellar
mass loss, and energetic phenomena such as solar flares. ALMA offers
new insights into all of these processes.

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Title: The Focusing Optics X-ray Solar Imager (FOXSI) SMEX Mission
Authors: Christe, S.; Shih, A. Y.; Krucker, S.; Glesener, L.;
Saint-Hilaire, P.; Caspi, A.; Allred, J. C.; Battaglia, M.; Chen, B.;
Drake, J. F.; Gary, D. E.; Goetz, K.; Gburek, S.; Grefenstette, B.;
Hannah, I. G.; Holman, G.; Hudson, H. S.; Inglis, A. R.; Ireland,
J.; Ishikawa, S. N.; Klimchuk, J. A.; Kontar, E.; Kowalski, A. F.;
Massone, A. M.; Piana, M.; Ramsey, B.; Schwartz, R.; Steslicki, M.;
Turin, P.; Ryan, D.; Warmuth, A.; Veronig, A.; Vilmer, N.; White,
S. M.; Woods, T. N.
2017AGUFMSH44A..07C Altcode:
We present FOXSI (Focusing Optics X-ray Solar Imager), a Small Explorer
(SMEX) Heliophysics mission that is currently undergoing a Phase A
concept study. FOXSI will provide a revolutionary new perspective
on energy release and particle acceleration on the Sun. FOXSI is
a direct imaging X-ray spectrometer with higher dynamic range and
better than 10x the sensitivity of previous instruments. Flown
on a 3-axis-stabilized spacecraft in low-Earth orbit, FOXSI uses
high-angular-resolution grazing-incidence focusing optics combined
with state-of-the-art pixelated solid-state detectors to provide direct
imaging of solar hard X-rays for the first time. FOXSI is composed of
a pair of x-ray telescopes with a 14-meter focal length enabled by a
deployable boom. Making use of a filter-wheel and high-rate-capable
solid-state detectors, FOXSI will be able to observe the largest flares
without saturation while still maintaining the sensitivity to detect
x-ray emission from weak flares, escaping electrons, and hot active
regions. This mission concept is made possible by past experience with
similar instruments on two FOXSI sounding rocket flights, in 2012 and
2014, and on the HEROES balloon flight in 2013. FOXSI's hard X-ray
imager has a field of view of 9 arcminutes and an angular resolution
of better than 8 arcsec; it will cover the energy range from 3 up to
50-70 keV with a spectral resolution of better than 1 keV; and it will
have sub-second temporal resolution.

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Title: Modeling the Ionosphere with GPS and Rotation Measure
Observations
Authors: Malins, J. B.; Taylor, G. B.; White, S. M.; Dowell, J.
2017AGUFMSA51D..01M Altcode:
Advances in digital processing have created new tools for looking at
and examining the ionosphere. We have combined data from dual frequency
GPSs, digital ionosondes and observations from The Long Wavelength Array
(LWA), a 256 dipole low frequency radio telescope situated in central
New Mexico in order to examine ionospheric profiles. By studying
polarized pulsars, the LWA is able to very accurately determine the
Faraday rotation caused by the ionosphere. By combining this data
with the international geomagnetic reference field, the LWA can
evaluate ionospheric profiles and how well they predict the actual
Faraday rotation. Dual frequency GPS measurements of total electron
content, as well as measurements from digisonde data were used to
model the ionosphere, and to predict the Faraday rotation to with in
0.1 rad/m2. Additionally, it was discovered that the predicted topside
profile of the digisonde data did not accurate predict faraday rotation
measurements, suggesting a need to reexamine the methods for creating
the topside predicted profile. I will discuss the methods used to
measure rotation measure and ionosphere profiles as well as discuss
possible corrections to the topside model.

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Title: Forecasting E &gt; 50-MeV Proton Events with the Proton
Prediction System (PPS)
Authors: Kahler, S. W.; White, S. M.; Ling, A. G.
2017AGUFMSH31A2723K Altcode:
Forecasting solar energetic (E &gt; 10 MeV) particle (SEP) events
is an important element of space weather. While several models
have been developed for use in forecasting such events, satellite
operations are particularly vulnerable to higher-energy (&gt; 50 MeV)
SEP events. Here we validate one model, the proton prediction system
(PPS), which extends to that energy range. We first develop a data
base of E &gt; 50-MeV proton events &gt; 1.0 proton flux units (pfu)
events observed on the GOES satellite over the period 1986 to 2016. We
modify the PPS to forecast proton events at the reduced level of 1 pfu
and run PPS for four different solar input parameters: (1) all &gt; M5
solar X-ray flares; (2) all &gt; 200 sfu 8800-MHz bursts with associated
&gt; M5 flares; (3) all &gt; 500 sfu 8800-MHz bursts; and (4) all &gt;
5000 sfu 8800-MHz bursts. For X-ray flare inputs the forecasted event
peak intensities and fluences are compared with observed values. The
validation contingency tables and skill scores are calculated for all
groups and used as a guide to use of the PPS. We plot the false alarms
and missed events as functions of solar source longitude.

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Title: ALMA Discovery of Solar Umbral Brightness Enhancement at λ =
3 mm
Authors: Iwai, K.; Loukitcheva, M.; Shimojo, M.; Solanki, S. K.;
White, S. M.
2017AGUFMSH43A2806I Altcode:
We report the discovery of a brightness enhancement in the center of
a large sunspot umbra at a wavelength of 3 mm using the Atacama Large
Millimeter/sub-millimeter Array (ALMA). Sunspots are among the most
prominent features on the solar surface, but many of their aspects are
surprisingly poorly understood. We analyzed a λ = 3 mm (100 GHz) mosaic
image obtained by ALMA that includes a large sunspot within the active
region AR12470, on 2015 December 16. The 3 mm map has a 300”×300”
field of view and 4.9”×2.2” spatial resolution, which is the highest
spatial resolution map of an entire sunspot in this frequency range. We
find a gradient of 3 mm brightness from a high value in the outer
penumbra to a low value in the inner penumbra/outer umbra. Within the
inner umbra, there is a marked increase in 3 mm brightness temperature,
which we call an umbral brightness enhancement. This enhanced emission
corresponds to a temperature excess of 800 K relative to the surrounding
inner penumbral region and coincides with excess brightness in the
1330 and 1400 Å slit-jaw images of the Interface Region Imaging
Spectrograph (IRIS), adjacent to a partial lightbridge. This λ = 3 mm
brightness enhancement may be an intrinsic feature of the sunspot umbra
at chromospheric heights, such as a manifestation of umbral flashes, or
it could be related to a coronal plume, since the brightness enhancement
was coincident with the footpoint of a coronal loop observed at 171 Å.

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Title: Anticipated Results from the FOXSI SMEX Mission
Authors: Shih, A. Y.; Christe, S.; Krucker, S.; Glesener, L.;
Saint-Hilaire, P.; Caspi, A.; Allred, J. C.; Battaglia, M.; Chen, B.;
Drake, J. F.; Gary, D. E.; Gburek, S.; Goetz, K.; Grefenstette, B.;
Gubarev, M.; Hannah, I. G.; Holman, G.; Hudson, H. S.; Inglis, A. R.;
Ireland, J.; Ishikawa, S. N.; Klimchuk, J. A.; Kontar, E.; Kowalski,
A. F.; Massone, A. M.; Piana, M.; Ramsey, B.; Ryan, D.; Schwartz,
R.; Steslicki, M.; Turin, P.; Veronig, A.; Vilmer, N.; Warmuth, A.;
White, S. M.; Woods, T. N.
2017AGUFMSH43C..03S Altcode:
While there have been significant advances in our understanding
of impulsive energy release at the Sun since the advent of RHESSI
observations, there is a clear need for new X-ray observations that
can capture the full range of emission in flares (e.g., faint coronal
sources near bright chromospheric sources), follow the intricate
evolution of energy release and changes in morphology, and search
for the signatures of impulsive energy release in even the quiescent
Sun. The FOXSI Small Explorer (SMEX) mission, currently undergoing a
Phase A concept study, combines state-of-the-art grazing-incidence
focusing optics with pixelated solid-state detectors to provide
direct imaging of hard X-rays for the first time on a solar
observatory. FOXSI's X-ray observations will provide quantitative
information on (1) the non-thermal populations of accelerated electrons
and (2) the thermal plasma distributions at the high temperatures
inaccessible through other wavelengths. FOXSI's major science questions
include: Where are electrons accelerated and on what time scales? Where
do escaping flare-accelerated electrons originate? What is the energy
input of accelerated electrons into the chromosphere and corona? How
much do flare-like processes heat the corona above active regions? Here
we present examples with simulated observations to show how FOXSI's
capabilities will address and resolve these and other questions.

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Title: Thermal and Nonthermal Emissions of a Composite Flare Derived
from NoRH and SDO Observations
Authors: Lee, Jeongwoo; White, Stephen M.; Jing, Ju; Liu, Chang;
Masuda, Satoshi; Chae, Jongchul
2017ApJ...850..124L Altcode:
Differential emission measure (DEM) derived from the extreme ultraviolet
(EUV) lines of the Atmospheric Imaging Assembly (AIA) on board the Solar
Dynamic Observatory is used in the analysis of a solar flare observed
by the Nobeyama Radioheliograph (NoRH). The target was a composite event
consisting of an impulsive flare, SOL2015-06-21T01:42 (GOES class M2.0),
and a gradual flare, SOL2015-06-21T02:36 (M2.6), for which separation
of thermal plasma heating from nonthermal particle acceleration was of
major interest. We have calculated the thermal free-free intensity maps
with the AIA-derived DEM and compared them against the observed NoRH
maps to attribute the difference to the nonthermal component. In this
way, we were able to locate three distinct sources: the major source
with thermal and nonthermal components mixed, a nonthermal source
devoid of thermal particles, and a thermal source lacking microwave
emission. Both the first and the second nonthermal sources produced
impulsively rising 17 GHz intensities and moved away from the local
magnetic polarization inversion lines in correlation with the flare
radiation. In contrast, the thermal sources stay in fixed locations
and show temporal variations of the temperature and emission measure
uncorrelated with the flare radiation. We interpret these distinct
properties as indicating that nonthermal sources are powered by
magnetic reconnection and thermal sources passively receive energy
from the nonthermal donor. The finding of these distinct properties
between thermal and nonthermal sources demonstrates the microwave and
EUV emission measure combined diagnostics.

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Title: The First ALMA Observation of a Solar Plasmoid Ejection from
an X-Ray Bright Point
Authors: Shimojo, M.; Hudson, H. S.; White, S. M.; Bastian, T.;
Iwai, K.
2017AGUFMSH41A2754S Altcode:
Eruptive phenomena are important features of energy releases events,
such solar flares, and have the potential to improve our understanding
of the dynamics of the solar atmosphere. The 304 A EUV line of helium,
formed at around 10^5 K, is found to be a reliable tracer of such
phenomena, but the determination of physical parameters from such
observations is not straightforward. We have observed a plasmoid
ejection from an X-ray bright point simultaneously with ALMA, SDO/AIA,
and Hinode/XRT. This paper reports the physical parameters of the
plasmoid obtained by combining the radio, EUV, and X-ray data. As
a result, we conclude that the plasmoid can consist either of
(approximately) isothermal ∼10^5 K plasma that is optically thin
at 100 GHz, or a ∼10^4 K core with a hot envelope. The analysis
demonstrates the value of the additional temperature and density
constraints that ALMA provides, and future science observations with
ALMA will be able to match the spatial resolution of space-borne and
other high-resolution telescopes.

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Title: High-Energy Aspects of Small-Scale Energy Release at the Sun
Authors: Glesener, L.; Vievering, J. T.; Wright, P. J.; Hannah,
I. G.; Panchapakesan, S. A.; Ryan, D.; Krucker, S.; Hudson, H. S.;
Grefenstette, B.; White, S. M.; Smith, D. M.; Marsh, A.; Kuhar, M.;
Christe, S.; Buitrago-Casas, J. C.; Musset, S.; Inglis, A. R.
2017AGUFMSM33E..04G Altcode:
Large, powerful solar flares have been investigated in detail for
decades, but it is only recently that high-energy aspects of small
flares could be measured. These small-scale energy releases offer
the opportunity to examine how particle acceleration characteristics
scale down, which is critical for constraining energy transfer theories
such as magnetic reconnection. Probing to minuscule flare sizes also
brings us closer to envisioning the characteristics of the small
"nanoflares" that may be responsible for heating the corona. A new
window on small-scale flaring activity is now opening with the use of
focusing hard X-ray instruments to observe the Sun. Hard X-rays are
emitted by flare-accelerated electrons and strongly heated plasma,
providing a relatively direct method of measuring energy release
and particle acceleration properties. This work will show the first
observations of sub-A class microflares using the FOXSI sounding
rocket and the NuSTAR astrophysics spacecraft, both of which directly
focus hard X-rays but have limited observing time on the Sun. These
instruments serve as precursors to a spacecraft version of FOXSI, which
will explore energy release across the entire range of flaring activity.

---------------------------------------------------------
Title: The Slowly Varying Corona: Findings from DEMs with the EVE
MEGS-A Dataset
Authors: Schonfeld, S.; White, S. M.; Hock, R. A.; Henney, C. J.;
McAteer, J.
2017AGUFMSH43B2812S Altcode:
We present analysis of the complete spectral dataset from the
Extreme-ultraviolet (EUV) Variability Experiment (EVE) MEGS-A
instrument. Using these data, we construct daily differential emission
measures (DEMs) and use them to analyze the long-term variability
of the global corona and the irradiance it produces. We identify a
discontinuity in the EUV irradiance and DEMs separating solar minimum
and maximum conditions. Using the DEMs we also study the relationship
between EUV and F10.7, the 10.7 cm (2.8 GHz) solar activity proxy. We
compare predictions of the geoeffective F10.7 from the DEMs and
photospheric magnetic field observations with the commonly used 81-day
averaged F10.7 to investigate their uses in parameterizing the solar
EUV irradiance.

---------------------------------------------------------
Title: Solar Flare Dynamic Microwave Imaging with EOVSA
Authors: Gary, D. E.; Chen, B.; Nita, G. M.; Fleishman, G. D.; Yu,
S.; White, S. M.; Hurford, G. J.; McTiernan, J. M.
2017AGUFMSH41A2755G Altcode:
The Expanded Owens Valley Solar Array (EOVSA) is both an expansion
of our existing solar array and serves as a prototype for a much
larger future project, the Frequency Agile Solar Radiotelescope
(FASR). EOVSA is now complete, and is producing daily imaging of the
full solar disk, including active regions and solar radio bursts
at hundreds of frequencies in the range 2.8-18 GHz. We present
highlights of the 1-s-cadence dynamic imaging spectroscropy of
radio bursts we have obtained to date, along with deeper analysis
of multi-wavelength observations and modeling of a well-observed
burst. These observations are revealing the full life-cycle of the
trapped population of high-energy electrons, from their initial
acceleration and subsequent energy-evolution to their eventual decay
through escape and thermalization. All of our data are being made
available for download in both quick-look image form and in the form
of the community-standard CASA measurement sets for subsequent imaging
and analysis.

---------------------------------------------------------
Title: First NuSTAR Limits on Quiet Sun Hard X-Ray Transient Events
Authors: Marsh, Andrew J.; Smith, David M.; Glesener, Lindsay;
Hannah, Iain G.; Grefenstette, Brian W.; Caspi, Amir; Krucker, Säm;
Hudson, Hugh S.; Madsen, Kristin K.; White, Stephen M.; Kuhar, Matej;
Wright, Paul J.; Boggs, Steven E.; Christensen, Finn E.; Craig,
William W.; Hailey, Charles J.; Harrison, Fiona A.; Stern, Daniel;
Zhang, William W.
2017ApJ...849..131M Altcode: 2017arXiv171105385M
We present the first results of a search for transient hard X-ray (HXR)
emission in the quiet solar corona with the Nuclear Spectroscopic
Telescope Array (NuSTAR) satellite. While NuSTAR was designed as
an astrophysics mission, it can observe the Sun above 2 keV with
unprecedented sensitivity due to its pioneering use of focusing
optics. NuSTAR first observed quiet-Sun regions on 2014 November 1,
although out-of-view active regions contributed a notable amount
of background in the form of single-bounce (unfocused) X-rays. We
conducted a search for quiet-Sun transient brightenings on timescales
of 100 s and set upper limits on emission in two energy bands. We set
2.5-4 keV limits on brightenings with timescales of 100 s, expressed
as the temperature T and emission measure EM of a thermal plasma. We
also set 10-20 keV limits on brightenings with timescales of 30, 60,
and 100 s, expressed as model-independent photon fluxes. The limits in
both bands are well below previous HXR microflare detections, though
not low enough to detect events of equivalent T and EM as quiet-Sun
brightenings seen in soft X-ray observations. We expect future
observations during solar minimum to increase the NuSTAR sensitivity
by over two orders of magnitude due to higher instrument livetime and
reduced solar background.

---------------------------------------------------------
Title: Solar ALMA Observations: Constraining the Chromosphere above
Sunspots
Authors: Loukitcheva, Maria A.; Iwai, Kazumasa; Solanki, Sami K.;
White, Stephen M.; Shimojo, Masumi
2017ApJ...850...35L Altcode: 2017arXiv171003812L
We present the first high-resolution Atacama Large
Millimeter/Submillimeter Array (ALMA) observations of a sunspot at
wavelengths of 1.3 and 3 mm, obtained during the solar ALMA Science
Verification campaign in 2015, and compare them with the predictions
of semi-empirical sunspot umbral/penumbral atmosphere models. For
the first time, millimeter observations of sunspots have resolved
umbral/penumbral brightness structure at the chromospheric heights,
where the emission at these wavelengths is formed. We find that the
sunspot umbra exhibits a radically different appearance at 1.3 and 3
mm, whereas the penumbral brightness structure is similar at the two
wavelengths. The inner part of the umbra is ∼600 K brighter than the
surrounding quiet Sun (QS) at 3 mm and is ∼700 K cooler than the QS
at 1.3 mm, being the coolest part of sunspot at this wavelength. On
average, the brightness of the penumbra at 3 mm is comparable to
the QS brightness, while at 1.3 mm it is ∼1000 K brighter than
the QS. Penumbral brightness increases toward the outer boundary in
both ALMA bands. Among the tested umbral models, that of Severino et
al. provides the best fit to the observational data, including both
the ALMA data analyzed in this study and data from earlier works. No
penumbral model among those considered here gives a satisfactory fit
to the currently available measurements. ALMA observations at multiple
millimeter wavelengths can be used for testing existing sunspot models,
and serve as an important input to constrain new empirical models.

---------------------------------------------------------
Title: Characteristics of Sustained &gt;100 MeV Gamma-ray Emission
Associated with Solar Flares
Authors: Share, G. H.; Murphy, R. J.; Tolbert, A. K.; Dennis, B. R.;
White, S. M.; Schwartz, R. A.; Tylka, A. J.
2017arXiv171101511S Altcode:
We characterize and provide a catalog of thirty &gt;100 MeV sustained
gamma-ray emission (SGRE) events observed by Fermi LAT. These
events are temporally and spectrally distinct from the associated
solar flares. Their spectra are consistent with decay of pions
produced by &gt;300 MeV protons and are not consistent with electron
bremsstrahlung. SGRE start times range from CME onset to two hours
later. Their durations range from about four minutes to twenty hours
and appear to be correlated with durations of &gt;100 MeV SEP proton
events. The &gt;300 MeV protons producing SGRE have spectra that
can be fit with power laws with a mean index of ~4 and RMS spread of
1.8. Gamma-ray line measurements indicate that SGRE proton spectra are
steeper above 300 MeV than they are below 300 MeV. The number of SGRE
protons &gt;500 MeV is on average about ten times more than then the
number in the associated flare and about fifty to one hundred times
less than the number in the accompanying SEP. SGRE can extend tens of
degrees from the are site. Sustained bremsstrahlung from MeV electrons
was observed in one SGRE event. Flare &gt;100 keV X-ray emission
appears to be associated with SGRE and with intense SEPs. From this
observation, we provide arguments that lead us to propose that sub-MeV
to MeV protons escaping from the flare contribute to the seed population
that is accelerated by shocks onto open field lines to produce SEPs
and onto field lines returning to the Sun to produce SGRE.

---------------------------------------------------------
Title: Forecasting E &gt; 50-MeV proton events with the proton
prediction system (PPS)
Authors: Kahler, Stephen W.; White, Stephen M.; Ling, Alan G.
2017JSWSC...7A..27K Altcode:
Forecasting solar energetic (E &gt; 10-MeV) particle (SEP) events
is an important element of space weather. While several models
have been developed for use in forecasting such events, satellite
operations are particularly vulnerable to higher-energy (≥50-MeV)
SEP events. Here we validate one model, the proton prediction system
(PPS), which extends to that energy range. We first develop a data
base of E ≥ 50-MeV proton events &gt;1.0 proton flux units (pfu)
events observed on the GOES satellite over the period 1986-2016. We
modify the PPS to forecast proton events at the reduced level of 1
pfu and run PPS for four different solar input parameters: (1) all
≥M5 solar X-ray flares; (2) all ≥200 sfu 8800-MHz bursts with
associated ≥M5 flares; (3) all ≥500 sfu 8800-MHz bursts; and (4)
all ≥5000 sfu 8800-MHz bursts. The validation contingency tables and
skill scores are calculated for all groups and used as a guide to use
of the PPS. We plot the false alarms and missed events as functions
of solar source longitude, and argue that the longitude-dependence
employed by PPS does not match modern observations. Use of the radio
fluxes as the PPS driver tends to result in too many false alarms
at the 500 sfu threshold, and misses more events than the soft X-ray
predictor at the 5000 sfu threshold.

---------------------------------------------------------
Title: Magnetic Diagnostics of the Solar Corona: Synthesizing Optical
and Radio Techniques
Authors: Casini, R.; White, S. M.; Judge, P. G.
2017SSRv..210..145C Altcode: 2017SSRv..tmp...91C
In this contribution we review the current state-of-the-art of
coronal magnetometry, in both optical and radio domains. We address
the achievable objectives and the challenges of present measurement
techniques and interpretation tools. In particular, we focus on the
role that these observations can play for constraining and validating
numerical models of the global coronal magnetic field. With regard
to optical techniques, we mainly focus on the use of M1 diagnostics,
further developing the theory of the formation of their polarization
signatures in the magnetized corona.

---------------------------------------------------------
Title: Microflare Heating of an Active Region Observed with NuSTAR,
Hinode/XRT, and SDO/AIA
Authors: Wright, Paul James; Hannah, Iain; Grefenstette, Brian;
Glesener, Lindsay; Krucker, Sam; Hudson, Hugh S.; Smith, David M.;
Marsh, Andrew; White, Stephen M.; Kuhar, Matej
2017SPD....4810802W Altcode:
We present the first joint observation of a GOES equivalent A0.2
microflare that occurred on the 29 Apr 2015 with Hinode/XRT and
NuSTAR. During the three hours of combined observation we observe
distinctive loop heating in the soft X-rays from Hinode/XRT, and
the hottest channels from SDO/AIA. Crucially the impulsive phase of
this microflare was also observed by NuSTAR, a highly sensitive hard
X-ray (2.5-80 keV; Harrison et al. 2013) focussing optics imaging
spectrometer. The NuSTAR spectrum before and after the microflare
is well-fitted by a single thermal model of about 3.3 - 3.5 MK, but
at the impulsive phase shows additional material up to 10 MK. This
higher temperature emission is confirmed when we produce the DEM
using a combination of SDO/AIA, Hinode/XRT, and NuSTAR data. During
the impulsive phase of the microflare we determine the heating rate to
be about 3 x 1025 erg s-1. Although non-thermal
emission is not detected we find upper-limits that are consistent with
the required heating rate.

---------------------------------------------------------
Title: Solar Commissioning Observations of the Sun with ALMA
Authors: White, Stephen M.; Shimojo, Masumi; Bastian, Timothy S.;
Iwai, Kazumasa; Hales, Antonio; Brajsa, Roman; Skokic, Ivica; Kim,
Sujin; Hudson, Hugh S.; Loukitcheva, Maria; Wedemeyer, Sven
2017SPD....4820402W Altcode:
PI-led science observations have commenced with the Atacama
Large Millimeter-submillimeter Array (ALMA) following an extensive
commissioning effort. This talk will summarize that effort and discuss
some of the scientific results derived from the commissioning data. As
the solar cycle declines, ALMA observations will mainly address
chromospheric science topics. Examples of data obtained during
commissioning, both from the interferometer and from single-dish
observations, will be presented. The temperatures of the layers that
ALMA is most sensitive to have been determined for the two frequency
bands currently used for solar observations. Curious behavior in a
sunspot umbra and an observations of a small chromospheric ejection
will be discussed.

---------------------------------------------------------
Title: Results from NuSTAR: Dynamics and time evolution in a sub-A
class hard X-ray flare
Authors: Glesener, Lindsay; Krucker, Sam; Hannah, Iain; Hudson,
Hugh S.; Grefenstette, Brian; White, Stephen M.; Smith, David M.;
Marsh, Andrew
2017SPD....4810803G Altcode:
We report a NuSTAR observation of a solar microflare,
SOL2015-09-01T04. Although it was too faint to be observed by the
GOES X-ray Sensor, we estimate the flare to be an A0.2 class flare in
brightness. This flare, with only ∼5 counts s-1 detector-1 observed
by RHESSI, is fainter than any hard X-ray (HXR) flare in the existing
literature. The flare occurred during a solar pointing by the highly
sensitive NuSTAR astrophysical observatory, which used its direct
focusing optics to produce detailed HXR flare spectra and images. The
flare exhibits HXR properties commonly observed in larger flares,
including a fast rise and more gradual decay, earlier peaking time with
higher energy, similar spatial dimensions to the RHESSI microflares,
and a high-energy excess beyond an isothermal spectral component
during the impulsive phase. The flare is small in emission measure,
temperature, and energy, though not in physical size; observations
are consistent with its arising via the interaction of at least two
magnetic loops. We estimate the increase in thermal energy at the time
of the flare to be 1.8×1027 ergs. The observation suggests that flares
do indeed scale down to extremely small energies and retain what we
customarily think of as “flarelike” properties.

---------------------------------------------------------
Title: Science with the Expanded Owens Valley Solar Array
Authors: Nita, Gelu M.; Gary, Dale E.; Fleishman, Gregory D.; Chen,
Bin; White, Stephen M.; Hurford, Gordon J.; McTiernan, James; Hickish,
Jack; Yu, Sijie; Nelin, Kjell B.
2017SPD....4811009N Altcode:
The Expanded Owens Valley Solar Array (EOVSA) is a solar-dedicated
radio array that makes images and spectra of the full Sun on a daily
basis. Our main science goals are to understand the basic physics of
solar activity, such as how the Sun releases stored magnetic energy
on timescales of seconds, and how that solar activity, in the form
of solar flares and coronal mass ejections, influences the Earth and
near-Earth space environment, through disruptions of communication
and navigation systems, and effects on satellites and systems on the
ground. The array, which is composed out of thirteen 2.1 m dishes
and two 27 m dishes (used only for calibration), has a footprint of
1.1 km EW x 1.2 km NS and it is capable of producing, every second,
microwave images at two polarizations and 500 science channels spanning
the 1-18 GHz frequency range. Such ability to make multi-frequency
images of the Sun in this broad range of frequencies, with a frequency
dependent resolution ranging from ∼53” at 1 GHz to ∼3”at 18
GHz, is unique in the world. Here we present an overview of the EOVSA
instrument and a first set of science-quality active region and solar
flare images produced from data taken during April 2017.This research
is supported by NSF grant AST-1615807 and NASA grant NNX14AK66G to
New Jersey Institute of Technology.

---------------------------------------------------------
Title: A comparison of solar ALMA maps with solar images obtained
at other wavelengths
Authors: Brajsa, Roman; Sudar, Davor; Skokic, Ivica; Benz, Arnold;
Kuhar, Matej; White, Stephen M.
2017SPD....4820403B Altcode:
We use recently released Commissioning and Science Verification
data of the Sun from the observing campaigns perfomed with the ALMA
radio telescope in December 2014 and in December 2015. The dataset
consists of calibrated maps of the Sun recorded in ALMA observing
band 3 (corresponding to a wavelength of 3 mm) and band 6 (1.2 mm)
which show both bright and dark areas and a background of highly
structured pattern. Solar ALMA maps are compared with images in EUV
(SDO/AIA), H-alpha (NISP, Cerro Tololo) and He 1083 nm (NSO/SOLIS),
as well as with magnetograms (SDO/HMI) recorded at times closest
to the ALMA observations. With a special software the images
are overlapped and a correspondence of identified structures is
checked in both ways. The visibility of active regions, sunspots,
inversion lines of global magnetic field, prominences on the disc,
coronal holes and coronal bright points is investigated in ALMA
images at mm wavelengths. Single-dish ALMA images of the Sun reveal
large-scale structures in the solar atmosphere, while high resolution
interferometric images are used to analyse the fine-scale chromospheric
structure. The intensities (the brightness temperatures) of identified
structures were determined and compared with selected model-based
predictions.

---------------------------------------------------------
Title: NuSTAR Hard X-Ray Observation of a Sub-A Class Solar Flare
Authors: Glesener, Lindsay; Krucker, Säm; Hannah, Iain G.; Hudson,
Hugh; Grefenstette, Brian W.; White, Stephen M.; Smith, David M.;
Marsh, Andrew J.
2017ApJ...845..122G Altcode: 2017arXiv170704770G
We report a Nuclear Spectroscopic Telescope Array (NuSTAR) observation
of a solar microflare, SOL2015-09-01T04. Although it was too faint
to be observed by the GOES X-ray Sensor, we estimate the event to be
an A0.1 class flare in brightness. This microflare, with only ∼5
counts s-1 detector-1 observed by the Reuven
Ramaty High Energy Solar Spectroscopic Imager (RHESSI), is fainter
than any hard X-ray (HXR) flare in the existing literature. The
microflare occurred during a solar pointing by the highly sensitive
NuSTAR astrophysical observatory, which used its direct focusing optics
to produce detailed HXR microflare spectra and images. The microflare
exhibits HXR properties commonly observed in larger flares, including a
fast rise and more gradual decay, earlier peak time with higher energy,
spatial dimensions similar to the RHESSI microflares, and a high-energy
excess beyond an isothermal spectral component during the impulsive
phase. The microflare is small in emission measure, temperature,
and energy, though not in physical size; observations are consistent
with an origin via the interaction of at least two magnetic loops. We
estimate the increase in thermal energy at the time of the microflare
to be 2.4 × 1027 erg. The observation suggests that flares
do indeed scale down to extremely small energies and retain what we
customarily think of as “flare-like” properties.

---------------------------------------------------------
Title: The Slowly Varying Corona: Findings using DEMs from the EVE
MEGS-A Dataset
Authors: Schonfeld, Samuel J.; White, Stephen M.; Hock, Rachel A.;
Henney, Carl John; McAteer, James
2017SPD....4840204S Altcode:
We present analysis of the complete spectral dataset from the
Extreme-ultraviolet (EUV) Variability Experiment (EVE) MEGS-A
instrument. With these data we construct daily differential emission
measures (DEMs) and use them to analyze the long-term variability of the
global corona. We identify a discontinuity in the DEMs separating solar
minimum and maximum conditions that suggests a fundamental change in
the coronal temperature structure with solar activity. Using the DEMs,
we also study the relationship between EUV and F10.7, the
10.7 cm (2.8 GHz) solar activity proxy. We compare the F10.7
predictions from the DEMs and photospheric magnetic field observations
with irradiance microwave observations to constrain the source
mechanisms of F10.7 and their relative contribution as a
function of solar activity. This has serious implications for the use
of F10.7 as an activity proxy in terrestrial atmospheric
modeling and we discuss our results in the context of previous
work. Comparing the DEMs with microwave observations also allows for
a determination of the coronal iron abundance and a measurement of
the FIP effect.

---------------------------------------------------------
Title: Microflare Heating of a Solar Active Region Observed with
NuSTAR, Hinode/XRT, and SDO/AIA
Authors: Wright, Paul J.; Hannah, Iain G.; Grefenstette, Brian W.;
Glesener, Lindsay; Krucker, Säm; Hudson, Hugh S.; Smith, David M.;
Marsh, Andrew J.; White, Stephen M.; Kuhar, Matej
2017ApJ...844..132W Altcode: 2017arXiv170606108W
NuSTAR is a highly sensitive focusing hard X-ray (HXR) telescope and has
observed several small microflares in its initial solar pointings. In
this paper, we present the first joint observation of a microflare
with NuSTAR and Hinode/XRT on 2015 April 29 at ∼11:29 UT. This
microflare shows the heating of material to several million Kelvin,
observed in soft X-rays with Hinode/XRT, and was faintly visible in
the extreme ultraviolet with SDO/AIA. For three of the four NuSTAR
observations of this region (pre-flare, decay, and post-flare phases),
the spectrum is well fitted by a single thermal model of 3.2-3.5 MK,
but the spectrum during the impulsive phase shows additional emission
up to 10 MK, emission equivalent to the A0.1 GOES class. We recover
the differential emission measure (DEM) using SDO/AIA, Hinode/XRT,
and NuSTAR, giving unprecedented coverage in temperature. We find that
the pre-flare DEM peaks at ∼3 MK and falls off sharply by 5 MK;
but during the microflare’s impulsive phase, the emission above 3
MK is brighter and extends to 10 MK, giving a heating rate of about
2.5× {10}25 erg s-1. As the NuSTAR spectrum is
purely thermal, we determined upper limits on the possible non-thermal
bremsstrahlung emission. We find that for the accelerated electrons to
be the source of heating, a power-law spectrum of δ ≥slant 7 with a
low-energy cutoff {E}c≲ 7 keV is required. In summary, this
first NuSTAR microflare strongly resembles much more powerful flares.

---------------------------------------------------------
Title: The Slowly Varying Corona. I. Daily Differential Emission
Measure Distributions Derived from EVE Spectra
Authors: Schonfeld, S. J.; White, S. M.; Hock-Mysliwiec, R. A.;
McAteer, R. T. J.
2017ApJ...844..163S Altcode: 2017arXiv170609525S
Daily differential emission measure (DEM) distributions of the solar
corona are derived from spectra obtained by the Extreme-ultraviolet
Variability Experiment (EVE) over a 4 yr period starting in 2010 near
solar minimum and continuing through the maximum of solar cycle 24. The
DEMs are calculated using six strong emission features dominated by
Fe lines of charge states viii, ix, xi, xii, xiv, and xvi that sample
the nonflaring coronal temperature range 0.3-5 MK. A proxy for the
non-Fe xviii emission in the wavelength band around the 93.9 Å line
is demonstrated. There is little variability in the cool component
of the corona (T &lt; 1.3 MK) over the 4 yr, suggesting that the
quiet-Sun corona does not respond strongly to the solar cycle, whereas
the hotter component (T &gt; 2.0 MK) varies by more than an order of
magnitude. A discontinuity in the behavior of coronal diagnostics in
2011 February-March, around the time of the first X-class flare of cycle
24, suggests fundamentally different behavior in the corona under solar
minimum and maximum conditions. This global state transition occurs
over a period of several months. The DEMs are used to estimate the
thermal energy of the visible solar corona (of order 1031
erg), its radiative energy loss rate ((2.5-8) × {10}27
erg s-1), and the corresponding energy turnover timescale
(about an hour). The uncertainties associated with the DEMs and these
derived values are mostly due to the coronal Fe abundance and density
and the CHIANTI atomic line database.

---------------------------------------------------------
Title: Observing the Sun with the Atacama Large
Millimeter/submillimeter Array (ALMA): High-Resolution Interferometric
Imaging
Authors: Shimojo, M.; Bastian, T. S.; Hales, A. S.; White, S. M.;
Iwai, K.; Hills, R. E.; Hirota, A.; Phillips, N. M.; Sawada, T.;
Yagoubov, P.; Siringo, G.; Asayama, S.; Sugimoto, M.; Brajša, R.;
Skokić, I.; Bárta, M.; Kim, S.; de Gregorio-Monsalvo, I.; Corder,
S. A.; Hudson, H. S.; Wedemeyer, S.; Gary, D. E.; De Pontieu, B.;
Loukitcheva, M.; Fleishman, G. D.; Chen, B.; Kobelski, A.; Yan, Y.
2017SoPh..292...87S Altcode: 2017arXiv170403236S
Observations of the Sun at millimeter and submillimeter wavelengths
offer a unique probe into the structure, dynamics, and heating of the
chromosphere; the structure of sunspots; the formation and eruption
of prominences and filaments; and energetic phenomena such as jets
and flares. High-resolution observations of the Sun at millimeter and
submillimeter wavelengths are challenging due to the intense, extended,
low-contrast, and dynamic nature of emission from the quiet Sun,
and the extremely intense and variable nature of emissions associated
with energetic phenomena. The Atacama Large Millimeter/submillimeter
Array (ALMA) was designed with solar observations in mind. The
requirements for solar observations are significantly different from
observations of sidereal sources and special measures are necessary
to successfully carry out this type of observations. We describe the
commissioning efforts that enable the use of two frequency bands,
the 3-mm band (Band 3) and the 1.25-mm band (Band 6), for continuum
interferometric-imaging observations of the Sun with ALMA. Examples of
high-resolution synthesized images obtained using the newly commissioned
modes during the solar-commissioning campaign held in December 2015
are presented. Although only 30 of the eventual 66 ALMA antennas
were used for the campaign, the solar images synthesized from the
ALMA commissioning data reveal new features of the solar atmosphere
that demonstrate the potential power of ALMA solar observations. The
ongoing expansion of ALMA and solar-commissioning efforts will continue
to enable new and unique solar observing capabilities.

---------------------------------------------------------
Title: Observing the Sun with the Atacama Large
Millimeter/submillimeter Array (ALMA): Fast-Scan Single-Dish Mapping
Authors: White, S. M.; Iwai, K.; Phillips, N. M.; Hills, R. E.; Hirota,
A.; Yagoubov, P.; Siringo, G.; Shimojo, M.; Bastian, T. S.; Hales,
A. S.; Sawada, T.; Asayama, S.; Sugimoto, M.; Marson, R. G.; Kawasaki,
W.; Muller, E.; Nakazato, T.; Sugimoto, K.; Brajša, R.; Skokić, I.;
Bárta, M.; Kim, S.; Remijan, A. J.; de Gregorio, I.; Corder, S. A.;
Hudson, H. S.; Loukitcheva, M.; Chen, B.; De Pontieu, B.; Fleishmann,
G. D.; Gary, D. E.; Kobelski, A.; Wedemeyer, S.; Yan, Y.
2017SoPh..292...88W Altcode: 2017arXiv170504766W
The Atacama Large Millimeter/submillimeter Array (ALMA) radio
telescope has commenced science observations of the Sun starting
in late 2016. Since the Sun is much larger than the field of view
of individual ALMA dishes, the ALMA interferometer is unable to
measure the background level of solar emission when observing the
solar disk. The absolute temperature scale is a critical measurement
for much of ALMA solar science, including the understanding of energy
transfer through the solar atmosphere, the properties of prominences,
and the study of shock heating in the chromosphere. In order to provide
an absolute temperature scale, ALMA solar observing will take advantage
of the remarkable fast-scanning capabilities of the ALMA 12 m dishes
to make single-dish maps of the full Sun. This article reports on the
results of an extensive commissioning effort to optimize the mapping
procedure, and it describes the nature of the resulting data. Amplitude
calibration is discussed in detail: a path that uses the two loads in
the ALMA calibration system as well as sky measurements is described
and applied to commissioning data. Inspection of a large number of
single-dish datasets shows significant variation in the resulting
temperatures, and based on the temperature distributions, we derive
quiet-Sun values at disk center of 7300 K at λ =3 mm and 5900 K at
λ =1.3 mm. These values have statistical uncertainties of about 100
K, but systematic uncertainties in the temperature scale that may be
significantly larger. Example images are presented from two periods
with very different levels of solar activity. At a resolution of about
25″, the 1.3 mm wavelength images show temperatures on
the disk that vary over about a 2000 K range. Active regions and plages
are among the hotter features, while a large sunspot umbra shows up as
a depression, and filament channels are relatively cool. Prominences
above the solar limb are a common feature of the single-dish images.

---------------------------------------------------------
Title: Laser Ablation Experiments on the Tamdakht H5 Chondrite
Authors: White, S. M.; Stern, E. C.
2017LPICo1987.6130W Altcode:
High-powered lasers were used to ablate and form surfaces similar
to naturally formed fusion crusts on Tamdakht and basalt. High speed
camera showed ablation during heating. IR reflectances at 15, 30 and
45 degrees observation angles are compared.

---------------------------------------------------------
Title: ALMA Discovery of Solar Umbral Brightness Enhancement at λ =
3 mm
Authors: Iwai, Kazumasa; Loukitcheva, Maria; Shimojo, Masumi; Solanki,
Sami K.; White, Stephen M.
2017ApJ...841L..20I Altcode: 2017arXiv170503147I
We report the discovery of a brightness enhancement in the center
of a large sunspot umbra at a wavelength of 3 mm using the Atacama
Large Millimeter/sub-millimeter Array (ALMA). Sunspots are among
the most prominent features on the solar surface, but many of their
aspects are surprisingly poorly understood. We analyzed a λ = 3 mm
(100 GHz) mosaic image obtained by ALMA that includes a large sunspot
within the active region AR12470, on 2015 December 16. The 3 mm map
has a 300″ × 300″ field of view and 4.″9 × 2.″2 spatial
resolution, which is the highest spatial resolution map of an entire
sunspot in this frequency range. We find a gradient of 3 mm brightness
from a high value in the outer penumbra to a low value in the inner
penumbra/outer umbra. Within the inner umbra, there is a marked increase
in 3 mm brightness temperature, which we call an umbral brightness
enhancement. This enhanced emission corresponds to a temperature
excess of 800 K relative to the surrounding inner penumbral region
and coincides with excess brightness in the 1330 and 1400 Å slit-jaw
images of the Interface Region Imaging Spectrograph (IRIS), adjacent
to a partial lightbridge. This λ = 3 mm brightness enhancement may be
an intrinsic feature of the sunspot umbra at chromospheric heights,
such as a manifestation of umbral flashes, or it could be related to
a coronal plume, since the brightness enhancement was coincident with
the footpoint of a coronal loop observed at 171 Å.

---------------------------------------------------------
Title: Millimeter radiation from a 3D model of the solar
atmosphere. II. Chromospheric magnetic field
Authors: Loukitcheva, M.; White, S. M.; Solanki, S. K.; Fleishman,
G. D.; Carlsson, M.
2017A&A...601A..43L Altcode: 2017arXiv170206018L
 Aims: We use state-of-the-art, three-dimensional non-local
thermodynamic equilibrium (non-LTE) radiative magnetohydrodynamic
simulations of the quiet solar atmosphere to carry out detailed tests
of chromospheric magnetic field diagnostics from free-free radiation at
millimeter and submillimeter wavelengths (mm/submm). Methods:
The vertical component of the magnetic field was deduced from the
mm/submm brightness spectra and the degree of circular polarization
synthesized at millimeter frequencies. We used the frequency bands
observed by the Atacama Large Millimeter/Submillimeter Array (ALMA)
as a convenient reference. The magnetic field maps obtained describe
the longitudinal magnetic field at the effective formation heights of
the relevant wavelengths in the solar chromosphere. Results:
The comparison of the deduced and model chromospheric magnetic fields
at the spatial resolution of both the model and current observations
demonstrates a good correlation, but has a tendency to underestimate
the model field. The systematic discrepancy of about 10% is probably
due to averaging of the restored field over the heights contributing
to the radiation, weighted by the strength of the contribution. On
the whole, the method of probing the longitudinal component of the
magnetic field with free-free emission at mm/submm wavelengths
is found to be applicable to measurements of the weak quiet-Sun
magnetic fields. However, successful exploitation of this technique
requires very accurate measurements of the polarization properties
(primary beam and receiver polarization response) of the antennas,
which will be the principal factor that determines the level to which
chromospheric magnetic fields can be measured. Conclusions:
Consequently, high-resolution and high-precision observations of
circularly polarized radiation at millimeter wavelengths can be a
powerful tool for producing chromospheric longitudinal magnetograms.

---------------------------------------------------------
Title: Editorial: Coronal Magnetometry
Authors: Gibson, Sarah E.; Rachmeler, Laurel A.; White, Stephen M.
2017FrASS...4....3G Altcode: 2017FrASS...4E...3G
No abstract at ADS

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Title: The First ALMA Observation of a Solar Plasmoid Ejection from
an X-Ray Bright Point
Authors: Shimojo, Masumi; Hudson, Hugh S.; White, Stephen M.; Bastian,
Timothy S.; Iwai, Kazumasa
2017ApJ...841L...5S Altcode: 2017arXiv170404881S
Eruptive phenomena such as plasmoid ejections or jets are important
features of solar activity and have the potential to improve our
understanding of the dynamics of the solar atmosphere. Such ejections
are often thought to be signatures of the outflows expected in
regions of fast magnetic reconnection. The 304 Å EUV line of helium,
formed at around 105 K, is found to be a reliable tracer
of such phenomena, but the determination of physical parameters
from such observations is not straightforward. We have observed
a plasmoid ejection from an X-ray bright point simultaneously at
millimeter wavelengths with ALMA, at EUV wavelengths with SDO/AIA,
and in soft X-rays with Hinode/XRT. This paper reports the physical
parameters of the plasmoid obtained by combining the radio, EUV, and
X-ray data. As a result, we conclude that the plasmoid can consist
either of (approximately) isothermal ∼105 K plasma that
is optically thin at 100 GHz, or a ∼104 K core with a
hot envelope. The analysis demonstrates the value of the additional
temperature and density constraints that ALMA provides, and future
science observations with ALMA will be able to match the spatial
resolution of space-borne and other high-resolution telescopes.

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Title: Evidence of Significant Energy Input in the Late Phase of a
Solar Flare from NuSTAR X-Ray Observations
Authors: Kuhar, Matej; Krucker, Säm; Hannah, Iain G.; Glesener,
Lindsay; Saint-Hilaire, Pascal; Grefenstette, Brian W.; Hudson, Hugh
S.; White, Stephen M.; Smith, David M.; Marsh, Andrew J.; Wright, Paul
J.; Boggs, Steven E.; Christensen, Finn E.; Craig, William W.; Hailey,
Charles J.; Harrison, Fiona A.; Stern, Daniel; Zhang, William W.
2017ApJ...835....6K Altcode: 2017arXiv170107759K
We present observations of the occulted active region AR 12222
during the third Nuclear Spectroscopic Telescope ARray (NuSTAR) solar
campaign on 2014 December 11, with concurrent Solar Dynamics Observatory
(SDO)/AIA and FOXSI-2 sounding rocket observations. The active region
produced a medium-size solar flare 1 day before the observations, at
∼18 UT on 2014 December 10, with the post-flare loops still visible
at the time of NuSTAR observations. The time evolution of the source
emission in the SDO/AIA 335 Å channel reveals the characteristics
of an extreme-ultraviolet late-phase event, caused by the continuous
formation of new post-flare loops that arch higher and higher in
the solar corona. The spectral fitting of NuSTAR observations yields
an isothermal source, with temperature 3.8-4.6 MK, emission measure
(0.3-1.8) × 1046 cm-3, and density estimated at
(2.5-6.0) × 108 cm-3. The observed AIA fluxes
are consistent with the derived NuSTAR temperature range, favoring
temperature values in the range of 4.0-4.3 MK. By examining the
post-flare loops’ cooling times and energy content, we estimate that
at least 12 sets of post-flare loops were formed and subsequently cooled
between the onset of the flare and NuSTAR observations, with their total
thermal energy content an order of magnitude larger than the energy
content at flare peak time. This indicates that the standard approach
of using only the flare peak time to derive the total thermal energy
content of a flare can lead to a large underestimation of its value.

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Title: Focusing Solar Hard X-rays: Expected Results from a FOXSI
Spacecraft
Authors: Glesener, L.; Christe, S.; Shih, A. Y.; Dennis, B. R.;
Krucker, S.; Saint-Hilaire, P.; Hudson, H. S.; Ryan, D.; Inglis,
A. R.; Hannah, I. G.; Caspi, A.; Klimchuk, J. A.; Drake, J. F.;
Kontar, E.; Holman, G.; White, S. M.; Alaoui, M.; Battaglia, M.;
Vilmer, N.; Allred, J. C.; Longcope, D. W.; Gary, D. E.; Jeffrey,
N. L. S.; Musset, S.; Swisdak, M.
2016AGUFMSH13A2282G Altcode:
Over the course of two solar cycles, RHESSI has examined high-energy
processes in flares via high-resolution spectroscopy and imaging of
soft and hard X-rays (HXRs). The detected X-rays are the thermal
and nonthermal bremsstrahlung from heated coronal plasma and from
accelerated electrons, respectively, making them uniquely suited to
explore the highest-energy processes that occur in the corona. RHESSI
produces images using an indirect, Fourier-based method and has made
giant strides in our understanding of these processes, but it has also
uncovered intriguing new mysteries regarding energy release location,
acceleration mechanisms, and energy propagation in flares. Focusing
optics are now available for the HXR regime and stand poised to perform
another revolution in the field of high-energy solar physics. With
two successful sounding rocket flights completed, the Focusing Optics
X-ray Solar Imager (FOXSI) program has demonstrated the feasibility and
power of direct solar HXR imaging with its vastly superior sensitivity
and dynamic range. Placing this mature technology aboard a spacecraft
will offer a systematic way to explore high-energy aspects of the
solar corona and to address scientific questions left unanswered by
RHESSI. Here we present examples of such questions and show simulations
of expected results from a FOXSI spaceborne instrument to demonstrate
how these questions can be addressed with the focusing of hard X-rays.

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Title: Signatures of Reconnection Observed in a Candle-Flame Solar
Flare at the Limb
Authors: Reeves, K.; Chen, B.; White, S. M.; Schanche, N.; Tian, H.
2016AGUFMSH31B2565R Altcode:
We examine a well-observed flare that occurred on the limb of the Sun
on March 7, 2015 in order to find possible signatures of a termination
shock due to outflows from reconnecting magnetic fields. Images of this
flare from Hinode/XRT and the SDO/AIA 131 bandpass show a cusp-shaped
morphology. The IRIS slit was positioned in the region of the current
sheet, above the flare loops. Fe XXI is detected in the IRIS spectra
with an average Doppler velocity of about 20 km/s. The non-thermal
widths in IRIS decrease steadily from 23:00 UT on the 7th until 00:20
UT the next day. This decrease correlates well with the microwave
radio flux observed by the Nobeyama Radioheliograph (NoRH), which is
primarily due to thermal free-free emission based on the examination
of NoRH images at 17 GHz and 34 GHz. Temperatures of the loop-top
source derived from RHESSI and XRT also show a steady decrease during
this time. We measure downflow velocities in the cusp region in the
AIA 131 A bandpass, and find that from 22-23 UT the flows are about
300-400 km/s, and they slow down to about 100 km/s after 23 UT. This
work supported by NASA Grant NNX15AJ93G.

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Title: The Focusing Optics X-ray Solar Imager (FOXSI) SMEX Mission
Authors: Christe, S.; Shih, A. Y.; Krucker, S.; Glesener, L.;
Saint-Hilaire, P.; Caspi, A.; Allred, J. C.; Battaglia, M.; Chen,
B.; Drake, J. F.; Gary, D. E.; Goetz, K.; Grefenstette, B.; Hannah,
I. G.; Holman, G.; Hudson, H. S.; Inglis, A. R.; Ireland, J.; Ishikawa,
S. N.; Klimchuk, J. A.; Kontar, E.; Kowalski, A. F.; Massone, A. M.;
Piana, M.; Ramsey, B.; Gubarev, M.; Schwartz, R. A.; Steslicki, M.;
Ryan, D.; Turin, P.; Warmuth, A.; White, S. M.; Veronig, A.; Vilmer,
N.; Dennis, B. R.
2016AGUFMSH13A2281C Altcode:
We present FOXSI (Focusing Optics X-ray Solar Imager), a recently
proposed Small Explorer (SMEX) mission that will provide a revolutionary
new perspective on energy release and particle acceleration on the
Sun. FOXSI is a direct imaging X-ray spectrometer with higher dynamic
range and better than 10x the sensitivity of previous instruments. Flown
on a 3-axis stabilized spacecraft in low-Earth orbit, FOXSI uses
high-angular-resolution grazing-incidence focusing optics combined
with state-of-the-art pixelated solid-state detectors to provide direct
imaging of solar hard X-rays for the first time. FOXSI is composed of
two individual x-ray telescopes with a 14-meter focal length enabled by
a deployable boom. Making use of a filter-wheel and high-rate-capable
solid-state detectors, FOXSI will be able to observe the largest flares
without saturation while still maintaining the sensitivity to detect
x-ray emission from weak flares, escaping electrons, and hot active
regions. This SMEX mission is made possible by past experience with
similar instruments on two sounding rocket flights, in 2012 and 2014,
and on the HEROES balloon flight in 2013. FOXSI will image the Sun
with a field of view of 9 arcminutes and an angular resolution of
better than 8 arcsec; it will cover the energy range from 3 to 100
keV with a spectral resolution of better than 1 keV; and it will have
sub-second temporal resolution.

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Title: Gamma-Ray Observations Related to the Acceleration of Ions
in the Corona
Authors: Share, G. H.; Murphy, R. J.; Tolbert, A. K.; White, S. M.;
Dennis, B. R.; Schwartz, R. A.; Tylka, A. J.
2016AGUFMSH32A..07S Altcode:
High-energy gamma-rays associated with solar flares have been observed
for over thirty-five years by various satellite experiments. The
most sensitive observations have been made recently by the Large Area
Telescope (LAT) experiment on the Fermi satellite. These observations
confirm the earlier observations in which &gt;100 MeV emission was
detected coincident with the impulsive flare hard X-rays and also in
the minutes and hours afterward. Spectral evidence from the largest
of these latter, time-extended events, indicate they arise from the
decay of neutral and charged pions produced by the interaction of
protons and alpha particles with energies &gt;300 MeV/nucl and &gt;200
MeV/nucl, respectively. These high-energy time-extended events, are
almost always associated with fast CME's and appear to begin from as
short as 1 min to as long as 100 min after the onset of the CME. The
events appear to last as short as 10 min to as long as 18 hr. Our
analysis indicates that the number of &gt;500 MeV protons producing
the time-extended emission typically is an order magnitude larger
than the number producing emission during the impulsive flare. The
observed delays from the CME and energetic comparisons suggest that
most of the energy in the ions producing the sustained time-extended
emission came from a source other than the impulsive flare. It is
likely that the particles were accelerated by shocks associated with
the CME's and thus may have an origin common with SEPs observed in
space. Our comparisons using GOES HEPAD and neutron monitor data, and
those reported in this Session by DeNolfo et al. using data from PAMELA,
suggest that the numbers of particles producing the gamma-ray emission
are typically at least an order of magnitude smaller than those observed
in space. We focus our discussion in this talk on the time-extended
gamma-ray events that begin within minutes of the CME onset as they
may reflect shock-acceleration of protons to hundreds of MeV deep in
the corona. This work was supported by the SHINE/NSF, NASA Fermi GI
and SR&amp;T, Chief of Naval Research, and EU HESPERIA programs.

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Title: Measuring the Magnetic Field of Coronal Mass Ejections Near
the Sun Using Pulsars
Authors: Howard, T. A.; Stovall, K.; Dowell, J.; Taylor, G. B.; White,
S. M.
2016ApJ...831..208H Altcode:
The utility of Faraday rotation to measure the magnetic field of
the solar corona and large-scale transients within is a small, yet
growing field in solar physics. This is largely because it has been
recognized as a potentially valuable frontier in space weather studies,
because the ability to measure the intrinsic magnetic field within
coronal mass ejections (CMEs) when they are close to the Sun is of
great interest for understanding a key element of space weather. Such
measurements have been attempted over the last few decades using radio
signals from artificial sources (I.e., spacecraft on the far side of
the Sun), but studies involving natural radio sources are scarce in
the literature. We report on a preliminary study involving an attempt
to detect the Faraday rotation of a CME that passed in front of a
pulsar (PSR B0950+08) in 2015 August. We combine radio measurements
with those from a broadband visible light coronagraph, to estimate
the upper limit of the magnetic field of the CME when it was in the
corona. We find agreement between different approaches for obtaining
its density, and values that are consistent with those predicted from
prior studies of CME density close to the Sun.

---------------------------------------------------------
Title: Observation of quasi-periodic solar radio bursts associated
with propagating fast-mode waves
Authors: Goddard, C. R.; Nisticò, G.; Nakariakov, V. M.; Zimovets,
I. V.; White, S. M.
2016A&A...594A..96G Altcode: 2016arXiv160804232G
 Aims: Radio emission observations from the Learmonth and Bruny
Island radio spectrographs are analysed to determine the nature of
a train of discrete, periodic radio "sparks" (finite-bandwidth,
short-duration isolated radio features) which precede a type II
burst. We analyse extreme ultraviolet (EUV) imaging from SDO/AIA
at multiple wavelengths and identify a series of quasi-periodic
rapidly-propagating enhancements, which we interpret as a fast
wave train, and link these to the detected radio features. 
Methods: The speeds and positions of the periodic rapidly propagating
fast waves and the coronal mass ejection (CME) were recorded using
running-difference images and time-distance analysis. From the frequency
of the radio sparks the local electron density at the emission location
was estimated for each. Using an empirical model for the scaling of
density in the corona, the calculated electron density was used to
obtain the height above the surface at which the emission occurs, and
the propagation velocity of the emission location. Results: The
period of the radio sparks, δtr = 1.78 ± 0.04 min, matches
the period of the fast wave train observed at 171 Å, δtEUV
= 1.7 ± 0.2 min. The inferred speed of the emission location of the
radio sparks, 630 km s-1, is comparable to the measured
speed of the CME leading edge, 500 km s-1, and the speeds
derived from the drifting of the type II lanes. The calculated height
of the radio emission (obtained from the density) matches the observed
location of the CME leading edge. From the above evidence we propose
that the radio sparks are caused by the quasi-periodic fast waves, and
the emission is generated as they catch up and interact with the leading
edge of the CME. The movie associated to Fig. 2 is available at <A
href="http://www.aanda.org/10.1051/0004-6361/201628478/olm">http://www.aanda.org</A>

---------------------------------------------------------
Title: F10.7 and the slowly varying corona from EVE DEMs
Authors: Schonfeld, Sam; White, S. M.; Hock, R. A.; McAteer, R. T. J.
2016shin.confE.193S Altcode:
We present a differential emission measure (DEM) analysis of the
slowly varying corona during the first half of solar cycle 24. Using
the Extreme ultraviolet Variability Experiment (EVE) and the CHIANTI
atomic line database we identify strong isolated iron emission lines
present in the non-flaring spectrum with peak emissions covering the
coronal temperature range of 5.7 &lt; log(T) &lt; 6.5. These lines
are used to generate daily DEMs from EVE spectra to observe the long
term variability of global coronal thermal properties. We discuss the
choice of emission lines and the implications of this data set for
the relationship between EUV and the F10.7 radio flux.

---------------------------------------------------------
Title: The First Focused Hard X-ray Images of the Sun with NuSTAR
Authors: Grefenstette, Brian W.; Glesener, Lindsay; Krucker, Säm;
Hudson, Hugh; Hannah, Iain G.; Smith, David M.; Vogel, Julia K.; White,
Stephen M.; Madsen, Kristin K.; Marsh, Andrew J.; Caspi, Amir; Chen,
Bin; Shih, Albert; Kuhar, Matej; Boggs, Steven E.; Christensen, Finn
E.; Craig, William W.; Forster, Karl; Hailey, Charles J.; Harrison,
Fiona A.; Miyasaka, Hiromasa; Stern, Daniel; Zhang, William W.
2016ApJ...826...20G Altcode: 2016arXiv160509738G
We present results from the the first campaign of dedicated solar
observations undertaken by the Nuclear Spectroscopic Telescope ARray
(NuSTAR) hard X-ray (HXR) telescope. Designed as an astrophysics
mission, NuSTAR nonetheless has the capability of directly imaging the
Sun at HXR energies (&gt;3 keV) with an increase in sensitivity of at
least two magnitude compared to current non-focusing telescopes. In
this paper we describe the scientific areas where NuSTAR will make
major improvements on existing solar measurements. We report on the
techniques used to observe the Sun with NuSTAR, their limitations
and complications, and the procedures developed to optimize solar
data quality derived from our experience with the initial solar
observations. These first observations are briefly described, including
the measurement of the Fe K-shell lines in a decaying X-class flare,
HXR emission from high in the solar corona, and full-disk HXR images
of the Sun.

---------------------------------------------------------
Title: The smallest hard X-ray flare?
Authors: Glesener, Lindsay; Krucker, Sam; Hannah, Iain; Smith, David
M.; Grefenstette, Brian; Marsh, Andrew; Hudson, Hugh S.; White,
Stephen M.; Chen, Bin
2016SPD....4740302G Altcode:
We report a NuSTAR observation of a small solar flare on 2015
September 1, estimated to be on the order of a GOES class A.05 flare
in brightness. This flare is fainter than any hard X-ray (HXR) flares
in the existing literature, and with a peak rate of only ∼5 counts
s-1 detector-1 observed by RHESSI, is effectively
the smallest that can just barely be detected by the current standard
(indirectly imaging) solar HXR instrumentation, though we expect
that smaller flares will continue to be discovered as instrumental
and observational techniques progress. The flare occurred during a
solar observation by the highly sensitive NuSTAR astrophysical HXR
spacecraft, which used its direct focusing optics to produce detailed
flare spectra and images. The flare exhibits properties commonly
observed in larger flares, including a fast rise and more gradual
decay, and similar spatial dimensions to the RHESSI microflares. We
will discuss the presence of non-thermal (flare-accelerated) electrons
during the impulsive phase. The flare is small in emission measure,
temperature, and energy, though not in physical dimensions. Its presence
is an indication that flares do indeed scale down to smaller energies
and retain what we customarily think of as “flarelike” properties.

---------------------------------------------------------
Title: Science Objectives of the FOXSI Small Explorer Mission Concept
Authors: Shih, Albert Y.; Christe, Steven; Alaoui, Meriem; Allred,
Joel C.; Antiochos, Spiro K.; Battaglia, Marina; Buitrago-Casas,
Juan Camilo; Caspi, Amir; Dennis, Brian R.; Drake, James; Fleishman,
Gregory D.; Gary, Dale E.; Glesener, Lindsay; Grefenstette, Brian;
Hannah, Iain; Holman, Gordon D.; Hudson, Hugh S.; Inglis, Andrew R.;
Ireland, Jack; Ishikawa, Shin-Nosuke; Jeffrey, Natasha; Klimchuk, James
A.; Kontar, Eduard; Krucker, Sam; Longcope, Dana; Musset, Sophie; Nita,
Gelu M.; Ramsey, Brian; Ryan, Daniel; Saint-Hilaire, Pascal; Schwartz,
Richard A.; Vilmer, Nicole; White, Stephen M.; Wilson-Hodge, Colleen
2016SPD....47.0814S Altcode:
Impulsive particle acceleration and plasma heating at the Sun, from the
largest solar eruptive events to the smallest flares, are related to
fundamental processes throughout the Universe. While there have been
significant advances in our understanding of impulsive energy release
since the advent of RHESSI observations, there is a clear need for
new X-ray observations that can capture the full range of emission
in flares (e.g., faint coronal sources near bright chromospheric
sources), follow the intricate evolution of energy release and changes
in morphology, and search for the signatures of impulsive energy
release in even the quiescent Sun. The FOXSI Small Explorer (SMEX)
mission concept combines state-of-the-art grazing-incidence focusing
optics with pixelated solid-state detectors to provide direct imaging
of hard X-rays for the first time on a solar observatory. We present
the science objectives of FOXSI and how its capabilities will address
and resolve open questions regarding impulsive energy release at the
Sun. These questions include: What are the time scales of the processes
that accelerate electrons? How do flare-accelerated electrons escape
into the heliosphere? What is the energy input of accelerated electrons
into the chromosphere, and how is super-heated coronal plasma produced?

---------------------------------------------------------
Title: The slowly varying corona from DEMs with the EVE data set
Authors: Schonfeld, Samuel J.; White, Stephen M.; Hock, Rachel A.;
McAteer, James
2016SPD....47.0333S Altcode:
We present a differential emission measure (DEM) analysis of the
slowly varying corona during the first half of solar cycle 24. Using
the Extreme ultraviolet Variability Experiment (EVE) and the CHIANTI
atomic line database we identify strong isolated iron emission lines
present in the non-flaring spectrum with peak emissions covering the
coronal temperature range of 5.7 &lt; log(T) &lt; 6.5. These lines
are used to generate daily DEMs from EVE spectra to observe the long
term variability of global coronal thermal properties. We discuss the
choice of emission lines and the implications of this data set for
the relationship between EUV and the F10.7 radio flux.

---------------------------------------------------------
Title: Solar Science with the Atacama Large Millimeter/Submillimeter
Array—A New View of Our Sun
Authors: Wedemeyer, S.; Bastian, T.; Brajša, R.; Hudson, H.;
Fleishman, G.; Loukitcheva, M.; Fleck, B.; Kontar, E. P.; De Pontieu,
B.; Yagoubov, P.; Tiwari, S. K.; Soler, R.; Black, J. H.; Antolin,
P.; Scullion, E.; Gunár, S.; Labrosse, N.; Ludwig, H. -G.; Benz,
A. O.; White, S. M.; Hauschildt, P.; Doyle, J. G.; Nakariakov, V. M.;
Ayres, T.; Heinzel, P.; Karlicky, M.; Van Doorsselaere, T.; Gary,
D.; Alissandrakis, C. E.; Nindos, A.; Solanki, S. K.; Rouppe van
der Voort, L.; Shimojo, M.; Kato, Y.; Zaqarashvili, T.; Perez, E.;
Selhorst, C. L.; Barta, M.
2016SSRv..200....1W Altcode: 2015SSRv..tmp..118W; 2015arXiv150406887W
The Atacama Large Millimeter/submillimeter Array (ALMA) is a new
powerful tool for observing the Sun at high spatial, temporal, and
spectral resolution. These capabilities can address a broad range
of fundamental scientific questions in solar physics. The radiation
observed by ALMA originates mostly from the chromosphere—a complex
and dynamic region between the photosphere and corona, which plays a
crucial role in the transport of energy and matter and, ultimately,
the heating of the outer layers of the solar atmosphere. Based on
first solar test observations, strategies for regular solar campaigns
are currently being developed. State-of-the-art numerical simulations
of the solar atmosphere and modeling of instrumental effects can help
constrain and optimize future observing modes for ALMA. Here we present
a short technical description of ALMA and an overview of past efforts
and future possibilities for solar observations at submillimeter and
millimeter wavelengths. In addition, selected numerical simulations
and observations at other wavelengths demonstrate ALMA's scientific
potential for studying the Sun for a large range of science cases.

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Title: The First X-Ray Imaging Spectroscopy of Quiescent Solar Active
Regions with NuSTAR
Authors: Hannah, Iain G.; Grefenstette, Brian W.; Smith, David M.;
Glesener, Lindsay; Krucker, Säm; Hudson, Hugh S.; Madsen, Kristin
K.; Marsh, Andrew; White, Stephen M.; Caspi, Amir; Shih, Albert Y.;
Harrison, Fiona A.; Stern, Daniel; Boggs, Steven E.; Christensen,
Finn E.; Craig, William W.; Hailey, Charles J.; Zhang, William W.
2016ApJ...820L..14H Altcode: 2016arXiv160301069H
We present the first observations of quiescent active regions (ARs)
using the Nuclear Spectroscopic Telescope Array (NuSTAR), a focusing
hard X-ray telescope capable of studying faint solar emission from
high-temperature and non-thermal sources. We analyze the first directly
imaged and spectrally resolved X-rays above 2 keV from non-flaring ARs,
observed near the west limb on 2014 November 1. The NuSTAR X-ray images
match bright features seen in extreme ultraviolet and soft X-rays. The
NuSTAR imaging spectroscopy is consistent with isothermal emission of
temperatures 3.1-4.4 MK and emission measures 1-8 × 1046
cm-3. We do not observe emission above 5 MK, but our short
effective exposure times restrict the spectral dynamic range. With
few counts above 6 keV, we can place constraints on the presence of an
additional hotter component between 5 and 12 MK of ∼ {10}46
cm-3 and ∼ {10}43 cm-3, respectively,
at least an order of magnitude stricter than previous limits. With
longer duration observations and a weakening solar cycle (resulting
in an increased livetime), future NuSTAR observations will have
sensitivity to a wider range of temperatures as well as possible
non-thermal emission.

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Title: Comparison of 30 THz impulsive burst time development to
microwaves, Hα, EUV, and GOES soft X-rays
Authors: Miteva, R.; Kaufmann, P.; Cabezas, D. P.; Cassiano, M. M.;
Fernandes, L. O. T.; Freeland, S. L.; Karlický, M.; Kerdraon, A.;
Kudaka, A. S.; Luoni, M. L.; Marcon, R.; Raulin, J. -P.; Trottet,
G.; White, S. M.
2016A&A...586A..91M Altcode: 2015arXiv151201763M
The recent discovery of impulsive solar burst emission in the 30 THz
band is raising new interpretation challenges. One event associated with
a GOES M2 class flare has been observed simultaneously in microwaves,
Hα, EUV, and soft X-ray bands. Although these new observations confirm
some features found in the two prior known events, they exhibit time
profile structure discrepancies between 30 THz, microwaves, and hard
X-rays (as inferred from the Neupert effect). These results suggest a
more complex relationship between 30 THz emission and radiation produced
at other wavelength ranges. The multiple frequency emissions in the
impulsive phase are likely to be produced at a common flaring site lower
in the chromosphere. The 30 THz burst emission may be either part of a
nonthermal radiation mechanism or due to the rapid thermal response to
a beam of high-energy particles bombarding the dense solar atmosphere.

---------------------------------------------------------
Title: EUV &amp; X-ray observations of microflare heating of AR12333
Authors: Hannah, I. G.; Wright, P. J.; Grefenstette, B.; Glesener,
L.; Hudson, H. S.; Smith, D. M.; Krucker, S.; Marsh, A.; White, S. M.
2015AGUFMSH13B2442H Altcode:
We present a study of the heating in AR12333 due to small microflares
between 10:30 and 13:30UT on 29 April 2015. This region is well observed
in EUV by the Solar Dynamics Observatory/Atmospheric Imaging Assembly
(SDO/AIA) as well as Hinode's X-ray Telescope (XRT) operating in
a higher cadence mode, switching through the five thicker filters
(sensitive to the higher temperature range). The Hinode observations
were a coordinated campaign with the NuSTAR hard X-ray focusing
optics telescope (Harrison et al. 2013). NuSTAR was conducting a
full disk mosaic observation of the Sun and caught AR12333 several
times, providing imaging spectroscopy &gt;2 keV. We investigate the
heating in the active region due to several small microflares (about
A1-Class). These were visible with the thicker XRT filters and only
clear in EUV once the FeXVIII component was extracted from SDO/AIA 94Å,
indicating heating primarily &gt;3MK. Using the regularized inversion
method of Hannah &amp; Kontar 2012, we recover the DEM from the SDO/AIA
and Hinode/XRT data and compare this to the thermal characteristics
derived from NuSTAR.

---------------------------------------------------------
Title: Probing the Sun with ALMA: Observations and Simulations
Authors: Loukitcheva, M.; Solanki, S. K.; White, S. M.; Carlsson, M.
2015ASPC..499..349L Altcode: 2015arXiv150805686L
ALMA will open a new chapter in the study of the Sun by providing a leap
in spatial resolution and sensitivity compared to currently available
mm wavelength observations. In preparation of ALMA, we have carried out
a large number of observational tests and state-of-the-art radiation
MHD simulations. Here we review the best available observations of
the Sun at millimeter wavelengths.Using state of the art radiation
MHD simulations of the solar atmosphere we demonstrate the huge
potential of ALMA observations for uncovering the nature of the solar
chromosphere. We show that ALMA will not only provide a reliable probe
of the thermal structure and dynamics of the chromosphere, it will also
open up a powerful new diagnostic of magnetic field at chromospheric
heights, a fundamentally important, but so far poorly known parameter.

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Title: Capabilities of a FOXSI Small Explorer
Authors: Inglis, A. R.; Christe, S.; Glesener, L.; Krucker, S.; Dennis,
B. R.; Shih, A.; Wilson-Hodge, C.; Gubarev, M.; Hudson, H. S.; Kontar,
E.; Buitrago Casas, J. C.; Drake, J. F.; Caspi, A.; Holman, G.; Allred,
J. C.; Ryan, D.; Alaoui, M.; White, S. M.; Saint-Hilaire, P.; Klimchuk,
J. A.; Hannah, I. G.; Antiochos, S. K.; Grefenstette, B.; Ramsey,
B.; Jeffrey, N. L. S.; Reep, J. W.; Schwartz, R. A.; Ireland, J.
2015AGUFMSH43B2456I Altcode:
We present the FOXSI (Focusing Optics X-ray Solar Imager) small explorer
(SMEX) concept, a mission dedicated to studying particle acceleration
and energy release on the Sun. FOXSI is designed as a 3-axis stabilized
spacecraft in low-Earth orbit making use of state-of-the-art grazing
incidence focusing optics, allowing for direct imaging of solar
X-rays. The current design being studied features three telescope
modules deployed in a low-inclination low-earth orbit (LEO). With a 15
meter focal length enabled by a deployable boom, FOXSI will observe
the Sun in the 3-50 keV energe range. The FOXSI imaging concept has
already been tested on two sounding rocket flights, in 2012 and 2014
and on the HEROES balloon payload flight in 2013. FOXSI will image
the Sun with an angular resolution of 5”, a spectral resolution of
0.5 keV, and sub-second temporal resolution using CdTe detectors. In
this presentation we investigate the science objectives and targets
which can be accessed from this mission. Because of the defining
characteristic of FOXSI is true imaging spectroscopy with high dynamic
range and sensitivity, a brand-new perspective on energy release on the
Sun is possible. Some of the science targets discussed here include;
flare particle acceleration processes, electron beams, return currents,
sources of solar energetic particles (SEPs), as well as understanding
X-ray emission from active region structures and the quiescent corona.

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Title: Towards a Data-Optimized Coronal Magnetic Field Model (DOC-FM):
Synthetic Test Beds and Multiwavelength Forward Modeling
Authors: Gibson, S. E.; Dalmasse, K.; Fan, Y.; Fineschi, S.; MacKay,
D.; Rempel, M.; White, S. M.
2015AGUFMSH54B..04G Altcode:
Understanding the physical state of the solar corona is key to
deciphering the origins of space weather as well as to realistically
representing the environment to be navigated by missions such as
Solar Orbiter and Solar Probe Plus. However, inverting solar coronal
observations to reconstruct this physical state -- and in particular
the three-dimensional coronal magnetic field - is complicated by
limited lines of sight and by projection effects. On the other hand,
the sensitivity of multiwavelength observations to different physical
mechanisms implies a potential for simultaneous probing of different
parts of the coronal plasma. In order to study this complementarity, and
to ultimately establish an optimal set of observations for constraining
the three-dimensional coronal magnetic field, we are developing a suite
of representative simulations to act as diagnostic test beds. We will
present three such test beds: a coronal active region, a quiescent
prominence, and a global corona. Each fully define the physical state
of density, temperature, and vector magnetic field in three dimensions
throughout the simulation domain. From these test beds, and using the
FORWARD SolarSoft IDL codes, we will create a broad range of synthetic
data. Radio observables will include intensity and circular polarization
(including gyroresonance effects) and Faraday rotation for a range of
frequencies. Infrared and visible forbidden line diagnostics of Zeeman
and saturated Hanle effects will yield full Stokes vector (I, Q, U,
V) synthetic data, and UV permitted line Hanle diagnostics will yield
intensity and linear polarization. In addition, we will synthesize
UV and SXR imager data, UV/EUV spectrometric data, and white light
brightness and polarized brightness. All of these synthetic data,
along with the "ground truth" physical state of the simulations from
which they are derived, will be made available to the community for
the purpose of testing coronal inversion techniques.

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Title: Coronal Sources of the Solar F10.7 Radio Flux
Authors: Schonfeld, S. J.; White, S. M.; Henney, C. J.; Arge, C. N.;
McAteer, R. T. J.
2015ApJ...808...29S Altcode: 2015arXiv150800599S
We present results from the first solar full-disk {{{F}}}10.7
(the radio flux at 10.7 cm, 2.8 GHz) image taken with the S-band
receivers on the recently upgraded Karl G. Jansky Very Large Array in
order to assess the relationship between the {{{F}}}10.7
index and solar extreme ultraviolet (EUV) emission. To identify the
sources of the observed 2.8 GHz emission, we calculate differential
emission measures from EUV images collected by the Atmospheric Imaging
Assembly and use them to predict the bremsstrahlung component of the
radio emission. By comparing the bremsstrahlung prediction and radio
observation we find that 8.1% ± 0.5% of the variable component of
the {{{F}}}10.7 flux is associated with the gyroresonance
emission mechanism. Additionally, we identify optical depth effects on
the radio limb which may complicate the use of {{{F}}}10.7
time series as an EUV proxy. Our analysis is consistent with a coronal
iron abundance that is four times the photospheric level.

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Title: Bright 30 THz impulsive solar bursts
Authors: Kaufmann, P.; White, S. M.; Marcon, R.; Kudaka, A. S.;
Cabezas, D. P.; Cassiano, M. M.; Francile, C.; Fernandes, L. O. T.;
Hidalgo Ramirez, R. F.; Luoni, M.; Marun, A.; Pereyra, P.; Souza, R. V.
2015JGRA..120.4155K Altcode: 2015arXiv150506177K
Impulsive 30 THz continuum bursts have been recently observed in solar
flares, utilizing small telescopes with a unique and relatively simple
optical setup concept. The most intense burst was observed together
with a GOES X2 class event on 27 October 2014, also detected at two
subterahertz (sub-THz) frequencies, Reuven Ramaty High Energy Solar
Spectroscopic Imager X-rays and Solar Dynamics Observatory/Helioseismic
and Magnetic Imager and EUV. It exhibits strikingly good correlation
in time and in space with white-light flare emission. It is likely
that this association may prove to be very common. All three 30 THz
events recently observed exhibited intense fluxes in the range of
104 solar flux units, considerably larger than those measured
for the same events at microwave and submillimeter wavelengths. The 30
THz burst emission might be part of the same spectral burst component
found at sub-THz frequencies. The 30 THz solar bursts open a promising
new window for the study of flares at their origin.

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Title: Coronal Magnetography of a Simulated Solar Active Region from
Microwave Imaging Spectropolarimetry
Authors: Wang, Zhitao; Gary, Dale E.; Fleishman, Gregory D.; White,
Stephen M.
2015ApJ...805...93W Altcode: 2015arXiv150305239W
We have simulated the Expanded Owens Valley Solar Array (EOVSA)
radio images generated at multiple frequencies from a model solar
active region, embedded in a realistic solar disk model, and explored
the resulting data cube for different spectral analysis schemes to
evaluate the potential for realizing one of EOVSA’s most important
scientific goals—coronal magnetography. In this paper, we focus on
modeling the gyroresonance and free-free emission from an on-disk solar
active region model with realistic complexities in electron density,
temperature and magnetic field distribution. We compare the magnetic
field parameters extrapolated from the image data cube along each line
of sight after folding through the EOVSA instrumental profile with the
original (unfolded) parameters used in the model. We find that even
the most easily automated, image-based analysis approach (Level-0)
provides reasonable quantitative results, although they are affected
by systematic effects due to finite sampling in the Fourier (UV)
plane. Finally, we note the potential for errors due to misidentified
harmonics of the gyrofrequency, and discuss the prospects for applying
a more sophisticated spectrally based analysis scheme (Level-1) to
resolve the issue in cases where improved UV coverage and spatial
resolution are available.

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Title: Millimeter radiation from a 3D model of the solar
atmosphere. I. Diagnosing chromospheric thermal structure
Authors: Loukitcheva, M.; Solanki, S. K.; Carlsson, M.; White, S. M.
2015A&A...575A..15L Altcode: 2015arXiv150102898L
 Aims: We use advanced 3D non-local thermodynamic equilibrium
radiative magnetohydrodynamic simulations of the solar atmosphere to
carry out detailed tests of chromospheric diagnostics at millimeter and
submillimeter wavelengths. Methods: We focused on the diagnostics
of the thermal structure of the chromosphere in the wavelength bands
from 0.4 mm up to 9.6 mm that can be accessed with the Atacama Large
Millimeter/Submillimeter Array (ALMA) and investigated how these
diagnostics are affected by the instrumental resolution. Results:
We find that the formation height range of the millimeter radiation
depends on the location in the simulation domain and is related to the
underlying magnetic structure. Nonetheless, the brightness temperature
is a reasonable measure of the gas temperature at the effective
formation height at a given location on the solar surface. There is
considerable scatter in this relationship, but this is significantly
reduced when very weak magnetic fields are avoided. Our results
indicate that although instrumental smearing reduces the correlation
between brightness and temperature, millimeter brightness can still
be used to reliably diagnose electron temperature up to a resolution
of 1”. If the resolution is more degraded, then the value of the
diagnostic diminishes rapidly. Conclusions: We conclude that
millimeter brightness can image the chromospheric thermal structure
at the height at which the radiation is formed. Thus multiwavelength
observations with ALMA with a narrow step in wavelength should provide
sufficient information for a tomographic imaging of the chromosphere.

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Title: Forecasting Solar UV &amp; F10.7 with ADAPT
Authors: Henney, C. J.; Hock, R. A.; Toussaint, W. A.; Schooley,
A. K.; Arge, C. N.; White, S. M.
2014AGUFMSA12A..07H Altcode:
A new method is reviewed here to forecast the solar 10.7 cm (2.8
GHz) radio flux, abbreviated F10.7, and selected bands of solar
ultraviolet (UV) irradiance, ranging from 0.1 to 175 nm, utilizing
advanced predictions of the global solar magnetic field generated by
the ADAPT (Air Force Data Assimilative Photospheric Flux Transport)
model. Initial results reveal a good correlation between the absolute
value of the observed photospheric magnetic field and the observed
F10.7 and selected UV bands. In Henney et al (2012), the observed
F10.7 signal is found to correlate well with strong magnetic field
regions. In addition, we find that observed integrated full-disk solar
UV signals are correlated with weaker fields. By evolving solar magnetic
maps forward 1 to 7 days with a flux transport model, this new method
provides a realistic estimation of the Earth-side solar magnetic field
distribution used to predict the F10.7 flux and UV irradiance. The
ADAPT model used in this work was developed with support by a grant
from the AFOSR (Air Force Office of Scientific Research).

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Title: Forecasting Sep Events with Same Active-Region Prior Flares
Authors: Kahler, S. W.; Ling, A. G.; White, S. M.
2014AGUFMSH41D..08K Altcode:
Forecasting large solar energetic (E &gt; 10 MeV) particle (SEP)
events is currently based on observed solar X-ray flare peak fluxes or
fluences. Recent work has indicated that the probability of a solar
eruptive event in an active region (AR) is enhanced when a large
flare has occurred in that AR during the previous day. In addition,
peak intensities Sp of SEP events associated with fast CMEs are larger
for CMEs with prior CMEs from the same associated ARs in the previous
day. This suggests that the associated SEP event probability and/or
Sp may be higher for a given solar X-ray flare with a recent prior
major flare in the same AR. We use data sets of NOAA flares and SEP
events from cycles 23 and 24 to test this idea statistically for
periods of prior flares ranging from 12 to 48 hours. The occurrence
probabilities of large SEP events are not higher for flares with prior
same-AR major flares, hence prior flare occurrence is not a useful
SEP event forecasting tool. We show an example of a flare-prolific AR
for which the SEP-associated flares are spatially distinct from the
numerous non-SEP associated flares, indicating how prior flares may
be unrelated to SEP-associated flares.

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Title: The Sources of F10.7 Emission
Authors: Schonfeld, Samuel Joseph; White, S. M.; Henney, C. J.;
McAteer, R. T. J.; Arge, C. N.
2014shin.confE..62S Altcode:
The solar radio flux at a wavelength of 10.7 cm, F10.7, serves as
a proxy for the Sun"s ionizing flux striking the Earth and is a
heavily used index for space weather studies. In principal both the
coronal sources of ionizing flux and strong coronal magnetic fields
contribute to F10.7 via different emission mechanisms. Recently the
Karl G. Jansky Very Large Array (VLA) has added the capability to make
high-spatial-resolution images of the Sun at 10.7 cm. In this work
we compare a trial F10.7 image from the VLA with the radio emission
predicted to be present from EUV images of the Sun acquired by the
AIA telescope on the Solar Dynamics Observatory at 6 wavelengths
covering the coronal temperature range. Photospheric magnetograms
are used to identify likely regions of strong coronal magnetic field,
and the circular polarization measured by the VLA is used as a tracer
of gyroresonance contributions to F10.7. We discuss the conversion
of the EUV data to bremsstrahlung radio fluxes via the construction
of differential emission measure images, and analyze the relative
contributions of the different sources of F10.7 flux.

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Title: Current and future solar observation using focusing hard
X-ray imagers
Authors: Glesener, Lindsay; Caspi, Amir; Christe, Steven; Hannah, Iain;
Hudson, Hugh S.; Hurford, Gordon J.; Grefenstette, Brian; Krucker,
Sam; Marsh, Andrew; Mewaldt, Richard A.; Pivovaroff, Michael; Shih,
Albert Y.; Smith, David M.; Vogel, Julia; White, Stephen M.
2014AAS...22412364G Altcode:
The efficient processes that accelerate particles in solar flares
are not currently understood. Hard X-rays (HXRs) are one of the
best diagnostics of flare-accelerated electrons, and therefore of
acceleration processes. Past and current solar HXR observers rely on
indirect Fourier imaging and thus lack the necessary sensitivity and
imaging dynamic range to make detailed studies of faint HXR sources in
the solar corona (where particle acceleration is thought to occur). A
future generation of solar HXR observers will instead likely rely on
direct HXR focusing, which can provide far superior sensitivity and
imaging dynamic range.The first wave of focused solar HXR studies
is already underway, including sounding rocket and high-altitude
balloon payloads, and, in the near future, solar observation by the
NuSTAR astrophysics observatory. This poster will (1) summarize the
capabilities of current solar HXR instruments, comparing the science
that can be done from each platform, and (2) discuss the scientific
power of a future, dedicated, spaceborne observatory optimized to
observe HXRs from the Sun.

---------------------------------------------------------
Title: The Sources of F10.7 Emission
Authors: Schonfeld, Samuel J.; White, Stephen M.; Henney, Carl John;
McAteer, James; Arge, Charles
2014AAS...22432323S Altcode:
The solar radio flux at a wavelength of 10.7 cm, F10.7, serves as
a proxy for the Sun’s ionizing flux striking the Earth and is a
heavily used index for space weather studies. In principal both the
coronal sources of ionizing flux and strong coronal magnetic fields
contribute to F10.7 via different emission mechanisms. Recently the
Expanded Very Large Array (EVLA) has added the capability to make
high-spatial-resolution images of the Sun at 10.7 cm. In this work
we compare a trial F10.7 image from the EVLA with the radio emission
predicted to be present from EUV images of the Sun acquired by the
AIA telescope on the Solar Dynamics Observatory at 6 wavelengths
covering the coronal temperature range. Photospheric magnetograms are
used to identify likely regions of strong coronal magnetic field, and
the circular polarization measured by the EVLA is used as a tracer
of gyroresonance contributions to F10.7. We discuss the conversion
of the EUV data to bremsstrahlung radio fluxes via the construction
of differential emission measure images, and analyze the relative
contributions of the different sources of F10.7 flux.

---------------------------------------------------------
Title: Forecasting Solar EUV/FUV &amp; F10.7
Authors: Henney, Carl J.; Hock, Rachel A.; Schooley, Alicia K.;
Toussaint, W. Alex; Arge, C. Nick; White, Stephen M.
2014shin.confE.160H Altcode:
A new method is presented here to forecast solar 10.7 cm (2.8 GHz)
radio flux, abbreviated F10.7, and selected bands of solar ultraviolet
(UV) and extreme UV irradiance, ranging from 0.1 to 175 nm, utilizing
advanced predictions of the global solar magnetic field generated by
the ADAPT (Air Force Data Assimilation Photospheric Flux Transport)
model. Initial results reveal a good correlation between the absolute
value of the observed photospheric magnetic field and the observed
F10.7 and selected UV bands. In Henney et al (2012), the observed
F10.7 signal is found to correlate strongly with strong magnetic field
regions. In addition, we find that observed integrated full-disk solar
UV signals are strongly correlated with weak field. By evolving solar
magnetic maps forward 1 to 7 days with a flux transport model, this
new method provides a realistic estimation of the Earth-side solar
magnetic field distribution used to forecast F10.7 and EUV/FUV. The
ADAPT model used in this work was developed with support by a grant
from the AFOSR (Air Force Office of Scientific Research).

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Title: Characteristics of Sustained &gt;100 MeV γ-ray Emissions
Observed by Fermi and their Association with Solar Eruptive Events
Authors: Share, Gerald H.; Murphy, Ronald; Tylka, Allan J.; Dennis,
Brian R.; Schwartz, Richard A.; Tolbert, Anne K; White, Stephen M.
2014AAS...22411101S Altcode:
The Fermi Large Area Telescope (LAT) has detected &gt;20 sustained
gamma-ray events &gt;100 MeV lasting up to 20 hours. Three of
these events have been discussed by the LAT Collaboration in two
papers. Similar high-energy events have been observed earlier and
were given the name Long Duration Gamma Ray Flares (LDGRFs; Ryan,
2000). We discuss a comprehensive study of the Fermi events beginning
with a list of 98 solar eruptive events (SEEs) from 2008 to 2012 May
with broad/fast (&gt;800 km/s) or &gt;100 keV hard X-ray emission or
SEPs with &gt;10 MeV proton fluxes above 1 proton flux unit. Our study
provides the following characteristics of LAT LDGRFs: of 67 disk SEEs,
41 had broad/fast CMEs and 20 had both broad/fast CMEs and impulsive
&gt;100 keV emission; 12 of these 20 were detected by LAT above 100 MeV;
no LAT events were detected in 21 events with broad/fast CMEs when hard
X-ray emission was &lt;100 keV; no LAT events were detected from the
31 CMEs originating from behind the disk. This suggests that sustained
emission appears to require both a broad-fast CME and a flare with
impulsive emission &gt;100 keV. From our studies of behind-the-limb
SEEs and LAT fluxes vs heliolongitude, we conclude that the protons
responsible for the sustained &gt;100 MeV events interact within
about 20-30 deg. of the active region, but not necessarily at the
footpoints of the flare loops. We also find in a study of all events:
&gt;300 MeV proton interactions producing the &gt;100 MeV emission
begin from &lt;1 min to tens of min from the peak of the HXR emission;
durations of the sustained emission events last from ~30 min to 20 hrs;
spectral indices of &gt;300 MeV protons at the Sun range from about -2.5
(2012 May 17 GLE) to steeper than -6 (average about -4.8); the proton
spectrum can both soften and harden in time; the numbers of &gt;500 MeV
solar protons producing the sustained emission are typically ten-times
larger than those in the impulsive flare, but there are exceptions;
the numbers of &gt;500 MeV protons producing sustained emission is
typically ten-times smaller than the numbers in SEPs and is well
correlated, based on a limited number of measurements. This work is
funded by the NSF/SHINE and NASA's Fermi/GI programs.

---------------------------------------------------------
Title: Coronal Magnetography of a Simulated Solar Active Region from
Microwave Imaging Spectropolarimetry
Authors: Wang, Zhitao; Gary, Dale E.; White, Stephen M.
2014AAS...22432345W Altcode:
We have simulated the Expanded Owens Valley Solar Array (EOVSA) radio
images generated at multiple frequencies from a model solar active
region, embedded in a realistic solar disk model, and evaluated
the resulting datacube for different spectral analysis schemes to
evaluate the potential for realizing one of EOVSA's most important
scientific goals — coronal magnetography. In this paper, we focus on
modeling the gyroresonance and free-free emission from an on-disk solar
active region model with realistic complexities in electron density,
temperature and magnetic field distribution. We compare the magnetic
field parameters extrapolated from the image datacube along each line
of sight after folding through the EOVSA instrumental profile with the
original (unfolded) parameters used in the model. We find that even
the most easily automated, image-based analysis approach (Level 0)
provides reasonable quantitative results, although they are affected
by systematic effects due to finite sampling in the Fourier (uv) plane.

---------------------------------------------------------
Title: The Expanded Owens Valley Solar Array (EOVSA)
Authors: Gary, Dale E.; Hurford, Gordon J.; Nita, Gelu M.; White,
Stephen M.; McTiernan, James; Fleishman, Gregory D.
2014AAS...22412360G Altcode:
The Expanded Owens Valley Solar Array (EOVSA) near Big Pine, CA is
undergoing commissioning as a solar-dedicated microwave imaging array
operating in the frequency range 2.5-18 GHz. The solar science to be
addressed focuses on the 3D structure of the solar corona (magnetic
field, temperature and density), and on the particle acceleration,
transport and heating in solar flares. The project will support
the scientific community by providing open data access and software
tools for analysis and modeling of the data, to exploit synergies with
on-going solar research in other wavelengths. The array consists of a
total of 15 antennas, including the two 27-m antennas with He-cooled
receivers for sensitive calibration, and thirteen 2.1-m antennas that
each view the entire disk of the Sun. The system includes a completely
new control system, broadband signal transmission, and high-speed
digital signal processing, using new technology developed for the
Frequency Agile Solar Radiotelescope (FASR). We present an overview
of the instrument, the current status of commissioning activities,
and some initial observations to assess performance.This research is
supported by NSF grants AST-1312802, and NASA grants NNX11AB49G and
NNX10AF27G to New Jersey Institute of Technology.

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Title: Observing the Sun with the Murchison Widefield Array
Authors: Oberoi, D.; Sharma, R.; Bhatnagar, S.; Lonsdale, C. J.;
Matthews, L. D.; Cairns, I. H.; Tingay, S. J.; Benkevitch, L.; Donea,
A.; White, S. M.; Bernardi, G.; Bowman, J. D.; Briggs, F.; Cappallo,
R. J.; Corey, B. E.; Deshpande, A.; Emrich, D.; Gaensler, B. M.; Goeke,
R.; Greenhill, L. J.; Hazelton, B. J.; Johnston-Hollitt, M.; Kaplan,
D. L.; Kasper, J. C.; Kratzenberg, E.; Lynch, M. J.; McWhirter, S. R.;
Mitchell, D. A.; Morales, M. F.; Morgan, E.; Offringa, A. R.; Ord,
S. M.; Prabu, T.; Rogers, A. E. E.; Roshi, A.; Salah, J. E.; Udaya
Shankar, N.; Srivani, K. S.; Subrahmanyan, R.; Waterson, M.; Wayth,
R. B.; Webster, R. L.; Whitney, A. R.; William, A.; Williams, C. L.
2014arXiv1403.6250O Altcode:
The Sun has remained a difficult source to image for radio telescopes,
especially at the low radio frequencies. Its morphologically complex
emission features span a large range of angular scales, emission
mechanisms involved and brightness temperatures. In addition, time and
frequency synthesis, the key tool used by most radio interferometers to
build up information about the source being imaged is not effective for
solar imaging, because many of the features of interest are short lived
and change dramatically over small fractional bandwidths. Building on
the advances in radio frequency technology, digital signal processing
and computing, the kind of instruments needed to simultaneously capture
the evolution of solar emission in time, frequency, morphology and
polarization over a large spectral span with the requisite imaging
fidelity, and time and frequency resolution have only recently begun
to appear. Of this class of instruments, the Murchison Widefield Array
(MWA) is best suited for solar observations. The MWA has now entered
a routine observing phase and here we present some early examples from
MWA observations.

---------------------------------------------------------
Title: Metrewave observations of the Sun
Authors: Oberoi, D.; Sharma, R.; Bhatnagar, S.; Lonsdale, C. J.;
Matthews, L. D.; Cairns, I. H.; Tingay, S. J.; Benkevitch, L.; Donea,
A.; White, S. M.; Bernardi, G.; Bowman, J. D.; Briggs, F.; Cappallo,
R. J.; Corey, B. E.; Deshpande, A.; Emrich, D.; Gaensler, B. M.; Goeke,
R.; Greenhill, L. J.; Hazelton, B. J.; Johnston-Hollitt, M.; Kaplan,
D. L.; Kasper, J. C.; Kratzenberg, E.; Lynch, M. J.; McWhirter, S. R.;
Mitchell, D. A.; Morales, M. F.; Morgan, E.; Ord, S. M.; Prabu, T.;
Rogers, A. E. E.; Roshi, A.; Salah, J. E.; Udaya-Shankar, N.; Srivani,
K. S.; Subrahmanyan, R.; Waterson, M.; Wayth, R. B.; Webster, R. L.;
Whitney, A. R.; Williams, A.; Williams, C. L.
2014ASInC..13...13O Altcode:
High fidelity solar imaging at low radio frequencies remains a
challenge. Solar emission is characterized by its large angular size,
complex and dynamic morphological features spanning a large range of
angular sizes, emission mechanisms spanning a wide range in brightness
temperatures, and temporal and spectral variability of the emission
over large ranges in time and frequency. Capturing the solar emission
processes with high fidelity and in sufficient detail hence requires
a capability to simultaneously track the emission in time, frequency
and morphology over a large bandwidth. Traditional interferometers
rely on time and frequency synthesis to produce high fidelity and
dynamic range imaging, and are hence intrinsically poorly suited
to the task of instantaneous imaging over narrow spectral spans. With the emergence of a new generation of large-N interferometers,
the situation has improved in a very significant manner. Of these
instruments, the Murchison Widefield Array (MWA), located at the site
chosen for the SKA in Western Australia, is the one most suited for
solar observations at low radio frequencies. The MWA has recently
commenced routine observing. Here we illustrate the diversity of
features seen in solar emission using the MWA data to substantiate
its suitability for solar studies.

---------------------------------------------------------
Title: Probing Magnetic Energy Release in a Solar Flare with Radio
Dynamic Imaging Spectroscopy
Authors: Chen, Bin; Bastian, T. S.; Gary, D. E.; White, S. M.
2014AAS...22311804C Altcode:
Solar flares involve sudden release of magnetic energy that is
previously stored in the Sun's corona. Yet details of the flare
energy release processes are still poorly understood. Solar radio
bursts are intense and short-lived radio emissions that occur in
solar flares. They are believed to be intimately related to flare
energy release processes. However, their potential in diagnosing flare
energy release has been greatly limited by the lack of simultaneous
spatial information. The upgraded Karl G. Jansky Very Large Array (VLA)
provides the first opportunity of radio synthesis imaging along with
high spectral and temporal resolution, making the new technique of radio
dynamic imaging spectroscopy possible. We report VLA observations of a
solar flare event using this new technique, during which a rich variety
of radio bursts are recorded. With the help of concurrent data in
extreme ultra-violet and X-ray wavelengths, these observations allow us
to establish the relation between the bursts and flare energy release,
and use them to probe physical properties of the energy release site.

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Title: The chromosphere above sunspots at millimeter wavelengths
Authors: Loukitcheva, M.; Solanki, S. K.; White, S. M.
2014A&A...561A.133L Altcode: 2014arXiv1403.3436L
 Aims: The aim of this paper is to demonstrate that millimeter
wave data can be used to distinguish between various atmospheric models
of sunspots, whose temperature structure in the upper photosphere
and chromosphere has been the source of some controversy. 
Methods: We use observations of the temperature contrast (relative
to the quiet Sun) above a sunspot umbra at 3.5 mm obtained with
the Berkeley-Illinois-Maryland Array (BIMA), complemented by submm
observations from Lindsey &amp; Kopp (1995) and 2 cm observations
with the Very Large Array. These are compared with the umbral contrast
calculated from various atmospheric models of sunspots. Results:
Current mm and submm observational data suggest that the brightness
observed at these wavelengths is low compared to the most widely used
sunspot models. These data impose strong constraints on the temperature
and density stratifications of the sunspot umbral atmosphere, in
particular on the location and depth of the temperature minimum and the
location of the transition region. Conclusions: A successful
model that is in agreement with millimeter umbral brightness should
have an extended and deep temperature minimum (below 3000 K). Better
spatial resolution as well as better wavelength coverage are needed
for a more complete determination of the chromospheric temperature
stratification above sunspot umbrae.

---------------------------------------------------------
Title: Solar Drivers for Space Weather Operations (Invited)
Authors: White, S. M.
2013AGUFMSM52C..03W Altcode:
Most space weather effects can be tied back to the Sun, and major
research efforts are devoted to understanding the physics of
the relevant phenomena with a long-term view of predicting their
occurrence. This talk will focus on the current state of knowledge
regarding the solar drivers of space weather, and in particular the
connection between the science and operational needs. Topics covered
will include the effects of solar ionizing flux on communications and
navigation, radio interference, flare forecasting, the solar wind and
the arrival of coronal mass ejections at Earth.

---------------------------------------------------------
Title: The detection of a bright 30 THz impulsive solar burst
Authors: White, Stephen M.; Kaufmann, P.; Freeland, S. L.; Marcon,
R.; Fernandes, L. T.; Kudaka, A. S.; de Souza, R. V.; Marun, A.;
Valio, A.; Raulin, J.; Gimenez de Castro, C.
2013SPD....4440206W Altcode:
One of the last unexplored wavelength frontiers for solar flares is
in the range of submillimeter to infrared wavelengths. We report the
detection of an intense impulsive burst at 30 THz using a new imaging
system. The 30 THz emission exhibited remarkable time coincidence with
peaks observed at microwave, mm/submm, visible, EUV and hard X-ray
wavelengths. The 30 THz burst location matches a weak white-light
feature, an intense EUV knot, and a hard X-ray source. The two spatial
structures at EUV are not time coincident, and appear to correspond to
two successive peaks at 30 THz and submm, the second one without time
correspondence with the impulsive component. The coincidence with a
white-light feature is consistent with heating below the temperature
minimum in the atmosphere. However, there are problems in attributing
the heating to accelerated electrons. The peak 30 THz flux is several
times larger than the usual microwave peak near 9 GHz, attributed
to non-thermal electrons in the corona. The 30 THz emission could
be consistent with an optically thick spectrum increasing from low
to high frequencies. It might be part of the same spectral component
found at sub-THz frequencies whose nature remains mysterious. Further
observations at these wavelengths will provide a new window for flare
studies.

---------------------------------------------------------
Title: A Bright Impulsive Solar Burst Detected at 30 THz
Authors: Kaufmann, P.; White, S. M.; Freeland, S. L.; Marcon, R.;
Fernandes, L. O. T.; Kudaka, A. S.; de Souza, R. V.; Aballay, J. L.;
Fernandez, G.; Godoy, R.; Marun, A.; Valio, A.; Raulin, J. -P.;
Giménez de Castro, C. G.
2013ApJ...768..134K Altcode: 2013arXiv1303.5894K
Ground- and space-based observations of solar flares from radio
wavelengths to gamma-rays have produced considerable insights but
raised several unsolved controversies. The last unexplored wavelength
frontier for solar flares is in the range of submillimeter and infrared
wavelengths. Here we report the detection of an intense impulsive burst
at 30 THz using a new imaging system. The 30 THz emission exhibited
remarkable time coincidence with peaks observed at microwave, mm/submm,
visible, EUV, and hard X-ray wavelengths. The emission location
coincides with a very weak white-light feature, and is consistent with
heating below the temperature minimum in the atmosphere. However, there
are problems in attributing the heating to accelerated electrons. The
peak 30 THz flux is several times larger than the usual microwave peak
near 9 GHz, attributed to non-thermal electrons in the corona. The
30 THz emission could be consistent with an optically thick spectrum
increasing from low to high frequencies. It might be part of the same
spectral component found at sub-THz frequencies whose nature remains
mysterious. Further observations at these wavelengths will provide a
new window for flare studies.

---------------------------------------------------------
Title: Solar flares at submillimeter wavelengths
Authors: Krucker, Säm; Giménez de Castro, C. G.; Hudson, H. S.;
Trottet, G.; Bastian, T. S.; Hales, A. S.; Kašparová, J.; Klein,
K. -L.; Kretzschmar, M.; Lüthi, T.; Mackinnon, A.; Pohjolainen, S.;
White, S. M.
2013A&ARv..21...58K Altcode:
We discuss the implications of the first systematic observations of
solar flares at submillimeter wavelengths, defined here as observing
wavelengths shorter than 3 mm (frequencies higher than 0.1 THz). The
events observed thus far show that this wave band requires a new
understanding of high-energy processes in solar flares. Several events,
including observations from two different observatories, show during
the impulsive phase of the flare a spectral component with a positive
(increasing) slope at the highest observable frequencies (up to 405
GHz). To emphasize the increasing spectra and the possibility that
these events could be even more prominent in the THz range, we term
this spectral feature a "THz component". Here we review the data and
methods, and critically assess the observational evidence for such
distinct component(s). This evidence is convincing. We also review the
several proposed explanations for these feature(s), which have been
reported in three distinct flare phases. These data contain important
clues to flare development and particle acceleration as a whole, but
many of the theoretical issues remain open. We generally have lacked
systematic observations in the millimeter-wave to far-infrared range
that are needed to complete our picture of these events, and encourage
observations with new facilities.

---------------------------------------------------------
Title: Imaging the Sun with the Murchison Widefield Array
Authors: Oberoi, D.; Matthews, L. D.; Cairns, I. H.; Tingay, S. J.;
Benkevitch, L.; Donea, A.; White, S. M.; Arcus, W.; Barnes, D.;
Bernardi, G.; Bowman, J. D.; Briggs, F.; Burns, S.; Bunton, J. D.;
Cappallo, R. J.; Corey, B. E.; Deshpande, A.; deSouza, L.; Emrich,
D.; Goeke, R.; Gaensler, B. M.; Greenhill, L. -J.; Hazelton, B. J.;
Herne, D.; Johnston-Hollitt, M.; Kaplan, D. L.; Kasper, J. C.;
Kincaid, B. B.; Koeing, R.; Kratzenberg, E.; Lonsdale, C. J.; Lynch,
M. J.; McWhirter, S. R.; Mitchell, D. A.; Morales, M. F.; Morgan, E.;
Ord, S. M.; Pathikulungara, J.; Prabu, T.; Remillard, R. A.; Rogers,
A. E. E.; Roshi, A.; Salah, J. E.; Sault, R. J.; Udaya-Shankar, N.;
Srivani, K. S.; Stevens, J.; Subrahmanyan, R.; Waterson, M.; Wayth,
R. B.; Webster, R. L.; Whitney, A. R.; Williams, A.; Williams, C. L.;
Wyithe, J. S. B.
2013ASInC..10..131O Altcode:
The Murchison Widefield Array (MWA) is a new generation low-frequency
radio (80--300 MHz) array. The MWA design exploits recent advances
in digital hardware capabilities and affordability of computational
capacity to meet the needs of low-frequency radio astronomy. Solar and
coronal imaging and studies of the heliosphere and the ionosphere via
their propagation effects on low-frequency radio waves comprise one of
the four key science goals of the MWA. Here we present some early solar
science results to highlight the exceptional imaging dynamic range
and fidelity of the MWA and its high time and frequency resolution,
ahead of commencement of the regular observing scheduled for mid 2013.

---------------------------------------------------------
Title: Tracing Electron Beams in the Sun's Corona with Radio Dynamic
Imaging Spectroscopy
Authors: Chen, Bin; Bastian, T. S.; White, S. M.; Gary, D. E.; Perley,
R.; Rupen, M.; Carlson, B.
2013ApJ...763L..21C Altcode: 2012arXiv1211.3058C
We report observations of type III radio bursts at decimeter wavelengths
(type IIIdm bursts)—signatures of suprathermal electron beams
propagating in the low corona—using the new technique of radio dynamic
imaging spectroscopy provided by the recently upgraded Karl G. Jansky
Very Large Array. For the first time, type IIIdm bursts were imaged with
high time and frequency resolution over a broad frequency band, allowing
electron beam trajectories in the corona to be deduced. Together with
simultaneous hard X-ray and extreme ultraviolet observations, we show
that these beams emanate from an energy release site located in the
low corona at a height below ~15 Mm, and propagate along a bundle of
discrete magnetic loops upward into the corona. Our observations enable
direct measurements of the plasma density along the magnetic loops,
and allow us to constrain the diameter of these loops to be less than
100 km. These overdense and ultra-thin loops reveal the fundamentally
fibrous structure of the Sun's corona. The impulsive nature of the
electron beams, their accessibility to different magnetic field lines,
and the detailed structure of the magnetic release site revealed by
the radio observations indicate that the localized energy release is
highly fragmentary in time and space, supporting a bursty reconnection
model that involves secondary magnetic structures for magnetic energy
release and particle acceleration.

---------------------------------------------------------
Title: Opportunities for Solar Science with NuSTAR
Authors: Glesener, Lindsay; Boggs, S. E.; Christensen, F.; Craig,
W. W.; Hailey, C. J.; Grefenstette, B.; Harrison, F.; Hudson, H. S.;
Hurford, G. J.; Krucker, S.; Marsh, A.; Mewaldt, R. A.; Pivovaroff,
M.; Smith, D. M.; Stern, D.; Vogel, J.; White, S. M.; Zhang, W.;
NuSTAR Team
2013AAS...22124423G Altcode:
While NuSTAR was designed to observe faint cosmic sources in hard
X-rays (HXR), its unprecedented sensitivity can also be used to address
several outstanding questions in high energy solar physics. Medium- and
large-sized solar flares have been well -studied in HXR by the Reuven
Ramaty High Energy Solar Spectroscopic Imager (RHESSI), launched in
2002. These flares are always found in active regions and usually
emit nonthermal HXR from accelerated electrons, along with thermal
bremsstrahlung as those electrons lose their energy and heat the
ambient plasma. To date, no HXR flares outside active regions have been
observed, though thermal brightenings in soft X-rays and EUV suggest
that small "nanoflares" may occur frequently across the entire solar
disk, even at quiet times when no active regions are present. Even a
few minutes of NuSTAR solar observations will allow a search for HXR
from quiet-Sun nanoflares with better sensitivity than any previous
study. These observations will have important implications for the
role of flares in supplying the corona with its surprisingly hot
temperature (1--2 MK, as compared with the photospheric temperature
of 5800 K). NuSTAR will also make the first observations of escaping
flare electrons associated with Type III radio emission, can image
faint coronal sources in partially occulted flares that are below
RHESSI's sensitivity, and, combined with RHESSI data, could study the
faint, earliest phase of flares, where direct signatures of particle
acceleration are most likely to be observed.

---------------------------------------------------------
Title: Solar Hard X-ray Observations with NuSTAR
Authors: Marsh, Andrew; Smith, D. M.; Krucker, S.; Hudson, H. S.;
Hurford, G. J.; White, S. M.; Mewaldt, R. A.; Harrison, F. A.;
Grefenstette, B. W.; Stern, D.
2012AAS...22052112M Altcode:
High-sensitivity imaging of coronal hard X-rays allows detection
of freshly accelerated nonthermal electrons at the acceleration
site. A few such observations have been made with Yohkoh and RHESSI,
but a leap in sensitivity could help pin down the time, place, and
manner of reconnection. Around the time of this meeting, the Nuclear
Spectroscopic Telescope ARray (NuSTAR), a NASA Small Explorer for high
energy astrophysics that uses grazing-incidence optics to focus X-rays
up to 80 keV, will be launched. Three weeks will be dedicated to solar
observing during the baseline two-year mission. NuSTAR will be 200
times more sensitive than RHESSI in the hard X-ray band. This will allow
the following new observations, among others: 1) Extrapolation of the
micro/nanoflare distribution by two orders of magnitude down in flux;
2) Search for hard X-rays from network nanoflares (soft X-ray bright
points) and evaluation of their role in coronal heating; 3) Discovery
of hard X-ray bremsstrahlung from the electron beams driving type III
radio bursts, and measurement of their electron spectrum; 4) Hard X-ray
studies of polar soft X-ray jets and impulsive solar energetic particle
events at the edge of coronal holes; 5) Study of coronal bremsstrahlung
from particles accelerated by coronal mass ejections as they are
first launched; 6) Study of particles at the coronal reconnection
site when flare footpoints and loops are occulted; 7) Search for weak
high-temperature coronal plasmas in active regions that are not flaring;
and 8) Search for hypothetical axion particles created in the solar
core via the hard X-ray signal from their conversion to X-rays in the
coronal magnetic field. NuSTAR will also serve as a pathfinder for a
future dedicated space mission with enhanced capabilities, such as a
satellite version of the FOXSI sounding rocket.

---------------------------------------------------------
Title: Direct Comparison Of A Moreton Wave, EUV Wave And CME
Authors: White, Stephen M.; Cliver, E.; Balasubramaniam, K.
2012AAS...22020412W Altcode:
The first period of major solar activity in the current cycle,
due to AR 11158 in mid February 2011, produced a sequence of solar
flares exhibiting both Moreton waves in H-alpha images and "EIT-waves"
seen in EUV images. Given the rarity of Moreton waves, this offers an
excellent opportunity to compare the properties of the two phenomena
with simultaneous observations. We focus on the event of 17:24 UT on
February 14, which was well-observed by a number of observatories. We
find a strong link between the Moreton wave, the EUV wave and the CME
in this event. The Moreton wave has the same speed as the EUV wave, but
it lags behind the leading edge of the EUV wave. A vertical signature
is seen in the H-alpha Doppler images. STEREO observations of the
CME indicate that initially the vertical speed of the disturbance was
not as high as the EUV wave speed, and the CME rapidly decelerates on
merging with a rising loop system. We interpret the results in light
of current models for such disturbances.

---------------------------------------------------------
Title: Forecasting F10.7 with solar magnetic flux
transport modeling
Authors: Henney, C. J.; Toussaint, W. A.; White, S. M.; Arge, C. N.
2012SpWea..10.2011H Altcode:
A new method is presented here to forecast the solar 10.7 cm (2.8
GHz) radio flux, abbreviated F10.7, utilizing advanced
predictions of the global solar magnetic field generated by a flux
transport model. Using indices derived from the absolute value of the
solar magnetic field, we find good correlation between the observed
photospheric magnetic activity and the observed F10.7
values. Comparing magnetogram data observed within 6 hours of the
F10.7 measurements during the years 1993 through 2010, the
Spearman correlation coefficient, rs, for an empirical model
of F10.7 is found to be 0.98. In addition, we find little
change in the empirical model coefficients and correlations between the
first and second 9 year intervals of the 18 year period investigated. By
evolving solar magnetic synoptic maps forward 1-7 days, this new method
provides a realistic estimation of the Earth-side solar magnetic field
distribution used to forecast F10.7. Spearman correlation
values of approximately 0.97, 0.95, and 0.93 are found for 1 day,
3 day, and 7 day forecasts, respectively. The method presented here
can be expanded to forecast other space weather parameters, e.g.,
total solar irradiance and extreme ultraviolet flux. In addition,
near-term improvements to the F10.7 forecasting method, e.g.,
including far-side magnetic data with solar magnetic flux transport,
are discussed.

---------------------------------------------------------
Title: The Solar Decimetric Spike Burst of 2006 December 6: Possible
Evidence for Field-aligned Potential Drops in Post-eruption Loops
Authors: Cliver, E. W.; White, S. M.; Balasubramaniam, K. S.
2011ApJ...743..145C Altcode:
A 1.4 GHz solar radio burst associated with a 3B/X6 eruptive flare
on 2006 December 6 had the highest peak flux density (~106
sfu) of any event yet recorded at this frequency. The decimetric event
characteristics during the brightest emission phase (numerous intense,
short-lived, narrow-band bursts that overlapped to form a continuous
spectrum) suggest electron cyclotron maser (ECM) emission. The peak 1.4
GHz emission did not occur during the flare impulsive phase but rather
~45 minutes later, in association with post-eruption loop activity
seen in Hα and by the Hinode EUV Imaging Spectrometer. During the
Waves/LASCO era, three other delayed bursts with peak intensities
&gt;105 sfu in the 1.0-1.6 GHz (L-band) frequency range
have been reported that appear to have characteristics similar to the
December 6 burst. In each of these three cases, high-frequency type
IV bursts were reported in a range from ~150 to ~1500 MHz. Assuming
a common ECM emission mechanism across this frequency range implies
a broad span of source heights in the associated post-eruption loop
systems. Difficulties with an ECM interpretation for these events
include the generation of the lower frequency component of the type
IVs and the long-standing problem of escape of the ECM emission from
the loops. Magnetic-field-aligned potential drops, analogous to those
observed for Earth's auroral kilometric radiation, could plausibly
remove both of these objections to ECM emission.

---------------------------------------------------------
Title: Sub-THz and Hα Activity during the Preflare and Main Phases
of a GOES Class M2 Event
Authors: Kaufmann, Pierre; Marcon, Rogério; Giménez de Castro,
C. Guillermo; White, Stephen M.; Raulin, Jean-Pierre; Correia, Emilia;
Olavo Fernandes, Luis; de Souza, Rodney V.; Godoy, Rodolfo; Marun,
Adolfo; Pereyra, Pablo
2011ApJ...742..106K Altcode: 2011arXiv1110.3013K
Radio and optical observations of the evolution of flare-associated
phenomena have shown an initial and rapid burst at 0.4 THz only followed
subsequently by a localized chromospheric heating producing an Hα
brightening with later heating of the whole active region. A major
instability occurred several minutes later producing one impulsive
burst at microwaves only, associated with an M2.0 GOES X-ray flare
that exhibited the main Hα brightening at the same site as the first
flash.The possible association between long-enduring time profiles at
soft X-rays, microwaves, Hα, and sub-THz wavelengths is discussed. In
the decay phase, the Hα movie shows a disrupting magnetic arch
structure ejecting dark, presumably chromospheric, material upward. The
time sequence of events suggests genuine interdependent and possibly
non-thermal instabilities triggering phenomena, with concurrent active
region plasma heating and material ejection.

---------------------------------------------------------
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.

---------------------------------------------------------
Title: Chromosphere above sunspots as seen at millimeter wavelengths
Authors: Loukitcheva, Maria A.; Solanki, Sami K.; White, Stephen M.
2011IAUS..273..408L Altcode:
Millimeter emission is known to be a sensitive diagnostic of temperature
and density in the solar chromosphere. In this work we use millimeter
wave data to distinguish between various atmospheric models of sunspots,
whose temperature structure in the upper photosphere and chromosphere
has been the source of some controversy. From mm brightness simulations
we expect a radio umbra to change its appearance from dark to bright
(compared to the Quiet Sun) at a given wavelength in the millimeter
spectrum (depending on the exact temperature in the model used). Thereby
the millimeter brightness observed above an umbra at several wavelengths
imposes strong constraints on temperature and density stratification of
the sunspot atmosphere, in particular on the location and depth of the
temperature minimum and the location of the transition region. Current
mm/submm observational data suggest that brightness observed at
short wavelengths is unexpectedly low compared to the most widely
used sunspot models such as of Maltby et al. (1986). A successful
model that is in agreement with millimeter umbral brightness should
have an extended and deep temperature minimum (below 3000 K), such as
in the models of Severino et al. (1994). However, we are not able to
resolve the umbra cleanly with the presently available observations
and better resolution as well as better wavelength coverage are
needed for accurate diagnostics of umbral brightness at millimeter
wavelengths. This adds one more scientific objective for the Atacama
Large Millimeter/Submillimeter Array (ALMA).

---------------------------------------------------------
Title: Microwave Depolarization above Sunspots
Authors: Lee, Jeongwoo; White, Stephen M.
2011IAUS..273..487L Altcode:
Microwave emissions from sunspots are circularly polarized in the
sense of rotation (right or left) determined by the polarity (north
or south) of coronal magnetic fields. However, they may convert into
unpolarized emissions under certain conditions of magnetic field and
electron density in the corona, and this phenomenon of depolarization
could be used to derive those parameters. We propose another diagnostic
use of microwave depolarization based on the fact that an observed
depolarization strip actually represents the coronal magnetic polarity
inversion line (PIL) at the heights of effective mode coupling, and its
location itself carries information on the distribution of magnetic
polarity in the corona. To demonstrate this diagnostic utility we
generate a set of magnetic field models for a complex active region
with the observed line-of-sight magnetic fields but varying current
density distribution and compare them with the 4.9 GHz polarization
map obtained with the Very Large Array (VLA). The field extrapolation
predicts very different locations of the depolarization strip in the
corona depending on the amount of electric currents assumed to exist
in the photosphere. Such high sensitivity of microwave depolarization
to the coronal magnetic field can therefore be useful for validating
electric current density maps inferred from vector magnetic fields
observed in the photosphere.

---------------------------------------------------------
Title: Solar Hard X-ray Observations with NuSTAR
Authors: Smith, David M.; Krucker, S.; Hudson, H. S.; Hurford, G. J.;
White, S. M.; Mewaldt, R. A.; Stern, D.; Grefenstette, B. W.; Harrison,
F. A.
2011SPD....42.1501S Altcode: 2011BAAS..43S.1501S
High-sensitivity imaging of coronal hard X-rays allows detection of
freshly accelerated nonthermal electrons at the acceleration site. A
few such observations have been made with Yohkoh and RHESSI, but a
leap in sensitivity could help pin down the time, place, and manner
of reconnection. In 2012, the Nuclear Spectroscopic Telescope
Array (NuSTAR), a NASA Small Explorer for high energy astrophysics
that uses grazing-incidence optics to focus X-rays up to 80 keV, will
be launched. NuSTAR is capable of solar pointing, and three weeks
will be dedicated to solar observing during the baseline two-year
mission. NuSTAR will be 200 times more sensitive than RHESSI in the
hard X-ray band. This will allow the following new observations, among
others: 1) Extrapolation of the micro/nanoflare distribution by two
orders of magnitude down in flux 2) Search for hard X-rays from
network nanoflares (soft X-ray bright points) and evaluation of their
role in coronal heating 3) Discovery of hard X-ray bremsstrahlung
from the electron beams driving type III radio bursts, and measurement
of their electron spectrum 4) Hard X-ray studies of polar soft
X-ray jets and impulsive solar energetic particle events at the edge
of coronal holes, and comparison of these events with observations
of 3He and other particles in interplanetary space 5) Study of
coronal bremsstrahlung from particles accelerated by coronal mass
ejections as they are first launched 6) Study of particles at
the coronal reconnection site when flare footpoints are occulted; and
7) Search for hypothetical axion particles created in the solar
core via the hard X-ray signal from their conversion to X-rays in the
coronal magnetic field. NuSTAR will also serve as a pathfinder
for a future dedicated space mission with enhanced capabilities,
such as a satellite version of the FOXSI sounding rocket.

---------------------------------------------------------
Title: Simultaneous Observations of Hα Moreton Waves and EUV Waves
Authors: White, Stephen M.; Balasubramanian, K. S.; Cliver, E. W.
2011SPD....42.1307W Altcode: 2011BAAS..43S.1307W
The first period of major solar activity in the current cycle,
due to AR 11158 in mid February 2011, produced a sequence of solar
flares exhibiting both Moreton waves in H-alpha images and "EIT-waves"
seen in EUV images. Given the rarity of Moreton waves, this offers an
excellent opportunity to compare the properties of the two phenomena
with simultaneous observations. We analyze several events and compare
the speeds and locations of the disturbances using high-cadence
H-alpha data from both the ISOON telescope at Sunspot, NM, and the
GONG network, together with EUV images in several wavelengths from
the SDO/AIA telescope, and interpret the results in light of current
models for such disturbances.

---------------------------------------------------------
Title: Impulsive High-Energy Particle Acceleration in
theSOL2010-06-12T00:57 M2 X-rayFlare
Authors: Share, Gerald H.; Briggs, M. S.; Gruber, D.; Longo, F.;
Murphy, R. J.; Omodei, N.; Schwartz, R. A.; White, S. M.; Tylka,
A. J.; Fermi LAT Collaboration; Fermi GBM Collaboration
2011SPD....42.1102S Altcode: 2011BAAS..43S.1102S
The GOES M2-class solar flare, SOL2010-06-12T00:57, was modest in
many respects yet exhibited remarkable acceleration of energetic
particles. While both radio and SDO/AIA UV/EUV images indicate a compact
flare with foot-point separation of just 10 arc sec, this small region
produced an 70 sec burst of hard X-and gamma-ray emission up to at least
200 MeV observed by the Fermi GBM and LAT experiments. The gamma-ray
line and &gt;300 keV bremsstrahlung fluences from this flare were
about ten times higher than that typically observed from this modest
GOES-class of X-ray flare. Analysis of the combined nuclear line and
high-energy gamma-ray emissions suggests that the accelerated proton
spectrum at the Sun softened significantly above 50 MeV. We compare
these observations with measurements of solar energetic protons to
determine whether the particle populations at the Sun and in space may
have a common origin. The 34 and 80 GHz microwave emissions are very
bright and well correlated with the few hundred keV X-ray emission,
but with small time lags suggesting mild trapping of electrons in
the corona.

---------------------------------------------------------
Title: The Great Decimetric Solar Spike Burst of 2006 December 6:
Possible Evidence for Field-aligned Potential Drops in Post-eruption
Loops
Authors: Cliver, Edward W.; White, S. M.; Balasubramaniam, K. S.
2011SPD....42.2223C Altcode: 2011BAAS..43S.2223C
A 1.4 GHz solar radio burst associated with a 3B/X6 eruptive flare
on 2006 December 6 had the highest peak flux density ( 106
sfu) of any event yet recorded at this frequency. The decimetric event
characteristics during the brightest emission phase (numerous intense,
short-lived, narrow-band bursts that overlapped to form a continuous
spectrum) suggest electron cyclotron maser (ECM) emission. The peak
1.4 GHz emission did not occur during the flare impulsive phase
but rather 45 minutes later, in association with post-eruption loop
activity seen in H-alpha and by Hinode EIS. During the Waves/LASCO era,
three other delayed bursts with peak intensities &gt;105
sfu in the 1.0-1.6 GHz (L-band) frequency range have been reported
and appear to have characteristics similar to the December 6 burst. In
each of these three cases type IV bursts were reported in a range from
150 to 1500 MHz. Assuming a common ECM emission mechanism across this
frequency range implies a broad span of source heights in the associated
post-eruption loop systems. Difficulties with an ECM interpretation for
these events include the generation of the lower frequency component
of the type IVs and the long-standing problem of escape of the ECM
emission from the loops. Magnetic-field-aligned potential drops,
analogous to those observed for Earth's auroral kilometric radiation,
could plausibly remove both of these objections to ECM emission.

---------------------------------------------------------
Title: The Expanded Owens Valley Solar Array
Authors: Gary, Dale E.; Hurford, G. J.; Nita, G. M.; White, S. M.;
Tun, S. D.; Fleishman, G. D.; McTiernan, J. M.
2011SPD....42.0102G Altcode: 2011BAAS..43S.0102G
The Expanded Owens Valley Solar Array (EOVSA) is now under construction
near Big Pine, CA as a solar-dedicated microwave imaging array
operating in the frequency range 1-18 GHz. The solar science to be
addressed focuses on the 3D structure of the solar corona (magnetic
field, temperature and density), on the sudden release of energy and
subsequent particle acceleration, transport and heating, and on space
weather phenomena. The project will support the scientific community
by providing open data access and software tools for analysis of the
data, to exploit synergies with on-going solar research in other
wavelengths. The New Jersey Institute of Technology (NJIT)
is expanding OVSA from its previous complement of 7 antennas to
a total of 15 by adding 8 new antennas, and will reinvest in the
existing infrastructure by replacing the existing control systems,
signal transmission, and signal processing with modern, far more
capable and reliable systems based on new technology developed for
the Frequency Agile Solar Radiotelescope (FASR). The project will be
completed in time to provide solar-dedicated observations during the
upcoming solar maximum in 2013 and beyond. We provide an update on
current status and our preparations for exploiting the data through
modeling and data analysis tools. This research is supported by
NSF grants AST-0908344, and AGS-0961867 and NASA grant NNX10AF27G to
New Jersey Institute of Technology.

---------------------------------------------------------
Title: First Spectroscopic Imaging Observations of the Sun at Low
Radio Frequencies with the Murchison Widefield Array Prototype
Authors: Oberoi, Divya; Matthews, Lynn D.; Cairns, Iver H.; Emrich,
David; Lobzin, Vasili; Lonsdale, Colin J.; Morgan, Edward H.; Prabu,
T.; Vedantham, Harish; Wayth, Randall B.; Williams, Andrew; Williams,
Christopher; White, Stephen M.; Allen, G.; Arcus, Wayne; Barnes, David;
Benkevitch, Leonid; Bernardi, Gianni; Bowman, Judd D.; Briggs, Frank
H.; Bunton, John D.; Burns, Steve; Cappallo, Roger C.; Clark, M. A.;
Corey, Brian E.; Dawson, M.; DeBoer, David; De Gans, A.; deSouza, Ludi;
Derome, Mark; Edgar, R. G.; Elton, T.; Goeke, Robert; Gopalakrishna,
M. R.; Greenhill, Lincoln J.; Hazelton, Bryna; Herne, David; Hewitt,
Jacqueline N.; Kamini, P. A.; Kaplan, David L.; Kasper, Justin C.;
Kennedy, Rachel; Kincaid, Barton B.; Kocz, Jonathan; Koeing, R.;
Kowald, Errol; Lynch, Mervyn J.; Madhavi, S.; McWhirter, Stephen R.;
Mitchell, Daniel A.; Morales, Miguel F.; Ng, A.; Ord, Stephen M.;
Pathikulangara, Joseph; Rogers, Alan E. E.; Roshi, Anish; Salah,
Joseph E.; Sault, Robert J.; Schinckel, Antony; Udaya Shankar, N.;
Srivani, K. S.; Stevens, Jamie; Subrahmanyan, Ravi; Thakkar, D.;
Tingay, Steven J.; Tuthill, J.; Vaccarella, Annino; Waterson, Mark;
Webster, Rachel L.; Whitney, Alan R.
2011ApJ...728L..27O Altcode: 2011arXiv1101.0620O
We present the first spectroscopic images of solar radio transients
from the prototype for the Murchison Widefield Array, observed on
2010 March 27. Our observations span the instantaneous frequency band
170.9- 201.6 MHz. Though our observing period is characterized as a
period of "low" to "medium" activity, one broadband emission feature
and numerous short-lived, narrowband, non-thermal emission features
are evident. Our data represent a significant advance in low radio
frequency solar imaging, enabling us to follow the spatial, spectral,
and temporal evolution of events simultaneously and in unprecedented
detail. The rich variety of features seen here reaffirms the coronal
diagnostic capability of low radio frequency emission and provides
an early glimpse of the nature of radio observations that will become
available as the next generation of low-frequency radio interferometers
come online over the next few years.

---------------------------------------------------------
Title: On the Origin of the Solar Moreton Wave of 2006 December 6
Authors: Balasubramaniam, K. S.; Cliver, E. W.; Pevtsov, A.; Temmer,
M.; Henry, T. W.; Hudson, H. S.; Imada, S.; Ling, A. G.; Moore, R. L.;
Muhr, N.; Neidig, D. F.; Petrie, G. J. D.; Veronig, A. M.; Vršnak,
B.; White, S. M.
2010ApJ...723..587B Altcode:
We analyzed ground- and space-based observations of the eruptive flare
(3B/X6.5) and associated Moreton wave (~850 km s-1 ~270°
azimuthal span) of 2006 December 6 to determine the wave driver—either
flare pressure pulse (blast) or coronal mass ejection (CME). Kinematic
analysis favors a CME driver of the wave, despite key gaps in coronal
data. The CME scenario has a less constrained/smoother velocity versus
time profile than is the case for the flare hypothesis and requires an
acceleration rate more in accord with observations. The CME picture is
based, in part, on the assumption that a strong and impulsive magnetic
field change observed by a GONG magnetograph during the rapid rise phase
of the flare corresponds to the main acceleration phase of the CME. The
Moreton wave evolution tracks the inferred eruption of an extended
coronal arcade, overlying a region of weak magnetic field to the west
of the principal flare in NOAA active region 10930. Observations of
Hα foot point brightenings, disturbance contours in off-band Hα
images, and He I 10830 Å flare ribbons trace the eruption from 18:42
to 18:44 UT as it progressed southwest along the arcade. Hinode EIS
observations show strong blueshifts at foot points of this arcade
during the post-eruption phase, indicating mass outflow. At 18:45
UT, the Moreton wave exhibited two separate arcs (one off each flank
of the tip of the arcade) that merged and coalesced by 18:47 UT to
form a single smooth wave front, having its maximum amplitude in
the southwest direction. We suggest that the erupting arcade (i.e.,
CME) expanded laterally to drive a coronal shock responsible for the
Moreton wave. We attribute a darkening in Hα from a region underlying
the arcade to absorption by faint unresolved post-eruption loops.

---------------------------------------------------------
Title: A Smoking Gun in the Carina Nebula
Authors: Hamaguchi, Kenji; Corcoran, Michael F.; Ezoe, Yuichiro;
Townsley, Leisa; Broos, Patrick; Gruendl, Robert A.; Vaidya, Kaushar;
White, Stephen M.; Strohmayer, Tod; Petre, Rob; Chu, You-Hua
2010AIPC.1248...17H Altcode:
Massive stars are born from giant molecular clouds along with many
lower mass stars, forming a stellar cluster or association. They
dominate the pressure of the interstellar gas through their strong
UV radiation, stellar winds and, ultimately, supernova explosions at
the end of their life. These processes help the formation of the next
generation of stars, but this trigger of star formation is not yet
well understood. The Carina Nebula is one of the youngest, most
active sites of massive star formation in our Galaxy. In this nebula,
we have discovered a bright X-ray source that has persisted for ~30
years. The soft X-ray spectrum, consistent with a kT~128 eV lackbody
with mild extinction, and no counterpart in the optical and infrared
wavelengths indicate that it is a 106 year-old neutron
star. Current star formation theory does not allow the progenitor of
the neutron star and the other massive stars in the Carina Nebula
(in particular η Carinae) to be coeval. This result suggests that
the Carina Nebula experienced at least two episodes of massive star
formation. The neutron star may be responsible for part or all of the
diffuse X-ray emission which permeates the Nebula.

---------------------------------------------------------
Title: Complexity Analysis of Impulsive Type IIIs and Type III-L
Solar Radio Bursts
Authors: Duffin, Robert Thomas; White, Stephen M.; Ray, Paul S.
2010shin.confE..78D Altcode:
Type III-L bursts are a sub-class of type III solar radio bursts
that tend to occur after the impulsive phase of flares; are longer in
duration than individual type IIIs and tend to be low-frequency. Work
has been developed on a Type III fitting tool. A Template is chosen
from a representative individual Type III burst and fit to individual
Type III bursts and components of Complex Type III bursts in order to
help analyze and distinguish these bursts. This Type III fitting tool
can also be used to fit and distinguish Impulsive Type IIIs and Type
III-L bursts and help analyze various characteristics of the components
of these bursts such as drift-rate and change in the duration of their
intensity-time profiles with frequency.

---------------------------------------------------------
Title: The ADAHELI solar mission: Investigating the structure of
Sun's lower atmosphere
Authors: Berrilli, F.; Bigazzi, A.; Roselli, L.; Sabatini, P.; Velli,
M.; Alimenti, F.; Cavallini, F.; Greco, V.; Moretti, P. F.; Orsini,
S.; Romoli, M.; White, S. M.; ADAHELI Team; Ascani, L.; Carbone, V.;
Curti, F.; Consolini, G.; Di Mauro, M. P.; Del Moro, D.; Egidi, A.;
Ermolli, I.; Giordano, S.; Pastena, M.; Pulcino, V.; Pietropaolo, E.;
Romano, P.; Ventura, P.; Cauzzi, G.; Valdettaro, L.; Zuccarello, F.;
ADAHELI Team
2010AdSpR..45.1191B Altcode: 2010AdSpR..45.1191A
ADAHELI (ADvanced Astronomy for HELIophysics) is a small-class
(500 kg) low-budget (50 MEuro) satellite mission for the study of
the solar photosphere and the chromosphere and for monitoring solar
flare emission. ADAHELI's design has completed its Phase-A feasibility
study in December 2008, in the framework of ASI's (Agenzia Spaziale
Italiana) 2007 "Small Missions" Program (calling for two missions at
50 MEeuros each, plus the launch budget). ADAHELI's main purpose is
to explore Sun's lower atmosphere in the near-infrared, a region so
far unexplored by solar observations from space. ADAHELI will carry
out observations of the solar photosphere and of the chromosphere at
high-temporal rate and high spatial and spectral resolutions. ADAHELI
will contribute to the understanding of Space Weather through the
study of particle acceleration during flares. A radiometer operating
in the millimeter radio band will continuously monitor the solar disk,
throughout the spacecraft's life time. ADAHELI's baseline instruments
are a 50-cm high-resolution telescope operating in the visible and
the near-infrared, and a lightweight full-disk radiometer operating at
millimeter wavelengths (90 GHz). The core of the telescope's focal plane
suite is the spectral imager based on two Fabry-Perot interferometers,
flying for the first time on a solar mission. The instrument
will return fast-cadence, full bi-dimensional spectral images at
high-resolution, thus improving on current slit-scan, mono-dimensional
architectures. Moreover, the possibility of working in polarized light
will enable full 3D magnetic field reconstruction on the photosphere
and the chromosphere. An optional instrumental package is also being
proposed to further extend ADAHELI's scope: a full-disk telescope for
helioseismology based on a double Magneto-Optical Filter, a Neutral
Particle Analyzer for magnetospheric research, an Extreme Ultraviolet
imaging and spectro-radiometry instrument. These options fall outside
the prescribed budget. ADAHELI, flying a Sun-Synchronous orbit at 800
km, will perform continuous, long-duration (4-h), daily acquisitions,
with the possibility of extending them up to 24 h. ADAHELI's operating
life is two years, plus one extension year. Launch would be nominally
planned for 2014.

---------------------------------------------------------
Title: Measurements of the Coronal Acceleration Region of a Solar
Flare
Authors: Krucker, Sam; Hudson, H. S.; White, S. M.; Masuda, S.; Lin,
R. P.
2010AAS...21630603K Altcode:
The most discussed coronal hard X-ray source has been the
above-the-loop-top source observed in the Masuda flare. We present new
RHESSI hard X-ray observations of a similar event with simultaneous
microwave observations by NoRH. These observations clearly establish
the non-thermal nature of the above-the-loop-top source and triggered
a new interpretation. To account for the extremely bright hard X-ray
source in a rather low ambient density plasma, all electrons in the
above-the-loop-top source seem to be accelerated, suggesting that the
above-the-loop-top source is itself the electron acceleration region.

---------------------------------------------------------
Title: Type III-L Solar Radio Bursts and Their Associations with
Solar Energetic Proton Events
Authors: Duffin, Robert T.; White, S. M.; Ray, P. S.; Kaiser, M. L.
2010AAS...21632106D Altcode: 2010BAAS...41..912D
Type III-L bursts are a sub-class of type III solar radio bursts
that tend to occur after the impulsive phase of flares; are longer in
duration than individual type IIIs and tend to be low-frequency. There
has been a proposal that type III-Ls are connected to solar energetic
proton (SEP) events. Most work on this connection has started
from samples of SEP events, but if type III-Ls are to be useful for
prediction of SEP events, then we need to understand the properties of
samples of type III-L bursts. This talk reports preliminary results
from such a study. An operating definition based on previous work is
used to identify type III-L events amongst M- and X-class flares from
2001; and then associations with other properties of these events are
investigated, including association with SEP events. If there is an
association with SEP events, one important factor that these bursts
allow us to address is the question of whether acceleration takes
place at an associated CME, or closer to the flare site well below the
CME. Work has been developed on a type III fitting tool. A Template
is chosen from a representative individual type III burst and fit to
individual type III bursts and components of Complex type III bursts
in order to help analyze and distinguish these bursts. This type III
fitting tool can also be used to fit and distinguish Impulsive type
III and type III-L bursts and help analyze various characteristics of
the components of these bursts such as drift-rate and change in the
duration of their intensity-time profiles with frequency. Funding
for this research came from the Naval Research Laboratory where basic
research in radio astronomy is funded by the Office of Naval Research,
and from NASA LWS Grant FRS 526249.

---------------------------------------------------------
Title: Measurements of the Coronal Acceleration Region of a Solar
Flare
Authors: Krucker, Säm; Hudson, H. S.; Glesener, L.; White, S. M.;
Masuda, S.; Wuelser, J. -P.; Lin, R. P.
2010ApJ...714.1108K Altcode:
The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and
the Nobeyama Radioheliograph (NoRH) are used to investigate coronal
hard X-ray and microwave emissions in the partially disk-occulted solar
flare of 2007 December 31. The STEREO mission provides EUV images of the
flare site at different viewing angles, establishing a two-ribbon flare
geometry and occultation heights of the RHESSI and NoRH observations
of ~16 Mm and ~25 Mm, respectively. Despite the occultation, intense
hard X-ray emission up to ~80 keV occurs during the impulsive phase
from a coronal source that is also seen in microwaves. The hard X-ray
and microwave source during the impulsive phase is located ~6 Mm above
thermal flare loops seen later at the soft X-ray peak time, similar in
location to the above-the-loop-top source in the Masuda flare. A single
non-thermal electron population with a power-law distribution (with
spectral index of ~3.7 from ~16 keV up to the MeV range) radiating
in both bremsstrahlung and gyrosynchrotron emission can explain
the observed hard X-ray and microwave spectrum, respectively. This
clearly establishes the non-thermal nature of the above-the-loop-top
source. The large hard X-ray intensity requires a very large number
(&gt;5 × 1035 above 16 keV for the derived upper limit
of the ambient density of ~8 × 109 cm-3)
of suprathermal electrons to be present in this above-the-loop-top
source. This is of the same order of magnitude as the number of ambient
thermal electrons. We show that collisional losses of these accelerated
electrons would heat all ambient electrons to superhot temperatures
(tens of keV) within seconds. Hence, the standard scenario, with hard
X-rays produced by a beam comprising the tail of a dominant thermal core
plasma, does not work. Instead, all electrons in the above-the-loop-top
source seem to be accelerated, suggesting that the above-the-loop-top
source is itself the electron acceleration region.

---------------------------------------------------------
Title: Observations of the solar chromosphere at millimeter
wavelengths
Authors: Loukitcheva, M.; Solanki, S. K.; White, S. M.
2010MmSAI..81..592L Altcode:
Millimeter wavelengths provide a powerful tool to study the thermal
structure of the solar chromosphere and its response to dynamic
processes. We present initial studies of chromospheric fine structure
and its dynamics obtained from observations of the quiet Sun with
BIMA at 3.5 mm with a resolution of 12 arcsec. The two-dimensional
millimeter maps of the solar chromosphere reveal brightness features
corresponding to supergranular network boundaries and bright points
within cells. Significant intensity oscillations with frequencies of
1.5 - 8.0 mHz with a tendency toward shorter-period oscillations in
the internetwork and longer periods in network regions are found in
the data. However, higher spatial resolution is required for a more
detailed study. We discuss the requirements imposed on observations in
the millimeter domain that might provide an insight into the fundamental
questions of solar physics. We also review the capabilities of the
current and future millimeter-wave interferometers, including the
CARMA and ALMA arrays.

---------------------------------------------------------
Title: Type III-L Solar Radio Bursts and their Associations with
Solar Energetic Proton Events
Authors: Duffin, R. T.; White, S. M.; Ray, P. S.; Kaiser, M. L.
2009AGUFMSH33A1475D Altcode:
Type III-L bursts are a sub-class of type III solar radio bursts
that tend to occur after the impulsive phase of flares; are longer in
duration than individual type IIIs and tend to be low-frequency. There
has been a proposal that type III-Ls are connected to solar energetic
proton (SEP) events. Most work on this connection has started
from samples of SEP events, but if type III-Ls are to be useful for
prediction of SEP events, then we need to understand the properties of
samples of type III-L bursts. This talk reports preliminary results
from such a study. An operating definition based on previous work is
used to identify type III-L events amongst M- and X-class flares from
2001; and then associations with other properties of these events are
investigated, including association with SEP events. If there is an
association with SEP events, one important factor that these bursts
allow us to address is the question of whether acceleration takes place
at an associated CME, or closer to the flare site well below the CME.

---------------------------------------------------------
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.

---------------------------------------------------------
Title: A Smoking Gun in the Carina Nebula
Authors: Hamaguchi, Kenji; Corcoran, M. F.; Ezoe, Y.; Townsley, L.;
Broos, P.; Gruendl, R.; Vaidya, K.; White, S. M.; Strohmayer, T.;
Petre, R.; Chu, Y. -H.
2009cfdd.confE.114H Altcode:
Massive stars are born from giant molecular clouds along with many
lower mass stars, forming a stellar cluster or association. They
dominate the pressure of the interstellar gas through their strong
UV radiation, stellar winds and, ultimately, supernova explosions
at the end of their life. These processes help the formation of
the next generation of stars, but this trigger of star formation is
not yet well understood. The Carina Nebula is one of the youngest,
most active sites of massive star formation in our Galaxy. In this
nebula, we have discovered a bright X-ray source that has persisted
for ∼30 years. The soft X-ray spectrum, consistent with a kT ∼128
eV blackbody with mild extinction, and no counterpart in the optical
and infrared wavelengths indicate that it is a 106 year-old neutron
star. Current star formation theory does not allow the progenitor
of the neutron star and the other massive stars in the Carina Nebula
(in particular Eta Carinae) to be coeval. This result suggests that
the Carina Nebula experienced at least two episodes of massive star
formation. The neutron star may be responsible for part or all of the
diffuse X-ray emission which permeates the Nebula.

---------------------------------------------------------
Title: Dynamically Driven Evolution of the Interstellar Medium in M51
Authors: Koda, Jin; Scoville, Nick; Sawada, Tsuyoshi; La Vigne,
Misty A.; Vogel, Stuart N.; Potts, Ashley E.; Carpenter, John M.;
Corder, Stuartt A.; Wright, Melvyn C. H.; White, Stephen M.; Zauderer,
B. Ashley; Patience, Jenny; Sargent, Anneila I.; Bock, Douglas C. J.;
Hawkins, David; Hodges, Mark; Kemball, Athol; Lamb, James W.; Plambeck,
Richard L.; Pound, Marc W.; Scott, Stephen L.; Teuben, Peter; Woody,
David P.
2009ApJ...700L.132K Altcode: 2009arXiv0907.1656K
Massive star formation occurs in giant molecular clouds (GMCs);
an understanding of the evolution of GMCs is a prerequisite to
develop theories of star formation and galaxy evolution. We report the
highest-fidelity observations of the grand-design spiral galaxy M51 in
carbon monoxide (CO) emission, revealing the evolution of GMCs vis-a-vis
the large-scale galactic structure and dynamics. The most massive GMCs
(giant molecular associations (GMAs)) are first assembled and then
broken up as the gas flow through the spiral arms. The GMAs and their
H2 molecules are not fully dissociated into atomic gas as
predicted in stellar feedback scenarios, but are fragmented into smaller
GMCs upon leaving the spiral arms. The remnants of GMAs are detected
as the chains of GMCs that emerge from the spiral arms into interarm
regions. The kinematic shear within the spiral arms is sufficient to
unbind the GMAs against self-gravity. We conclude that the evolution
of GMCs is driven by large-scale galactic dynamics—their coagulation
into GMAs is due to spiral arm streaming motions upon entering the arms,
followed by fragmentation due to shear as they leave the arms on the
downstream side. In M51, the majority of the gas remains molecular
from arm entry through the interarm region and into the next spiral
arm passage.

---------------------------------------------------------
Title: Type III-L Solar Radio Bursts and their Associations with
Solar Energetic Proton Events
Authors: Duffin, Robert Thomas; White, Stephen M.; Ray, Paul S.;
L., Michael
2009shin.confE.164D Altcode:
Type III-L bursts are a sub-class of type III solar radio bursts
that tend to occur after the impulsive phase of flares; are longer in
duration than individual type IIIs and tend to be low-frequency. There
has been a proposal that type III-Ls are connected to solar energetic
proton (SEP) events. Most work on this connection has started
from samples of SEP events, but if type III-Ls are to be useful for
prediction of SEP events, then we need to understand the properties of
samples of type III-L bursts. This talk reports preliminary results
from such a study. An operating definition based on previous work is
used to identify type III-L events amongst M- and X-class flares from
2001; and then associations with other properties of these events are
investigated, including association with SEP events. If there is an
association with SEP events, one important factor that these bursts
allow us to address is the question of whether acceleration takes place
at an associated CME, or closer to the flare site well below the CME.

---------------------------------------------------------
Title: Type III-L Solar Radio Bursts and their Associations with
Solar Energetic Proton Events
Authors: Duffin, Robert T.; White, S. M.; Ray, P. S.; Kaiser, M. L.
2009SPD....40.2117D Altcode:
Type III-L bursts are a sub-class of type III solar radio bursts
that tend to occur after the impulsive phase of flares; are longer in
duration than individual type IIIs and tend to be low-frequency. There
has been a proposal that type III-Ls are connected to solar energetic
proton (SEP) events. Most work on this connection has started
from samples of SEP events, but if type III-Ls are to be useful for
prediction of SEP events, then we need to understand the properties of
samples of type III-L bursts. This talk reports preliminary results
from such a study. An operating definition based on previous work is
used to identify type III-L events amongst M- and X-class flares from
2001; and then associations with other properties of these events
are investigated, including association with SEP events. If there
is an association with SEP events, one important factor that these
bursts allow us to address is the question of whether acceleration
takes place at an associated CME, or closer to the flare site well
below the CME. Research described in this talk will contribute
towards the PhD dissertation for author RTD. Basic research in
radio astronomy at the Naval Research Laboratory is supported by the
Office of Naval Research.

---------------------------------------------------------
Title: Direct Observations of the Coronal Acceleration Region of a
Solar Flare
Authors: Krucker, Sam; Hudson, H. S.; White, S. M.; Lin, R. P.
2009SPD....40.3601K Altcode:
Solar flares essentially convert the intrinsic energy of coronal
magnetic field into the kinetic energy of accelerated particles. Hard
X-ray emission from flare-accelerated electrons produced by the
bremsstrahlung mechanism provides the most direct diagnostics of
electron acceleration. The most discussed coronal hard X-ray source has
been the above-the-loop-top source observed in the Masuda flare. The
poor spectral resolution of these observations, however, made an
interpretation ambiguous, and the exact location of the acceleration
remained elusive. We present high spatial and spectral resolution
RHESSI hard X-ray observations of an above-the-loop-top source with
simultaneous microwave observations from NoRH. These observations
provide a unambiguous interpretation of above-the-loop-top sources:
The above-the-loop-top source itself is the acceleration region, where
all electrons within an extended volume (1e27 cm3) are accelerated. The
distribution of the accelerated electrons is definitely non-thermal,
with a power law distribution extending from 10 keV up to the
relativistic range (few MeV). The plasma beta in the acceleration region
changes from the pre-flare value of 0.01 to 1, indicating that roughly
half of the magnetic energy has been transformed into kinetic energy.

---------------------------------------------------------
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.

---------------------------------------------------------
Title: A Smoking Gun in the Carina Nebula
Authors: Hamaguchi, Kenji; Corcoran, Michael F.; Ezoe, Yuichiro;
Townsley, Leisa; Broos, Patrick; Gruendl, Robert; Vaidya, Kaushar;
White, Stephen M.; Strohmayer, Tod; Petre, Rob; Chu, You-Hua
2009ApJ...695L...4H Altcode: 2009arXiv0902.4162H
The Carina Nebula is one of the youngest, most active sites of massive
star formation in our Galaxy. In this nebula, we have discovered a
bright X-ray source that has persisted for ~30 years. The soft X-ray
spectrum, consistent with kT ~ 128 eV blackbody radiation with mild
extinction, and no counterpart in the near- and mid-infrared wavelengths
indicates that it is a ~106 year old neutron star housed in
the Carina Nebula. Current star formation theory does not suggest that
the progenitors of the neutron star and massive stars in the Carina
Nebula, in particular η Car, are coeval. This result suggests that
the Carina Nebula experienced at least two major episodes of massive
star formation. The neutron star may be responsible for remnants of
high-energy activity seen in multiple wavelengths.

---------------------------------------------------------
Title: On the relation between photospheric magnetic field and
chromospheric emission in the quiet Sun
Authors: Loukitcheva, Maria A.; Solanki, Sami K.; White, Stephen M.
2009IAUS..259..185L Altcode:
In this contribution we present an observational study of the
interaction of the photosphere with different chromospheric layers. We
study the correlations between emissions at varying temperature from the
temperature minimum region (UV continuum at 1600 Å from TRACE) through
the low chromosphere (CaII K-line from BBSO) to the middle chromosphere
(continuum at 3.5 mm from BIMA) and photospheric magnetic field from
MDI/SOHO. For the first time millimeter observational data are included
in such analysis. We report a high degree of correlation between
considered emissions formed at different heights in the chromosphere. A
power law is found to be a good representation for the relationship
between photospheric magnetic field and chromospheric emissions at
all considered wavelengths. Our analysis shows that the dependence
of chromospheric intensities on magnetic field is different for the
network and internetwork regions. In the network a power law provides
the best fit with the exponent being close to 0.5-0.6, while almost
no dependence of chromospheric intensity on magnetic flux is found for
the cell interiors. The obtained results support the idea of different
heating mechanisms acting in the network (magnetic) and cell interiors
(acoustic).

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Title: The relationship between chromospheric emissions and magnetic
field strength
Authors: Loukitcheva, M.; Solanki, S. K.; White, S. M.
2009A&A...497..273L Altcode: 2009arXiv0910.1985L
Aims: We analyze observational data from 4 instruments to study the
correlations between chromospheric emission, spanning the heights
from the temperature minimum region to the middle chromosphere,
and photospheric magnetic field. Methods: The data consist of
radio images at 3.5 mm from the Berkeley-Illinois-Maryland Array
(BIMA), UV images at 1600 Å from TRACE, Ca II K-line filtergrams
from BBSO, and MDI/SOHO longitudinal photospheric magnetograms. For
the first time interferometric millimeter data with the highest
currently available resolution are included in such an analysis. We
determine various parameters of the intensity maps and correlate the
intensities with each other and with the magnetic field. Results:
The chromospheric diagnostics studied here show a pronounced similarity
in their brightness structures and map out the underlying photospheric
magnetic field relatively well. We find a power law to be a good
representation of the relationship between photospheric magnetic field
and emission from chromospheric diagnostics at all wavelengths. The
dependence of chromospheric brightness on magnetic field is found to
be different for network and internetwork regions.

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Title: A Resolved Ring of Debris Dust around the Solar Analog
HD 107146
Authors: Corder, Stuartt; Carpenter, John M.; Sargent, Anneila I.;
Zauderer, B. Ashley; Wright, Melvyn C. H.; White, Stephen M.; Woody,
David P.; Teuben, Peter; Scott, Stephen L.; Pound, Marc W.; Plambeck,
Richard L.; Lamb, James W.; Koda, Jin; Hodges, Mark; Hawkins, David;
Bock, Douglas C. -J.
2009ApJ...690L..65C Altcode: 2008arXiv0811.2713C
We present resolved images of the dust continuum emission from the
debris disk around the young (80-200 Myr) solar-type star HD 107146
with CARMA at λ = 1.3 mm and the CSO at λ = 350 μ. Both images show
that the dust emission extends over an approximately 10” diameter
region. The high-resolution (3”) CARMA image further reveals that
the dust is distributed in a partial ring with significant decrease
in a flux inward of 97 AU. Two prominent emission peaks appear within
the ring separated by ~140° in the position angle. The morphology of
the dust emission is suggestive of dust captured into a mean motion
resonance, which would imply the presence of a planet at an orbital
radius of ~45-75 AU.

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Title: Hard X-ray emission from the solar corona
Authors: Krucker, S.; Battaglia, M.; Cargill, P. J.; Fletcher, L.;
Hudson, H. S.; MacKinnon, A. L.; Masuda, S.; Sui, L.; Tomczak, M.;
Veronig, A. L.; Vlahos, L.; White, S. M.
2008A&ARv..16..155K Altcode: 2008A&ARv.tmp....8K
This review surveys hard X-ray emissions of non-thermal electrons in the
solar corona. These electrons originate in flares and flare-related
processes. Hard X-ray emission is the most direct diagnostic of
electron presence in the corona, and such observations provide
quantitative determinations of the total energy in the non-thermal
electrons. The most intense flare emissions are generally observed
from the chromosphere at footpoints of magnetic loops. Over the years,
however, many observations of hard X-ray and even γ-ray emission
directly from the corona have also been reported. These coronal sources
are of particular interest as they occur closest to where the electron
acceleration is thought to occur. Prior to the actual direct imaging
observations, disk occultation was usually required to study coronal
sources, resulting in limited physical information. Now RHESSI has
given us a systematic view of coronal sources that combines high
spatial and spectral resolution with broad energy coverage and high
sensitivity. Despite the low density and hence low bremsstrahlung
efficiency of the corona, we now detect coronal hard X-ray emissions
from sources in all phases of solar flares. Because the physical
conditions in such sources may differ substantially from those of
the usual “footpoint” emission regions, we take the opportunity
to revisit the physics of hard X-radiation and relevant theories of
particle acceleration.

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Title: The ADAHELI Solar Mission
Authors: Berrilli, F.; Velli, M.; Roselli, L.; Bigazzi, A.; Moretti,
P. F.; Romoli, M.; Orsini, S.; Cavallini, F.; Greco, V.; Carbone,
V.; Consolini, G.; Di Mauro, M. P.; Ermolli, I.; Pietropaolo, E.;
Romano, P.; Ventura, P.; White, S. M.; Zuccarello, F.; Cauzzi, G.;
Valdettaro, L.
2008ESPM...12..6.6B Altcode:
ADAHELI (Advanced Astronomy for HELIOphysics) is an Italian Space
project for the investigation of solar photospheric and chromospheric
dynamics, via high-resolution spectro-polarimetric observations in the
near-infrared spectral range. The mission has been financed for phase
A study in the framework of ASI Italian Space Agency Small Missions
Program call of September 2007. Four fields have been selected
to highlight the specific benefits of ADAHELI scientific payload: 1)
Photospheric and chromospheric dynamics and structure, 2) Emergence and
evolution of solar active regions and solar irradiance, 3) Chromospheric
and corona heating and turbulence, 4) Solar flares in the millimeter
wavelength region. The principal science instrument, ISODY, is
a 50 cm solar telescope equipped with an innovative Focal Plane Suite
composed of a spectro-polarimetric imager, based upon two Fabry-Perot
interferometers operating in the NIR regions around 845nm and 1083nm, a
broad band imager, and a correlation tracker used as image stabilization
system. Designed Mission Profiles for ADAHELI intend to achieve
continuous high-spectral and spatial resolution observations of the
Sun for a routine duration of 4 hours with a goal to be extended to
24 hours. ADAHELI also carries MIOS, a millimeter wavelengths
radiometer operating at around 90 GHz for flare detection. The
ADAHELI payload's instrument suite integrates and complements, without
overlap, the present major objectives of ESA, NASA and the International
Living with a Star program, in particular Solar Dynamics Observatory,
PICARD, Solar Orbiter, and the Solar Probe missions. Proposals
for optional instruments are also under evaluation: DIMMI-2h, a
double channel MOF based full disk imager operating at 589nm and
770nm, allowing high temporal resolution velocity and magnetic field
measurements; EISR a two channel spectrometer operating in the 50-130
nm wavelength range, and NPA, an in-situ Neutral Particle Analyzer
to detect Energetic Neutral Atoms (ENA). Science objectives related
to optional instruments include: solar high and low-degree p modes
oscillations, EUV solar structures and variability, solar gravitational
red-shift measurement, detection of ENA originating from the plasma
region in the Earth's magnetosphere and undergoing reflection from
the Earth's atmosphere.

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Title: Coronal Hard X-Ray Emission Associated with Radio Type
III Bursts
Authors: Krucker, Säm; Saint-Hilaire, P.; Christe, S.; White, S. M.;
Chavier, A. D.; Bale, S. D.; Lin, R. P.
2008ApJ...681..644K Altcode:
We report on a purely coronal hard X-ray source detected in a partially
disk-occulted solar flare by the Reuven Ramaty High Energy Solar
Spectroscopic Imager (RHESSI) that is associated with radio type
III bursts and a suprathermal electron event detected near 1 AU by
the WIND 3-D Plasma and Energetic Particle (3DP) instrument. Several
observational characteristics suggest that the coronal hard X-ray source
is thin target bremsstrahlung emission from the escaping electrons that
produce the radio type III bursts. The hard X-ray emission correlates
in time with the radio type III bursts and originates from a radially
elongated source in the corona with a length (~65 Mm) similar to typical
coronal density scale heights. Furthermore, the difference between the
hard X-ray photon spectral index (γ = 4.1 +/- 0.4) and the electron
spectral index of the in situ observed event (δin situ = 2.9
+/- 0.3) is around 1, consistent with the thin target interpretation. A
further test for the thin target scenario is to compare the number of
electrons needed to produce the observed hard X-ray emission with the
number of in situ observed electrons. However, the number of escaping
electrons derived from the single-spacecraft WIND measurement is in the
best case an order of magnitude estimate and could easily underestimate
the actual number of escaping electrons. Using the WIND observations,
the estimated number of escaping electrons is about an order of
magnitude too low. Thus, the thin target interpretation only holds
if the WIND measurements are significantly underestimating the actual
number of escaping electrons. Future multispacecraft observations with
STEREO, Solar Orbiter, and Sentinels will resolve this uncertainty.

---------------------------------------------------------
Title: Positions of Fiber Bursts in the 2006 December 6 Flare
Authors: White, S. M.; Liu, Z.; Gary, D. E.
2008AGUSMSP44A..07W Altcode:
The large flare of 2006 December 6 produced one of the brightest radio
bursts ever recorded. The burst was observed with very rapid sampling
by the FASR Subsystem Testbed, operating on 3 antennas of the OVSA
array at Owens Valley. The burst contained a range of emission types
within the FST band (1.0-1.5 GHz), including continuum and "fiber"
bursts. This is the first time that fiber bursts have been observed
over a significant frequency range with an interferometer. Data
are processed into visibilities using a software correlator with
positional information retained. We present an analysis of the fiber
bursts relative to the continuum, in order to investigate whether the
projected position of the bursts varies with frequency. This information
is used to test models for fiber bursts, in particular the model that
they represent propagating whistler wave trains.

---------------------------------------------------------
Title: Solar Flare Hard X-Ray Emission from the High Corona
Authors: Krucker, Säm; White, S. M.; Lin, R. P.
2007ApJ...669L..49K Altcode:
One of the largest solar hard X-ray (HXR) flares and solar energetic
particle (SEP) events recorded by the Mars Odyssey mission while
orbiting Mars occurred on 2002 October 27 and is related to a very
fast (~2300 km s-1) coronal mass ejection (CME). From the
Earth, the flare site is 40.4° +/- 3.5° behind the solar limb and
only emissions from the high corona at least 1.5 × 105
km radially above the main flare site can be seen. Nevertheless,
the Earth-orbiting Reuven Ramaty High Energy Solar Spectroscopic
Imager (RHESSI) observed HXR emission up to 60 keV with a relatively
flat, nonthermal spectrum (γ between 3 and 3.5) that has an onset
simultaneous with the main HXR emission observed above 60 keV by
the Gamma-Ray Spectrometer (GRS) orbiting Mars. While GRS records
several smaller enhancements after the main peak, the high coronal
source observed by RHESSI shows a long exponential decay (τ = 135
+/- 5 s) with progressive spectral hardening. The emissions from the
high corona originate from an extended source (~1.5 × 105
km in diameter) that expands (390 +/- 70 km s-1) and moves
upwards (750 +/- 80 km s-1) in the same direction as the
CME. These observations reveal the existence of energetic electrons in
the high corona in closed magnetic structures related to the CME that
are accelerated at the same time as the main energy release in the
flare. Although the number of energetic electrons in the high corona
is only a small fraction of the total accelerated electrons, about 10%
of all electrons in the high coronal source are nonthermal (&gt;10 keV).

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Title: Deep Impact's Small Telescope Science Program: Phase II Results
Authors: McFadden, Lucy-Ann A.; Kuppusamy, V. A.; Papp, G. M.; Beal,
S. E.; Clarke, T.; Skillman, D. R.; White, S. M.; McLaughlin, S. A.;
Warner, E. M.; Observers, STSP
2007DPS....39.2704M Altcode: 2007BAAS...39..463M
From February, 2000 through August, 2005, the Deep Impact mission's
science and education and public outreach team received images of Comet
9P/Tempel 1 from small telescope owners around the world. Deep Impact
explored the composition and structure of the nucleus of Comet Tempel
1. The Small Telescope Program (STSP) engaged technically proficient
observers to complement and augment the comet's characterization
carried out by large telescopes in support of planning and analysis
of the mission results. The first phase of the program is reported in
McLaughlin et al. 2004. Over 3700 images of Tempel 1 from 64 observers
were submitted to the second phase of STSP between December 2004 and
August 2005. Telescopes ranging in size from 10 - 80 cm, with CCD
cameras and a range of filters including unfiltered, V, R (625-740 nm)
and I (750-1000 nm) filters were used. Both calibrated and uncalibrated
images were submitted. We report on the cataloging and analysis of this
dataset. The field of view and orientation of each image was measured
using catalogue overlays generated by the Astrometrica program. The
orientation of the images and the star fields are identified, the star
fluxes are calculated and the counts are converted to instrumental
magnitude. Scaling to apparent photometric magnitude is made from
magnitudes available in the USNO-B1.0 star catalog. Photometry of
the comet was then determined for a circular aperture of radius of
27,000 km around the comet in each filter. We examine the resulting
magnitudes as a function of time before perihelion and calculate Af [?],
a measurement of dust activity. Dust activity increased by a factor of
6 between 203 and 62 days before perihelion, then decreased by &gt;2x,
2 days before perihelion. At impact it increased by 3x. This work is
supported by NASA grant NNX07AG22G.

---------------------------------------------------------
Title: Radio Frequency Interference Excision Using Spectral-Domain
Statistics
Authors: Nita, Gelu M.; Gary, Dale E.; Liu, Zhiwei; Hurford, Gordon
J.; White, Stephen M.
2007PASP..119..805N Altcode:
A radio frequency interference (RFI) excision algorithm based on
spectral kurtosis, a spectral variant of time-domain kurtosis, is
proposed and implemented in software. The algorithm works by providing
a robust estimator for Gaussian noise that, when violated, indicates
the presence of non-Gaussian RFI. A theoretical formalism is used that
unifies the well-known time-domain kurtosis estimator with past work
related to spectral kurtosis, and leads naturally to a single expression
encompassing both. The algorithm accumulates the first two powers of M
power spectral density (PSD) estimates, obtained via Fourier transform,
to form a spectral kurtosis (SK) estimator whose expected statistical
variance is used to define an RFI detection threshold. The performance
of the algorithm is theoretically evaluated for different time-domain
RFI characteristics and signal-to-noise ratios η. The theoretical
performance of the algorithm for intermittent RFI (RFI present in R
out of M PSD estimates) is evaluated and shown to depend greatly on the
duty cycle, d=R/M. The algorithm is most effective for d=1/(4+η), but
cannot distinguish RFI from Gaussian noise at any η when d=0.5. The
expected efficiency and robustness of the algorithm are tested using
data from the newly designed FASR Subsystem Testbed radio interferometer
operating at the Owens Valley Solar Array. The ability of the algorithm
to discriminate RFI against the temporally and spectrally complex
radio emission produced during solar radio bursts is demonstrated.

---------------------------------------------------------
Title: Electron acceleration in a post-flare decimetric continuum
source
Authors: Subramanian, P.; White, S. M.; Karlický, M.; Sych, R.;
Sawant, H. S.; Ananthakrishnan, S.
2007A&A...468.1099S Altcode: 2007astro.ph..3612S
Aims:To calculate the power budget for electron acceleration and the
efficiency of the plasma emission mechanism in a post-flare decimetric
continuum source. Methods: We have imaged a high brightness
temperature (∼ 109 K) post-flare source at 1060 MHz with
the Giant Metrewave Radio Telescope (GMRT). We use information from
these images and the dynamic spectrum from the Hiraiso spectrograph
together with the theoretical method described in Subramanian &amp;
Becker (2006, Sol. Phys., 237, 185) to calculate the power input to the
electron acceleration process. The method assumes that the electrons
are accelerated via a second-order Fermi acceleration mechanism. Results: We find that the power input to the nonthermal electrons
is in the range 3× 1025-1026 erg/s. The
efficiency of the overall plasma emission process starting from electron
acceleration and culminating in the observed emission could range from
2.87× 10-9 to 2.38 × 10-8.

---------------------------------------------------------
Title: Positional Properties of Solar Decimetric Fiber Bursts
Authors: Liu, Zhiwei; Gary, D. E.; Nita, G. M.; White, S. M.; Hurford,
G. J.
2007AAS...210.9328L Altcode: 2007BAAS...39..215L
The large solar flare of 2006 December 6 was detected by the newly
constructed FASR Subsystem Testbed (FST; Liu et al. 2007, PASP,
119), which is operating on three antennas of Owens Valley Solar
Array. This record-setting burst produced an especially fine set of
fibers bursts--so-called intermediate-drift bursts that drift from
high to low frequencies over 6-10s. According to a leading theory, the
fibers are generated by packets of whistler waves propagating along a
magnetic loop, which coalesce with Langmuir waves to produce escaping
electromagnetic radiation in the decimeter band. With this three element
interferometer, for the first time fiber burst source locations can be
determined. We use the radio information over a 500 MHz band (1.0-1.5
GHz) to determine the trajectories of the bursts. We attempt to define
three-dimensional trajectories by combining the two-dimensional radio
positions with height of the fiber source determined from a coronal
density model.

---------------------------------------------------------
Title: Interferometric Observations of the Record-Breaking Decimetric
Solar Radio Event of 2006 December 06
Authors: Gary, Dale E.; White, S. M.; Hurford, G. J.; Nita, G. M.;
Liu, Z.
2007AAS...210.9329G Altcode: 2007BAAS...39..216G
The radio burst associated with the 2006 Dec 06, X6.5 solar
flare attained a record-breaking radio flux density of nearly 1
million solar flux units in the decimetric ( 1 GHz) frequency band,
exceeding the previous record by nearly a factor of 10. The event was
so strong in the range 1-2 GHz that it caused loss of lock of Global
Positioning System (GPS) receivers everywhere in the sunlit hemisphere
of Earth. The event was observed with a new instrument operating at
the Owens Valley Solar Array (OVSA), the FASR Subsystem Testbed (FST),
which features not only unprecedented time and frequency resolution (
1 microsecond and &lt; 1 MHz, respectively), but also interferomety
on three baselines to provide corresponding spatial information on
a 10 arcsecond scale. The event produced about 10 million individual
decimetric spike bursts produced by the Electron Cyclotron Maser (ECM)
mechanism over a period of nearly 1 hour. We discuss the spectral,
temporal, and positional characteristics of individual spike bursts,
their statistical properties and their relation to the flare observed
at other wavelengths. This work is supported by NSF grant AST-0352915
to the New Jersey Institute of Technology. We acknowledge additional
support for the Owens Valley Solar Array through NSF grant AST-0607544
and NASA grant NNG06GJ40G.

---------------------------------------------------------
Title: Fiber Bursts in Solar Flares at High Time and Frequency
Resolution
Authors: White, Stephen M.; Liu, Z.; Gary, D. E.; Nita, G. M.; Hurford,
G. J.
2007AAS...210.6806W Altcode: 2007BAAS...39..176W
The FASR Subsystem Testbed (FST), operating on three dishes of the
Owens Valley Solar Array, detected radio fiber bursts in two large
solar flares in 2006. The frequencies of observation correspond to
densities of order 10 to the 10 per cc, so the bursts are being emitted
low in the corona, presumably near the energy release region. The
fiber bursts drift in frequency with time, and appear to be travelling
outwards. In one model, fiber bursts can be used to infer the magnetic
field in the corona in the emission site. The FST data provide radio
spectra of the bursts with a time resolution of milliseconds: using
this exceptional data, we present the properties of the bursts and
discuss their physical interpretation.

---------------------------------------------------------
Title: A Subsystem Test Bed for the Frequency-Agile Solar
Radiotelescope
Authors: Liu, Zhiwei; Gary, Dale E.; Nita, Gelu M.; White, Stephen M.;
Hurford, Gordon J.
2007PASP..119..303L Altcode:
This paper describes the design and operation of the Frequency-Agile
Solar Radiotelescope (FASR) Subsystem Testbed (FST) and the first
observational results. Three antennas of the Owens Valley Solar
Array have been modified so that each sends a 1-9 GHz band of radio
frequency to a central location using a broadband analog optical fiber
link. A dynamically selected 500 MHz subset of this frequency range is
digitized at 1 Gsps (gigasample per second) and recorded to disk. The
full-resolution time-domain data thus recorded are then correlated
through offline software to provide interferometric phase and amplitude
spectra on three baselines. An important feature of this approach is
that the data can be reanalyzed multiple times with different digital
signal-processing techniques (e.g., different bit-sampling, windowing,
and radio frequency interference [RFI] excision methods) to test
the effect of different designs. As a prototype of the FASR system,
FST provides the opportunity to study the design, calibration, and
interference-avoidance requirements of FASR. In addition, FST provides,
for the first time, the ability to perform broadband spectroscopy of
the Sun with spectrograph-like spectral and temporal resolution, while
providing locating ability for simple sources. Initial observations of
local RFI, geostationary satellite signals, global positioning system
(GPS) satellite signals, and the Sun are presented to illustrate the
system performance.

---------------------------------------------------------
Title: High-resolution millimeter-interferometer observations of
the solar chromosphere
Authors: White, S. M.; Loukitcheva, M.; Solanki, S. K.
2006A&A...456..697W Altcode:
The use of millimeter-interferometer data for the study of chromospheric
structure and dynamics is tested using 85 GHz observations with the
10-element Berkeley-Illinois-Maryland Array (BIMA). Interferometer
data have the advantage over single-dish data that they allow both high
spatial resolution and dense temporal sampling simultaneously. However,
snapshot imaging of the quiet solar atmosphere with a small number of
dishes is challenging. We demonstrate that techniques are available to
carry out this task successfully using maximum entropy deconvolution
from a default image constructed from the entire observation: one of
our results is that the solar chromosphere at millimeter wavelengths
exhibits features that are long-lasting and the map of the entire
observation is significant provided that atmospheric phase errors do
not prevent deconvolution. We compare observations of quiet Sun, active
region and coronal hole targets. The interferometer is not sensitive
to the disk emission and the positivity constraint of the maximum
entropy algorithm used forces the zero level in the images to be at
the temperature of the coolest feature in each field. The brightest
features in the images are typically 1000-1500 K above the zero level,
with a snapshot noise level of order 100 K. We use extensive tests to
determine whether oscillation power can be recovered from sequences of
snapshot images and show that individual sources can be down to quite
weak levels at locations in the image where significant flux is present;
oscillation power located in cool regions of the image is not well
recovered due to the deconvolution method used and may be redistributed
to brighter regions of the millimeter image. We then investigate
whether the data do show oscillation power using uninterrupted 30-min
scans of the target regions. Intensity oscillations with significant
power in the frequency range 1.5-8.0 mHz are found in the quiet-Sun
and active region targets. For the quiet-Sun region we compare the
oscillation properties of network boundaries and cell interiors
(internetwork) in the spatially-resolved time series. In agreement
with investigations at other wavelengths, in the millimeter data the
power in the network tends to be at periods of 5 min and longer while
power in the internetwork is present also at shorter (3-min) periods.

---------------------------------------------------------
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˚.

---------------------------------------------------------
Title: Solar Radio Astronomy with the Long Wavelength Array
Authors: Duffin, Robert T.; Erickson, W. C.; Kassim, N. E.; Ray,
P. S.; White, S. M.
2006SPD....37.0816D Altcode: 2006BAAS...38..233D
The Long Wavelength Array (LWA) will be a ground-based interferometric
array of up to 50 stations, with an operating frequency range of 20
to 80 MHz. Each station will have about 256 active dipoles with a
maximum station-to-station baseline of 400 km. The long baselines
and large area, combined with advances in ionospheric calibration,
will allow the LWA to achieve angular resolution and sensitivity
more than two orders of magnitude better than previous instruments in
this frequency range. The LWA will perform a broad range of studies
of the Sun in the metric and decametric regime, where a diverse range
of emission mechanisms carry information about processes occurring in
the solar atmosphere and in interplanetary space. It will also enable
low frequency imaging of solar activity and brightness distributions in
support of the upcoming STEREO (Solar Terrestrial Relations Observatory)
observations at lower frequencies. Solar emission observed by the LWA
will help us to better understand particle acceleration and shocks in
the solar atmosphere and the dynamics of coronal mass ejections (CMEs)
which travel from the sun's lower atmosphere to Earth. Basic research
in radio astronomy at the Naval Research Laboratory is supported by
the Office of Naval Research.

---------------------------------------------------------
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.

---------------------------------------------------------
Title: FASR Subsystem Testbed
Authors: Liu, Zhiwei; Gary, D. E.; Nita, G. M.; White, S. M.; Hurford,
G. J.
2006SPD....37.0602L Altcode: 2006BAAS...38..225L
The construction of the Frequency Agile Solar Radiotelescope (FASR)
Subsystem Testbed (FST) and first results are described. Three
antennas of Owens Valley Solar Array (OVSA) are upgraded with the
newly designed, state of art technology. The 1-9 GHz RF signal from
the feed is transmitted through the fiber optical system to the control
room. Then it is downconverted to a 500 MHz single-sideband signal that
can be tuned across the 1-9 GHz RF band. The data are sampled with an
8-bit, 1 GHz sampling-rate digitizer, and further saved to the hard
disk. The correlated (phase and amplitude) spectra are derived through
offline software. As a prototype of the FASR system, FST provides the
opportunity to study the design, calibration, and interference-avoidance
requirements of FASR. FST provides, for the first time, the ability to
perform broadband imaging spectroscopy with high spectral, temporal and
moderate spatial resolution. With this three element interferometer, we
have the ability to determine the location of simple source structures
with very high time resolution (20 ms) and frequency resolution ( &lt;1
MHz) as well as the dynamic spectrum. Initial examples of geostationary
satellite, GPS satellite and solar observations are presented.

---------------------------------------------------------
Title: First Solar Results with the FASR Subsystem Testbed
Authors: Gary, Dale E.; Hurford, G. J.; Liu, Z.; Nita, G. M.; White,
S. M.
2006SPD....37.2502G Altcode: 2006BAAS...38..252G
The Frequency Agile Solar Radiotelescope (FASR) Subsystem Testbed
(FST) is a new, three-element interferometer, utilizing three antennas
of the Owens Valley Solar Array. FST is the first radio instrument
capable of measuring solar burst locations with spectrograph-like
time and frequency resolution. Operating with 500 MHz instantaneous
bandwidth, tunable anywhere in the 1-9 GHz range, FST can measure
centroid locations of typical bursts on millisecond timescales and
MHz frequency resolution. The system is designed as a prototype for
FASR, for several purposes including the study of radio frequency
interference (RFI) mitigation techniques, a testbed for the design of
FASR's digitial signal processing, and investigating use of satellite
signals for calibration. In addition, however, FST is unique in its
ability to locate solar bursts on the extremely fine frequency and
time scales on which their emission varies.A technical description of
the instrument can be found in an accompanying poster (Liu et al.),
along with first results on the several topics mentioned above. In
this talk we focus on the solar applications of FST. We describe the
operation of the system for solar observations, the science goals of the
instrument, and some first results of observations of solar bursts. The
first recorded burst, obtained on the first day of solar observations,
was a group of type III bursts associated with a B5.1 X-ray burst, also
observed with RHESSI. Individual type IIIs show downward propagation
(reverse-frequency slope), with significant positional differences
from one type III to another, while within a type III are seen smaller
positional changes as a function of frequency. This suggests smooth
trajectories for individual bursts, but widely diverging locations
for separate bursts. We describe joint RHESSI/FST observations and
findings for those bursts observed so far. This work is supported by
NSF grant AST-0352915 to NJIT.

---------------------------------------------------------
Title: Imaging Observations of a Very High Frequency Type II Burst
Authors: White, S. M.; Mercier, C.; Bradley, R.; Bastian, T.; Kerdraon,
A.; Pick, M.
2006AGUSMSH24A..05W Altcode:
A remarkable Type II burst was detected by the high-frequency system of
the Green Bank Solar Radio Burst Spectrometer on 2005 November 14. The
harmonic branch of the Type II extended up to 800 MHz, making it one
of the highest frequency Type II bursts ever detected, but it failed
to propagate to heights corresponding to frequencies below 100 MHz. At
such high frequencies, it implies the formation of a shock relatively
low in the corona. No coronal mass ejection was evident in the LASCO
data for this east limb event. It is one of the few Type II bursts to
be observable at every frequency of observation of the Nancay Radio
Heliograph (164-432 MHz). Here we present analysis of images of the
event, including simultaneous imaging of the fundamental and harmonic
branches.

---------------------------------------------------------
Title: The FASR Reference Instrument
Authors: Bastian, T. S.; Gary, D. E.; Hurford, G. J.; Kawakubo, H.;
Ruf, C.; White, S. M.; Zurbuchen, T.
2006AGUSMSH33A..08B Altcode:
The Frequency Agile Solar Radiotelescope (FASR) is a unique,
solar-dedicated radio facility slated for completion by 2012. The
instrument will address an extremely broad range of solar and
space weather science, including routine measurement of coronal
magnetic fields, imaging coronal mass ejections near the solar
surface, quantitative diagnostics of energy release and particle
acceleration in flares, and the extension of the solar corona into
the heliosphere. Although the precise details of the FASR design
are still being developed, we present for the first time a complete
high-level design referred to as the FASR Reference Instrument. The
Reference Instrument meets the science requirements and will serve
as the basis for cost estimates for construction and operation of
the instrument. This paper gives an overview of the FASR Reference
Instrument, describes the science goals and objectives, and gives the
flowdown of science goals to engineering specifications. The innovative
aspects of the FASR design are highlighted, and a complete, end-to-end
description of the instrument is given. The instrument operations plan
is also discussed.

---------------------------------------------------------
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.

---------------------------------------------------------
Title: Solar Radio Astronomy With the Long Wavelength Array
Authors: Duffin, R. T.; Erickson, W. C.; Kassim, N. E.; Ray, P. S.;
White, S. M.
2006AGUSMSH33A..05D Altcode:
The Long Wavelength Array (LWA) will be a ground-based interferometric
array of up to 50 stations, with an operating frequency range of 20
to 80 MHz. Each station will have about 256 active dipoles with a
maximum station-to-station baseline of 400 km. The long baselines
and large area, combined with advances in ionospheric calibration,
will allow the LWA to achieve angular resolution and sensitivity
more than two orders of magnitude better than previous instruments in
this frequency range. The LWA will perform a broad range of studies
of the Sun in the metric and decametric regime, where a diverse range
of emission mechanisms carry information about processes occurring in
the solar atmosphere and in interplanetary space. It will also enable
low frequency imaging of solar activity and brightness distributions in
support of the upcoming STEREO (Solar Terrestrial Relations Observatory)
observations at lower frequencies. Solar emission observed by the LWA
will help us to better understand particle acceleration and shocks in
the solar atmosphere and the dynamics of coronal mass ejections (CMEs)
which travel from the sun's lower atmosphere to Earth. Basic research
in radio astronomy at the Naval Research Laboratory is supported by
the Office of Naval Research.

---------------------------------------------------------
Title: Radio Measurements of the Height of Strong Coronal Magnetic
Fields Above Sunspots at the Solar Limb
Authors: Brosius, Jeffrey W.; White, Stephen M.
2006ApJ...641L..69B Altcode:
We measure coronal magnetic field strengths of 1750 G at a height of
8000 km above a large sunspot in NOAA AR 10652 at the west solar limb on
2004 July 29 using coordinated observations with the Very Large Array,
the Transition Region and Coronal Explorer, and three instruments
(CDS, EIT, MDI) aboard the Solar and Heliospheric Observatory. This
observation is the first time that coronal radio brightness temperatures
have been analyzed in a 15 GHz solar radio source projected above the
limb. Observations at 8 GHz yield coronal magnetic field strengths
of 960 G at a height of 12,000 km. The field strength measurements
combine to yield a magnetic scale height LB=6900 km. The
radio brightness temperature maxima are located away from a sunspot
plume that appears bright in EUV line emission formed at temperatures
around several ×105 K. We use the density-sensitive
emission-line intensity ratio of O IV 625.8 Å/554.5 Å to derive
an electron density ne (in units of cm-3) of
logne=10.1+/-0.2 at the base of the plume.

---------------------------------------------------------
Title: Preflare Nonthermal Emission Observed in Microwaves and
Hard X-Rays
Authors: Asai, Ayumi; Nakajima, Hiroshi; Shimojo, Masumi; White,
Stephen M.; Hudson, Hugh S.; Lin, Robert P.
2006PASJ...58L...1A Altcode:
We present a detailed examination on nonthermal emissions during
the preflare phase of the X4.8 flare that occurred on 2002 July
23. The microwave (17GHz and 34GHz) data obtained with the Nobeyama
Radioheliograph at Nobeyama Solar Radio Observatory and the hard X-ray
data taken with the Reuven Ramaty High Energy Solar Spectroscopic Imager
obviously showed nonthermal features in the preflare phase. We also
found a faint ejection associated with the flare in the EUV images
taken with the Transition Region and Coronal Explorer. We discuss
the temporal and spatial features of the nonthermal emissions in the
preflare phase, and their relation with the ejection.

---------------------------------------------------------
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.

---------------------------------------------------------
Title: Preflare Nonthermal Emission Observed in Microwaves and
Hard X-Rays
Authors: Asau, A.; Nakajima, H.; Shimojo, M.; White, S. M.; Hudson,
H. S.
2006apri.meet...46A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Preflare Features in Microwaves and in Hard X-Rays
Authors: Asai, Ayumi; Nakajima, Hiroshi; Shimojo, Masumi; White,
Stephen M.
2006aogs....2...33A Altcode:
We present a detailed examination on the nonthermal emissions during
the pre-flare phase of the X4.8 flare which occurred on July 23,
2002. The microwave (17 and 34 GHz) data obtained with Nobeyama
Radioheliograph (NoRH), at Nobeyama Solar Radio Observatory, National
Astronomical Observatory of Japan, and the hard X-ray (HXR) data taken
with Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI)
distinctly showed nonthermal features. We examined the temporal,
spatial, and spectroscopic characteristics of the emission sources,
and found loop-top sources during the preflare phase both in HXRs and
in microwaves. Moreover, we found that the electron spectral index
derived from microwave emission closely corresponds to that obtained
from the HXR emission. We also discuss the energy release mechanism
in the preflare phase.

---------------------------------------------------------
Title: Low-Frequency Solar Radio Bursts from Green Bank
Authors: White, S. M.; Bastian, T. S.; Bradley, R.; Parashare, C.;
Wye, L.
2005ASPC..345..176W Altcode:
A low-frequency spectrometer for the study of solar radio bursts is
under development at Green Bank. Since January 2004 an 18-70 MHz system
has been operating daily. The system is described and examples of data
from the low-frequency system are shown..

---------------------------------------------------------
Title: Instrument Development for the Green Bank Solar Radio Burst
Spectrometer (GB/SRBS)
Authors: Bradley, R.; Parashare, C.; White, S. M.; Bastian, T. S.
2005ASPC..345..357B Altcode:
Details of two on-going technical development projects for the Green
Bank Solar Radio Burst Spectrometer (GB/SRBS) are presented. One is
a high dynamic range active balun covering 20-350 MHz. The other is
a log periodic array feed for the Green Bank 45-Foot radio telescope
covering 300-3000 MHz. Basic design, fabrication, and evaluation
information are included for both projects.

---------------------------------------------------------
Title: Radio Measurements of Coronal Magnetic Fields
Authors: White, S. M.
2005ESASP.596E..10W Altcode: 2005ccmf.confE..10W
No abstract at ADS

---------------------------------------------------------
Title: Multiwavelength Analysis of a Solar Flare on 2002 April 15
Authors: Sui, Linhui; Holman, Gordon D.; White, Stephen M.; Zhang, Jie
2005ApJ...633.1175S Altcode:
We carried out a multiwavelength analysis of the solar limb flare on
2002 April 15. The observations all indicate that the flare occurred in
an active region with an asymmetric dipole magnetic configuration. The
earlier conclusion that magnetic reconnection is occurring in a
large-scale current sheet in this flare is further supported by these
observations: (1) Several bloblike sources, seen in RHESSI 12-25 keV
X-ray images later in the flare, appeared along a line above the flare
loops. These indicate the continued presence of the current sheet and
are likely to be magnetic islands in the stretched sheet produced
by the tearing-mode instability. (2) A cusplike structure is seen
in Nobeyama Radioheliograph (NoRH) 34 GHz microwave images around
the time of the peak flare emission. We quantitatively demonstrate
that the X-ray-emitting thermal plasma seen with RHESSI had a higher
temperature than the microwave-emitting plasma seen with NoRH. Since
the radio data preferentially see cooler thermal plasma, this result
is consistent with the picture in which energy release occurs at
progressively greater heights and the hard X-rays see hot new loops
while the radio sees older cooling loops. The kinetic energy of the
coronal mass ejection (CME) associated with this flare was found to be
about 1 order of magnitude less than both the thermal energy in the hot
plasma and the nonthermal energy carried by the accelerated electrons
in the flare, as deduced from the RHESSI observations. This contrasts
with the higher CME kinetic energies typically deduced for large flares.

---------------------------------------------------------
Title: The Radio Cycle of Eta Carinae
Authors: White, S. M.; Duncan, R. A.; Chapman, J. M.; Koribalski, B.
2005ASPC..332..126W Altcode: 2005ASPC..332..129W
We briefly summarize recent radio observations of the η Car cycle,
including the surprising failure to detect a velocity shift from binary
motion in the system.

---------------------------------------------------------
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.

---------------------------------------------------------
Title: Antenna Configurations for the FASR B Array
Authors: Tun, S. D.; Gary, D.; White, S. M.
2005AGUSMSP43A..09T Altcode:
The proposed Frequency-Agile Solar Radiotelescope (FASR) is to
produce high space, time, and frequency resolution full disk solar
images. These will allow the reconstructions of the 3-D structure
of the Sun's atmosphere from chromosphere to mid-corona. The
high resolutions are required to carry out detailed diagnostics
of fast-moving phenomena, such as flares and CMEs, as well as of
quasi-static structures above active and quiet regions. The full disk
images will capture all activity in the corona, even when there are
many active regions at solar maximum. One of the tasks necessary to
ensure optimal imaging for the array is to determine the best antenna
configuration. The current poster presents work done towards this
goal. We focus on the FASR-B array, which will cover the 200-3000 MHz
range with 60 to 90 antennas of 6-m diameter. We have examined the
imaging characteristics for a 3 arm, log-spiral configuration with
radius of about 3 km. Multi-frequency observations are simulated for
arrays varying in initial antenna spacing, number of antenna elements,
and number of turns for each arm. The images reconstructed from the
simulated snapshot observations are compared to the original model,
convolved with the appropriate beam, to see which configuration yields
the most faithful images. We discuss the implications of the findings
for the planning of the FASR array configurations.

---------------------------------------------------------
Title: Millimeter-Interferometer Observations of Oscillations in
the Solar Chromosphere
Authors: White, S. M.; Loukitcheva, M.; Solanki, S. K.
2005AGUSMSH12A..03W Altcode:
The use of millimeter-interferometer data for the study of chromospheric
structure and dynamics is tested using 85 GHz observations with the
10-element Berkeley-Illinois-Maryland Array (BIMA). Interferometer
data have the advantage over single-dish data that they allow both high
spatial resolution and dense temporal sampling simultaneously. However,
snapshot imaging of the quiet solar atmosphere with a small number of
dishes is challenging. We demonstrate that techniques are available to
carry out this task successfully. We compare observations of quiet Sun,
active region and coronal hole targets using images with 10 arcsec
resolution at 15 second cadence. The brightest features in the images
are typically 1500 K above the background level, with a snapshot noise
level of order 100 K. We use extensive tests to determine whether
oscillation power can be recovered from sequences of snapshot images
and show that they can down to quite weak levels. Intensity oscillations
with significant power in the frequency range 1.5-8.0 mHz are found in
the quiet-Sun and active region targets. For the quiet-Sun region we
use the spatially-resolved time series to investigate the properties
of network boundaries and cell interiors (internetwork) separately. In
agreement with investigations at other wavelengths, the millimeter
data show that power in the network tends to be at periods of 5 minutes
and longer while power in the internetwork is present also at shorter
(3-minute) periods.

---------------------------------------------------------
Title: Imaging Type IIIdm Burst Trajectories
Authors: Liu, Z.; Gary, D. E.; Nita, G. M.; White, S. M.; Hurford,
G. J.
2005AGUSMSP21B..06L Altcode:
Type IIIdm radio bursts are important diagnostics of the upward and
downward directed beams of nonthermal electrons that originate in the
energy release site. Because these bursts have a very high frequency
drift rate ( |df/dt|=(0.09±0.03)× f1.35±0.10, Melendez et al.,
1999), high time and frequency resolution is a necessary for their
observation. Since existing interferometers do not have this combination
of spectral and time resolution in the decimetric range, we still do
not have detailed information about the location and trajectory of
Type IIIdm bursts. We are developing the new FASR Subsystem Testbed
(FST) with three existing antennas of Owens Valley Solar Array (OVSA)
that will permit imaging with high time and spectral resolution
over the 1-9 GHz band. To accomplish this, the received signal is
downconverted to 500 MHz bandwidth, then digitized with 1 GHz sampling
rate, with digital correlation performed offline. With this three
element interferometer, we have the ability to determine the centroid
of simple source structures with very high time resolution (10 ms)
and frequency resolution (&lt;1 MHz). Such centroids as a function of
frequency may outline the trajectories of nonthermal electron beams
and so may show the magnetic topology at the energy release site. The
FST is expected to be operational in early 2006. This poster presents
the FST system configuration and the results of simulations of such
trajectories, using a loop model with a simple magnetic geometry,
density and temperature profiles given by hydrostatic equilibrium,
for different loop heating functions (Aschwanden 2004, Physics of The
Solar Corona, Chapter 3).

---------------------------------------------------------
Title: Updated Expressions for Determining Temperatures and Emission
Measures from Goes Soft X-Ray Measurements
Authors: White, Stephen M.; Thomas, Roger J.; Schwartz, Richard A.
2005SoPh..227..231W Altcode:
{We investigate the conversion of the 0.5-4 and 1-8 Å soft X-ray
flux measurements made by detectors on the Geostationary Operational
Environmental Satellites (GOES) into temperature and emission measures
of coronal plasma using modern spectral models and modern understanding
of coronal abundances. In particular, the original analysis by
Thomas, Starr and Crannell (1985) is updated to take into account
the realization that coronal abundances may be quite different from
photospheric abundances. An important result of this analysis is that
the derived temperatures and emission measures depend strongly on the
assumed abundances even at high temperatures where continuum rather than
spectral lines dominates the Sun's X-ray spectrum. This occurs because
the higher coronal abundances mean that most of the continuum is due
to free-bound emission processes, not free-free emission, and thus is
abundance-dependent. We find significant differences between modern
calculations of the temperature response of the flux measurements
and the versions currently in use: for a typical flare, emission
measures may be up to a factor of 4 smaller than the current software
suggests. Derived temperatures are similar for both photospheric and
coronal abundances for cool flares (e.g., 15 MK), but for hot flares
(e.g., 35 MK) coronal abundances can lead to significantly (~25%)
lower temperatures being derived.

---------------------------------------------------------
Title: Molecular Line Observations of IRAM 04191+1522
Authors: Lee, Chin-Fei; Ho, Paul T. P.; White, Stephen M.
2005ApJ...619..948L Altcode:
We have mapped the CO, HCO+, CS, and
N2H+ emission around a low-luminosity Class
0 source IRAM 04191+1522 in the Taurus molecular cloud using the
Berkeley-Illinois-Maryland Association array. A bipolar molecular
outflow is seen in CO, HCO+, and CS emission originating
from around the IRAM source, while a flattened envelope is seen in
N2H+ emission surrounding the waist of the
molecular outflow around the IRAM source. Outflow, rotation, and
probably infall are seen around the Class 0 source, indicating a
complicated context for star formation in the earliest stages. The
N2H+ envelope is a thick clumpy torus with a
tenuous outer part and a ringlike dense inner edge. The dense inner
edge has a mean radius of 10", or 1400 AU. The outer part of the torus
exhibits differential rotation, and the infalling material appears to
carry angular momentum inward toward the central source. The region
surrounded by the inner edge of the torus may have a solid-body
rotation. The envelope may result from the collapse of a rotating,
magnetized toroid toward the central source. Outflow motion is seen
in the outer part of the inner edge of the torus, probably due to an
interaction with the molecular outflow. Two armlike structures are
seen extending out from the inner edge in the torus. One of them is
clearly seen with the velocity increasing roughly linearly with the
distance. The HCO+ emission around the source may trace the
central core around the source, showing a velocity structure connecting
to that of the outer part of the torus. The molecular outflow is
best seen in CO. It is bipolar with both a southwest and a northeast
lobe. Two internal structures are seen along the main outflow axis
within the lobes: (1) a strong CO emission at ~20" to the northeast
of the IRAM source, likely tracing an internal bow shock driven by a
collimated, episodic jet and (2) a linear HCO+ structure
of ~50" length at low blueshifted velocity to the southwest of the
IRAM source, requiring some interaction with a jet to be produced. In
addition, a dense condensation is also seen in HCO+ and CS
to the south of the IRAM source, likely representing a recent strong
outflow interaction.

---------------------------------------------------------
Title: High-Cadence Radio Observations of an EIT Wave
Authors: White, S. M.; Thompson, B. J.
2005ApJ...620L..63W Altcode:
Sensitive radio observations of the 1997 September 24 EIT wave show
its velocity to be 830 km s-1. The wave first appears a
short distance from the flare site, and its trajectory projects back to
the flare site at the peak of the impulsive phase. The radio spectrum
appears to be consistent with optically thin coronal emission rather
than chromospheric emission. The observed radio brightness temperatures
are consistent with the EIT fluxes if the temperature of the emitting
gas is not at the peak formation temperature of the Fe XII 195 Å line
or if abundances are closer to photospheric than coronal. An important
result is that no deceleration is observed during the 4 minutes that the
wave is visible in the radio images: the discrepancy between EIT wave
and Hα Moreton wave speeds requires that EIT waves slow substantially
as they propagate, if they are the same disturbance.

---------------------------------------------------------
Title: The solar stellar connection
Authors: White, S. M.
2004NewAR..48.1319W Altcode: 2004astro.ph..9157W
Stars have proven to be surprisingly prolific radio sources and the
added sensitivity of the Square Kilometer Array will lead to advances
in many directions. This chapter discusses prospects for studying the
physics of stellar atmospheres and stellar winds across the HR diagram.

---------------------------------------------------------
Title: Coronal Magnetic Field Measurements Through Gyroresonance
Emission
Authors: White, Stephen M.
2004ASSL..314...89W Altcode:
This article reviews the use of gyroresonance emission at radio
wavelengths to measure coronal magnetic fields. The spiralling motion
of electrons in the 200-2000 G fields in the solar corona produces
sufficient opacity to render the corona optically thick, making it
easy to recognize such sources in microwave images from their coronal
brightness temperatures. Where gyroresonance sources are present they
may be used as sensitive probes of the magnetic field strength above
active regions, and this unique capability is one of the strengths
of radio observations. Typically a gyroresonance radio source shows
the temperature on an optically thick surface of constant magnetic
field within the corona. Since each radio frequency corresponds to
a different magnetic field strength, the coronal structure can be
"peeled away" by using different frequencies.

---------------------------------------------------------
Title: FASR Simulation of Solar Flare Microwave Spectrum
Authors: Lee, J.; Gary, D. E.; White, S. M.
2004AAS...204.5414L Altcode: 2004BAAS...36..760L
We investigate microwave diagnostics on solar flare electrons at the
quality of imaging spectroscopy expected from the proposed Frequency
Agile Solar Radiotelescope (FASR). We mainly concern ourselves with
influence of the spatial inhomogeneities upon microwave spectral
features and realistic magnetic configurations of flare active
regions. Solar flare microwave radiations are calculated by using
nonthermal electrons distributed along a set of reconnected field
lines, and by sampling the resulting gyrosynchrotron intensities
at the resolution of the FASR. The simulated observations are then
compared with reference spectra of homogeneous source models to find
a strategy for inversion of the observed spectrum to the physical
parameters of flare electrons. This work is supported by the NSF
grant AST-0138317 and NASA grant NAG5-10891 to New Jersey Institute
of Technology.

---------------------------------------------------------
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.

---------------------------------------------------------
Title: Close Association of an Extreme-Ultraviolet Sunspot Plume
with Depressions in the Sunspot Radio Emission
Authors: Brosius, Jeffrey W.; White, Stephen M.
2004ApJ...601..546B Altcode:
We obtained coordinated observations of the large sunspot in NOAA
Region 8539 on 1999 May 9 and 13 with the Very Large Array and
three instruments (CDS, EIT, MDI) aboard the Solar and Heliospheric
Observatory satellite. The EUV observations reveal a plume in the
sunspot umbra on both observing dates. The plume appears brightest
in emission lines formed at temperatures between 1.6×105
and 5.0×105 K. Radio emission from the sunspot umbra is
dominated by thermal gyroemission from the plume, which accounts for
radio brightness temperatures &lt;1×106 K in the umbra on
both dates, as well as umbral brightness temperature depressions in the
4.535 and 8.065 GHz observations on May 13. A compact 14.665 GHz source
persists near the umbra/penumbra boundary during our observing period,
indicating a long-lived, compact flux tube with coronal magnetic field
strength of at least 1748 G. It occurs in a portion of the sunspot
that appears very dark in EUV emission.

---------------------------------------------------------
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: Coronal Magnetic Fields in a Sunspot Plume at the Limb
Authors: Brosius, J. W.; White, S. M.
2003AGUFMSH42B0507B Altcode:
We obtained coordinated EUV and radio observations of NOAA Active
Region 10139 on 2002 October 14 when the region was on the west limb
of the Sun. Observations were obtained with the Very Large Array (VLA)
and three instruments aboard the Solar and Heliospheric Observatory
(SOHO) satellite, including the Coronal Diagnostic Spectrometer (CDS),
the Extreme-ultraviolet Imaging Telescope (EIT), and the Michelson
Doppler Imager (MDI). A sunspot plume is clearly seen in EUV emission
lines formed at temperatures between about 0.2 and 0.5 MK. Polarized
8 GHz radio emission from the plume suggests 4th harmonic gyroemission
(from 760 Gauss fields) above the limb, and 3rd harmonic gyroemission
(from 960 Gauss fields) on the disk.

---------------------------------------------------------
Title: Coronal Magnetic Diagnostics With FASR
Authors: White, S. M.; Gary, D. E.; Lee, J.; Giordano, G.
2003AGUFMSH42D..04W Altcode:
Coronal magnetography is one of the main scientific drivers for the
proposed Frequency Agile Solar Radiotelescope (FASR). Radio emission
is particularly valuable as a diagnostic of coronal magnetic fields
because (a) the emission mechanisms all depend on magnetic field,
and (b) typical values of the electron gyroresonance frequency f_B
for coronal field strengths lie in the radio domain. The microwave
emission from active regions is dominated by thermal gyroresonance
emission at low harmonics of f_B and this provides a well-understood
diagnostic. Since f_B is proportional to magnetic field strength,
there is a simple mapping between frequency and magnetic field. A
wide range of coronal magnetic field strengths can be sampled by
observing across a wide range of radio frequencies simultaneously,
and FASR is designed to do this quickly enough to follow changes in
coronal fields. We demonstrate the ability to measure coronal fields
with this technique by simulating a FASR observation of a realistic
three-dimensional model of an active region and then determining the
coronal magnetic field at the base of the corona from the simulated
images. Comparison with radio images of gyroresonance emission from
active regions is also a valuable tool for assessing extrapolations
of surface magnetic field measurements into the corona, and we discuss
several applications of this comparison. Gyrosynchrotron radio emission
from nonthermal electrons accelerated by solar flares also can reveal
the magnetic topology of the flare source and we discuss this briefly.

---------------------------------------------------------
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: Radio and RHESSI X-ray Studies of Solar Flares
Authors: White, S. M.
2003SPD....34.1403W Altcode: 2003BAAS...35..829W
Correlative studies of particle acceleration in solar flares using
radio data and RHESSI hard X-ray data will be discussed. In particular,
the big flares of 2002 (April 21 and July 23) will be reviewed. The
July 23 flare is notable as the first event in which we can compare
radio images of nonthermal gyrosynchrotron-emitting electrons with hard
X-ray images at photon energies above 100 keV. Quantitatively this event
indicates that the same nonthermal electron population is responsible
for both the radio and hard X-ray emission. However, both the radio
and hard X-ray data imply extreme number densities for the nonthermal
electrons: over 1010 cm-3 at energies above 20
keV. The April 21 flare is a much more extended event, and features
a peculiar nonthermal radio source in the later stages of the event.

---------------------------------------------------------
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: The Frequency Agile Solar Radiotelescope (FASR)
Authors: White, S. M.; Gary, D. E.; Bastian, T. S.; Hurford, G. J.;
Lanzerotti, L. J.
2003EAEJA....11021W Altcode:
The Frequency Agile Solar Radiotelescope (FASR) is a radio
interferometer designed to make high spatial resolution images of the
Sun across a broad range of radio wavelengths simultaneously, allowing
the technique of imaging spectroscopy to be exploited on a routine
basis. The telescope will cover the frequency range 0.1-30 GHz using
several sets of receiving elements that provide full-disk imaging,
with of order 100 antennas at highest frequency range. FASR will be
optimized for solar radio phenomena and will be the most powerful
and versatile radioheliograph ever built, providing an improvement of
orders of magnitude in image quality over existing instruments. FASR
recently received the top ranking amongst all small projects considered
by the decadal survey of the National Academy of Science Committee on
Solar and Space Physics. FASR will probe all phenomena in the solar
atmosphere from the mid-chromosphere outwards. In particular, FASR
will provide direct measurement of coronal magnetic field strengths,
will image the nonthermal solar atmosphere and show directly the
locations of electrons accelerated by solar flares, will provide
images of coronal mass ejections travelling outwwards through the
solar corona, and supply extensive data products for forecasting and
synoptic studies. A major emphasis in the project is to make FASR data
as widely and easily used as possible, i.e., providing the general
user with processed, fully-calibrated high-quality images that do not
need particular knowledge of radio astronomy for interpretation. This
paper will describe the telescope and its science goals, and summarize
its current status.

---------------------------------------------------------
Title: Radio evidence of recent mass ejection from η Carinae
Authors: Duncan, R. A.; White, S. M.
2003MNRAS.338..425D Altcode:
The luminous blue variable η Carinae is almost certainly a double star:
a hot secondary in an eccentric orbit around a massive primary. Radio
observations with the Australia Telescope Compact Array at a wavelength
of 3 cm, covering the period from 1992 to 2002, suggest that at the
time of last periastron, 1998.0, material was tidally lifted from the
primary star into its equatorial disc.

---------------------------------------------------------
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: Recent X-ray Variability of Eta Car Approaching The X-ray
Eclipse
Authors: Corcoran, M.; Swank, J. H.; Ishibashi, K.; Gull, T.;
Humphreys, R.; Damineli, A.; Walborn, N.; Hillier, D. J.; Davidson,
K.; White, S. M.; Petre, R.; Pittard, J.; Butt, Y.; Verner, K.
2002AAS...201.4901C Altcode: 2002BAAS...34.1184C
We discuss recent X-ray spectral variability of the supermassive
star Eta Car in the interval since the last X-ray eclipse in 1998. We
concentrate on the interval just prior to the next X-ray eclipse which
is expected to occur in June 2003. We compare the X-ray behavior
during the 2001-2003 cycle with the previous cycle (1996-1998) and
note similarities and differences in the temporal X-ray behavior. We
also compare a recent X-ray observation of Eta Car obtained with
the Chandra high energy transmission grating in October 2002 with an
earlier observation from Nov 2002, and interpret these results in terms
of the proposed colliding wind binary model for the star. In addition
we discuss planned observations for the upcoming X-ray eclipse.

---------------------------------------------------------
Title: The Solar Atmosphere at Radio Wavelengths
Authors: White, S. M.
2002ASPC..277..299W Altcode: 2002sccx.conf..299W
No abstract at ADS

---------------------------------------------------------
Title: Investigating the HH 212 Molecular Outflow: the Jet- and
Wind-Driven Models
Authors: Chapman, N. L.; Mundy, L. G.; Lee, C. -F.; White, S. M.
2002AAS...201.2001C Altcode: 2002BAAS...34.1133C
Molecular outflows are a common stage in star formation and over
200 outflows have been discovered to date, but the fundamental
driving mechanism for outflows remains uncertain. The current leading
theories are the wide-angle wind-driven model (Shu et al. 1991) and
the jet-driven model (Raga &amp; Cabrit 1993; Masson &amp; Chernin
1993). Using the BIMA interferometer, we have made observations of the
HH 212 molecular outflow in several molecules (CO, HCO+,
SiO). This outflow was selected because of its high-degree of bipolar
symmetry, the numerous well- defined H2 bow shocks (Zinnecker
et al. 1998), and excellent morphological relationship of H2
to CO (Lee et al. 2000). Molecular shock physics describes how molecules
behave at different temperatures and velocities. Using this, it is
possible to describe the emission characteristics expected in both
wind- and jet-driven scenarios. We compare our observations with the
models to investigate the driving mechanism of molecular outflows. This
research was supported by NASA grant NAG 510611.

---------------------------------------------------------
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: New radio instrumentation for the study of sunspots and
starspots
Authors: White, S. M.
2002AN....323..265W Altcode:
Much of the radio emission from the Sun and similar stars depends
directly on magnetic fields for its origin. For this reason, radio
emission contains important diagnostic information on solar and
stellar magnetic fields. This paper reviews radio measurements of
coronal magnetic fields and discusses new radio instrumentation that
will exploit this technique.

---------------------------------------------------------
Title: Radio Observations of the Onset of an EIT Wave
Authors: White, S. M.; Thompson, B. J.
2002AAS...200.2904W Altcode: 2002BAAS...34R.681W
We present observations of the early development of an “EIT wave” made
with the Nobeyama Radio Heliograph at 17 GHz. EIT waves are propagating
disturbances generated in conjunction with solar flares. They have
most easily been seen to date as emission enhancements in full-disk
EUV images taken in spectral lines sensitive to 1-2 million degree
material. We demonstrate that they can also be seen in high dynamic
range radio observations as well. The high cadence of the radio data
allows us to show that the EIT wave is not visible until after the onset
of the impulsive phase of the flare. A radio movie of the event will
be shown. We discuss the implications of this result for the nature
of EIT waves and their relationship with other phenomena such as CMEs.

---------------------------------------------------------
Title: Measuring Coronal Magnetic Fields
Authors: White, S. M.
2002AAS...200.4903W Altcode: 2002BAAS...34..721W
Coronal magnetic fields are implicated in most active phenomena in
the Sun's corona but their measurement is a difficult problem. While
a selection of coronal magnetic field lines can be seen in soft
X-ray and EUV images, they contain no information on magnetic field
strength. Magnetic field measurements in the lower solar atmosphere are
a priority for the Solar-B and Solar Dynamics Observatory missions,
but they will not measure coronal magnetic fields directly, relying
instead on extrapolations of surface field measurements. On the other
hand, radio measurements can determine the magnetic field strength
in the corona, including regions seen against the solar disk, in a
straightforward fashion at least for field strengths larger than a
few hundred gauss. This talk will discuss progress in the established
technique of measuring active region magnetic fields through their
gyroresonance emission at centimeter wavelengths and prospects
for vastly improved measurements with the Frequency Agile Solar
Radiotelescope. Such measurements can be valuable for establishing
the validity of extrapolations and, e.g., resolving the 180 degree
ambiguity of vector magnetic field measurements, in addition to their
direct diagnostic power. The basis of the method and examples of its
application will be discussed, and comparison with other approaches
will be made. This work is supported by the NSF and NASA.

---------------------------------------------------------
Title: New Measurements of 3-D Sunspot Coronal Magnetic Fields From
Coordinated SOHO EUV and VLA Radio Observations
Authors: Brosius, J. W.; White, S. M.; Landi, E.; Cook, J. W.; Newmark,
J. S.; Gopalswamy, N.; Lara, A.
2002AAS...200.0307B Altcode: 2002BAAS...34..642B
Three-dimensional sunspot coronal magnetograms were derived from
coordinated extreme-ultraviolet (EUV) and radio observations of NOAA
regions 8108 (N21E18 on 1997 November 18) and 8539 (N20W12 on 1999 May
13). The EUV spectra and images, obtained with the Coronal Diagnostic
Spectrometer (CDS) and the Extreme-ultraviolet Imaging Telescope (EIT)
aboard the Solar and Heliospheric Observatory (SOHO) satellite, were
used to derive the differential emission measure (DEM) and the plasma
electron density for each spatial pixel (along each line of sight)
within both regions. These were subsequently used to calculate maps
of the expected thermal bremsstrahlung brightness temperature at the
Very Large Array (VLA) radio observing frequencies of 1.4, 4.9, 8.4,
and 15 GHz. The thermal bremsstrahlung maps reproduce neither the
structure nor the intensity of the observed maps, and indicate that
thermal gyroemission must dominate the observed radio emission. The
radio observations were used to constrain the magnetic scale height and
the gross temperature structure of the atmosphere. These, along with
the DEM, electron density, and observed radio brightness temperature
maps, were used to derive the temperature distribution of the coronal
magnetic field strength B(T) that reproduced simultaneously the observed
right-hand and left-hand circularly polarized emission at the radio
observing frequencies for each spatial pixel in the images. Magnetic
field strengths corresponding to 3rd harmonic gyroemission at 4.9 GHz
(580 Gauss) are found in coronal plasmas at temperatures as high as
3.2 MK, while magnetic field strengths corresponding to 3rd harmonic
gyroemission at 15 GHz (1800 Gauss) are found in coronal plasmas at
temperatures as high as 1.6 MK. B(T) was ultimately converted to B(h)
and compared with extrapolations from photospheric magnetograms.

---------------------------------------------------------
Title: Radio images of four luminous blue variable stars
Authors: Duncan, R. A.; White, S. M.
2002MNRAS.330...63D Altcode:
We have used the Australia Telescope Compact Array to image four
southern luminous blue variable stars: AG Car, He3-519, HR Car and
WRA 751, at wavelengths of 3 and 6cm, and resolutions of 1 and 2arcsec
respectively. With the partial exception of HR Car, all radio images
show an unresolved stellar core surrounded by a large ionized gaseous
nebula, and agree well with published Hα and [Nii] optical images. The
image of WRA 751 shows a stellar torus or disc. HR Car's radio image
is unusual, and seems best explained by the presence of a hot binary
companion.

---------------------------------------------------------
Title: Correlation effects in microwave observations of selected RS
CVn-like stars
Authors: Budding, E.; Lim, J.; Slee, O. B.; White, S. M.
2002NewA....7...35B Altcode:
Sets of dual frequency microwave data on selected chromospherically
active stars, from the Australia Telescope Compact Array, have been
investigated for their auto and cross-correlation effects. Comparison
of cross-correlation peak values with theoretical expectation indicates
a high degree of real physical connection between the emission at the
pairs of frequencies (4.8 and 8.64 GHz) compared. This fact should
help constrain models for the emission mechanism. The timescale of
observed time-shifts between the emissions at the two frequencies
is consistent, in general, with the underlying energization being
propagated by magnetohydrodynamic waves in a compact turbulent medium.

---------------------------------------------------------
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.

---------------------------------------------------------
Title: The Timing of Radio Emission in Flares and CMEs
Authors: White, S. M.
2001AGUFMSH31C..06W Altcode:
Radio observations are very sensitive to emission by electrons
accelerated in the solar corona. This talk will review evidence for
acceleration in flares and coronal mass ejections from the radio
perspective, focussing on the timing of radio emission in relation to
other high-energy phenomena. Amongst other topics, the relationship
of coronal type II radio bursts and coronal mass ejections will be
discussed in the light of Zhang et al's LASCO data, and recent results
on radio emission from CMEs by Bastian et al will be reviewed.

---------------------------------------------------------
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.

---------------------------------------------------------
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.

---------------------------------------------------------
Title: R Aquarii: Evidence for Differential Rotation of the SiO
Maser Shell
Authors: Hollis, J. M.; Boboltz, D. A.; Pedelty, J. A.; White, S. M.;
Forster, J. R.
2001ApJ...559L..37H Altcode:
We previously reported Very Large Array and Berkeley-Illinois-Maryland
Association (BIMA) array observations that suggested rotation of the
SiO maser shell surrounding the long-period variable (LPV) in the R
Aquarii binary system. In the present Very Long Baseline Array (VLBA)
work, we report high spatial and spectral resolution observations of
the v=1, J=1-0, SiO maser line that confirm our previous result and
further suggest that the LPV maser shell is undergoing differential
rotation. The 8-34 yr range of rotational periods resulting
from differential rotation of the maser shell contains the ~18
yr period reported previously. The velocity structure of the VLBA
data suggests a rotation symmetry axis oriented at a position angle
of ~150°. The differential rotation model can be envisioned as a
series of nested thin spherical shells that have a common rotation
axis; each thin shell is characterized by its radius, r, with the
innermost shell rotating fastest and the outermost shell slowest,
in accordance with an equatorial plane velocity law of the form
v~(1/rq)1/2. We find that q~1.09 is necessary to
approximate the VLBA data, suggesting that the differential rotation
is approximately Keplerian.

---------------------------------------------------------
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.

---------------------------------------------------------
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.

---------------------------------------------------------
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.

---------------------------------------------------------
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.

---------------------------------------------------------
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.

---------------------------------------------------------
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.

---------------------------------------------------------
Title: The Frequency-Agile Solar Radiotelescope (FASR) (invited)
Authors: Gary, D. E.; Bastian, T. S.; White, S. M.; Hurford, G. J.
2001aprs.conf..236G Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Observations of Solar Coronal Magnetic Fields
Authors: White, S. M.
2001ASPC..248...67W Altcode: 2001mfah.conf...67W
No abstract at ADS

---------------------------------------------------------
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

---------------------------------------------------------
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.

---------------------------------------------------------
Title: R Aquarii: Constraints on the Rotational Period of the
Long-Period Variable
Authors: Hollis, J. M.; Pedelty, J. A.; Forster, J. R.; White, S. M.;
Boboltz, D. A.; Alcolea, J.
2000ApJ...543L..81H Altcode:
We report Very Large Array (VLA) observations taken in 1996 November and
1998 May of the v=1, J=1-0, SiO maser line and BIMA array observations
taken in 1999 December and 2000 February of the v=1, J=2-1, SiO maser
line associated with the long-period variable (LPV) in the R Aquarii
binary system that suggest rotation of the maser shell. From these
interferometric data cubes, we determine that the maser shell rotation
axis is approximately northeast-southwest, thus aligning approximately
with the direction of the R Aqr jet; the sense of the maser shell
rotation is such that northwest is approaching and southeast is
receding; the period of rotation is ~17 yr. Alternatively, co-adding
72 time series spectra of the v=1, J=1-0, SiO maser line obtained
during the period 1984 July-1990 May with a single-dish antenna, we
constructed a composite spectral emission envelope that shows the LSR
velocity limits of maser emission over this epoch. From this composite
spectral emission envelope and Very Long Baseline Array observations
in 1996 February of the v=1, J=1-0, SiO maser line, which show the
maximal spatial extent of the maser shell, we obtain a shell rotation
period of ~18 yr, which is in excellent agreement with the VLA and
BIMA array results and represents the maximum rotation period of the
LPV if corotating with the maser shell. On the other hand, we obtain
a minimum rotation period for the LPV of ~5 yr if the LPV supplies
material to the maser shell under the constraint of conservation
of angular momentum. The ~5-18 yr range for the rotational period
of the LPV determined here and the ~18 yr rotational period for the
hot companion determined by previous investigators suggest that tidal
effects at successive periastron passages in the R Aqr binary system
are tending to synchronize these stellar rotational periods to the
orbital period of ~44 yr.

---------------------------------------------------------
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.

---------------------------------------------------------
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 Radio Nebula around HR Carinae
Authors: White, S. M.
2000ApJ...539..851W Altcode:
We present a sensitive radio image of the nebula associated with
the luminous blue variable star HR Carinae. This nebula is small and
difficult to observe optically because of the presence of the bright
star. The radio image shows the filaments in the outer regions of the
nebula as seen in optical coronagraphic images. The core of the nebula
is elongated north-south on the sky. A compact source associated with
HR Car is clearly detected at the western edge of the nebula, but
the nebula is very asymmetric with respect to the star, lying almost
entirely to the east. The inner nebula shows no evidence for the bipolar
structure inferred to exist from observations of the outer nebula:
the symmetry axes in the inner nebula are 45° away from the bipolar
axes. If the compact radio emission at the location of the star is a
classical stellar wind source, we estimate a mass-loss rate for ionized
gas of 1.8×10-5 Msolar yr-1. The
mass in the central core of the nebula is about 0.3 Msolar,
while the outer nebula may contain as much as 0.5 Msolar. We
believe that a colliding winds explanation of the nebula is unlikely;
a symbiotic-like explanation in which ionization of neutral ejecta is
provided by a hot companion star may be possible if the companion star
is on the far side of the nebula and heavily extincted, but it is not
clear whether the properties required of this star are compatible with
the fact that it is not detected in a 10 μm image. A B0 V companion
without much dust may be consistent with the data.

---------------------------------------------------------
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: 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: 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: The Contributions of the VLA to the Study of Radio Stars
Authors: White, Stephen M.
2000riss.conf...86W Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Ultracompact HII-region G45.07+0.13: An Ionized Bipolar
Outflow?
Authors: Lim, J.; White, S. M.
1999sf99.proc..306L Altcode:
We present continuum and hydrogen recombination line observations of
the ultracompact HII-region G45.07+0.13 at cm-wavelengths with the VLA,
as well as molecular line observations of the surrounding neutral gas
at 3 mm with the BIMA-array. We show that the bright inner region of
G45.07+0.13 has a bipolar structure, which is well aligned with and
has a velocity gradient in the same sense as the larger-scale bipolar
molecular outflow seen in 13CO. We discuss the possibility
that G45.07+0.13 is an ionized bipolar outflow. The bipolar structure
may reflect the preferential expansion of an ionized stellar wind or the
stellar UV ionization front along the less dense polar direction of the
surrounding molecular gas core, partially or nearly entirely evacuated
in this direction by the passage of a bipolar outflow. Alternatively,
the stellar UV may be lighting up a genuine, ongoing bipolar outflow.

---------------------------------------------------------
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: Millimeter Interferometer Observations of Flares
Authors: White, S. M.
1999spro.proc..223W Altcode:
This paper addresses the current state of millimeter interferometry
of solar flares and the issues which can be addressed by such
observations. Millimeter interferometers such as BIMA detect
gyrosynchrotron emission from MeV--energy electrons in the impulsive
phase of solar flares as well as from hot dense plasma in the thermal
decay phase. BIMA now consists of 10 antennas and is capable of snapshot
imaging of solar flares with excellent spatial resolution and dynamic
range of up to 100. The properties of MeV--energy electrons deduced
from such observations vary widely: in some flares they are present
for a much shorter time than the lower--energy hard--X--ray producing
electrons, while in other flares they are present longer. Examples of
both circumstances are given. It is widely observed that the energy
distribution determined from the optically--thin radio spectrum is
inconsistent with that determined from hard X--ray data: generally
this is interpreted to mean that the electron energy distribution
is flatter at higher energies, but even this interpretation can run
into difficulties. This discrepancy between radio and hard X--ray
spectral indices may be revealing something fundamental about electron
acceleration in solar flares.

---------------------------------------------------------
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 Versus EUV/X-Ray Observations of the Solar Atmosphere
Authors: White, S. M.
1999SoPh..190..309W Altcode:
This paper reviews the contrasting properties of radio and EUV/X-ray
observations for the study of the solar atmosphere. The emphasis
is placed on explaining the nature of radio observations to an
EUV/X-ray audience. Radio emission is produced by mechanisms which are
well-understood within classical physics. Bremsstrahlung tends to be
dominant at low frequencies, while gyro-resonance emission from strong
magnetic fields produces bright sources at higher frequencies. At
most radio frequencies the images of the Sun are dominated almost
everywhere by bremsstrahlung opacity, which may be optically thick
or thin depending on circumstances. Where gyro-resonance sources
are present they may be used as sensitive probes of the regions
above active regions where magnetic field strengths exceed several
hundred gauss, and this unique capability is one of the strengths of
radio observations. Typically a gyro-resonance radio source shows
the temperature on an optically thick surface of constant magnetic
field within the corona. Since each radio frequency corresponds to
a different magnetic field strength, the coronal structure can be
`peeled away' by using different frequencies. The peculiarities of
radio observing techniques are discussed and contrasted with EUV/X-ray
techniques. Radio observations are strong at determining temperatures
and coronal magnetic field strengths while EUV/X-ray observations
better sense densities and reveal coronal magnetic field lines: in
this way the two wavelength domains are nicely complementary.

---------------------------------------------------------
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: 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: FASR - A Frequency-Agile Solar Radiotelescope
Authors: Hurford, G. J.; Gary, D. E.; Bastian, T. S.; White, S. M.
1999AAS...194.7603H Altcode: 1999BAAS...31..956H
The Frequency-Agile Solar Radiotelescope (FASR) is a multi-frequency
imaging array designed specifically for imaging spectroscopy of the
Sun. Using &lt; 100 antennas, it will combine high-quality/high spatial
resolution imaging (1" resolution at 20 GHz) with spectroscopy (dnu
/nu 0.01-0.03) and high time resolution (&lt;1 s) across two decades in
frequency from 0.3-30 GHz. In so doing, it will produce a continuous,
dynamic, three-dimensional picture of the solar atmosphere from the
chromosphere through the mid-corona. These capabilities represent a
quantum leap beyond existing solar radio instruments, yet are well
within reach of emerging technologies. The range of science that
can be addressed by such an instrument is as broad as solar physics
itself. Virtually every solar feature from within a few hundred km
of the visible surface of the Sun to high in the solar corona can be
studied in detail with the unique diagnostics available in the radio
regime. Particular diagnostics include measuring the properties of
both thermal and nonthermal electrons accelerated in solar flares
from the largest events to the tiniest microflares/nanoflares,
measuring coronal magnetic field strengths in active regions and
elsewhere (coronal magnetography), and mapping kinetic electron
temperatures throughout the chromosphere and corona. In addition,
FASR's far-reaching exploration of the Sun in the radio regime gives
the instrument tremendous potential for new discoveries beyond those
that we can now anticipate. FASR is expected to be one of the major
new ground-based solar instruments of the next decade, and can be
operational by 2006, well before the decade is out. It will play a
major role in supporting NASA space missions with the unique diagnostics
and perspective provided by high-resolution radio imaging/spectroscopy.

---------------------------------------------------------
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: 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: Continuum and Spectral Observations of η Carinae at
Wavelengths of 3 &amp; 6 Centimeters
Authors: Duncan, R. A.; White, S. M.; Reynolds, J. E.; Lim, J.
1999ASPC..179...54D Altcode: 1999ecm..conf...54D
No abstract at ADS

---------------------------------------------------------
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: Images of Gradual Millimeter Emission and Multi-Wavelength
Observations of the 17 august 1994 Solar Flare
Authors: Silva, Adriana V. R.; Lin, R. P.; de Pater, Imke; White,
Stephen M.; Shibasaki, K.; Nakajima, H.
1998SoPh..183..389S Altcode:
We present a comprehensive analysis of the 17 August 1994 flare,
the first flare imaged at millimeter (86 GHz) wavelengths. The
temporal evolution of this flare displays a prominent impulsive peak
shortly after 01:02 UT, observed in hard X-rays and at microwave
frequencies, followed by a gradual decay phase. The gradual phase was
also detected at 86 GHz. Soft X-ray images show a compact emitting
region (≲20”), which is resolved into two sources: a footpoint and
a loop top source. Nonthermal emissions at microwave and hard X-ray
wavelengths are analyzed and the accelerated electron spectrum is
calculated. This energy spectrum derived from the microwave and hard
X-ray observations suggests that these emissions were created by the
same electron population. The millimeter emission during the gradual
phase is thermal bremsstrahlung originating mostly from the top of
the flaring loop. The soft X-rays and the millimeter flux density
from the footpoint source are only consistent with the presence of a
multi-temperature plasma at the footpoint.

---------------------------------------------------------
Title: The Composition of Centaur 5145 Pholus
Authors: Cruikshank, D. P.; Roush, T. L.; Bartholomew, M. J.; Geballe,
T. R.; Pendleton, Y. J.; White, S. M.; Bell, J. F.; Davies, J. K.;
Owen, T. C.; de Bergh, C.; Tholen, D. J.; Bernstein, M. P.; Brown,
R. H.; Tryka, K. A.; Dalle Ore, C. M.
1998Icar..135..389C Altcode:
We present a new spectrum of the Centaur object 5145 Pholus between
1.15 and 2.4 μm. We model this, and the previously published
(0.4- to 1.0-μm) spectrum, using Hapke scattering theory. Seen in
absorption are the 2.04-μm band of H2O ice and a strong
band at 2.27 μm, interpreted as frozen methanol and/or a photolytic
product of methanol having small molecular weight. The presence of
small molecules is indicative of a chemically primitive surface,
since heating and other processes remove the light hydrocarbons in
favor of macromolecular carbon of the kind found in carbonaceous
meteorites. The unusually red slope of Pholus' spectrum is matched
by fine grains of a refractory organic solid (tholin), as found
previously by M. Hoffmannet al. (1993,J. Geophys. Res.98, 7403-7407)
and P. D. Wilsonet al.(1994,Icarus107, 288-303). Olivine (which we
model with Fo 82) also appears to be present on Pholus. We present a
five-component model for the composite spectrum of all spectroscopic
and photometric data available for 5145 Pholus and conclude that this
is a primitive object which has not yet been substantially processed
by solar heat. The properties of Pholus are those of the nucleus of
a large comet that has never been active.

---------------------------------------------------------
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: Centaur 5145 Pholus As a Comet Nucleus
Authors: Cruikshank, D. P.; Roush, T. L.; Bartholomew, M. J.;
Pendleton, Y. J.; White, S. M.; Bernstein, M. P.; Dalle Ore, C. M.;
Khare, B. N.; Geballe, T. R.; Davies, J. K.; Owen, T. C.; Tholen,
D. J.; de Bergh, C.; Bell, J. F., III; Brown, R. H.; Tryka, K. A.
1998DPS....30.4201C Altcode: 1998BAAS...30.1094C
New spectra and models of the surface of Centaur 5145 Pholus suggest
that this object is the equivalent of a giant comet nucleus that is
not, and may have never been, active. We have used published spectra
and our own data, plus the radiometrically estimated diameter of
190 km, to compile the reflectance spectrum from 0.4 to 2.4 mu
m. The photovisual spectrum slopes steeply upward toward the red,
a characteristic matched by some refractory organic solids. The
spectrum shows two absorption bands of H2O ice (1.5
and 2.0 mu m), and a third clear absorption near 2.27 mu m, at the
position of two absorption bands in solid CH3OH and other
solid hydrocarbons (e.g., (CH2)6N4
= hexamethylenetetramine). We computed Hapke scattering models with
the ices of H2O and CH3OH (although we do not
claim a firm identification of CH3OH), plus the refractory
organic solid known as Titan tholin (B. N. Khare et al. 1984, Icarus
60, 127), plus amorphous carbon to adjust the albedo. An additional
component is required to fit the spectrum at 1-1.4 mu m; olivine (Fo
82) provides exactly the absorption needed. In this two-terrain model,
38.5 % of Pholus is covered with an intimate mixture of 55 % olivine
(grain size 20 mu m), 15 % Titan tholin (1 mu m), 15 % H2O
ice (10 mu m), and 15 % CH3OH ice (10 mu m); the second
terrain material, amorphous carbon, covers 61.5 % of the surface. The
spectrally active components in our model are the principal constituents
of a comet nucleus. We suggest that if Pholus were to approach the Sun
and begin sublimating, it would show the compositional characteristics
of a comet. This work is in Press in Icarus.

---------------------------------------------------------
Title: Broadband microwave imaging spectroscopy with a solar-dedicated
array
Authors: Bastian, Tim S.; Gary, D. E.; White, S. M.; Hurford, Gordon J.
1998SPIE.3357..609B Altcode:
For many years, ground-based radio observations of the Sun have
proceeded into two directions: (1) high resolution imaging at a few
discrete wavelengths; (2) spectroscopy with limited or no spatial
resolution at centimeter, decimeter, and meter wavelengths. Full
exploitation of the radio spectrum to measure coronal magnetic fields
in both quiescent active regions and flares, to probe the thermal
structure of the solar atmosphere, and to study energy release and
particle energization in transient events, requires a solar-dedicated,
frequency-agile solar radiotelescope, capable of high-time, - spatial,
and -spectral resolution imaging spectroscopy. In this paper we
summarize the science program and instrument requirements for such a
telescope, and present a strawman interferometric array composed of
many (greater than 40), small (2 m) antenna elements, each equipped
with a frequency- agile receiver operating over the range 1 - 26.5 GHz.

---------------------------------------------------------
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: 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: Large convection cells as the source of Betelgeuse's extended
atmosphere
Authors: Lim, Jeremy; Carilli, Chris L.; White, Stephen M.; Beasley,
Anthony J.; Marson, Ralph G.
1998Natur.392..575L Altcode:
Supergiant stars such as Betelgeuse have very extended atmospheres,
the properties of which are poorly understood. Alfvén waves, acoustic
waves,, and radial pulsations have all been suggested as likely
mechanisms for elevating these atmospheres and driving the massive
outflows of gas seen in these stars: such mechanisms would heat the
atmosphere from below, and there are indeed observations showing
that Betelgeuse's extended atmosphere is hotter than the underlying
photosphere,. Here we report radio observations of Betelgeuse that
reveal the temperature structure of the extended atmosphere from two to
seven times the photospheric radius. Close to the star, we find that
the atmosphere has an irregular structure, and a temperature (3,450
+/- 850K) consistent with the photospheric temperature but much lower
than that of gas in the same region probed by optical and ultraviolet
observations. This cooler gas decreases steadily in temperature with
radius, reaching 1,370 +/- 330K by seven stellar radii. The cool gas
coexists with the hot chromospheric gas, but must be much more abundant
as it dominates the radio emission. Our results suggest that a few
inhomogeneously distributed large convective cells (which are widely
believed to be present in such stars) are responsible for lifting the
cooler photospheric gas into the atmosphere; radiation pressure on dust
grains that condense from this gas may then drive Betelgeuse's outflow.

---------------------------------------------------------
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: Toward a Frequency-Agile Solar Radiotelescope
Authors: Bastian, T. S.; Gary, D. E.; White, S. M.; Hurford, G. J.
1998ASPC..140..563B Altcode: 1998ssp..conf..563B
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: 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: Flares on AB Doradus Observed with ASCA
Authors: Ortolani, A.; Pallavicini, R.; Maggio, A.; Reale, F.; White,
S. M.
1998ASPC..154.1532O Altcode: 1998csss...10.1532O
ASCA observations of the young rapidly rotating star AB
Doradus are analysed with special emphasis on its flaring
behaviour. Multitemperature model fits with either fixed or variable
abundances are used. The results for the quiescent emission are compared
with those obtained previously by Mewe et al. (1996) confirming the
very low coronal metallicity (nearly one tenth solar) of this star in
spite of its measured solar photospheric metallicity. The results for
the flares are compared with recent models based on full hydrodynamic
calculations (Reale et al. 1997) and realistic values for the loop
length and the heating duration are derived. It is shown that the
flare is essentially a high temperature phenomenon with little effect
on the low-temperature component of the quiescent star.

---------------------------------------------------------
Title: The Radio Outburst of Eta Carinae
Authors: White, S. M.; Duncan, R. A.; Lim, J.; Drake, S. A.
1997AAS...191.3404W Altcode: 1997BAAS...29.1261W
The massive star Eta Carinae has been undergoing a radio outburst since
1993 which has made it one of the brightest stellar radio sources in the
sky. The cause of the outburst is apparently ionization of previously
neutral gas within several arcseconds (several hundredths of a parsec)
of the star. The nature of the ionizing radiation is not known, but the
coincidence of the radio flux increase with the X-ray outburst reported
by Corcoran et al is clearly important. In this paper we report on
continued monitoring of the radio outburst as the star approaches the
shell phase of the 5.5-year cycle proposed by Damineli. At this stage
the radio flux behaviour appears to be consistent with the presence
of such a cycle.

---------------------------------------------------------
Title: The Measurement of Solar Active Region Properties with EUV
Spectra and Spectroheliograms from SERTS
Authors: Brosius, J. W.; Davila, J. M.; Thomas, R. J.; White, S. M.
1997AAS...191.7315B Altcode: 1997BAAS...29.1323B
The Goddard Space Flight Center's Solar EUV Rocket Telescope and
Spectrograph (SERTS) was successfully flown on six different occasions,
and results from several of those flights are presented here. For the
flight of 1995 May 15, SERTS included a multilayer coated toroidal
diffraction grating which enhanced the throughput above that of a
standard gold coated grating for wavelengths between about 170 and
220 Angstroms, with a peak response around 192 Angstroms. Emission
lines in this wavelength range are seen in second order. First order
lines between about 235 and 335 Angstroms are also detected. A total
of nearly 140 lines are identifiable in the combined first and second
order wavebands. These include lines from several ionization stages of
Ca, Mg, Ni, S, and Si, as well as lines from at least nine ionization
stages of Fe (IX -- XVII). Many of the lines are useful for calibration
verification, plasma diagnostics, or both. Results from analyses
of the high spectral resolution (30 m Angstroms in second order,
and 55 m Angstroms in first), spatially resolved (4.4 arcsec spatial
resolution) active region spectra are presented. For the flight of 1993
August 17, SERTS included a multilayer coated grating which enhanced
the instrumental sensitivity within the first order waveband. For
this flight we also obtained coordinated Very Large Array (VLA) radio
observations at 20 and 6 cm wavelengths. Because the radio emission is
sensitive to the coronal magnetic field while the EUV emission is not,
we were able to derive solar coronal magnetograms from the combined
SERTS and VLA observations. (This work was supported by NASA grants
NASW-96006 and NASW-4933.)

---------------------------------------------------------
Title: Evolution of the radio outburst from the supermassive star
eta Carinae from 1992 to 1996
Authors: Duncan, R. A.; White, S. M.; Lim, J.
1997MNRAS.290..680D Altcode:
An earlier paper, describing observations at a wavelength of 3 cm with
the Australia Telescope Compact Array between 1992 June and 1994 May,
showed the supermassive star eta Carinae to be in the throes of a major
outburst. This paper, based on observations at wavelengths of both 3
and 6 cm, describes the evolution of the outburst since 1994 May. From
1994 May to 1995 December, eta Carinae's image continued to expand, and
its total flux density to increase. These dramatic changes were caused,
we believe, by an outburst of UV luminosity, and consequent ionization
of pre-existing circumstellar gas clouds. Since 1995 December, eta
Carinae's total flux density has fallen. The large-scale structure of
the radio image closely resembles Hα optical images of the eta Carinae
`Homunculus' nebula. In addition, the central area shows fine-scale
structure, principally comprising a secondary source about 1.2 arcsec to
the north-west of the star, which we believe to be a dense gas cloud,
and a ridge of length 4 arcsec centred on the optical position of
the star, which we believe to be an equatorial disc or torus. These
structures are seen also in 3-cm (H91alpha) recombination-line emission.

---------------------------------------------------------
Title: Coronal Magnetography of a Solar Active Region Using
Coordinated SERTS and VLA Observations
Authors: Brosius, Jeffrey W.; Davila, Joseph M.; Thomas, Roger J.;
White, Stephen M.
1997ApJ...488..488B Altcode:
We observed NOAA region 7563 simultaneously with Goddard Space Flight
Center's Solar EUV Rocket Telescope and Spectrogaph (SERTS) and with
the Very Large Array (VLA) on 1993 August 17. SERTS obtained spectra
in the 280-420 Å wavelength range, and images in the lines of Mg IX
λ368.1, Fe XV λ284.1, and Fe XVI λ335.4. The VLA obtained microwave
images at 20 and 6 cm wavelengths. The microwave emission depends upon
the coronal temperature, density, column emission measure, and magnetic
field; therefore, the coronal magnetic field can be derived when all of
these other quantities are measured. Here we demonstrate this approach
by using the SERTS data to derive all the relevant plasma parameters and
then fitting the radio observations to a magnetic field model in order
to determine the magnetic field structure. We used the method of
Monsignori-Fossi &amp; Landini and the coronal elemental abundances of
Feldman et al. to derive the differential emission measure (DEM) curve
for region 7563 from numerous EUV emission lines in spatially averaged
SERTS spectra. A similar curve was estimated for each point (i.e.,
each pixel or each spatial location) in the two-dimensional region by
scaling the average DEM curve with corresponding pixel intensities
in the Mg IX, Fe XV, and Fe XVI images. We integrated each such DEM
over narrow temperature ranges to obtain the column emission measure
(CEM) as a function of temperature, CEM(T). We also obtained electron
density measurements from EUV line intensity ratios in the spatially
averaged spectrum for several ionization stages of iron. These were
used to derive a functional relation between density and temperature,
ne(T). We derived the temperature dependence of the
coronal magnetic field [B(T)] at each point in the two-dimensional
region by incorporating CEM(T) and ne(T) into expressions for
the thermal bremsstrahlung and the gyroresonance opacities, and varying
B(T) so as to minimize the difference between the calculated and the
observed microwave intensities. The resulting calculated 20 and 6 cm
microwave intensity images reproduce the observed images very well. We
found that thermal bremsstrahlung alone is not sufficient to produce
the observed microwave intensities: gyroemission is required. Further,
contrary to several earlier studies, we found no evidence for cool,
absorbing plasma in the solar corona above the active region. The
coronal magnetic fields derived with our method typically exceed the
coronal fields extrapolated with a simple potential model, suggesting
the presence of coronal electric currents. However, in the diminutive
sunspot which dominates the 6 cm emission this difference is relatively
small, suggesting that the sunspot magnetic field itself is nearly
potential. Although we cannot firmly establish the uniqueness of our
solution in this particular case, the method is quite powerful and
should be repeated with other similar data sets. Variations in the
coronal elemental abundances could affect the determination of the
microwave emission mechanism(s), introduce evidence for the presence
of cool coronal plasma, and alter the strengths of the derived coronal
magnetic fields.

---------------------------------------------------------
Title: First Images of Impulsive Millimeter Emission and Spectral
Analysis of the 1994 August 18 Solar Flare
Authors: Silva, Adriana V. R.; Gary, Dale E.; White, Stephen M.; Lin,
R. P.; de Pater, Imke
1997SoPh..175..157S Altcode:
We present here the first images of impulsive millimeter emission of
a flare. The flare on 1994 August 18 was simultaneously observed at
millimeter (86 GHz), microwave (1-18 GHz), and soft and hard X-ray
wavelengths. Images of millimeter, soft and hard X-ray emission show
the same compact ( 8”) source. Both the impulsive and the gradual
phases are studied in order to determine the emission mechanisms. During
the impulsive phase, the radio spectrum was obtained by combining the
millimeter with simultaneous microwave emission. Fitting the nonthermal
radio spectra as gyrosynchrotron radiation from a homogeneous source
model with constant magnetic field yields the physical properties
of the flaring source, that is, total number of electrons, power-law
index of the electron energy distribution, and the nonthermal source
size. These results are compared to those obtained from the hard X-ray
spectra. The energy distribution of the energetic electrons inferred
from the hard X-ray and radio spectra is found to follow a double
power-law with slope ∼6-8 below ∼50 keV and ∼3-4 above those
energies. The temporal evolution of the electron energy spectrum and its
implication for the acceleration mechanism are discussed. Comparison of
millimeter and soft X-ray emissions during the gradual phase implies
that the millimeter emission is free-free radiation from the same hot
soft X-ray emitting plasma, and further suggests that the flare source
contains multiple temperatures.

---------------------------------------------------------
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: High-Resolution Imagery of BD + 30degree3639 and Its Dusty Halo
Authors: Harrington, J. Patrick; Lame, Nancy Joanne; White, Stephen
M.; Borkowski, Kazimierz J.
1997AJ....113.2147H Altcode:
The planetary nebula BD +30\arcdeg3639 has been imaged by the Hubble
Space Telescope through nine narrow-band filters. A high resolution
radio map has been obtained with the VLA. Comparison of Hβ , Hα and
radio images allow us to derive the point-to-point variations in both
the extinction and the ratio of total to selective absorption. The
extinction shows (1) a gradient across the nebula, and (2) a large dust
clump in the northeast and many small ( ~ 0farcs2 ) dust features. The
ratio of total to selective absorption for this nebula is close to
the normal ISM value, and can be modeled by a power law distribution
of amorphous carbon grains. It is found that the optical images show a
substantial halo due to light scattered by dust in the neutral envelope
surrounding the ionized shell. Monte Carlo models indicate that such
scattering could result from a dust halo with an optical depth of unity
and an albedo of ~ 0.4. Such a high albedo is not consistent with pure
carbon dust models. The halo images in [O I]lambda 6300 and [S II]lambda
6717,31 show anomalous structures not seen in the other lines, which
seem to be in emission. The strongest [O I] feature is coincident with
halo emission previously observed in the 1-0 S(1) transition of H_2. The
[O I] and [S II] emission may indicate shock heating of the halo.

---------------------------------------------------------
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: 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: Sun
Authors: White, Stephen M.
1997msma.conf...19W Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Eclipsing Radio Emission of the Precataclysmic Binary
V471 Tau
Authors: Lim, J.; White, S. M.; Cully, S. L.
1997tcca.conf..370L Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Radio Outbursts from Eta Carinae
Authors: White, S. M.; Duncan, R. A.; Lim, J.; Drake, S. A.
1997ASPC..120..282W Altcode: 1997lbv..conf..282W
No abstract at ADS

---------------------------------------------------------
Title: Abundances and Flares in the ASCA Observation of the Young
k0 Star AB Doradus
Authors: White, S. M.; Pallavicini, R.; Mewe, R.; Kaastra, J. S.;
Lim, J.
1997xisc.conf..573W Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Simultaneous EUVE &amp; ASCA observations of AB Doradus:
temperature structure and abundances of the quiescent corona.
Authors: Mewe, R.; Kaastra, J. S.; White, S. M.; Pallavicini, R.
1996A&A...315..170M Altcode:
We have analyzed EUV and X-ray spectra of the non-flaring state of AB
Dor, obtained from simultaneous observations with EUVE and ASCA. The
coronal temperature structure and the coronal elemental abundances
have been derived by jointly fitting the spectra, including lines
and continuum. We have applied a multi-temperature fitting method
and we have found that an optically thin plasma model with solar
abundances (relative to hydrogen) does not yield a good fit. A 4-T
fit allowing the abundances of the more important elements (Fe, S,
Si, Mg, Ne, and O) plus four other less important abundances (N, Ar,
Ca, and Ni) to vary improves the fit markedly. This results in values
of the first 6 abundances relative to solar photospheric values that
are significantly (a factor 2-3) below solar except for Ne, which is
solar, while most of the remaining four abundances are consistent both
with solar and reduced abundances. In the course of the 4-T fitting
we have determined a best-fit value for the interstellar hydrogen
column density of N_H_=(2.0+/-0.5)10^18^cm^-2^. We have applied four
differential emission measure (DEM) distribution analysis techniques,
viz.: (i) regularization method, (ii) polynomial method, (iii) clean
algorithm, and (iv) genetic algorithm. The four different methods
all yield a qualitatively similar DEM, showing two maxima in the
temperature intervals 5-8MK and 20-30MK. Our analysis demonstrates the
great value of simultaneous ASCA and EUVE observations in determining
the fundamental parameters of stellar coronae.

---------------------------------------------------------
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: Limits to Mass Outflows from Late-Type Dwarf Stars
Authors: Lim, Jeremy; White, Stephen M.
1996ApJ...462L..91L Altcode:
We show that the mass-loss rates of active late-type dwarf stars
must be significantly lower than recent estimates of up to ~5 x 10-10
Msolar yr-1, 4 orders of magnitude higher than that of the Sun. First,
we present aperture-synthesis observations at 3.5 mm of the dMe flare
stars YZ CMi and AD Leo, during which neither star was detected at an
upper limit of 10 mJy. Although compatible with the tentative detection
of YZ CMi at 1.1 mm reported by Mullan and coworkers if the millimeter
emission originates from a ~104 K, 300 km s-1 wind with M dot ~ 5 x
10-10 Msolar yr-1, we show that such a wind would completely absorb the
observed radiation from coronal radio flares originating from close
to the stellar surface. From this contradiction, we show that the
mass-loss rate of any ~104 K wind with solar-wind--like velocities of
300--600 km s-1 must be less than ~10-13 Msolar yr-1, more than 3 orders
of magnitude below that inferred by Mullan et al. The corresponding
upper limit to a wind at a solar-wind--like temperature of ~106 K is M
dot ~ 10-12 Msolar yr-1, an order of magnitude below the lower limit
predicted theoretically by Badalyan &amp; Livshits. Our arguments
apply to all classes of stars that display coronal radio flares,
implying that the mass-loss rate of active late-type dwarf stars from
any ~104 or ~106 K winds with solar-wind--like velocities can be no
more than 1 or 2 orders of magnitude, respectively, higher than the
solar mass-loss rate of ~3 x 10-14 Msolar yr-1. We show that coronal
mass ejections also are unlikely to explain the reported millimeter
emission from dMe flare stars, and that the time-averaged mass-loss
rate from such events can be no higher than in the case of a steady,
spherically symmetric stellar wind.

---------------------------------------------------------
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: The Radio Properties of the dMe Flare Star Proxima Centauri
Authors: Lim, Jeremy; White, Stephen M.; Slee, O. B.
1996ApJ...460..976L Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Eclipsing Radio Emission of the Precataclysmic Binary
V471 Tauri
Authors: Lim, Jeremy; White, Stephen M.; Cully, Scott L.
1996ApJ...461.1009L Altcode:
We present strong evidence confirming the presence of eclipses in the
centimeter radio emission of the eclipsing binary V471 Tau, comprising
a K2 dwarf and a white dwarf. In observations spanning two complete
orbital periods, we detected one eclipse per orbit: in all, we observed
one near-complete radio eclipse, the ingress phase of two other radio
eclipses, and the egress phase of yet another radio eclipse. The minimum
of the observed near-complete radio eclipse is centered at the orbital
phase φ = 0 when the white dwarf is eclipsed and directly behind the
K dwarf, and it has a full width of Δφ ≍ 0.3; by comparison, the
optical eclipse of the white dwarf occupies only Δφ = 0.066. Inside
eclipse, the total flux density of V471 Tau falls to a level ∼20%
of that outside eclipse, implying that a large fraction of the radio
emission originates from the region between the two stars. Outside
eclipse, the radio emission varies slowly and follows, in large part,
the same phase dependence over the two observed orbits (separated by
one orbit). This suggests that much of the modulation observed outside
eclipse may be due to an apparent change in the observed radiation
pattern of the source with orbital revolution, rather than intrinsic
variability in the radio emission process. From the data, we place
constraints on the physical parameters of both the occulter and the
occulted radio source; we find that the radio source is most probably
radiating by nonthermal gyrosynchrotron emission. We favor a model
where the radio-emitting electrons are accelerated by the interaction
(collision) between the magnetospheres of the K dwarf and the white
dwarf. This region of interaction is likely to be located very close
to the surface of the white dwarf, leading naturally to a picture
where the radio emission originates from large magnetic structures
associated with the K dwarf. Such a model can qualitatively explain
many of the features observed in the radio light curve. The proposed
magnetic structures may provide the means by which mass is transferred
from the K dwarf to the white dwarf, accounting partly or wholly for
the inferred accretion of the white dwarf.

---------------------------------------------------------
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: 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: Broadband Imaging Spectroscopy with the Solar Radio Telescope
Authors: Bastian, T. S.; Gary, D. E.; Hurford, G. J.; Hudson, H. S.;
Klimchuk, J. A.; Petrosian, V.; White, S. M.
1996ASPC...93..430B Altcode: 1996ress.conf..430B
No abstract at ADS

---------------------------------------------------------
Title: The X-ray spectra of flares from AB Doradus
Authors: White, S. M.; Pallavicini, R.; Lim, J.
1996ASPC..109..299W Altcode: 1996csss....9..299W
No abstract at ADS

---------------------------------------------------------
Title: The Eclipsing Radio Emission of the Precataclysrnic Binary
V471 Tau
Authors: Lim, J.; White, S. M.; Cully, S. L.
1996ASPC...93..327L Altcode: 1996ress.conf..327L
No abstract at ADS

---------------------------------------------------------
Title: Radio emission from cool stars
Authors: White, S. M.
1996ASPC..109...21W Altcode: 1996csss....9...21W
No abstract at ADS

---------------------------------------------------------
Title: Millimeter Continuum Observations of Stars
Authors: Pallavicini, Roberto; White, S. M.
1996slma.conf..268P Altcode:
We review the scientific advances to be expected from millimeter
continuum observations of stars by a Large Southern Array (LSA). We
discuss briefly several topics including millimeter observations of the
Sun, winds of hot stars, circumstellar disks of pre-main sequence stars,
circumstellar shells and mass loss in cool giants, symbiotic stars,
and non-thermal emission in active binaries, flare stars and accretion
powered X-ray sources. We show that even in the more limited area of
continuum observations, the proposed LSA will allow major advances in
virtually all fields of stellar astronomy.

---------------------------------------------------------
Title: First Radio Detection of Solar-Type Stars in an Open Cluster:
The Pleiades
Authors: Lim, J.; White, S. M.
1996ASPC...93..455L Altcode: 1996ress.conf..455L
No abstract at ADS

---------------------------------------------------------
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: Radio emission from solar-type stars in the Pleiades
Authors: Lim, J.; White, S. M.
1996ASPC..109..369L Altcode: 1996csss....9..369L
No abstract at ADS

---------------------------------------------------------
Title: The corona of AB Dor: temperatures and abundances determined
with ASCA and EUVE
Authors: Mewe, R.; Kaastra, J. S.; White, S. M.; Pallavicini, R.
1996ASPC..109..273M Altcode: 1996csss....9..273M
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: EUVE and VLA Observations of the Eclipsing Pre-Cataclysmic
Variable V471 Tauri
Authors: Cully, S. L.; Dupuis, J.; Rodriguez-Bell, T.; Basri, G.;
Siegmund, O. H. W.; Lim, J.; White, S. M.
1996aeu..conf..349C Altcode: 1996IAUCo.152..349C
No abstract at ADS

---------------------------------------------------------
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: Radio Detection of Late-Type (G--K) Dwarf Stars in the Pleiades
Authors: Lim, Jeremy; White, Stephen M.
1995ApJ...453..207L Altcode:
We report deep 3.6 cm radio observations of a small sample of the most
rapidly rotating G-K dwarf stars in the Pleiades. Of the four ultrafast
rotators (UFRs) observed, three were detected. The G8 dwarf H II 1136,
the fastest rotating G dwarf known in the Pleiades, displayed a flare
that rose to a peak flux density of ∼1 mJy (peak radio luminosity
of ∼2 × 1016 ergs Hz-1 s-1) in
less than ∼1 hr, stayed at approximately this level for ∼2 hr,
and then decayed apparently exponentially with an e-folding time of
∼1.4 hr. Following the flare, H II 1136 was detected in what may
be its quasi steady state with a flux density of 0.16±0.02 mJy. The
K2 dwarf H II 1883, the fastest rotating K dwarf in the Pleiades, was
detected on two separate occasions, both times as an apparently steady
source. The stellar flux density, however, appeared to change from
0.10±0.02 mJy to 0.05±0.01 mJy in the two observations separated
by about 3 months. By contrast, the K0 dwarf H II 625 displayed
slowly varying emission with an average flux density of 0.16±0.02
mJy. For all the stars detected, the average radio luminosity of their
quasi-steady (perhaps quiescent) emission is 1-3 × 1015
ergs Hz-1 s-1. For the single undetected star,
the K2 dwarf H II 3163, we placed an upper limit (5 σ) of 0.12 mJy
on its flux density or 2 × 1015 ergs Hz-1
s-1 on its luminosity. Our results represent the
first detection of late-type dwarf stars in the Pleiades and indeed of
any apparently single stars in an open cluster. It demonstrates that
solar-type stars recently descended to the zero-age main sequence can be
copious radio emitters. Both in their quasi-steady and flaring states,
the radio luminosities of the Pleiades stars are similar to those of
equally rapidly rotating but relatively nearby late-type dwarf stars
belonging to the Local Association, which provides further support
for the idea that such stars are physical counterparts of UFRs in the
Pleiades. When averaged over the stellar surface, the surface radio
luminosity of the Pleiades stars is comparable to that of the most
active T Tauri stars, a trend recently noted for the surface soft
X-ray emission of these two classes of stars. This may suggest that
the magnetic dynamo of rapidly rotating late-type stars operates at
a saturated level as these stars descend to the main sequence.

---------------------------------------------------------
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: Spectroscopic EUVE Observations of the Active Star AB Doradus
Authors: Rucinski, Slavek M.; Mewe, Rolf; Kaastra, Jelle S.; Vilhu,
Osmi; White, Stephen M.
1995ApJ...449..900R Altcode:
We present observations of the pre-main-sequence, rapidly rotating
(0.515 day) late-type star, AB Doradus (HD 36705), made by the Extreme
Ultraviolet Explorer (EUVE) satellite. A spectrum from 80 to 700 Å with
a resolution Δλ ≍ 0.5-2 Å was accumulated between 1993 November
4-11, with an effective exposure time of about 40 hours. No obvious
EUV flares were detected during the observation. The data constrain
the coronal temperature structure between several 104 K
up to roughly 2 × 107 K through a differential emission
measure analysis using the optically thin MEKA plasma model. The
resulting differential emission measure (DEM) distribution shows: (1)
dominant emission from plasma between about 2 × 106 and 2
× 107 K, which may show a substructure with two components
around 3 × 106 and 107 K; (2) very little
emission from plasma between 105 and 2 × 106 K;
and (3) emission from plasma below about 105 K. If solar
photospheric abundances are assumed, then the formal DEM solution
also requires the presence of a strong high-temperature component
(above about 3 × 107 K) in order to explain the strong
continuum emission below about 150 Å. We believe that this component
of the solution is not physical: it is not present in the solution if
we assume lower iron abundance, or if there is significant resonance
scattering in some of the stronger (mainly iron) spectral lines with
subsequent photon absorption in the lower, dense atmosphere. Finally,
the DEM analysis gives a best-fit value for the interstellar hydrogen
column density of NH = (2.4±0.5) × 1018
cm-2.

---------------------------------------------------------
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: Composition of 5145 Pholus
Authors: Cruikshank, D. P.; Roush, T.; Bartholomew, M. J.; Geballe,
T. R.; Davies, J. K.; Brown, R. H.; White, S. M.; Tryka, K. A.; Owen,
T. C.; de Bergh, C.; Moroz, L. V.; Pendleton, Y. J.; Bell, J. F., III
1995DPS....27.0106C Altcode: 1995BAAS...27.1056C
No abstract at ADS

---------------------------------------------------------
Title: VLA Observations of the Effects of the SL-9 impact on the
Synchrotron Emission from the Jovian Magnetosphere at 3 and 6 cms
Authors: Kundu, A.; Wang, J. C.; Grossman, A. W.; White, S. M.;
Muhleman, D. O.; Gurwell, M. A.
1995DPS....27.2615K Altcode: 1995BAAS...27.1129K
No abstract at ADS

---------------------------------------------------------
Title: Circular Polarization in the Radio Emission of RS Canum
Venaticorum Binaries
Authors: White, Stephen M.; Franciosini, Elena
1995ApJ...444..342W Altcode:
A puzzling feature of the polarization of the radio emission of RS CVn
binary systems is the observed reversal in the sense of polarization
between high and low frequencies. This reversal has been assumed to be
a property of the quiescent emission of these systems, which is widely
agreed to be gyrosynchrotron emission. However, the reversal has proved
difficult to explain in terms of plausible gyrosynchrotron models,
and we demonstrate that its location with respect to the spectral peak
is not consistent with such models. Instead we propose that a form of
coherent radio emission is common at low frequencies in these systems
and present several examples in which such a component is clearly
present. This coherent component is highly circularly polarized in
the sense opposite to that of the higher frequency gyrosynchrotron
emission. At low freqeuncies the gyrosynchrotron component is also
present and may be stronger than the coherent component, but is probably
weakly polarized so that the polarization of the integrated emission is
dominated by the coherent component. Based on the sense of polarization
of the coherent component, we suggest that it is probably a form of
plasma emission. It can show both rapid variability as well as slower
modulation similar to that of the gyrosynchrotron component and has
a bandwidth of at least 80 MHz. We also point out that the observed
fact that the degree of polarization of the quiescent emission at high
frequencies tends to increase with frequency is also inconsistent with
gyrosynchrotron models.

---------------------------------------------------------
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: A Solar Radio Telescope for the Future: Science Summary from
the SRT Workshop
Authors: Gary, D. E.; Bastian, T. S.; Hudson, H. S.; Hurford, G. J.;
Klimchuk, J. A.; Petrosian, V.; White, S. M.
1995SPD....26..801G Altcode: 1995BAAS...27..971G
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: RE J1255+266: detection of an extremely bright EUV transient.
Authors: Dahlem, M.; Kreysing, H. -C.; White, S. M.; Engels, D.;
Condon, J. J.; Harmon, B. A.; Zhang, S. N.; Kouveliotou, C.; Paciesas,
W. S.; Voges, W.
1995A&A...295L..13D Altcode:
During a pointed ROSAT observation in the direction of the Coma
cluster of galaxies an exceptionally bright EUV source, RE J1255+266,
was detected serendipitously. The source is located close to the
Galactic North pole, at b_II_~=89deg. Its observed EUV flux (62-110eV)
at the time of the detection was of order 7x10-9ergs/s/cm2, making
RE J1255+266 temporarily one of the brightest EUV sources on the
sky. The EUV flare of RE J1255+266 has a light curve with a decay time
of about 0.86days. With respect to earlier non-detections, the source
brightened by a factor of ~7000. Such a behaviour has not been observed
before. Thus, it is unclear what type of source RE J1255+266 might
be. Up to now no positive identification with any known source could be
obtained. Emission at the position of the source was previously only
detected in the 1987 Green Bank radio continuum survey. Simultaneous
observations with CGRO/BATSE resulted in non-detections of the source
in the 8-50keV energy range.

---------------------------------------------------------
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: A Solar Radio Telescope for the Future: Strawman Concept from
the SRT Workshop
Authors: Hurford, G. J.; Bastian, T. S.; Gary, D. E.; Hudson, H. S.;
Klimchuk, J. A.; Petrosian, V.; White, S. M.
1995SPD....26..802H Altcode: 1995BAAS...27..971H
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: Coherent Radio Bursts from RS CVn Binaries
Authors: Franciosini, Elena; White, Stephen M.
1995LNP...454...40F Altcode: 1995IAUCo.151...40F; 1995flfl.conf...40F
No abstract at ADS

---------------------------------------------------------
Title: ASCA X-ray Spectra of Quiescent and Flaring Emission from
AB Doradus
Authors: White, S. M.; Pallavicini, R.; Lim, J.
1995LNP...454..168W Altcode: 1995IAUCo.151..168W; 1995flfl.conf..168W
No abstract at ADS

---------------------------------------------------------
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: Energetic electron populations in solar flares
Authors: White, Stephen M.
1994AIPC..294..199W Altcode: 1994hesp.conf..199W
Millimeter-interferometer observations of flares are used to study the
MeV-energy electrons accelerated in solar flares. The focus of this
study is a remarkable similarity found in the time profiles of emission
associated with the impulsive onset of a flare. In a large fraction
of flares, the impulsive phase emission at millimeter wavelengths
consists of a rapid rise (~5 seconds) linear in time to a sharp peak,
followed by an exponential decay with a decay constant of order 15
seconds. The onset of millimeter emission may be delayed by several
seconds with respect to the onset of hard X-rays. The implications of
this homologous property are discussed briefly.

---------------------------------------------------------
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: Directivity of the Radio Emission from the K1 Dwarf Star
AB Doradus
Authors: Lim, Jeremy; White, Stephen M.; Nelson, Graam J.; Benz,
Arnold O.
1994ApJ...430..332L Altcode:
We present measurements of the spectrum and polarization of the
flaring radio emission from the K1 dwarf star AB Doradus, together with
previously reported single frequency measurements (with no polarization
information) on 3 other days. On all 4 days spanning a 6 month period,
the emission was strong and, when folded with the stellar rotation
period, showed similar time variations with two prominant peaks
at phase 0.35 and 0.75. These peaks coincide in longitude with two
large starspots identified from the stellar optical light curve and
have half-powe widths as small as 0.1 rotations and no larger than
0.2 rotations. The modulated emission shows no measurable circular
polarization, and its two peaks have different turnover frequencies.

---------------------------------------------------------
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: Microwave Imaging of Jupiter's Troposphere During Impact with
Comet P/Shoemaker-Levy 9
Authors: Grossman, A. W.; White, S. M.; Muhleman, D. O.; Gurwell, M. A.
1994DPS....26.0314G Altcode: 1994BAAS...26.1587G
No abstract at ADS

---------------------------------------------------------
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: 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 Radio Spectra of Weak-Lined T Tauri Stars
Authors: White, S. M.; Pallavicini, R.; Lim, J.
1994ASPC...64..501W Altcode: 1994csss....8..501W
No abstract at ADS

---------------------------------------------------------
Title: A Search for Radio Emission in the Alpha Persei Cluster.
Authors: White, S. M.; Prosser, C. F.; Schmitt, J. H. M. M.
1994ASPC...64..504W Altcode: 1994csss....8..504W
No abstract at ADS

---------------------------------------------------------
Title: The Coronae of DM Stars
Authors: White, Stephen M.
1994euve.prop...80W Altcode:
Optical spectroscopy recently revealed that one of the brightest
unidentified sources in the EUVE catalogs, EUVEJ2056-17.1, is an active
dM0e flare star located at a distance of ~50 pc. A large flare with
energy in excess of 10E35 erg was observed during the EUVE observations
in the Deep Survey Lex/B band (60-200 A). This is the most energetic
flare event observed on a star of this spectral class. EUVEJ2056-17.1
has a strong Li I 6707.8 line in the spectrum. The unsually high
abundance of Li and the high activity of this source favors an
interpretation of Li production by spallation reactions during very
energetic flares. We request 150 ksec of EUVE time on this source. The
requested observing time will provide valuable insights on the energy
budget of flares from low mass stars and will allow us to investigate
further the Li production by spallation.

---------------------------------------------------------
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: The Radio Continuum from Classical T Tauri Stars
Authors: White, S. M.; Mundy, L. G.; Grossman, A. W.
1993AAS...183.3204W Altcode: 1993BAAS...25.1341W
We have carried out a survey of radio continuum emission from the
classical T Tauri stars in the Taurus and Ophiuchus star-forming clouds
not previously observed with the Very Large Array. The detection rate
is surprisingly low. We combine our results with those of other surveys
in order to analyze the correlation of radio continuum luminosity with
other properties of T Tauri stars, and discuss the nature of the radio
continuum and its relationship to the winds of these stars.

---------------------------------------------------------
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: 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: 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: 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: The Coronae of dM Stars
Authors: White, Stephen M.
1993euve.prop...93W Altcode:
We propose to use the excellent discrimination of EUVE
in the temperature range around 10^(6.7-7.0) K to study the
temperature/emission measure distribution in the coronae of the inactive
dM2 star GJ 411 and the apparently weakly active dM2e star BD -21
1074. The aims are to determine the emission measure distribution in
M dwarf coronae over a wide range in activity levels, to test whether
there is a component in the corona of GJ 411 at 10^6.8 K as reported,
and thereby indirectly to test an explanation for the presence of the
hot 10^7.2 K) component in the coronae of active flare stars as due
to stability points in the radiative cooling curve. We request 160
ksec for GJ 411 and 60 ksec for BD -21 1074.

---------------------------------------------------------
Title: 3D reconstruction methods of coronal structures by radio
observations.
Authors: Aschwanden, M. J.; White, S. M.; Bastian, T. S.
1992ESASP.348..217A Altcode: 1992cscl.work..217A
The ability to carry out a three-dimensional reconstruction of
structures in the solar corona would represent a major advance
in our study of the physical properties in active regions and
in flares. The authors describe several new methods which allow
a geometric reconstruction of quasi-stationary coronal structures
(e.g. active region loops) or dynamic structures (e.g. flaring loops):
(1) steroscopy of multi-day imaging observations by the VLA. (2)
Tomography of optically thin emission (in radio or soft X-rays). (3)
Multi-frequency band imaging by the VLA. (4) Tracing of magnetic field
lines by propagating electron beams.

---------------------------------------------------------
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: 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: 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: 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: 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: 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: 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: Simultaneous EUV, Microwave, and Magnetic Field Observations
of Solar Active Regions
Authors: Brosius, J. W.; Davila, J. M.; Thompson, W. T.; Gopalswamy,
N.; White, S. M.; Jones, H. P.; Metcalf, T. R.
1991BAAS...23.1388B 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: 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: 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: 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: 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: 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: 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: 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: 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: 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: 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: 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: 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: On the Source Conditions for Herringbone Structure in Type-II
Solar Radio Bursts
Authors: Cane, H. V.; White, S. M.
1989SoPh..120..137C Altcode:
We investigate the correlation of the occurrence of the herringbone
phenomenon in type II solar radio bursts with various flare
properties. We show that herringbone is strongly correlated with
the intensity of the type II burst: whereas about 21% of all type II
bursts show herringbone, about 60% of the most intense bursts contain
herringbone. This fact can explain most of the correlations between
herringbone and other properties such as intense type III bursts,
type IV emission, and high type II starting frequencies. We also show
that when this is taken into account, there is no need to postulate two
classes of type II burst in order to explain why there appears to be a
difference in herringbone occurrence between the set of type II bursts
associated with the leading edges of coronal mass ejections, and those
not so associated. We argue that the data are consistent with the idea
that all coronal type II bursts are due to blast waves from flares.

---------------------------------------------------------
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: 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: 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: 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: 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: 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: 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: 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: 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: 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: 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: 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: 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: 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: 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: 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: 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: Particle Propagation Effects on Wave Growth in a Solar
Flux Tube
Authors: White, S. M.; Melrose, D. B.; Dulk, G. A.
1986ApJ...308..424W Altcode:
The evolution of a distribution of electrons is followed after they
are injected impulsively at the top of a coronal magnetic loop, with
the objective of studying the plasma instabilities which result. At
early times the downgoing electrons have beamlike distributions and
amplify electrostatic waves via the Cerenkov resonance; the anomalous
Doppler resonance is found to be less important. Slightly later, while
the electrons are still predominantly downgoing, they are unstable
to cyclotron maser generation of z-mode waves with omega(p) much less
than Omega, or to second harmonic x-mode waves. The energetics of these
instabilities, including saturation effects and heating of the ambient
plasma, are discussed. It is suggested that coalescence of two z-mode
waves generated by cyclotron maser emission of the downgoing electrons
may produce the observed microwave spike bursts.

---------------------------------------------------------
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: 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: Particle propagation, wave growth and energy dissipation in
a flaring flux tube
Authors: White, S. M.; Melrose, D. B.; Dulk, G. A.
1986AdSpR...6f.163W Altcode: 1986AdSpR...6..163W
We investigate wave amplification by downgoing particles in a common
flare model. The flare is assumed to occur at the top of a coronal
magnetic flux loop, and results in the heating of plasma in the flaring
region. The hot electrons propagate down the legs of the flux tube
towards increasing magnetic field. It is simple to demonstrate that
the velocity distributions which result in this model are unstable
to both beam instabilities and cyclotron maser action. We present an
explanation for the propagation effects on the distribution, and explore
the properties of the resulting amplified waves. We concentrate on
cyclotron maser action, which has properties (emission in the z mode
below the local gyrofrequency) quite different from maser action by
other distributions considered in the context of solar flares. The
z mode waves will be damped in the coronal plasma surrounding the
flaring flux tube, and lead to heating there. This process may be
important in the overall energy budget of the flare. We compare the
downgoing maser with the loss cone maser, which is more likely to
produce observable bursts.

---------------------------------------------------------
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: 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: Thermal Effects in the Ultrarelativistic Two-Stream Instability
Authors: White, S. M.
1985Ap&SS.116..173W Altcode:
The dispersion relation for longitudinal waves in a one-dimensional
ultrarelativistic plasma is calculated. Analytical and numerical results
for the growth rate and frequency of the two-stream instability are
presented as a function of the energy spread in the denser stream when
the dilute stream is cold. The case of energy spreads in both beams
is investigated numerically: it is found that relatively small energy
spreads in both streams can lead to suppression of the instability.

---------------------------------------------------------
Title: On damping of auroral z mode waves
Authors: White, S. M.
1985JGR....90.7471W Altcode:
This paper discusses the constraints on auroral z mode waves implied
by damping. Damping of the magnetoinic z mode in a thermal plasma
with ωp &lt;&lt;Q is calculated and shown to be strong
near the gyrofrequency. Analytic formulae for the optical depth of the
corresponding absorption layer are presented. Ray tracing calculations
are used to investigate the effect of refraction during the propagation
of a z mode ray: refraction is found to be particularly important in the
vicinity of the gyrofrequency layer and tends to cause the wave vector
of the ray to change so that it is strongly damped. The results are
applied to models for the generation of auroral z mode waves. A point
of particular interest concerns the possibility of explaining observed
emissions whose bandwidths straddle the gyrofrequency by an emission
mechanism which amplifies waves either only above or only below the
gyrofrequency. For a dipolar magnetic field and radial plasma density
gradient it is found that a z mode ray in the auroral zone is unlikely
to be able to pass through the gyrofrequency layer without significant
damping occurring.

---------------------------------------------------------
Title: Damping of the MagnetoIonic Z Mode
Authors: White, S. M.; Melrose, D. B.; Dulk, G. A.
1985ASSL..116...47W Altcode: 1985rst..conf...47W
The authors consider two effects here: damping of the z-mode waves as
they propagate through the ambient coronal plasma, and coalescence of
z-mode waves to produce second-harmonic radiation.

---------------------------------------------------------
Title: Electron cyclotron masers during solar flares
Authors: White, S. M.; Melrose, D. B.; Dulk, G. A.
1983PASA....5..188W Altcode: 1983PASAu...5..188W
It has been suggested that solar microwave spike bursts are due to
electron cyclotron maser action. The objective of the study reported
here is to explore a simple model for the dynamics of the electrons
producing the maser emission and to use the model to investigate the
conditions under which the maser turns on. It is shown that there are
two phases in which maser action is likely to occur following a solar
flare. In the later phase, loss cones in upgoing particles develop and
are unstable to wave growth; the resulting maser produces radiation at
low harmonics. Maser action is also likely to occur in an earlier phase
when the particles are predominantly downgoing. The resulting maser
emits radiation which should be reflected or reabsorbed at a level
where its frequency equals the critical frequency of the appropriate
mode. The radiation propagates nearly perpendicular to the field lines
so that heating over a large area is possible. The implications of
the results obtained are briefly examined.

---------------------------------------------------------
Title: Coherent gyromagnetic emission
Authors: White, S. M.; Melrose, D. B.
1982PASA....4..362W Altcode: 1982PASAu...4..362W
The properties of interference radiation in coherent gyrotron emission
are examined. The idea of interference is analytically explained,
and the kinematic requirements for it to occur are identified. The
possibility of absorption or maser action is excluded. The dependence
of the interference energy on the particle velocities is shown, and
the current associated with each particle is presented. These describe
the incoherent radiation of each particle. The remaining term is a
cross-product between the two particles on the radiation. The results
suggest that taking account of the dispersion of particles in bunches
emitting coherent curvature radiation permits the expectation that
the spectral properties and angular characteristics of the resulting
radiation will differ from the predictions of incoherent curvature
emission theory.

---------------------------------------------------------
Title: Precipitation from an asymmetric magnetic flux tube
Authors: Melrose, D. B.; White, S. M.
1981JGR....86.2183M Altcode:
A simple model for precipitation of trapped particles from an
asymmetric magnetic flux tube is formulated and analytic solutions
are found in the strong diffusion and weak diffusion limits. The
loss cones α&lt;α1 and α&gt;π-α2 (α =
pitch angle) are assumed unequal (α1&lt;α2),
the pitch angle diffusion coefficient D(α) is assumed asymmetric
(D(α)≠D(π-α)), and the particles are assumed to be injected
at an angle αs≠π/2. The steady state solution
in the strong diffusion limit implies that the ratio of the
precipitation rates at the two feet is equal to the ratio of the
solid angles filled by the loss cones, R1/R2
= α21/α22. An
explicit result for R1 is obtained in the weak diffusion
limit. For α2-α1&gt;&gt;αD1,
where αD1 is roughly the typical angle a particle is
deflected in one transit across the flux tube from foot 2 to foot 1,
R1 is smaller than R2 by a factor of order
exp[-(α2-α1)/αD1]. The effect
of asymmetric diffusion, which is to favor precipitation at foot
1 for D(α1)&gt;D(α2) and at foot 2 for
D(α2)&gt;D(α1), is described in terms of a
factor F(d) of an asymmetry parameter d given by equations (35) and
(24), respectively. Applications to the solar corona, to Jupiter's radio
emission and to the terrestrial magnetosphere are discussed briefly.

---------------------------------------------------------
Title: Amplified Cerenkov emission of auroral hiss: Limitations
implied by quasi-linear theory
Authors: Melrose, D. B.; White, S. M.
1980JGR....85.3442M Altcode:
Auroral hiss is attributed to amplified Cerenkov emission of nearly
resonant whistlers. such emission occurs only when the pricipitating
electron flux corresponds to a one-dimensional distribution with a peak
in parallel energy. Only particles below this peak contribute to the
amplified emission. The back reaction of the hiss on the electrons
is treated by using quasi-linear theory. The primary effect is to
reduce the positive gradient in energy below the peak. This tends to
suppress the generation of the waves. A relation between the expected
intensity of the hiss and the properties of the stream is derived. The
observational data are consistent with limitation of the intensity by
quasi-linear relation.

---------------------------------------------------------
Title: The gyrosynchrotron emission from quasi-thermal electrons
and applications to solar flares
Authors: Dulk, G. A.; Melrose, D. B.; White, S. M.
1979ApJ...234.1137D Altcode:
We present theoretical results on the gyrosynchrotron radiation
from electrons with a Maxwellian energy distribution. We review the
analytical expressions for the gyromagnetic absorption coefficient
and find two which cover the range of interest for microwave emission
from solar flares, i.e., frequencies ω to ∼100Ωe
and temperatures Te to ∼109 K. Numerical
calculations are used to check the analytic expressions and to
derive simplified empirical formulae which relate the observable
characteristics of the radiation to the temperature and magnetic
field in the source. We apply the results to the sources of
impulsive microwave and hard X-ray bursts from solar flares. For an
isothermal source the theory predicts a microwave spectrum where the
flux density rises as f2 at low frequencies, maximizes as
some frequency fpeak, and falls very rapidly thereafter;
this shape fits the observed spectra qualitatively. The optical
depth τ of the source varies rapidly with f, with τ = 1 at f ≍
fpeak. For Te ≳ 108 K we derive
the relation fpeak ∝ Te0.7B, which
allows a direct estimate of the magnetic field B in the impulsive
burst source if the temperature is known-for instance, from hard X-ray
observations. For the impulsive burst of 1972 May 18, reported by Hoyng
and Stevens, we find that the microwave and hard X-ray data are well
fitted by a model source with Te ≍ 2.3 × 108
K, B ≍ 370 gauss, ne 2 × 109 cm-3,
and scale length L ≍ 8600 km.

---------------------------------------------------------
Title: Effect of asymmetry on a trap model for solar hard X-ray bursts
Authors: Melrose, D. B.; White, S. M.
1979PASA....3..369M Altcode: 1979PASAu...3..369M
The model proposed by Melrose and White (1979) for the precipitation of
trapped energetic particles in an asymmetric flux tube is examined. It
is shown that scattering due to Coulomb interactions should be weak for
the electrons which emit hard X-rays in a trap model for solar hard
X-ray bursts. The X-ray emission would then consist of thin target
emission from the trap and thick target emission from the weaker foot
of the flux tube, with no emission from the other (stronger-field)
foot. The lifetime of the hard X-ray burst provides a measure of the
scattering time and electron density in the trap.

---------------------------------------------------------
Title: A gyro-synchrotron maser in the solar corona?
Authors: Melrose, D. B.; White, S. M.
1978PASA....3..231M Altcode: 1978PASAu...3..231M
It is found that a gyrosynchrotron maser is a possible interpretation
of observed high brightness temperatures (10 to the 10th K) in
some moving Type IV bursts. However, unless considerably higher
brightness temperatures at lower frequencies are found, it appears that
nonamplified emission from electrons with energies (about 1 MeV) higher
than considered in the past is a more plausible interpretation (Stewart
et al., 1978). If the brightness temperature at lower frequencies is
found to be much higher (e.g., 10 to the 12th K at 20 MHz), this would
provide evidence in favor of the maser mechanism.