Author name code: sylwester-barbara
ADS astronomy entries on 2022-09-14
author:"Sylwester, Barbara"
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Title: On the Variability of Calcium Abundance during Flare Decays
Authors: Sylwester, Barbara; Sylwester, Janusz; Kepa, Anna; Phillips,
Kenneth
Bibcode: 2022cosp...44.2570S
Altcode:
The NASA Solar Maximum Mission (operational 1980—1989) carried
instruments designed to observe solar flares during an especially
high-activity period. Among the instruments was a bent crystal X-ray
spectrometer (BCS) viewing high-temperature lines of ionized calcium
and iron. The BCS channel including the Ca lines is of particular
interest as lines (due to He-like Ca or Ca XIX with satellite lines)
and continuum uncontaminated by instrumental background could be
observed, emitted by hot (T > 7 MK) parts of the flare plasma. The
line-to-continuum ratios directly give the abundance of Ca, A(Ca), which
can be examined for individual intervals during decays of the numerous
flares observed. A recent re-assessment of instrumental parameters shows
that non-uniformities in the curvature of the Ca channel crystal need
to be allowed for, which has been done in a new analysis of 194 flare
decays reported here. The ratio of the entire line spectrum (rather than
only the Ca XIX resonance line) to the continuum is measured. Updated
atomic data to describe the theoretical spectrum have been used. The
results confirm an earlier analysis in that flare-to-flare changes in
A(Ca) are taking place, the average for all flares included being A(Ca)
= 6.74 (log scale with A(H) =12) and standard deviation of 0.08, which
largely reflects real changes (the estimated uncertainty for individual
spectra is only about 0.03). There are indications that flares with
shorter durations and smaller GOES importance have slightly higher
A(Ca), with a range of about 7.2 down to 6.7. The photospheric A(Ca)
is 6.32, so our values strongly indicate a "FIP" effect which, as Ca
is a low-FIP element, has a coronal (flare) abundance about 2.6 times
larger than photospheric.
Title: Differential evolution method for simultaneous determination
of elemental abundances and DEM distribution based on X-ray spectra
Authors: Kepa, Anna; Sylwester, Janusz; Sylwester, Barbara; Siarkowski,
Marek
Bibcode: 2022cosp...44.2582K
Altcode:
The basic characteristics of astrophysical plasma are its chemical
composition and differential emission measure (DEM) distribution. Since
spectral lines and continuum intensities (which are inputs data
for DEM reconstruction) depend directly on the absolute elemental
abundance, the results of any DEM inversion strongly depend on
assumed chemical composition. In this contribution we propose a new
approach based on the differential evolution method for X-ray spectra
analysis in which DEM distribution and the abundances of elements
are calculated simultaneously. We will present the usefulness of this
approach based on the corresponding tests and show the results of its
application to the analysis of the RESIK/Coronas-F and the Solar X-ray
Monitor/Chandrayaan-2 spectra.
Title: New Solar Flare Calcium Abundances with No Surprises: Results
from the Solar Maximum Mission Bent Crystal Spectrometer
Authors: Sylwester, J.; Sylwester, B.; Phillips, K. J. H.; Kępa, A.
Bibcode: 2022ApJ...930...77S
Altcode: 2022arXiv220302257S
The calcium abundance in flare plasmas is estimated using X-ray spectra
from the Solar Maximum Mission Bent Crystal Spectrometer (BCS) during
the decays of 194 flares (Geostationary Operational Environmental
Satellite, GOES, classifications from B6.4 to X13) occurring between
1980 and 1989. Previous work by Sylwester et al. found that the
abundance varied from flare to flare. That analysis is improved on
here using updated instrument parameters and by including all calcium
lines viewed by the BCS instead of only the resonance line, so greatly
enhancing the photon count statistics. The abundance variations are
confirmed with the average abundance, A(Ca) (expressed logarithmically
with A(H) = 12), equal to 6.77 ± 0.20 for 194 flares (141 of which are
new in this study). This range corresponds to factors of between 1.7 and
7.2 larger than the photospheric abundance, and so our results are in
line with a "first ionization potential" (FIP) effect whereby low-FIP
elements like Ca (FIP = 6.11 eV) have enhanced coronal abundances. The
Ca flare abundance is uncorrelated with solar activity indices, but
weak correlations are suggested with GOES flare class and duration
(larger A(Ca) for smaller and shorter flares). The ponderomotive force
theory of Laming explaining the FIP effect gives a range of parameters
within which our estimates of A(Ca) agree with the theory. However, this
then gives rise to disagreements with previous estimates of the flare
silicon and sulfur abundances, although those of argon and iron are in
good agreement. Small adjustments of the theory may thus be necessary.
Title: On the Application of Differential Evolution to the Analysis
of X-Ray Spectra
Authors: Kępa, Anna; Sylwester, Barbara; Siarkowski, Marek; Sylwester,
Janusz
Bibcode: 2022ApJ...927...19K
Altcode: 2022arXiv220209302K
Using methods of differential evolution (DE), we determined the
coronal elemental abundances and the differential emission measure
(DEM) distributions for the plasma flaring on 2003 January 21. The
analyses have been made based on RESIK X-ray spectra. DE belongs to
the family of evolutionary algorithms. DE is conceptually simple and
easy to implement, so it has been applied to solve many problems in
science and engineering. In this study we apply this method in a new
context: simultaneous determination of plasma composition and DEM. In
order to increase the confidence of the results obtained using DE,
we tested the use of its algorithms by comparing the DE synthesized
with respective spectra observed by RESIK. Extensive discussion of the
DE method used and the obtained physical characteristics of flaring
plasma is presented. * Released on 2021 March 1.
Title: KORTES mission for solar activity monitoring onboard
International Space Station
Authors: Kirichenko, Alexey; Kuzin, Sergey; Shestov, Sergey; Ulyanov,
Artem; Pertsov, Andrey; Bogachev, Sergey; Reva, Anton; Loboda, Ivan;
Vishnyakov, Eugene; Dyatkov, Sergey; Erkhova, Nataliya; Stȩślicki,
Marek; Sylwester, Janusz; Płocieniak, Stefan; Podgórski, Piotr;
Kowaliński, Mirosław; Bakała, Jarosław; Szaforz, Żaneta;
Siarkowski, Marek; Ścisłowski, Daniel; Mrozek, Tomasz; Sylwester,
Barbara; Malyshev, Ilya; Pestov, Alexey; Polkovnikov, Vladimir;
Toropov, Mikhail; Salashchenko, Nikolay; Tsybin, Nikolay; Chkhalo,
Nikolay
Bibcode: 2021FrASS...8...66K
Altcode:
We present a description of the recent advances in the development
of the KORTES assembly -- the first solar oriented mission designed
for the Russian segment of International Space Station. The KORTES
consists of several imaging and spectroscopic instruments collectively
covering a wide spectral range extending from extreme ultraviolet (EUV)
wavelengths to X-rays. The EUV telescopes inside KORTES will trace the
origination and dynamics of various solar phenomena, e.g. flares,
CMEs, eruptions etc. EUV spectra provided by grazing-incidence
spectroheliographs will enable precise DEM-diagnostics during these
events. The monochromatic X-ray imager will observe the formation
of hot plasma in active regions and outside them. The SolpeX module
inside KORTES will offer an opportunity to measure fluxes, Doppler
shifts and polarization of soft X-ray emission both in lines and
continuum. SolpeX observations will contribute to studies of particle
beams and chromospheric evaporation. The instrumentation of KORTES
will employ a variety of novel multilayer and crystal optics to be
discussed. The deployment of KORTES is planned of 2024.
Title: A Unique Resource for Solar Flare Diagnostic Studies: The
SMM Bent Crystal Spectrometer
Authors: Sylwester, J.; Sylwester, B.; Phillips, K. J. H.; Kępa,
A.; Rapley, C. G.
Bibcode: 2020ApJ...894..137S
Altcode: 2020arXiv200403241S
The Bent Crystal Spectrometer (BCS) on the NASA Solar Maximum Mission
spacecraft observed the X-ray spectra of numerous solar flares during
the periods 1980 February-November and 1984-1989. The instrument,
the first of its kind to use curved crystal technology, observed the
resonance lines of He-like Ca (Ca XIX) and Fe (Fe XXV), and neighboring
satellite lines, allowing the study of the rapid evolution of flare
plasma temperature, turbulence, mass motions etc. To date there has
not been a solar X-ray spectrometer with comparable spectral and
time resolution, while subsequent solar cycles have delivered far
fewer and less intense flares. The BCS data archive thus offers an
unparalleled resource for flare studies. A recent reassessment of
the BCS calibration and its operations is extended here by using data
during a spacecraft scan in the course of a flare on 1980 November 6
that highlights small deformations in the crystal curvature of the
important channel 1 (viewing lines of Ca XIX and satellites). The
results explain long-standing anomalies in spectral line ratios which
have been widely discussed in the past. We also provide an in-flight
estimation of the BCS collimator field of view which improves the
absolute intensity calibration of the BCS. The BCS channel 1 background
is shown to be entirely due to solar continuum radiation, confirming
earlier analyses implying a time-variable flare abundance of Ca. We
suggest that BCS high-resolution Ca XIX and Fe XXV line spectra be
used as templates for the analysis of X-ray spectra of nonsolar sources.
Title: A Multiwavelength Analysis of the Long-duration Flare Observed
on 15 April 2002
Authors: Kepa, Anna; Sylwester, Barbara; Sylwester, Janusz; Mrozek,
Tomasz; Siarkowski, Marek
Bibcode: 2020SoPh..295...22K
Altcode: 2019arXiv191207984K
We present a multiwavelength analysis of the long-duration flare
observed on 15 April 2002 (soft X-ray peak time at 03:55 UT,
SOL2002-04-15T03:55). This flare occurred on the disk (S15W01) in NOAA
9906 and was observed by a number of space instruments including the
Extreme-Ultraviolet Imaging Telescope on the Solar and Heliospheric
Observatory (SOHO/EIT), the RESIK spectrometer onboard the Coronas-F
spacecraft, and the Ramaty High Energy Solar Spectroscopic Imager
(RHESSI). We have performed a complex analysis of these measurements
and studied the morphology and physical parameters characterizing
the conditions in flaring plasmas. The 195 Å SOHO/EIT images have
been used to study evolution of flaring loops. Analysis of RHESSI
data provided the opportunity for a detailed analysis of hard X-ray
emission with 1 keV energy resolution. We have used Geostationary
Operational Environmental Satellite (GOES) observations for isothermal
interpretation of the X-ray measurements. Temperature diagnostics of
the flaring plasma have been carried out by means of a differential
emission measure (DEM) analysis based on RESIK X-ray spectra. The DEM
distributions were calculated based on two methods: Withbroe-Sylwester
(WS) and differential evolution (DE). Both of the approaches provided
similar results. We obtained two-component DEM distributions independent
of the evolutionary flare phase. We found that the amount of energy
of thermal plasma for this flare is of the order of 1030
ergs. The values obtained by assuming an isothermal plasma model are
lower than those determined from the differential emission measure
distributions.
Title: Solar Soft X-ray Variations from the 2008-2019 Solar Cycle
inferred from CORONAS/SphinX, GOES/XRS, Hinode/XRT, MinXSS, NuSTAR,
and RHESSI Instruments
Authors: Moore, C.; Takeda, A.; Sylwester, B.; Sylwester, J.; Hannah,
I.; Dennis, B.; Reeves, K.; Woods, T.
Bibcode: 2020AAS...23535901M
Altcode:
The Solar spectral irradiance (SSI) is vital for understanding the
physics of all layers of the solar atmosphere from the photosphere to
the corona. While most of the contribution to the Total Solar Irradiance
(TSI) reside in visible and infrared light, the UV and X-rays have the
largest change in magnitude. Quantifying the UV and X-ray variations
over the solar cycle is critical for constraining the physics of solar
flares, active regions, the quiet Sun, as well as the atmospheres
of planets and moons in the heliosphere. The GOES/XRS spectrally
integrated 0.1 - 0.8 nm energy flux has been a longstanding diagnostic
of soft x-ray variations, but is limited by non-linearities in signal
response for low solar flux levels and an observed minimum detection
limit. The Hinode/XRT filter images provide a unique alternative proxy
for solar soft X-ray flux inferences with larger dynamic range and a
lower flux sensitivity. We compare the spectral irradiance estimate
from a Hinode/XRT filter-ratio technique results to the lowest spectra
measured-to-date between 1.25 - 3 keV by CORONAS/SPhinX in 2009,
and MinXSS CubeSat spectra in 2016 - 2019. We also highlight the
large variability in the soft X-ray spectra as directly measured by
CORONAS/SphinX, MinXSS, NuSTAR, and RHESSI intermittently between 2009
- 2019.
Title: Analysis of Quiescent Corona X-ray Spectra from SphinX During
the 2009 Solar Minimum
Authors: Sylwester, B.; Sylwester, J.; Siarkowski, M.; Phillips,
K. J. H.; Podgorski, P.; Gryciuk, M.
Bibcode: 2019SoPh..294..176S
Altcode: 2019arXiv191203082S
The SphinX X-ray spectrophotometer on the CORONAS-PHOTON mission
observed the 1 - 15 keV X-ray spectrum of the spatially integrated
solar corona during the deep minimum of 2009, when solar activity was
exceptionally low. Its sensitivity for energies >1.2 keV was higher
than that of any other solar X-ray spectrometer in orbit at the time,
including the detectors on the Geostationary Operational Environmental
Satellites (GOES). Using much improved instrumental data than was
used previously, we analysed SphinX spectra in 576 intervals for which
there was no discernible activity (NA), 40 intervals when there were
X-ray brightenings (B), and 16 intervals when there were micro-flares
with peak emission less than GOES A1 (F). An instrumental background
spectrum, formed over 34 hours of spacecraft night-time periods and
including electronic noise and particle radiation, was subtracted from
the solar spectra. Theoretical spectra were used to deduce temperatures
on an isothermal assumption for the NA, B, and F intervals (1.69,
1.81, and 1.86 MK, respectively). Differential emission measure (DEM)
analysis for the same spectra revealed a "cooler" component (logT =6.2
or T ≈1.6 MK) in each case, but with a second hotter component having
a less well-defined peak temperature varying from ≈2.5 to ≈3.5 MK
(logT =6.4 and 6.55) and an emission measure between two and three
orders smaller than that of the cooler component. These results are
similar to those obtained at times just after solar minimum with the
EVE instrument. A very hot component that might indicate the signature
of nano-flare heating of the corona is not evident in SphinX data.
Title: The soft X-ray spectrometer polarimeter SolpeX
Authors: Sylwester, J.; Stȩślicki, M.; Bąkała, J.; Płocieniak,
S.; Szaforz, Ż.; Kowaliński, M.; Ścisłowski, D.; Podgórski, P.;
Mrozek, T.; Barylak, J.; Makowski, A.; Siarkowski, M.; Kordylewski,
Z.; Sylwester, B.; Kuzin, S.; Kirichenko, A.; Pertsov, A.; Bogachev, S.
Bibcode: 2019ExA....47..199S
Altcode: 2019ExA...tmp...10S; 2019arXiv190306163S
We present a novel X-ray assembly of functionally related instrument
blocks intended to measure solar flare and active region (AR) spectra
from within the Russian instrument complex KORTES, to be mounted
aboard the International Space Station ( ISS). SolpeX consists of
three blocks: fast-rotating multiple flat crystal Bragg spectrometer,
pin-hole X-ray spectral imager and Bragg polarimeter. This combination
of measuring blocks will offer an opportunity to detect/measure
possible X-ray polarization in soft X-ray emission lines/continuum and
record spectra of solar flares, in particular during their impulsive
phases. Polarized Bremsstrahlung and line emission may arise from
presence of directed particle beams colliding with denser regions of
flares. As a result of evaporation, the X-ray spectral-components are
expected to be Doppler shifted, which will also be measured. In this
paper, we present details of the construction of three SolpeX blocks
and discuss their functionality. Delivery of KORTES with SolpeX to
ISS is expected in 2020/2021.
Title: Analysis of the differential emission measure distributions
for solar flares observed by RESIK
Authors: Kepa, A.; Sylwester, B.; Sylwester, J.; Gryciuk, M.;
Siarkowski, M.
Bibcode: 2018JASTP.179..545K
Altcode:
The Polish X-ray spectrometer RESIK observed the spectra in four
wavelength bands from 3.3 Å to 6.1 Å. This spectral range contains
many emission lines of H- and He-like ions for Si, S, Ar and K formed
in the high temperature of solar coronal plasma. Analysis of measured
spectra gives a possibility to study the differential emission measure
distributions (DEM) in the temperature range between 1 MK and 30
MK. We present the analysis of DEM distributions of the multi-peaked
C9.8 flare observed by RESIK on 9 January 2003 adopting the model of
elementary flare profile (EFP). The model allows to distinguish the
individual flare components based on the observed light curves in
selected spectral bands.
Title: Highly Ionized Calcium and Argon X-Ray Spectra from a Large
Solar Flare
Authors: Phillips, K. J. H.; Sylwester, J.; Sylwester, B.; Kowaliński,
M.; Siarkowski, M.; Trzebiński, W.; Płocieniak, S.; Kordylewski, Z.
Bibcode: 2018ApJ...863...10P
Altcode: 2018arXiv180608584P
X-ray lines of helium-like calcium (Ca XIX) between 3.17 and 3.21 Å
and associated Ca XVIII dielectronic satellites have previously been
observed in solar flare spectra, and their excitation mechanisms are
well established. Dielectronic satellites of lower-ionization stages
(Ca XVII-Ca XV) are not as well characterized. Several spectra during
a large solar flare in 2001 by the DIOGENESS X-ray spectrometer on the
CORONAS-F spacecraft show the Ca XVII and Ca XVI satellites, as well
as lines of ionized argon (Ar XVII, Ar XVI), including dielectronic
satellites. The DIOGENESS spectra are compared with spectra from a
synthesis code developed here based on an isothermal assumption with
various atomic sources including dielectronic satellite data from the
Cowan Hartree-Fock code. Best-fit comparisons are made by varying the
temperature as the code’s input (Ar/Ca abundance ratio fixed at 0.33);
close agreement is achieved, although with adjustments to some ion
fractions. The derived temperature is close to that derived from the
two GOES X-ray channels, T GOES . Some lines are identified
for the first time. Similar spectra from the P78-1 spacecraft and the
Alcator C-Mod tokamak have also been analyzed and similar agreements
were obtained. The importance of blends of calcium and argon lines is
emphasized, affecting line ratios used for temperature diagnostics. This
analysis will be applied to the Solar Maximum Mission Bent Crystal
Spectrometer archive and to X-ray spectra expected from the ChemiX
instrument on the Sun-orbiting Interhelioprobe spacecraft, while the
relevance to X-ray spectra from non-solar sources is indicated.
Title: Solar Microflares Observed by SphinX and RHESSI
Authors: Mrozek, Tomasz; Gburek, Szymon; Siarkowski, Marek; Sylwester,
Barbara; Sylwester, Janusz; Kepa, Anna; Gryciuk, Magdalena
Bibcode: 2018SoPh..293..101M
Altcode:
In 2009, the Russian Complex Orbital Observations Near-Earth of Activity
of the Sun (CORONAS-Photon) spacecraft was launched, carrying the Polish
Solar PHotometer In X-rays (SphinX). The SphinX was most sensitive in
the spectral range 1.2 - 15 keV, thus an excellent opportunity appeared
for comparison with the low-energy end of Ramaty High Energy Solar
Spectroscopic Imager (RHESSI) spectra. Common spectral measurements
with these instruments cover the range where most of the flare energy
is accumulated. We have chosen four consecutive small solar events
observed on 4 July 2009 at 13:43 UT, 13:48 UT, 13:52 UT, and 13:55
UT (RHESSI flare peak times) and used them to compare the data and
results from the two instruments. Moreover, we included Geostationary
Operational Environmental Satellite (GOES) records in our analysis. In
practice, the range of comparison performed for SphinX and RHESSI
is limited roughly to 3 - 6 keV. RHESSI fluxes measured with a use
of one, four, and nine detectors in the 3 - 4 keV energy band agree
with SphinX measurements. However, we observed that SphinX spectral
irradiances are three times higher than those of RHESSI in the 4 -
6 keV energy band. This effect contributes to the difference in
obtained emission measures, but the derived temperatures of plasma
components are similar. RHESSI spectra were fitted using a model with
two thermal components. We have found that the RHESSI hot component
is in agreement with GOES, and the RHESSI hotter component fits the
SphinX flaring component well. Moreover, we calculated the so-called
thermodynamic measure and the total thermal energy content in the four
microflares that we studied. The results obtained show that SphinX is
a very sensitive complementary observatory for RHESSI and GOES.
Title: Highly Ionized ca X-Ray Spectra from Flares Seen with the
Diogeness Spectrometer
Authors: Sylwester, Janusz; Kowalinski, Miroslaw; Sylwester, Barbara;
Siarkowski, Marek; Kordylewski, Zbigniew; Plocieniak, Stefan;
Trzebinski, Witold; Phillips, Kenneth
Bibcode: 2018cosp...42E3313S
Altcode:
X-ray lines of helium-like calcium (Ca XIX) and nearby Ca XVIII
dielectronic satellites have been observed in solar flares with a
number of high-resolution spectrometers. The DIOGENESS instrument
on the CORONAS-F spacecraft, a scanning crystal spectrometer which
operated in 2001, observed these lines but in addition satellites
of lower ionization stages of Ca as well as ionized Ar lines in the
spectral range 3.05-3.35 Angstroms. In this work, spectra from flares
including the X5 flare on 2001 August 25 are analyzed and compared
with synthetic spectra. The latter were generated with a specially
written code based on various theoretical data including results from
the Cowan Hartree-Fock pseudo-relativistic code run for satellite
lines. Solar flare spectra taken with the P78-1 SOLFLEX instrument
in 1980-1981 are also analyzed. There is close agreement between the
solar flare and synthetic spectra for the Ca XIX lines and Ca XVIII
satellites (3.17-3.21 Angstroms) and also the Ca XVII satellites at
3.215-3.235 Angstroms clearly seen in DIOGENESS and some SOLFLEX
spectra. In addition, fainter line emission at longer wavelengths
(λ> 3.24 Angstroms) in DIOGENESS spectra is identified with Ca XVI
satellites and with the Ca XVIII "o" and "p" satellites as well as a
feature due to Ar XVI. These identifications are confirmed by recent
analysis of X-ray Ar and Ca spectra from the Alcator-C Mod tokamak
high-temperature plasmas. The synthetic code developed for this work
will be used for analysis of X-ray spectra, recently characterized
with new calibration data, from the Solar Maximum Mission Bent Crystal
Spectrometer, and spectra expected from the Polish high-resolution
ChemiX spectrometer/dopplerometer, due to fly on the [two] Russian
Interhelioprobe spacecraft in 2025/2026.
Title: Hydrodynamical 1D modelling of flaring loops during a B8.3
flare on July 04, 2009
Authors: Awasthi, Arun Kumar; Sylwester, Janusz; Sylwester, Barbara;
Reale, Fabio; Liu, Rui
Bibcode: 2018cosp...42E.147A
Altcode:
Hydrodynamical evolution of flaring plasma is crucial in understanding
the response of various layers of solar atmospheres and the role of
plasma energy transport and radiative loss processes. Although the
insights obtained from the analysis of multi-wavelength emission are
limited by the sensitivity of the observing instruments, numerical
modelling constrained by observable provides a comprehensive picture of
the underlying processes. In this regard, we investigate the evolution
of thermal characteristics of plasma during a B8.9 flare of July 04,
2009 using Palermo-Harvard (PH) 1D hydrodynamic (HD) model. The X-ray
spectra during the event, observed commonly by SphinX (1-15 keV), SOXS
(4-25 keV) and Fermi (≥6 keV) instruments, were analysed in order to
derive thermal characteristics of flaring plasma. EUV images available
from SOHO and STEREO-twin satellites were used to derive projection-free
geometrical characteristics of flaring loop(s) which are provided as an
input to the PH model along with a number of heating profiles varying
spatially across the loop and in time. Resulting temperature and density
profiles along the loop were convolved with the response matrix of GOES
X-ray monitors to derive respective fluxes and then compared with that
observed. The PH exercise which best-represented the GOES observations
during the flare was further used in mapping the spatial distribution
of emission along the flaring loop(s) as well as the evolution of
flaring plasma on the diagnostic diagram (DD; log T against log EM)
as determined from the EUV and X-ray channels. Moreover, a comparison
of differential emission measure distribution (DEM[T]) derived
from the PH model were compared with that obtained by applying the
Withbroe-Sylwester deconvolution algorithm on the combined observation
of STEREO, SphinX, SOXS and Fermi instruments. This investigation
provides an exhaustive comparison of spatial and temporal evolution
of thermal characteristics of flaring plasma as determined from the
HD modelling with that available from the EUV and X-ray measurements.
Title: Nonequilibrium Processes in the Solar Corona, Transition
Region, Flares, and Solar Wind (Invited Review)
Authors: Dudík, Jaroslav; Dzifčáková, Elena; Meyer-Vernet, Nicole;
Del Zanna, Giulio; Young, Peter R.; Giunta, Alessandra; Sylwester,
Barbara; Sylwester, Janusz; Oka, Mitsuo; Mason, Helen E.; Vocks,
Christian; Matteini, Lorenzo; Krucker, Säm; Williams, David R.;
Mackovjak, Šimon
Bibcode: 2017SoPh..292..100D
Altcode: 2017arXiv170603396D
We review the presence and signatures of the non-equilibrium processes,
both non-Maxwellian distributions and non-equilibrium ionization, in
the solar transition region, corona, solar wind, and flares. Basic
properties of the non-Maxwellian distributions are described
together with their influence on the heat flux as well as on the
rates of individual collisional processes and the resulting optically
thin synthetic spectra. Constraints on the presence of high-energy
electrons from observations are reviewed, including positive detection
of non-Maxwellian distributions in the solar corona, transition
region, flares, and wind. Occurrence of non-equilibrium ionization
is reviewed as well, especially in connection to hydrodynamic and
generalized collisional-radiative modeling. Predicted spectroscopic
signatures of non-equilibrium ionization depending on the assumed
plasma conditions are summarized. Finally, we discuss the future
remote-sensing instrumentation that can be used for the detection of
these non-equilibrium phenomena in various spectral ranges.
Title: Flare Characteristics from X-ray Light Curves
Authors: Gryciuk, M.; Siarkowski, M.; Sylwester, J.; Gburek, S.;
Podgorski, P.; Kepa, A.; Sylwester, B.; Mrozek, T.
Bibcode: 2017SoPh..292...77G
Altcode:
A new methodology is given to determine basic parameters of flares from
their X-ray light curves. Algorithms are developed from the analysis
of small X-ray flares occurring during the deep solar minimum of 2009,
between Solar Cycles 23 and 24, observed by the Polish Solar Photometer
in X-rays (SphinX) on the Complex Orbital Observations Near-Earth
of Activity of the Sun-Photon (CORONAS-Photon) spacecraft. One is a
semi-automatic flare detection procedure that gives start, peak, and end
times for single ("elementary") flare events under the assumption that
the light curve is a simple convolution of a Gaussian and exponential
decay functions. More complex flares with multiple peaks can generally
be described by a sum of such elementary flares. Flare time profiles
in the two energy ranges of SphinX (1.16 - 1.51 keV, 1.51 - 15 keV)
are used to derive temperature and emission measure as a function
of time during each flare. The result is a comprehensive catalogue -
the SphinX Flare Catalogue - which contains 1600 flares or flare-like
events and is made available for general use. The methods described
here can be applied to observations made by Geosynchronous Operational
Environmental Satellites (GOES), the Reuven Ramaty High Energy Solar
Spectroscopic Imager (RHESSI) and other broad-band spectrometers.
Title: Thermal Characteristics and the Differential Emission Measure
Distribution During a B8.3 Flare on 2009 July 4
Authors: Awasthi, Arun Kumar; Sylwester, Barbara; Sylwester, Janusz;
Jain, Rajmal
Bibcode: 2016ApJ...823..126A
Altcode: 2016arXiv160401935A
We investigate the evolution of the differential emission measure
distribution (DEM[T]) in various phases of a B8.3 flare which occurred
on 2009 July 04. We analyze the soft X-ray (SXR) emission in the
1.6-8.0 keV range, recorded collectively by the Solar Photometer in
X-rays (SphinX; Polish) and the Solar X-ray Spectrometer (Indian)
instruments. We conduct a comparative investigation of the best-fit
DEM[T] distributions derived by employing various inversion schemes,
namely, single Gaussian, power-law functions and a Withbroe-Sylwester
(W-S) maximum likelihood algorithm. In addition, the SXR spectrum in
three different energy bands, that is, 1.6-5.0 keV (low), 5.0-8.0
keV (high), and 1.6-8.0 keV (combined), is analyzed to determine
the dependence of the best-fit DEM[T] distribution on the selection
of the energy interval. The evolution of the DEM[T] distribution,
derived using a W-S algorithm, reveals multi-thermal plasma during
the rise to the maximum phase of the flare, and isothermal plasma in
the post-maximum phase of the flare. The thermal energy content is
estimated by considering the flare plasma to be (1) isothermal and
(2) multi-thermal in nature. We find that the energy content during
the flare, estimated using the multi-thermal approach, is in good
agreement with that derived using the isothermal assumption, except
during the flare maximum. Furthermore, the (multi-) thermal energy
estimated while employing the low-energy band of the SXR spectrum
results in higher values than that derived from the combined energy
band. On the contrary, the analysis of the high-energy band of the
SXR spectrum leads to lower thermal energy than that estimated from
the combined energy band.
Title: ChemiX: a Bragg crystal spectrometer for the Interhelioprobe
interplanetary mission
Authors: Siarkowski, M.; Sylwester, J.; Bąkała, J.; Szaforz, Ż.;
Kowaliński, M.; Kordylewski, Z.; Płocieniak, S.; Podgórski, P.;
Sylwester, B.; Trzebiński, W.; Stȩślicki, M.; Phillips, K. J. H.;
Dudnik, O. V.; Kurbatov, E.; Kuznetsov, V. D.; Kuzin, S.; Zimovets,
I. V.
Bibcode: 2016ExA....41..327S
Altcode: 2016ExA...tmp....1S
Interhelioprobe (IHP), an analogue to the ESA Solar Orbiter, is the
prospective Russian space solar observatory intended for in-situ and
remote sensing investigations of the Sun and the inner heliosphere
from a heliocentric orbit with the perihelion of about 60 solar
radii. One of several instruments on board will be the Bragg crystal
spectrometer ChemiX which will measure X-ray spectra from solar corona
structures. Analysis of the spectra will allow the determination of
the elemental composition of plasma in hot coronal sources like flares
and active regions. ChemiX is under development at the Wrocław Solar
Physics Division of the Polish Academy of Sciences Space Research
Centre in collaboration with an international team (see the co-author
list). This paper gives an overview of the ChemiX scientific goals
and design preparatory to phase B of the instrument development.
Title: Solar X-rays from 0.3 a.u.: the ChemiX Bragg Spectrometer
on Interhelioprobe
Authors: Sylwester, Janusz; Siarkowski, Marek; Bąkała, Jarosław;
Szaforz, Żaneta; Kowaliński, Mirosław; Stęślicki, Marek;
Sylwester, Barbara; Kordylewski, Zbigniew; Dudnik, Oleksiy; Kuznetsov,
Vladimir D.; Polansky, Valery; Kuzin, Sergey; Phillips, Kenneth J. H.
Bibcode: 2016IAUS..320..442S
Altcode:
ChemiX is a Bragg crystal spectrometer that will fly on the two
Interhelioprobe spacecraft due for launch in 2025 and 2026. The
spacecraft perihelion will be only 0.3 a.u. and the orbit inclination
up to 30°, and so instruments on board will have a close view of
solar active regions and flares and regions near each solar pole. The
ChemiX X-ray spectrometer, built by a consortium of groups led by
the Space Research Centre, Polish Academy of Sciences, will fly
on each of the spacecraft, and observe X-ray spectra in the 1.5 -
9 Å range. Spectral lines in this range include resonance lines of
helium-like and hydrogen-like ions of elements such as Fe, Ca, Ar, S,
and Si, with less abundant elements such as K and Cl represented by
weaker lines which the high sensitivity of ChemiX should be able to
detect. The free-free and free-bound continua should also be detected
since instrumental background will be eliminated. Three of the seven
channels of ChemiX will be in a ``dopplerometer'' arrangement by
which spatial and spectral shifts present in flare impulsive stages
can be disentangled.
Title: High-temperature solar flare plasma behaviour from crystal
spectrometer observations
Authors: Sylwester, Barbara; Sylwester, Janusz; Phillips, Kenneth
J. H.; Kepa, Anna; Mrozek, Tomasz
Bibcode: 2016IAUS..320...80S
Altcode:
We present results of analysis of the spectra collected with Polish
instrument RESIK flown on CORONAS-F satellite. RESIK was the bent
crystal spectrometer, measuring spectra in the spectral range 3.3 -
6.1 Å with a high cadence during flares. The emission lines as well
as the continuum observed by RESIK are formed in hotter (T > 3 MK)
plasmas of active regions and flares. RESIK observed various types of
flares: from X-ray class B and C up to strongest flares of X-class,
for both, short and long duration events. The analysis of absolute and
relative spectral intensities of the lines and continuum observed for
33 events allowed for determining the plasma elemental composition with
subsequent detailed study of time changes of the temperature structure
of the sources described in terms of the differential emission measure
(DEM). As an example we present the typical DEM evolutionary patterns
for the C1.9 flare (SOL2002-12-26T08:35) and discuss its thermodynamics.
Title: Thermal characteristics of a B8.3 flare observed on July
04, 2009
Authors: Awasthi, Arun Kumar; Sylwester, Barbara; Sylwester, Janusz;
Jain, Rajmal
Bibcode: 2016IAUS..320..112A
Altcode: 2016arXiv160401926A
We explore the temporal evolution of flare plasma parameters including
temperature (T) - differential emission measure (DEM) relationship
by analyzing high spectral and temporal cadence of X-ray emission in
1.6-8.0 keV energy band, recorded by SphinX (Polish) and Solar X-ray
Spectrometer (SOXS; Indian) instruments, during a B8.3 flare which
occurred on July 04, 2009. SphinX records X-ray emission in 1.2-15.0
keV energy band with the temporal and spectral cadence as good as 6
μs and 0.4 keV, respectively. On the other hand, SOXS provides X-ray
observations in 4-25 keV energy band with the temporal and spectral
resolution of 3 s and 0.7 keV, respectively. We derive the thermal
plasma parameters during impulsive phase of the flare employing
well-established Withbroe-Sylwester DEM inversion algorithm.
Title: Multitemperature analysis of solar flare observed on 2003
March 29
Authors: Kepa, Anna; Sylwester, Barbara; Sylwester, Janusz; Siarkowski,
Marek; Mrozek, Tomasz; Gryciuk, Magdalena
Bibcode: 2016IAUS..320...86K
Altcode:
We present results of multitemperature analysis of GOES C7.2 class
flare SOL2003-03-29T10:15. This event occurred close to the centre of
the solar disk and had two maxima in soft X-rays. We have performed
analysis of physical parameters characterizing evolution of conditions
in the flaring plasma. The temperature diagnostics have been carried
out using the differential emission measure (DEM) approach based on the
soft X-ray spectra collected by RESIK Bragg spectrometer. Analysis of
data obtained by RHESSI provided opportunity to estimate the volume
and thus calculating the density and thermal energy content of hot
flaring plasma.
Title: Solar flare soft X-ray spectra from Diogeness observations
Authors: Stȩślicki, Marek; Sylwester, Janusz; Sylwester, Barbara;
Szaforz, Żaneta; Kordylewski, Zbigniew; Płocieniak, Stefan;
Siarkowski, Marek; Phillips, Kenneth J. H.
Bibcode: 2016IAUS..320..109S
Altcode:
Diogeness was an uncollimated scanning flat crystal spectrometer
observing solar flare X-ray spectra in four narrow wavelength bands
in the vicinity of Ca xix, S xv and Si xiii He-like line `triplets'
around 3.18 Å, 5.04 Å and 6.65 Å. In two of the spectral channels,
emission lines around the Ca xix 3.178 Å resonance line were scanned
in opposite directions, being diffracted from precisely adjusted
identical Quartz crystals mounted on a common shaft in a so-called
Dopplerometer (tachometer) configuration. Observations of solar X-ray
spectra made by Diogeness provide a direct diagnostic information on
plasma characteristics during the impulsive flare energy release. We
present a sample of events which occurred during the Diogeness operation
time from August 16, 2001 to September 17, 2001.
Title: X-ray Flare Spectra from the DIOGENESS Spectrometer and Its
Concept Applied to ChemiX on the Interhelioprobe Spacecraft
Authors: Sylwester, Janusz; Kordylewski, Zbigniew; Płocieniak,
Stefan; Siarkowski, Marek; Kowaliński, Mirosław; Nowak, Stanisław;
Trzebiński, Witold; Śtęślicki, Marek; Sylwester, Barbara;
Stańczyk, Eugeniusz; Zawerbny, Ryszard; Szaforz, Żaneta; Phillips,
Kenneth J. H.; Fárník, František; Stepanov, Anatolyi
Bibcode: 2015SoPh..290.3683S
Altcode: 2015SoPh..tmp....4S; 2014arXiv1411.0850S
The DIOGENESS X-ray crystal spectrometer on the CORONAS-F spacecraft
operated only for a single month (25 August to 17 September) in 2001,
but in its short lifetime obtained one hundred and forty high-resolution
spectra of eight solar flares with GOES importance ranging from C9 to
X5. The instrument included four scanning flat crystals with wavelength
ranges covering the regions of Si XIII (6.65 Å), S XV (5.04 Å), and Ca
XIX (3.18 Å) X-ray lines and associated dielectronic satellites. Two
crystals covering the Ca XIX lines were oriented in a "dopplerometer"
manner, i.e. such that spatial and spectral displacements, both of which
commonly occur in flares, can be separated. We describe the DIOGENESS
spectrometer and the spectra obtained during flares that include lines
not hitherto seen from spacecraft instruments. An instrument with
a very similar concept is currently being built for the two Russian
Interhelioprobe spacecraft that are scheduled for launch in 2020 and
2022 and will make a near-encounter (perihelion ∼ 0.3 AU) with the
Sun in its orbit. We outline the results that are likely to be obtained.
Title: Multitemperature analysis of solar flare observed on 2003
March 29
Authors: Kepa, Anna; Sylwester, Barbara; Sylwester, Janusz; Siarkowski,
Marek; Mrozek, Tomasz; Gryciuk, Magdalena
Bibcode: 2015IAUGA..2254863K
Altcode:
We present results of multitemperature analysis of GOES C7.2 class flare
observed on 2003 March 29. This event occurred close to the centre of
the solar disk (S12W14) at 10:11 UT and had two maxima in X-rays. We
have performed analysis of physical parameters characterizing evolution
of conditions in the flaring plasma. The temperature diagnostics
have been carried out using the differential emission measure (DEM)
approach based on the soft X-ray spectra collected by RESIK Bragg
spectrometer. Analysis of data obtained by RHESSI provided opportunity
for a detailed analysis of HXR emission with good energy and spatial
resolutions.
Title: Analysis of selected solar flares soft X-ray spectra from
Diogeness observations
Authors: Steslicki, Marek; Sylwester, Janusz; Sylwester, Barbara;
Szaforz, Zaneta Anna; Kordylewski, Zbigniew; Plocieniak, Stefan;
Siarkowski, Marek; Phillips, Kenneth J. H.
Bibcode: 2015IAUGA..2254871S
Altcode:
Diogeness was the uncollimated scanning flat crystal spectrometer
observing flare X-ray spectra in four narrow wavelength bands in
vicinity of Ca XIX, S xv and Si XIII He-like line 'triplets' around
3.18 Å, 5.04 Å and 6.65 Å. In the two spectral channels, the
same emission lines around Ca XIX 3.178 Å resonance are scanned in
opposite directions, being diffracted from precisely adjusted identical
Quartz crystals mounted on the common shaft in so-called Dopplerometer
(tachometer) configuration. The observations of the solar X-ray spectrum
made by Diogeness provides a direct diagnostic information on plasma
characteristics during the impulsive flare energy release. We present
results of analysis for selected events which occurred during the
Diogeness operation time from August 16, 2001 to September 17, 2001.
Title: The X-Ray Line Feature at 3.5 KeV in Galaxy Cluster Spectra
Authors: Phillips, K. J. H.; Sylwester, B.; Sylwester, J.
Bibcode: 2015ApJ...809...50P
Altcode: 2015arXiv150704619P
Recent work by Bulbul et al. and Boyarsky et al. has suggested that
a line feature at ∼3.5 keV in the X-ray spectra of galaxy clusters
and individual galaxies seen with XMM-Newton is due to the decay of
sterile neutrinos, a dark matter candidate. This identification has
been criticized by Jeltema & Profumo on the grounds that model
spectra suggest that atomic transitions in helium-like potassium (K
xviii) and chlorine (Cl xvi) are more likely to be the emitters. Here
it is pointed out that the K xviii lines have been observed in numerous
solar flare spectra at high spectral resolution with the RESIK crystal
spectrometer and also appear in Chandra HETG spectra of the coronally
active star σ Gem. In addition, the solar flare spectra at least
indicate a mean coronal potassium abundance, which is a factor between
9 and 11 higher than the solar photospheric abundance. This fact,
together with the low statistical quality of the XMM-Newton spectra,
completely account for the ∼3.5 keV feature and there is therefore
no need to invoke a sterile neutrino interpretation of the observed
line feature at ∼3.5 keV.
Title: High-temperature solar flare plasma behaviour from crystal
spectrometer observations
Authors: Sylwester, Barbara; Sylwester, Janusz; Phillips, Kenneth
J. H.; Kepa, Anna; Mrozek, Tomasz
Bibcode: 2015IAUGA..2254762S
Altcode:
We discuss an analysis of spectra obtained from the Polish RESIK
instrument flown on the CORONAS-F satellite. RESIK was a bent crystal
spectrometer operating in the 3.3—6.1 Å range at high spectral and
time resolution during flares over the 2002—2003 period, at the
peak of the last solar cycle. Unlike many previous spectrometers,
RESIK was accurately (20%) calibrated and crystal fluorescence was
either eliminated or reduced to a minimum. The emission lines and
continuum observed are formed at high temperatures (T > 3 MK) that
are commonly present in active regions and flares. The spectra were
observed during flares ranging in GOES importance from B and C up to
multiples of X and with durations that were short and impulsive up
to several hours. An analysis of absolute and relative intensities of
lines and continuum that we performed for 33 flare events allowed the
determination of the plasma composition (abundances of Si, S, Ar, K, and
even the low-abundance element Cl) as well as a detailed study of the
time evolution of the flare temperature structure from the differential
emission measure (DEM). We will present the typical DEM evolutionary
patterns of the flares seen and discuss their thermodynamics which
helps our understanding of flares.
Title: X-ray spectra and analysis tools to be used in interpretation
of ChemiX Bragg spectrometer under construction for the
Interhelioprobe
Authors: Sylwester, Janusz; Siarkowski, Marek; Bakala, Jaroslaw;
Szaforz, Zaneta Anna; Kowalinski, Miroslaw; Steslicki, Marek;
Sylwester, Barbara; Volodymyrovich Dudnik, Oleksiy; Dmitrievich
Kuznetsov, Vladimir; Vadimovich Kuzin, Sergey; Phillips, Kenneth J. H.
Bibcode: 2015IAUGA..2254649S
Altcode:
ChemiX (CHEMical composition In X-rays) is a next-generation bent
crystal spectrometer designed for detailed fast-cadence measurements of
the soft X-ray spectra of solar sources in the spectral range 1.3 -
9 Angstroms instantaneously at all wavelengths. The instrument will
be placed on each of the two Russian interplanetary Interhelioprobe
missions (Solar Orbiter orbit), to be launched in 2020 and
2022. Phase B of the instrument construction is to be completed
soon.I shall describe the instrument in some detail (pin-hole
imager, background particle detector, four spectral atlas channels,
three ``Dopplerometer'' sections) focusing on the spectra to be
measured (and synthesized) for various types of solar X-ray sources
(flares with various characteristics, non-flaring active regions,
and the quiet corona). The likely observing modes to be used will
be discussed, covering various phases of the mission. Some example
spectral analysis tools will also be illustrated, allowing the study
of source characteristics including plasma composition, differential
emission measure, turbulent and directed bulk plasma motions, thermal
energy content etc. The sensitivity of the spectrometer to plasma
non-equilibrium effects will also be indicated.
Title: Thermal characteristics of multi-wavelength emission during
a B8.3 flare occurred on July 04, 2009
Authors: Awasthi, Arun Kumar; Sylwester, Barbara; Sylwester, Janusz;
Jain, Rajmal
Bibcode: 2015IAUGA..2254894A
Altcode:
We explore the temporal evolution of flare plasma parameters including
temperature (T) - differential emission measure (DEM) relationship
by analyzing high spectral and temporal cadence X-ray emission in
1.2-20 keV energy band, recorded by SphinX (Polish) and Solar X-ray
Spectrometer (SOXS; Indian) instruments, during a B8.3 flare which
occurred on July 04, 2009. SphinX records X-ray emission in 1.2-15 keV
energy band with the temporal and spectral cadence as good as 6µs
and 0.4 keV, respectively. On the other hand, SOXS provides X-ray
observations in 4-25 keV energy band with the temporal and spectral
resolution of 3s and 0.7 keV, respectively. In addition, we integrate
co-temporal EUV line emission in 171, 194 and 284 angstrom obtained
from STEREO mission in order to explore low-temperature response to the
flare emission. In order to fit observed evolution of multi-wavelength
emission during the flare, we incorporate multi-Gaussian and
well-established Withbroe - Sylwester maximum likelihood DEM inversion
algorithms. Thermal energetics are also estimated using geometrically
corrected flaring loop structure obtained through EUV images of the
active region from STEREO twin satellites. In addition, we also study
the trigger and energy release scenario of this low-intensity class
flare in terms of magnetic field as well as multi-wavelength emission.
Title: Resik Solar X-Ray Flare Element Abundances on a Non-isothermal
Assumption
Authors: Sylwester, B.; Phillips, K. J. H.; Sylwester, J.; Kępa, A.
Bibcode: 2015ApJ...805...49S
Altcode: 2015arXiv150300979S
Solar X-ray spectra from the REntgenovsky Spektrometr s Izognutymi
Kristalami (RESIK) crystal spectrometer on the CORONAS-F spacecraft
(spectral range 3.3-6.1 Å) are analyzed for 33 flares using a
method to derive abundances of Si, S, Ar, and K, emission lines
of which feature prominently in the spectra. For each spectrum,
the method first optimizes element abundances and then derives the
differential emission measure as a function of temperature based on
a procedure given by Sylwester et al. and Withbroe. This contrasts
with our previous analyses of RESIK spectra in which an isothermal
assumption was used. The revised abundances (on a logarithmic scale with
A(H)=12) averaged for all the flares in the analysis are A(Si)=7.53+/-
0.08 (previously 7.89 ± 0.13), A(S)=6.91+/- 0.07 (7.16 ± 0.17),
A(Ar)=6.47+/- 0.08 (6.45 ± 0.07), and A(K)=5.73+/- 0.19 (5.86 ±
0.20), with little evidence for time variations of abundances within
the evolution of each flare. Our previous estimates of the Ar and K
flare abundances are thus confirmed by this analysis, but those for
Si and S are reduced. This suggests that the flare abundances of Si
and Ar are very close to the photospheric abundance or solar proxies,
while S is significantly less than photospheric and the K abundance is
much higher than photospheric. These estimates differ to some extent
from those in which a single enhancement factor applies to elements
with first ionization potential less than 10 eV.
Title: Solar activity during the deep minimum of 2009
Authors: Sylwester, Janusz; Siarkowski, Marek; Gburek, Szymon; Gryciuk,
Magdalena; Kepa, Anna; Kowaliński, Mirosław; Mrozek, Tomek; Phillips,
Kenneth J. H.; Podgórski, Piotr; Sylwester, Barbara
Bibcode: 2014pas..conf...82S
Altcode:
We discuss the character of the unusually deep solar activity minimum
of 2009 between Solar Cycles 23 and 24. Levels of solar activity in
various parts of the solar atmosphere -- photosphere, chromosphere,
transition region, and corona -- were observed to be at their lowest
for a century. The soft X-ray emission from the corona (hot outer part
of the Sun's atmosphere) was measured throughout most of 2009 with the
Polish-built SphinX spectrophotometer. Unlike other X-ray monitoring
spacecraft, this sensitive spacecraft-borne instrument was able to
continue measurements throughout this extended period of low activity.
Title: Solar Flare Composition and Thermodynamics from RESIK X-Ray
Spectra
Authors: Sylwester, B.; Sylwester, J.; Phillips, K. J. H.; Kępa,
A.; Mrozek, T.
Bibcode: 2014ApJ...787..122S
Altcode: 2014arXiv1404.5775S
Previous estimates of the solar flare abundances of Si, S, Cl, Ar,
and K from the RESIK X-ray crystal spectrometer on board the CORONAS-F
spacecraft were made on the assumption of isothermal X-ray emission. We
investigate the effect on these estimates by relaxing this assumption
and instead determining the differential emission measure (DEM) or
thermal structure of the emitting plasma by re-analyzing RESIK data
for a GOES class M1.0 flare on 2002 November 14 (SOL2002-11-14T22:26)
for which there was good data coverage. The analysis method uses a
maximum-likelihood (Withbroe-Sylwester) routine for evaluating the
DEM. In a first step, called here AbuOpt, an optimized set of abundances
of Si, S, Ar, and K is found that is consistent with the observed
spectra. With these abundances, the DEM evolution during the flare
is found. The abundance optimization leads to revised abundances of
silicon and sulfur in the flare plasma: A(S) = 6.94 ± 0.06 and A(Si)
= 7.56 ± 0.08 (on a logarithmic scale with A(H) = 12). Previously
determined abundances of Ar, K, and Cl from an isothermal assumption
are still the preferred values. During the flare's maximum phase,
the X-ray-emitting plasma has a basically two-temperature structure,
with the cooler plasma with approximately constant temperature (3-6 MK)
and a hotter plasma with temperature 16-21 MK. Using imaging data from
the RHESSI hard X-ray spacecraft, the emission volume of the hot plasma
is deduced from which lower limits of the electron density Ne
and the thermal content of the plasma are given.
Title: Soft X-ray spectra of strong flares seen by Bragg flat crystal
spectrometer aboard Coronas-F
Authors: Sylwester, Barbara; Sylwester, Janusz; Farnik, Frantisek;
Siarkowski, Marek; Kordylewski, Zbigniew; Plocieniak, Stefan; Phillips,
Kenneth; Steslicki, Marek
Bibcode: 2014cosp...40E3257S
Altcode:
The uncollimated flat crystal spectrometer Diogeness was one of the
instruments observing the high-temperature plasma in 2001, around
the time of the maximum of Solar Cycle 23, from the payload of the
CORONAS-F satellite. This Polish-built scanning spectrometer measured
spectra with very high spectral resolution in three selected bands in
the vicinity of He-like triplets of Ca XIX, S XV and Si XIII, around
3.18 Å, 5.04 Å and 6.65 Å respectively. During its operation, a few
thousand spectral scans were performed and unique spectral sequences
obtained for a number of strong flares. Tens of lines are seen on the
spectra, some of them for Mg, Ar and Ca ions identified for the first
time. The time-evolution of spectral line profiles and intensities
will be presented and discussed for selected events. Reduced line
intensities will be interpreted in terms of differential emission
measure distributions.
Title: Analysis of selected microflares observed by SphinX over the
last minimum of solar activity
Authors: Siarkowski, Marek; Sylwester, Janusz; Sylwester, Barbara;
Gryciuk, Magdalena
Bibcode: 2014cosp...40E3068S
Altcode:
The Solar Photometer in X-rays (SphinX) was designed to observe
soft X-ray solar emission in the energy range between 1 keV and 15
keV with the resolution better than 0.5 keV. The instrument operated
from February until November 2009 aboard CORONAS-Photon satellite,
during the phase of exceptionally low minimum of solar activity. Here
we use SphinX data for analysis of selected microflare-class events. We
selected events of unusual lightcurves or location. Our study involves
determination of temporal characteristics (times of start, maximum
and end of flares) and analysis of physical conditions in flaring
plasma (temperature, emission measure). Dedicated method has been
used in order to remove emission not related to flare. Supplementary
information about morphology and evolution of investigated events has
been derived from the analysis of XRT/Hinode and SECCHI /STEREO images.
Title: Chromospheric dynamics from RHESSI and RESIK data.
Authors: Mrozek, Tomasz; Sylwester, Janusz; Sylwester, Barbara;
Gburek, Szymon; Siarkowski, Marek; Kolomanski, Sylwester; Gryciuk,
Magdalena; Kepa, Anna; Szaforz, Zaneta; Steslicki, Marek
Bibcode: 2014cosp...40E2191M
Altcode:
We used RHESSI and RESIK observations of solar flares with clearly
seen double foot points morphology. RESIK spectra were obtained for
individual flare phases and used for estimation of the time evolution
of thermodynamical characteristics of flare loop-top source. The
analysis of HXR foot point sources, seen by RHESSI in narrow energy
bands, enabled us to trace changes of their altitude. The changes
are connected with the energy carried by non-thermal electrons which
penetrate deeper into solar atmosphere when of higher energies. Study
of time-dependent pattern of locations allowed us to trace changes of
the plasma density within very small volumes where the non-thermal
electrons deposit their energy. The relation between energy and
altitude of the HXR foot point sources provides unique opportunity to
study real plasma dynamics (the moving mass content may be estimated),
not only kinematics. It was found that the estimated mass that flows
during chromospheric evaporation is comparable to the additional mass
that supplies the loop top source. The analysis of plasma velocity
was used for calculation of full energy balance of analysed flares
and for the comparison with results of hydrodynamical flare modeling.
Title: Observations of Doppler Shifts of X-Ray Lines in Solar Flare
Spectra Based on DIOGENESS Spectrometer Data
Authors: Kordylewski, Z.; Sylwester, J.; Sylwester, B.; Siarkowski,
M.; Płocieniak, S.; Kȩpa, A.; Kowaliński, M.; Trzebiński, W.;
Farnik, F.
Bibcode: 2014ASSL..400..149K
Altcode:
The idea of measurement of X-ray lines Doppler shifts in spectra of
the Sun, applied in DIOGENESS spectrometer, was previously developed
and verified in rocket experiment with RDR X-ray Dopplerometer
(Vertical-11 Rocket, 1981). Upon the obtained results two X-ray
DIOGENESS spectrometers have been manufactured; the first one was
operated aboard the CORONAS-I satellite (launch in 1994), while the
second was operated aboard the CORONAS-F.
Title: Investigations of Physical Processes in Solar Flare Plasma
on the Basis of RESIK Spectrometer Observations
Authors: Kordylewski, Z.; Sylwester, J.; Sylwester, B.; Kȩpa, A.;
Kowaliński, M.; Trzebiński, W.
Bibcode: 2014ASSL..400..157K
Altcode:
Simultaneous registration of spectra of quickly varying sources may
be obtained through the use of curved fixed crystals instead of the
scanning flat crystals spectrometer. Illuminating such a curved crystal
with parallel X-ray beam allows to obtain, after the reflection, the
whole spectrum covering certain wavelengths range, as the incidence
angle at curved crystal surface represents a monotonous function of
incidence point position measured along the crystal. The RESIK bent
crystal spectrometer was developed in Poland with the help from experts
of Naval Research Laboratory (USA), Rutherford Appleton Laboratory (UK),
and Mullard Space Science Laboratory (MSSL, UK). The development work
was also supported by scientists of Pushkov Institute of Terrestrial
Magnetism, Ionosphere and Radio Waves Propagation of the Russian
Academy of Sciences. Unique RESIK spectra and the results obtained
are presented and discussed.
Title: Common observations of solar X-rays from SPHINX/CORONAS-PHOTON
and XRS/MESSENGER
Authors: Kepa, Anna; Sylwester, Janusz; Sylwester, Barbara; Siarkowski,
Marek; Mrozek, Tomasz; Gryciuk, Magdalena; Phillips, Kenneth
Bibcode: 2014cosp...40E1451K
Altcode:
SphinX was a soft X-ray spectrophotometer constructed in the Space
Research Centre of Polish Academy of Sciences. The instrument was
launched on 30 January 2009 aboard CORONAS-PHOTON satellite as a
part of TESIS instrument package. SphinX measured total solar X-ray
flux in the energy range from 1 to 15 keV during the period of very
low solar activity from 20 February to 29 November 2009. For these
times the solar detector (X-ray Spectrometer - XRS) onboard MESSENGER
also observed the solar X-rays from a different vantage point. XRS
measured the radiation in similar energy range. We present results
of the comparison of observations from both instruments and show the
preliminary results of physical analysis of spectra for selected flares.
Title: Anomalous intensities of lines observed in RESIK soft X-ray
flare spectra
Authors: Sylwester, Barbara; Sylwester, Janusz; Mrozek, Tomasz; Kepa,
Anna; Phillips, Kenneth
Bibcode: 2014cosp...40E3256S
Altcode:
RESIK was a high-resolution solar X-ray Bragg spectrometer, the most
recent ever to be launched, being operational from 2001 to 2003. Its
nominal wavelength coverage, 3.3 Å - 6.1 Å, has considerable
diagnostic potential. RESIK observed numerous flares as well as
non-flaring active regions. During flares, the data gathering intervals
were as short as 2 s. Analysis of the data continues to the present
time; at the time of writing, data for more than 50 flares have been
reduced to science grade (level 2). The spectra include spectral
lines formed by H- and He-like ions of various elements as well as
continuum. The lines and continua are formed by hot coronal plasma
corresponding to temperatures T>2 MK if interpreted thermally. This
makes RESIK spectra uniquely suitable for investigations of the
physical conditions of the hotter plasma component of flares and active
regions. Many spectra were taken during the rise phase of flares. For
some events, anomalous line intensity ratios are evident, possibly
reflecting the presence of non-equilibrium conditions in flaring
plasma -- the observed intensity ratios are not easily explained by
isothermal or multi-thermal assumptions. In our presentation, we will
show examples of such observations and give possible interpretations.
Title: Flat crystal Bragg observations of the X-ray spectra during
impulsive phases of solar flares
Authors: Steslicki, Marek; Sylwester, Janusz; Farnik, Frantisek;
Sylwester, Barbara; Gburek, Szymon; Mrozek, Tomasz; Kordylewski,
Zbigniew; Plocieniak, Stefan; Trzebinski, Witold; Szaforz, Zaneta
Bibcode: 2014cosp...40E3203S
Altcode:
Diogeness is the uncollimated scanning flat crystal spectrometer
observing high-resolution flare X-ray spectra in four narrow wavelength
bands in the vicinity of Ca XIX, S xv and Si XIII He-like line
'triplets' around 3.18 Å, 5.04 Å and 6.65 Å. For? two spectral
channels, the same emission lines around Ca XIX 3.178 Å triplet
are scanned in opposite directions, being diffracted from precisely
adjusted identical Quartz crystals mounted on the common shaft in
so-called Dopplerometer configuration. The observations of the solar
X-ray spectra made by Diogeness during rising phases provide a direct
diagnostic of the impulsive energy release of the flare. We present
results of analysis for of a several events occurred between August 16,
2001 and September 17, 2001.
Title: Erratum: "Stellar Coronae, Solar Flares: A Detailed Comparison
of σ Gem, HR 1099, and the Sun in High-resolution X-Rays" (2013, ApJ, 768, 135)
Authors: Huenemoerder, David P.; Phillips, Kenneth J. H.; Sylwester,
Janusz; Sylwester, Barbara
Bibcode: 2013ApJ...776..139H
Altcode:
No abstract at ADS
Title: Solar flares observed simultaneously with SphinX, GOES
and RHESSI
Authors: Mrozek, Tomasz; Gburek, Szymon; Siarkowski, Marek; Sylwester,
Barbara; Sylwester, Janusz; Kępa, Anna; Gryciuk, Magdalena
Bibcode: 2013IAUS..294..571M
Altcode:
In February 2009, during recent deepest solar minimum, Polish Solar
Photometer in X-rays (SphinX) begun observations of the Sun in the
energy range of 1.2-15 keV. SphinX was almost 100 times more sensitive
than GOES X-ray Sensors. The silicon PIN diode detectors used in the
experiment were carefully calibrated on the ground using Synchrotron
Radiation Source BESSY II. The SphinX energy range overlaps with
the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) energy
range. The instrument provided us with observations of hundreds of
very small flares and X-ray brightenings. We have chosen a group of
solar flares observed simultaneously with GOES, SphinX and RHESSI and
performed spectroscopic analysis of observations wherever possible. The
analysis of thermal part of the spectra showed that SphinX is a very
sensitive complementary observatory for RHESSI and GOES.
Title: Stellar Coronae, Solar Flares: A Detailed Comparison of σ GEM,
HR 1099, and the Sun in High-resolution X-Rays
Authors: Huenemoerder, David P.; Phillips, Kenneth J. H.; Sylwester,
Janusz; Sylwester, Barbara
Bibcode: 2013ApJ...768..135H
Altcode: 2013arXiv1304.0408H
The Chandra High Energy Transmission Grating Spectrometer (HETG) spectra
of the coronally active binary stars σ Gem and HR 1099 are among the
highest fluence observations for such systems taken at high spectral
resolution in X-rays with this instrument. This allows us to compare
their properties in detail to solar flare spectra obtained with the
Russian CORONAS-F spacecraft's RESIK instrument at similar resolution in
an overlapping bandpass. Here we emphasize the detailed comparisons of
the 3.3-6.1\,{\mathring{\rm{A}}} region (including emission from highly
ionized S, Si, Ar, and K) from solar flare spectra to the corresponding
σ Gem and HR 1099 spectra. We also model the larger wavelength range
of the HETG, from 1.7 to 25\,{\mathring{\rm{A}}}—having emission
lines from Fe, Ca, Ar, Si, Al, Mg, Ne, O, and N—to determine coronal
temperatures and abundances. σ Gem is a single-lined coronally
active long-period binary which has a very hot corona. HR 1099 is a
similar, but shorter period, double-lined system. With very deep HETG
exposures we can even study emission from some of the weaker species,
such as K, Na, and Al, which are important since they have the lowest
first ionization potentials, a parameter well known to be correlated
with elemental fractionation in the solar corona. The solar flare
temperatures reach ≈20 MK, comparable to the σ Gem and HR 1099
coronae. During the Chandra exposures, σ Gem was slowly decaying from a
flare and its spectrum is well characterized by a collisional ionization
equilibrium plasma with a broad temperature distribution ranging from
2 to 60 MK, peaking near 25 MK, but with substantial emission from 50
MK plasma. We have detected K XVIII and Na XI emission which allow us
to set limits on their abundances. HR 1099 was also quite variable in
X-rays, also in a flare state, but had no detectable K XVIII. These
measurements provide new comparisons of solar and stellar coronal
abundances, especially at the lowest first ionization potential (FIP)
values. The low FIP elements do not show enhancement in the stellar
coronae as they do in the Sun, except perhaps for K in σ Gem. While
σ Gem and HR 1099 differ in their emission measure distributions,
they have very similar elemental abundances.
Title: SphinX: The Solar Photometer in X-Rays
Authors: Gburek, Szymon; Sylwester, Janusz; Kowalinski, Miroslaw;
Bakala, Jaroslaw; Kordylewski, Zbigniew; Podgorski, Piotr; Plocieniak,
Stefan; Siarkowski, Marek; Sylwester, Barbara; Trzebinski, Witold;
Kuzin, Sergey V.; Pertsov, Andrey A.; Kotov, Yurij D.; Farnik,
Frantisek; Reale, Fabio; Phillips, Kenneth J. H.
Bibcode: 2013SoPh..283..631G
Altcode: 2012SoPh..tmp..326G
Solar Photometer in X-rays (SphinX) was a spectrophotometer developed to
observe the Sun in soft X-rays. The instrument observed in the energy
range ≈ 1 - 15 keV with resolution ≈ 0.4 keV. SphinX was flown on
the Russian CORONAS-PHOTON satellite placed inside the TESIS EUV and X
telescope assembly. The spacecraft launch took place on 30 January 2009
at 13:30 UT at the Plesetsk Cosmodrome in Russia. The SphinX experiment
mission began a couple of weeks later on 20 February 2009 when the first
telemetry dumps were received. The mission ended nine months later on 29
November 2009 when data transmission was terminated. SphinX provided an
excellent set of observations during very low solar activity. This was
indeed the period in which solar activity dropped to the lowest level
observed in X-rays ever. The SphinX instrument design, construction,
and operation principle are described. Information on SphinX data
repositories, dissemination methods, format, and calibration is given
together with general recommendations for data users. Scientific
research areas in which SphinX data find application are reviewed.
Title: Silicon Abundance from RESIK Solar Flare Observations
Authors: Sylwester, B.; Phillips, K. J. H.; Sylwester, J.; Kȩpa, A.
Bibcode: 2013SoPh..283..453S
Altcode: 2012arXiv1212.2914S
The RESIK instrument on the CORONAS-F spacecraft obtained solar
flare and active-region X-ray spectra in four channels covering the
wavelength range 3.8 - 6.1 Å in its operational period between 2001
and 2003. Several highly ionized silicon lines were observed within
the range of the long-wavelength channel (5.00 - 6.05 Å). The fluxes
of the Si XIV Ly-β line (5.217 Å) and the Si XIII 1s2
- 1s3p line (5.688 Å) during 21 flares with optimized pulse-height
analyzer settings on RESIK have been analyzed to obtain the silicon
abundance relative to hydrogen in flare plasmas. As in previous work,
the emitting plasma for each spectrum is assumed to be characterized
by a single temperature and emission measure given by the ratio
of emission in the two channels of GOES. The silicon abundance is
determined to be A(Si)=7.93±.21 (Si XIV) and 7.89±.13 (Si XIII)
on a logarithmic scale with H=12. These values, which vary by only
very small amounts from flare to flare and times within flares, are
2.6±1.3 and 2.4±0.7 times the photospheric abundance, and are about
a factor of three higher than RESIK measurements during a period of
very low activity. There is a suggestion that the Si/S abundance ratio
increases from active regions to flares.
Title: Diagnostics of Non-Thermal Distribution from RESIK and RHESSI
Flare Spectra
Authors: Kulinová, A.; Kašparová, J.; Dzifčáková, E.; Sylwester,
J.; Sylwester, B.
Bibcode: 2012ASPC..454..329K
Altcode:
Solar flare spectra observed by the X-ray spectrometers RESIK and
RHESSI with high energy resolution enabled us to analyse possible
non-thermality of plasma electron distribution in the keV range. For
RESIK diagnostics (in the 2-4 keV range) we assumed that the bulk
of the plasma is represented by the so-called n-distribution, which
describes the deviations from the Maxwellian distribution by two
parameters: n and T. Using thick-target approximation for RHESSI
spectral analysis, we obtained characteristics of injected electron
power-law distribution in the deka-keV range. The event presented here
shows a very good time correlation of non-thermality obtained from
the RESIK spectra with appearance of non-thermal component in RHESSI
and/or radio spectra. However, a thermal component was still present
in RHESSI. Both spectral and imaging information in RHESSI soft and
hard X-ray ranges were used for the estimation of the ratio of thermal
to non-thermal electron densities of the X-ray emitting plasma.
Title: Review of Solar Active Region Properties During Very Low
Activity Level
Authors: Gburek, Szymon; Sylwester, Barbara; Siarkowski, Marek;
Gryciuk, Magdalena
Bibcode: 2012cosp...39..598G
Altcode: 2012cosp.meet..598G
No abstract at ADS
Title: The Solar Flare Sulfur Abundance from RESIK Observations
Authors: Sylwester, J.; Sylwester, B.; Phillips, K. J. H.; Kuznetsov,
V. D.
Bibcode: 2012ApJ...751..103S
Altcode: 2012arXiv1203.5888S
The RESIK instrument on CORONAS-F spacecraft observed several sulfur
X-ray lines in three of its four channels covering the wavelength range
3.8-6.1 Å during solar flares. The fluxes are analyzed to give the
sulfur abundance. Data are chosen for when the instrument parameters
were optimized. The measured fluxes of the S XV 1s 2-1s4p
(w4) line at 4.089 Å gives A(S) = 7.16 ± 0.17 (abundances on a
logarithmic scale with A(H) = 12) which we consider to be the most
reliable. Estimates from other lines range from 7.13 to 7.24. The
preferred S abundance estimate is very close to recent photospheric
abundance estimates and to quiet-Sun solar wind and meteoritic
abundances. This implies no fractionation of sulfur by processes tending
to enhance the coronal abundance from the photospheric that depend on
the first ionization potential (FIP), or that sulfur, though its FIP
has an intermediate value of 10.36 eV, acts like a "high-FIP" element.
Title: SphinX Measurements of the 2009 Solar Minimum X-Ray Emission
Authors: Sylwester, J.; Kowalinski, M.; Gburek, S.; Siarkowski, M.;
Kuzin, S.; Farnik, F.; Reale, F.; Phillips, K. J. H.; Bakała, J.;
Gryciuk, M.; Podgorski, P.; Sylwester, B.
Bibcode: 2012ApJ...751..111S
Altcode: 2012arXiv1203.6809S
The SphinX X-ray spectrophotometer on the CORONAS-PHOTON spacecraft
measured soft X-ray emission in the 1-15 keV energy range during
the deep solar minimum of 2009 with a sensitivity much greater
than GOES. Several intervals are identified when the X-ray flux
was exceptionally low, and the flux and solar X-ray luminosity
are estimated. Spectral fits to the emission at these times
give temperatures of 1.7-1.9 MK and emission measures between
4 × 1047 cm-3 and 1.1 × 1048
cm-3. Comparing SphinX emission with that from the Hinode
X-ray Telescope, we deduce that most of the emission is from general
coronal structures rather than confined features like bright points. For
one of 27 intervals of exceptionally low activity identified in the
SphinX data, the Sun's X-ray luminosity in an energy range roughly
extrapolated to that of ROSAT (0.1-2.4 keV) was less than most nearby
K and M dwarfs.
Title: Common SphinX and RHESSI observations of solar flares
Authors: Mrozek, T.; Gburek, S.; Siarkowski, M.; Sylwester, B.;
Sylwester, J.; Gryciuk, M.
Bibcode: 2012CEAB...36...71M
Altcode:
The Polish X-ray spectrofotometer SphinX has observed a great number
of solar flares in the year 2009 - during the most quiet solar
minimum almost over the last 100 years. Hundreds of flares have been
recorded due to excellent sensitivity of SphinX's detectors. The Si-PIN
diodes are about 100 times more sensitive to X-rays than GOES X-ray
Monitors. SphinX detectors were absolutely calibrated on Earth with a
use of the BESSY synchrotron. In space observations were made in the
range 1.2-15~keV with 480~eV energy resolution. SphinX data overlap
with the low-energy end of the Ramaty High Energy Solar Spectroscopic
Imager (RHESSI) data. RHESSI detectors are quite old (7 years in 2009),
but still sensitive enough to provide us with observations of extremely
weak solar flares such as those which occurred in 2009. We have selected
a group of flares simultaneously observed by RHESSI and SphinX and
performed a spectroscopic analysis of the data. Moreover, we compared
the physical parameters of these flares plasma. Preliminary results
of the comparison show very good agreement between both instruments.
Title: The Solar Flare Chlorine Abundance from RESIK X-Ray Spectra
Authors: Sylwester, B.; Phillips, K. J. H.; Sylwester, J.; Kuznetsov,
V. D.
Bibcode: 2011ApJ...738...49S
Altcode: 2011arXiv1106.1387S
The abundance of chlorine is determined from X-ray spectra obtained
with the RESIK instrument on CORONAS-F during solar flares between 2002
and 2003. Using weak lines of He-like Cl, Cl XVI, between 4.44 and
4.50 Å, and with temperatures and emission measures from GOES on an
isothermal assumption, we obtained A(Cl) = 5.75 ± 0.26 on a scale A(H)
= 12. The uncertainty reflects an approximately a factor of two scatter
in measured line fluxes. Nevertheless, our value represents what is
probably the best solar determination yet obtained. It is higher by
factors of 1.8 and 2.7 than Cl abundance estimates from an infrared
sunspot spectrum and nearby H II regions. The constancy of the RESIK
abundance values over a large range of flares (GOES class from below
C1 to X1) argues for any fractionation that may be present in the low
solar atmosphere to be independent of the degree of solar activity.
Title: Diagnostics of non-thermal distributions in solar flare
spectra observed by RESIK and RHESSI
Authors: Kulinová, A.; Kašparová, J.; Dzifčáková, E.; Sylwester,
J.; Sylwester, B.; Karlický, M.
Bibcode: 2011A&A...533A..81K
Altcode: 2011arXiv1109.1011K
Context. During solar flares an enormous amount of energy is released,
and the charged particles, like electrons, are accelerated. These
non-thermal electrons interact with the plasma in various parts
of solar flares, where the distribution function of electrons can
therefore be non-Maxwellian.
Aims: We focus on the non-thermal
components of the electron distribution in the keV range and analyse
high-energy resolution X-ray spectra detected by RESIK and RHESSI for
three solar flares.
Methods: In the 2-4 keV range we assume that
the electron distribution can be modelled by an n-distribution. Using
a method of line-intensity ratios, we analyse allowed and satellite
lines of Si observed by RESIK and estimate the parameters of this
n-distribution. At higher energies we explore RHESSI bremsstrahlung
spectra. Adopting a forward-fitting approach and thick-target
approximation, we determine the characteristics of injected electron
beams.
Results: RHESSI non-thermal component associated with
the electron beam is correlated well with presence of the non-thermal
n-distribution obtained from the RESIK spectra. In addition, such an
n-distribution occurs during radio bursts observed in the 0.61-15.4
GHz range. Furthermore, we show that the n-distribution could also
explain RHESSI emission below ~5 keV. Therefore, two independent
diagnostics methods indicate the flare plasma being affected by
the electron beam can have a non-thermal component in the ~2-5 keV
range, which is described by the n-distribution well. Finally,
spectral line analysis reveals that the n-distribution does not
occupy the same location as the thermal component detected by RHESSI
at ~10 keV. Appendix A is available in electronic form at http://www.aanda.org
Title: SphinX soft X-ray spectrophotometer: Science objectives,
design and performance
Authors: Gburek, S.; Sylwester, J.; Kowalinski, M.; Bakala, J.;
Kordylewski, Z.; Podgorski, P.; Plocieniak, S.; Siarkowski, M.;
Sylwester, B.; Trzebinski, W.; Kuzin, S. V.; Pertsov, A. A.; Kotov,
Yu. D.; Farnik, F.; Reale, F.; Phillips, K. J. H.
Bibcode: 2011SoSyR..45..189G
Altcode:
The goals and construction details of a new design Polish-led X-ray
spectrophotometer are described. The instrument is aimed to observe
emission from entire solar corona and is placed as a separate block
within the Russian TESIS X- and EUV complex aboard the CORONAS-PHOTON
solar orbiting observatory. SphinX uses silicon PIN diode detectors
for high time resolution measurements of the solar spectra in the
range 0.8-15 keV. Its spectral resolution allows for discerning more
than hundred separate energy bands in this range. The instrument
dynamic range extends two orders of magnitude below and above these
representative for GOES. The relative and absolute accuracy of spectral
measurements is expected to be better than few percent, as follows
from extensive ground laboratory calibrations.
Title: Soft X-ray variability over the present minimum of solar
activity as observed by SphinX
Authors: Gburek, S.; Siarkowski, M.; Kepa, A.; Sylwester, J.;
Kowalinski, M.; Bakala, J.; Podgorski, P.; Kordylewski, Z.; Plocieniak,
S.; Sylwester, B.; Trzebinski, W.; Kuzin, S.
Bibcode: 2011SoSyR..45..182G
Altcode:
Solar Photometer in X-rays (SphinX) is an instrument designed to
observe the Sun in X-rays in the energy range 0.85-15.00 keV. SphinX
is incorporated within the Russian TESIS X and EUV telescope complex
aboard the CORONAS-Photon satellite which was launched on January 30,
2009 at 13:30 UT from the Plesetsk Cosmodrome, northern Russia. Since
February, 2009 SphinX has been measuring solar X-ray radiation nearly
continuously. The principle of SphinX operation and the content of the
instrument data archives is studied. Issues related to dissemination
of SphinX calibration, data, repository mirrors locations, types of
data and metadata are discussed. Variability of soft X-ray solar flux
is studied using data collected by SphinX over entire mission duration.
Title: Physical Characteristics of AR 11024 Plasma Based on SPHINX
and XRT Data
Authors: Sylwester, B.; Sylwester, J.; Siarkowski, M.; Engell, A. J.;
Kuzin, S. V.
Bibcode: 2011CEAB...35..171S
Altcode:
We have studied the evolution of basic physical properties of plasma
within the coronal part of the isolated, new cycle region (AR 11024)
during its crossing over the solar disc in July 2009. Our analysis
is based on the high temporal and spectral resolution measurements
performed by the Polish X-ray spectrometer SphinX onboard the
CORONAS-Photon satellite. Hinode XRT images provide information on
spatial extension of the emission within this active region. It is
found that the average temperature of the plasma within the analysed
region is the highest (∼6 MK) when the region is young and gradually
declines to ∼2 MK when the emission measure is the highest. An
average density during this first part of the evolution is estimated
to be ∼2 x 10^9 cm^{-3}.
Title: Flares and Their Underlying Magnetic Complexity
Authors: Engell, Alexander J.; Siarkowski, Marek; Gryciuk, Magda;
Sylwester, Janusz; Sylwester, Barbara; Golub, Leon; Korreck, Kelly;
Cirtain, Jonathan
Bibcode: 2011ApJ...726...12E
Altcode:
SphinX (Solar PHotometer IN X-rays), a full-disk-integrated
spectrometer, observed 137 flare-like/transient events with active
region (AR) 11024 being the only AR on disk. The Hinode X-Ray Telescope
(XRT) and Solar Optical Telescope observe 67 of these events and
identified their location from 12:00 UT on July 3 through 24:00 UT 2009
July 7. We find that the predominant mechanisms for flares observed
by XRT are (1) flux cancellation and (2) the shearing of underlying
magnetic elements. Point- and cusp-like flare morphologies seen by XRT
all occur in a magnetic environment where one polarity is impeded by
the opposite polarity and vice versa, forcing the flux cancellation
process. The shearing is either caused by flux emergence at the
center of the AR and separation of polarities along a neutral line
or by individual magnetic elements having a rotational motion. Both
mechanisms are observed to contribute to single- and multiple-loop
flares. We observe that most loop flares occur along a large portion
of a polarity inversion line. Point- and cusp-like flares become
more infrequent as the AR becomes organized with separation of the
positive and negative polarities. SphinX, which allows us to identify
when these flares occur, provides us with a statistically significant
temperature and emission scaling law for A and B class flares: EM =
6.1 × 1033 T 1.9±0.1.
Title: A Solar Spectroscopic Absolute Abundance of Argon from RESIK
Authors: Sylwester, J.; Sylwester, B.; Phillips, K. J. H.; Kuznetsov,
V. D.
Bibcode: 2010ApJ...720.1721S
Altcode: 2010arXiv1007.3574S
Observations of He-like and H-like Ar (Ar XVII and Ar XVIII) lines at
3.949 Å and 3.733 Å, respectively, with the RESIK X-ray spectrometer
on the CORONAS-F spacecraft, together with temperatures and emission
measures from the two channels of GOES, have been analyzed to obtain
the abundance of Ar in flare plasmas in the solar corona. The line
fluxes per unit emission measure show a temperature dependence like
that predicted from theory and lead to spectroscopically determined
values for the absolute Ar abundance, A(Ar) = 6.44 ± 0.07 (Ar
XVII) and 6.49 ± 0.16 (Ar XVIII), which are in agreement to within
uncertainties. The weighted mean is 6.45 ± 0.06, which is between
two recent compilations of the solar Ar abundance and suggests that
the photospheric and coronal abundances of Ar are very similar.
Title: Soft X-ray coronal spectra at low activity levels observed
by RESIK
Authors: Sylwester, B.; Sylwester, J.; Phillips, K. J. H.
Bibcode: 2010A&A...514A..82S
Altcode: 2010arXiv1003.2980S
Context. The quiet-Sun X-ray emission is important for deducing
coronal heating mechanisms, but it has not been studied in detail
since the Orbiting Solar Observatory (OSO) spacecraft era. Bragg
crystal spectrometer X-ray observations have generally concentrated
on flares and active regions. The high sensitivity of the RESIK
(REntgenovsky Spectrometer s Izognutymi Kristalami) instrument on the
CORONAS-F solar mission has enabled the X-ray emission from the quiet
corona to be studied in a systematic way for the first time.
Aims: Our aim is to deduce the physical conditions of the non-flaring
corona from RESIK line intensities in several spectral ranges using
both isothermal and multithermal assumptions.
Methods: We
selected and analyzed spectra in 312 quiet-Sun intervals in January
and February 2003, sorting them into 5 groups according to activity
level. For each group, the fluxes in selected spectral bands have been
used to calculate values of parameters for the best-fit that leads
to intensities characteristic of each group. We used both isothermal
and multitemperature assumptions, the latter described by differential
emission measure (DEM) distributions. RESIK spectra cover the wavelength
range (3.3-6.1 Å). This includes emission lines of highly ionized Si,
S, Cl, Ar, and K, which are suitable for evaluating temperature and
emission measure, were used.
Results: The RESIK spectra during
these intervals of very low solar activity for the first time provide
information on the temperature structure of the quiet corona. Although
most of the emission seems to arise from plasma with a temperature
between 2 MK and 3 MK, there is also evidence of a hotter plasma (T
~ 10 MK) with an emission measure 3 orders smaller than the cooler
component. Neither coronal nor photospheric element abundances appear
to describe the observed spectra satisfactorily.
Title: The Solar X-ray Continuum Measured by RESIK
Authors: Phillips, K. J. H.; Sylwester, J.; Sylwester, B.; Kuznetsov,
V. D.
Bibcode: 2010ApJ...711..179P
Altcode: 2010arXiv1001.2412P
The solar X-ray continuum emission at five wavelengths between 3.495
Å and 4.220 Å for 19 flares in a 7-month period in 2002-2003 was
observed by the RESIK (REntgenovsky Spektrometr s Izognutymi Kristalami)
crystal spectrometer on CORONAS-F. In this wavelength region, free-free
and free-bound emissions have comparable fluxes. With a pulse-height
analyzer having settings close to optimal, the fluorescence background
was removed so that RESIK measured true solar continuum in these
bands with an uncertainty in the absolute calibration of ±20%. With
an isothermal assumption, and temperature and emission measure derived
from the ratio of the two GOES channels, the observed continuum emission
normalized to an emission measure of 1048 cm-3
was compared with theoretical continua using the CHIANTI atomic
code. The accuracy of the RESIK measurements allows photospheric
and coronal abundance sets, important for the free-bound continuum,
to be discriminated. It is found that there is agreement to about 25%
of the measured continua with those calculated from CHIANTI assuming
coronal abundances in which Mg, Si, and Fe abundances are four times
photospheric.
Title: Highly Ionized Potassium Lines in Solar X-ray Spectra and
the Abundance of Potassium
Authors: Sylwester, J.; Sylwester, B.; Phillips, K. J. H.; Kuznetsov,
V. D.
Bibcode: 2010ApJ...710..804S
Altcode: 2010arXiv1001.1502S
The abundance of potassium is derived from X-ray lines observed during
flares by the RESIK instrument on the solar mission CORONAS-F between
3.53 Å and 3.57 Å. The lines include those emitted by He-like K and
Li-like K dielectronic satellites, which have been synthesized using
the CHIANTI atomic code and newly calculated atomic data. There is good
agreement between observed and synthesized spectra, and the theoretical
behavior of the spectra with varying temperature estimated from the
ratio of the two GOES channels is correctly predicted. The observed
fluxes of the He-like K resonance line per unit emission measure give
log A(K) = 5.86 (on a scale log A(H) = 12), with a total range of a
factor 2.9. This is higher than photospheric abundance estimates by
a factor 5.5, a slightly greater enhancement than for other elements
with first ionization potential (FIP) less than ~10 eV. There is, then,
the possibility that enrichment of low-FIP elements in coronal plasmas
depends weakly on the value of the FIP which for K is extremely low
(4.34 eV). Our work also suggests that fractionation of elements to
form the FIP effect occurs in the low chromosphere rather than higher
up, as in some models.
Title: Short time variability of solar corona during recent solar
cycle minimum
Authors: Siarkowski, Marek; Gryciuk, Magdalena; Gburek, Szymon;
Sylwester, Janusz; Sylwester, Barbara; Kepa, Anna; Buczkowska,
Agnieszka; Kowalinski, Miroslaw
Bibcode: 2010cosp...38.2905S
Altcode: 2010cosp.meet.2905S
Sphinx is the X-ray spectrophotometer designed to measure X-ray
emission from the Sun in the energy range between 0.8 keV and 15
keV. The instrument is placed onboard Russian KORONAS-PHOTON satellite
launched on January 30, 2009. In this paper we present the observations
of coronal emission obtained between March-April and August-September
2009, i.e. the times towards the end of the last, very prolonged and
deep minimum of solar activity. Prompt analysis of SphinX spectra reveal
the variability of the average coronal plasma charac-teristics like
the temperature and emission measure. These data are used to compare
SphinX and GOES measurements, for selected times. Examples of many
sub/microflare events with maxima of the X-ray flux, observed much
below the GOES sensitivity threshold level will be presented.
Title: Determination of Differential Emission Measure Distribution
of Coronal Structures Observed by SphinX During Recent Minimum of
Solar Activity
Authors: Kepa, Anna; Gburek, Szymon; Siarkowski, Marek; Sylwester,
Barbara; Sylwester, Janusz; Kowalinski, Miroslaw
Bibcode: 2010cosp...38.2907K
Altcode: 2010cosp.meet.2907K
SphinX is a high-sensitivity soft X-ray spectrophotometer which
measures soft X-ray spectra in the energy range between 0.8 keV and
15 keV. From February to November 2009 the instrument has observed
unusually quiet solar coronal emission as well as a number of weak
solar flares. Based on SphinX spectra it is possible to study the
differential emission measure distributions (DEM) in the temperature
range roughly between 1 MK and 10 MK. The aim of the present study is
to unveil DEM plasma distributions for selected activity conditions
and analyze their variability.
Title: Evolution of plasma characteristics for weak X-ray brightenings
seen by SphinX during recent deep minimum of solar activity
Authors: Sylwester, Barbara; Sylwester, Janusz; Siarkowski, Marek;
Gburek, Szymon; Phillips, Kenneth
Bibcode: 2010cosp...38.2896S
Altcode: 2010cosp.meet.2896S
Very high sensitivity of SphinX soft X-ray spectrophotometer
aboard Coronas-Photon allows to observe spectra of small X-ray
brightenings(microflares), many of them with maximum intensities well
below the GOES or RHESSI sensitivity thresholds. Hundreds of such small
flare-like events have been observed in the period between March and
November 2009 with energy resolution better than 0.5 keV. The spectra
have been measured in the energy range extending above 1 keV. In this
study we investigate the time variability of basic plasma parameters:
temperature T and emission measure EM for a number of these weak
flare-like events and discuss respective evolutionary patterns on the
EM-T diagnostic diagrams. For some of these events, unusual behavior
is observed, different from this characteristic for a "normal" flares
of higher maximum intensities. Physical scenarios providing possible
explanation of such unusual evolutionary patterns will be discussed.
Title: Non-thermal Diagnostics of a Flare Observed by RESIK
Authors: Kulinová, A.; Dzifčáková, E.; Sylwester, B.; Sylwester, J.
Bibcode: 2009CEAB...33..243K
Altcode:
The Polish soft X-ray spectrometer RESIK operated on Russian Coronas-F
spacecraft during the years 2001 - 2003. It has observed several flares
of different classes in a wavelength band of 3.35, 6.05 Å. We have
analysed two flares especially in a region of 5.0 - 6.05 Å which is
dominated by allowed lines of Si XIII, Si XIV ions, and satellite lines
of Si XII (Si XIId). The flare spectra showed unexpectedly high fluxes
of Si XIId satellite lines as compared with fluxes of allowed lines of
Si XIII ion which we attempted to explain under the assumption of a
non-thermal electron distribution. We have investigated the temporal
dependence of the deviation of the non-thermal distribution from the
Maxwell distribution during a flare. The maximal deviation from thermal
distribution correlates with times of observed radio bursts.
Title: Differential emission measure distributions in X-ray solar
flares
Authors: Kepa, A.; Sylwester, B.; Siarkowski, M.; Sylwester, J.
Bibcode: 2008AdSpR..42..828K
Altcode:
X-ray spectrometer RESIK has observed spectra in the four wavelength
bands from 3.3 Å to 6.1 Å. This spectral range contains many emission
lines of H- and He-like ions for Si, S, Ar and K. These lines are formed
in plasma of coronal temperatures (T > 3 MK). Analysis of their
intensities allows studying differential emission measure distributions
(DEM) in temperature range roughly between 3 MK and 30 MK. The aim
of present study was to check whether any relationship exists between
the character of DEM distribution, the event phase and the X-ray flare
class. To do this we have calculated and analyzed the DEM distributions
for a set of flares belonging to different GOES classes from the range
B5.6 X1. The DEM distributions have been calculated using “Withbroe
Sylwester” multiplicative, maximum likelihood iterative algorithm. As
the input data we have used absolute fluxes observed by RESIK in several
spectral bands (lines + continuum). Respective emission functions have
been calculated using the CHIANTI v. 5.2 atomic data package.
Title: He-like Ar XVII triplet observed by RESIK
Authors: Sylwester, B.; Sylwester, J.; Phillips, K. J. H.; Landi, E.
Bibcode: 2008AdSpR..42..833S
Altcode:
We present the observations of He-like Ar triplet lines obtained by
RESIK spectrometer aboard CORONAS-F. Interpretation of intensity ratios
between triplet lines of lower Z elements is known to provide useful
diagnostics of plasma conditions within the emitting source. Here, we
investigate whether triplet line ratios are useful for interpretation
of higher Z element spectra. A high sensitivity, low background and
precise absolute calibration of RESIK allow to consider in addition
also the continuum contribution. This provides a way to determine
the Ar absolute abundance from the observed triplet component
ratios. The method is presented and the results are shown for two
selected flares. Derived values of Ar absolute abundance for these
flares are found to be similar: 2.6 × 10 -6 and 2.9 × 10
-6. They fall in the range between presently accepted Ar
photospheric and coronal abundances.
Title: Determination of K, Ar, Cl, S, Si and Al flare abundances
from RESIK soft X-ray spectra
Authors: Sylwester, J.; Sylwester, B.; Landi, E.; Phillips, K. J. H.;
Kuznetsov, V. D.
Bibcode: 2008AdSpR..42..838S
Altcode:
The RESIK is a high sensitivity, uncollimated bent crystal spectrometer
which successfully operated aboard Russian CORONAS-F solar mission
between 2001 and 2003. It measured for the first time in a systematic
way solar soft X-ray spectra in the four wavelength channels from 3.3
Å to 6.1 Å. This range includes characteristic strong lines of H-
and He-like ions of K, Ar, Cl, Si, S and Al in the respective spectral
channels. A distinguishing feature of RESIK is its possibility
of making reliable measurements of the continuum radiation in
flares. Interpretation of line and the continuum intensities observed
in vicinity of respective strong lines provides diagnostics of plasma
temperature and absolute abundances of K, Ar, Cl, S, Si and Al in
several flares. We analyzed the observed intensities of spectral
lines and the nearby continuum using the CHIANTI v5.2 atomic data
package. A specific, so-called “locally isothermal” approach has
been used in this respect allowing us to make not only flare-averaged
abundance estimates, but also to look into a possible variability of
plasma composition during the course of flares.
Title: Nonthermal and thermal diagnostics of a solar flare observed
with RESIK and RHESSI
Authors: Dzifčáková, E.; Kulinová, A.; Chifor, C.; Mason, H. E.;
Del Zanna, G.; Sylwester, J.; Sylwester, B.
Bibcode: 2008A&A...488..311D
Altcode:
Aims: We aim to prove and diagnose the occurrence of nonthermal
electron distributions in solar flare plasma using X-ray spectral
observations.
Methods: An M4.9 flare on 2003 January 7/8 was
observed with the RESIK instrument in the 3-6 Å wavelength range (2-4
keV) and with RHESSI at energies above 6 keV. The temporal behavior
of RESIK flare spectra has been analyzed for two different types of
velocity distributions - a thermal (Maxwellian) distribution and a
nonthermal plasma distribution of free electrons. The Si XIV, Si XIII,
and Si XIId satellite lines observed with RESIK in the 5-6 Å range
were used to determine the degree of deviation from Maxwellian, and
the equivalent non-Maxwellian pseudo-temperature, τ. The diagnostics
presented are sensitive to the shape of the distribution in the energy
range where the maximum of the electron distribution occurs (where
the bulk of electrons reside) and does not include the influence
of the shape of the high-energy tail of the distribution. Under
the assumption of a Maxwellian distribution of electron velocities,
the plasma temperature was determined from an emission measure (EM)
loci analysis and a differential emission measure (DEM) analysis of
RESIK spectra. The high-energy end of the flare radiative emission
was investigated through RHESSI spectral analysis.
Results:
The nonthermal analysis of RESIK spectra has shown that the largest
deviations of the plasma electron distribution from Maxwellian appeared
during the impulsive phase of the flare. The decay phase spectra had
an almost isothermal character. The pseudo-temperature, τ, reached
its maximum around the peak time of the soft and hard X-ray fluxes. The
temporal behavior of the temperatures derived from the thermal analysis
was similar to the behavior of the nonthermal pseudo-temperature. The
values of the pseudo-temperature were consistent with the temperatures
obtained in both thermal analyses, but lower than the temperatures
derived from the slope of the RHESSI continua. In comparison with the
synthetic isothermal or multithermal spectra, the nonthermal synthetic
spectra fitted the observed Si XIId satellite lines much more closely
(the error is less than 10%). The fluxes in the Si XIId satellite lines
in isothermal or multithermal spectra have been underestimated by a
factor of three or more in comparison to the observed fluxes. The
value of this factor varies with time and it is different for the
different satellite lines.
Conclusions: Evidence was found for
considerable deviations of the distribution of free electrons from
Maxwellian in the plasma during a solar flare. These occurred mainly
during the flare impulsive phase and can be diagnosed using existing
X-ray spectral observations.
Title: RESIK Observations of Helium-like Argon X-Ray Line Emission
in Solar Flares
Authors: Sylwester, J.; Sylwester, B.; Phillips, K. J. H.
Bibcode: 2008ApJ...681L.117S
Altcode: 2008arXiv0806.1462S
The Ar XVII X-ray line group principally due to transitions
1s2-1s2l (l = s, p) near 4 Å was observed in numerous flares
by the RESIK bent crystal spectrometer aboard CORONAS-F between 2001
and 2003. The three line features include Ar XVII w (resonance line),
a blend of x and y (intercombination lines), and z (forbidden line),
all of which are blended with Ar XVI dielectronic satellites. The
ratio G, equal to [ I(x) + I(y) + I(z) ]/I(w) , varies with electron
temperature Te mostly because of unresolved dielectronic
satellites. With temperatures estimated from GOES X-ray emission,
the observed G ratios agree fairly well with those calculated from
CHIANTI and other data. With a two-component emission measure,
better agreement is achieved. Some S XV and S XVI lines blend with
the Ar lines, the effect of which occurs at temperatures gsim8 MK,
allowing the S/Ar abundance ratio to be determined. This is found to
agree with coronal values. A nonthermal contribution is indicated for
some spectra in the repeating-pulse flare of 2003 February 6.
Title: X-ray studies of flaring plasma
Authors: Sylwester, B.; Sylwester, J.; Phillips, K. J. H.
Bibcode: 2008JApA...29..147S
Altcode:
No abstract at ADS
Title: Cycle 23 flare temperatures and emission measures as derived
from GOES X-ray data
Authors: Gburek, S.; Sylwester, B.; Sylwester, J.
Bibcode: 2008JASTP..70..241G
Altcode:
Solar X-ray observations recorded by the series of geostationary
observational environmental satellites (GOES) are analyzed over a
time interval of the 23rd solar cycle. Statistical analysis of a
large database of GOES events is performed. Temperature and emission
measures derived based on GOES fluxes for all events are compared and
analyzed. A specific application of GOES X-ray measurements to space
weather forecasting is discussed. Namely, using an information about
maximum temperature and maximum emission measure of a given flare one
can assign a probability to this flare of being "non-SEP associated".
Title: Coronal plasma composition from RESIK soft X-ray spectra
Authors: Sylwester, Barbara; Sylwester, Janusz; Szymon, Gburek;
Kuznetsov, Vladimir
Bibcode: 2008cosp...37.3110S
Altcode: 2008cosp.meet.3110S
We investigated a number of solar flares' spectra obtained with
the high-sensitive Bragg spectrometer (RESIK) aboard the CORONAS-F
satellite. Using multi-temperature approach, we optimized the fits
of the synthetic and observed spectra in the spectral range from 3.2
˚ to 6 ˚ A A in respect with the adopted plasma composition. The
results indicate that even percent level plasma composition variations
noticeably influence the quality of the fit and therefore allow for a
precise determinations of actual plasma abundances in the investigated
flares. Example patterns of composition variability between flares
are presented.
Title: (im)Balance of Forces in the Corona
Authors: Sylwester, J.; Sylwester, B.
Bibcode: 2007CEAB...31..229S
Altcode:
Observed pattern of variability of solar atmosphere plasma
structures, often accompanied by respective measured Doppler
shifts, provides a direct evidence of imbalanced forces acting in
this environment. Observed motions have been studied in various
energy bands, extending from radio to hard X-rays using ground and
space-borne instruments. Here, we present the results of a dedicated
study of present observational databases in selected energy ranges
with a special interest focused on TRACE movies. In our search we
included also recently released wavelet-processed EIT and LASCO movies
(from SOHO) as they provide additional support to the conclusions
of this study. The main outcome of the work performed is our
better understanding of a basic role played by plasma kernels in
every ``layer'' of the solar atmosphere. These kernels appear to
be present, and rapidly evolve at the locations of violent (intense)
energy release locations. Subsequent formation of a more stable coronal
magnetic structures seen in the form of ``spiders'' or ``scorpions''
is due to self-reorganization of plasma kernels. It comes out that the
spider structure represents a basic, quasi-equilibrium building block
of the solar atmosphere. When observed in a particular image, within
a limited energy band, i.e. optical, EUV, soft or hard X-rays, only a
part of this spider plasma structure can usually be seen, noticeably
resembling a loop-like structure with a brighter top, or an arcade
of loops connected along the ridge of summit kernels, or seemingly
isolated oval source. This energy-dependent visibility effects caused
a general confusion present in solar physics and led to proliferation
of simple fluxtube scenarios. In our study presented herewith, we used
the images obtained with the best available resolution, being enhanced
numerically where possible. For the first time we enhanced the TRACE
image data cube in a systematic way for a particular flare. Based on
the results of analysis of a large number of images, we push forward a
qualitative toy model of atmospheric connectivity pattern (Sylwester,
J. and Sylwester, B., 2004). This hierarchic model is able to handle
in a natural way observed complexity of atmospheric phenomena. Here, we
discuss to some extent verifiable predictions of the hierarchical model
outlining a number of new studies which might prove the concept. These
predictions arise concurrently with the first data coming down from new
missions being recently launched into orbit: the Hinode and the Stereo.
Title: X-Ray Study of Compact Flare Kernels
Authors: Sylwester, B.; Sylwester, J.
Bibcode: 2007CEAB...31...77S
Altcode:
We have selected eight compact X-ray sources observed by Soft X-ray
Telescope (SXT) during the Yohkoh mission. Respective sequences of
images have been deconvolved in order to remove the instrumental
blur. In this way the spatial resolution on the images has been
increased to ∼ 1 arcsec. The analysis of deconvolved images allowed
us to study the dynamics and morphology of these compact plasma kernels
and infer their thermodynamic characteristics. Corresponding Hard X-ray
Telescope (HXT) observations were incorporated into the analysis where
possible. In addition the standard X-ray emission in the two channels
observed by GOES satellite has been incorporated into the analysis.
Title: A benchmark study for CHIANTI based on RESIK solar flare
spectra
Authors: Chifor, C.; Del Zanna, G.; Mason, H. E.; Sylwester, J.;
Sylwester, B.; Phillips, K. J. H.
Bibcode: 2007A&A...462..323C
Altcode:
Aims:To perform a benchmark analysis for the recent version of the
CHIANTI atomic database (v. 5.2) based on high-resolution solar
flare X-ray spectra in the range 3.4-6.1 Å from the RESIK crystal
spectrometer on the CORONAS-F spacecraft.
Methods: A C5.8 flare
occurring on 2003 February 22 was chosen for analysis. RESIK spectra
of this flare include emission lines of He-like and H-like K, Ar,
S, and Si, with some dielectronic lines. Initially, two independent
plasma diagnostic techniques are employed: an emission measure
(EM) loci analysis using the line flux and the line contribution
function G(T_e, N_e), and a new method based on continuum fluxes and
contribution functions. We further apply a differential emission measure
(DEM) analysis, from which CHIANTI synthetic spectra are derived. The
continuum from RESIK spectra is checked against simultaneous RHESSI and
GOES observations. Comparisons of CHIANTI synthetic spectra with those
from the MEKAL code in the 3.4-6.1 Å range are also presented.
Results: The emitting plasma appears multi-thermal, having one
dominant temperature component determined independently from the line
and continuum EM loci and DEM analyses. Consistency between line
and continuum emissions requires photospheric elemental abundances
(Asplund et al. 2005), with a depleted sulphur abundance. With the
exception of RESIK channel 4 (5.0-6.1 Å), we find overall very
good agreement between the calculated and observed intensities. From
comparisons with other instruments, RESIK's precision in the continuum
level is confirmed to be within the estimated 20% uncertainties in the
intensity calibration. We find general agreement between CHIANTI and
MEKAL isothermal spectra, but we note that the atomic data for the
Si xii and Si xiii ions contained in CHIANTI are more complete.
Conclusions: .RESIK observations of both lines and continua are
suitable for characterising the properties of the flaring plasma such
as temperature, emission measure and elemental abundance. These spectra
can be used to evaluate any atomic database.
Title: Determination of differential emission measure from X-ray
solar spectra registered by RESIK aboard CORONAS-F
Authors: Kepa, A.; Sylwester, J.; Sylwester, B.; Siarkowski, M.;
Stepanov, A. I.
Bibcode: 2006SoSyR..40..294K
Altcode:
The differential emission measure (DEM) describes the temperature
distribution of the emitting plasma. The DEM distribution allows one
to study the physical conditions and the energy of flares in detail
(including the mean temperature and the total emission measure). In
this paper, we analyze the time changes of the DEM distributions
for a selected flare, which has been observed with the RESIK
instrument. To calculate the differential emission measure, we used
the Withbroe-Sylwester (W-S) iterative algorithm corresponding to
the maximum likelihood procedure. The required emission functions
were calculated with the CHIANTI package. We calculated the DEM for
four available estimates of the ionization equilibrium and coronal
composition of plasma.
Title: RESIK Flare X-ray Spectra: Benchmark Analysis And Plasma
Diagnostics Based On CHIANTI
Authors: Chifor, Cristina; Del Zanna, G.; Sylwester, J.; Sylwester,
B.; Phillips, K. J. H.
Bibcode: 2006SPD....37.1314C
Altcode: 2006BAAS...38..243C
We perform a benchmark analysis between the recent version 5.2 of the
CHIANTI atomic database and high-resolution solar flare X-ray spectra
obtained with the RESIK instrument in the wavelength range 3.4-6.1
Angstrom. The physical properties of emitting plasmas during a C-class
solar flare on 2003 February 22 are determined through two independent
plasma diagnostic techniques: an emission measure analysis applied to
strong, unblended atomic lines and a new method analyzing continuum
contributions. From these parameters, synthetic spectra are derived
using the CHIANTI database and software. The predicted spectra are then
benchmarked against observed RESIK lines and continuum. Comparisons
between CHIANTI and the MEKAL spectral code are also presented. In
order to evaluate the level of confidence in RESIK's calibration, RESIK
continuum levels are checked against simultaneous RHESSI observations
as well as GOES continua obtained from parameters derived from GOES
channel ratios.
Title: Thermodynamics of selected solar flares as determined from
the analysis of the spectra obtained with the RESIK instrument
Authors: Sylwester, B.; Sylwester, J.; Kepa, A.; Kordylewski, Z.;
Phillips, K. J. H.; Kuznetsov, V. D.
Bibcode: 2006SoSyR..40..125S
Altcode:
The RESIK instrument is an X-ray spectrometer with bent crystals
onboard the CORONAS-F satellite. It was used to observe the spectra
of solar flares, active regions, and quiet corona. During the period
of the instrument’s operation, many spectra were collected in four
energy channels covering the wavelength range from 3.2 to 6.1 Å. For
the present analysis, we selected solar flares of various X-ray classes
(B, C, and M in the GOES notation), which were observed during moderate
level of solar activity (from January to March 2003). The analysis
of the RESIK spectra fulfilled with different techniques allowed
us to determine the temperature, emission measure, and temperature
distribution of the differential emission measure, as well as to
examine their time variability.
Title: Si XII X-Ray Satellite Lines in Solar Flare Spectra
Authors: Phillips, K. J. H.; Dubau, J.; Sylwester, J.; Sylwester, B.
Bibcode: 2006ApJ...638.1154P
Altcode:
The temperature dependence of the Si XII n=3 and 4 dielectronic
satellite line features at 5.82 and 5.56 Å, respectively, near the
Si XIII 1s2-1s3p and 1s2-1s4p lines (5.681 and
5.405 Å), is calculated using atomic data presented here. The resulting
theoretical spectra are compared with solar flare spectra observed by
the RESIK spectrometer on the CORONAS-F spacecraft. The satellites, like
the more familiar n=2 satellites near the Si XIII 1s2-1s2p
lines, are formed mostly by dielectronic recombination, but unlike the
n=2 satellites, are unblended. The implications for similar satellite
lines in flare Fe spectra are discussed.
Title: Determination of flaring plasma characteristics from RESIK
X-ray spectra
Authors: Sylwester, B.; Sylwester, J.; Kepa, A.; Phillips, K. J. H.
Bibcode: 2006IAUS..233..165S
Altcode:
We present spectral analysis methods suitable for diagnostics of
flaring plasma from RESIK spectra. RESIK is the uncollimated bent
crystal spectrometer aboard the Russian CORONAS-F solar mission. It
collected many flare and active region spectra in the wavelength
range 3.3 Å-6.1 Å, where strong emission lines of Si, S, Ar, and K
are present. Based on a careful instrument calibration the absolute
fluxes in the individual spectral lines have been obtained. These
fluxes have been used for determination of a set of thermodynamic
parameters characterizing the emitting plasma and for studies their
time behavior during selected flares.
Title: He-like triplets observed by RESIK
Authors: Sylwester, B.; Sylwester, J.; Phillips, K. J. H.; Landi, E.
Bibcode: 2006cosp...36.2877S
Altcode: 2006cosp.meet.2877S
The RESIK is a high sensitivity uncollimated bent crystal spectrometer
which successfully operated aboard Russian CORONAS-F solar mission
between 2001 and 2003 It measured systematically for the first time
solar soft X-ray spectra in the four wavelength channels from 3 3 AA to
6 1 AA This range includes characteristic triplet lines of He-like ions
of K Ar Cl and S in the respective spectral channels Interpretation of
observed line ratios within each triplet provides diagnostics of plasma
conditions in the emitting source We reduced the observed spectra for
a number of flares using the absolute RESIK calibration software We
analyzed the observed intensities of spectral line components comprising
the triplets and investigated their time variability The evolution of
important plasma parameters like temperature and emission measure have
been studied for selected events Flaring plasma densities were measured
from these parameters using X-ray brightness maps as determined from
the RHESSI observations The CHIANTI v5 1 atomic data package was used
as a consistent tool for spectral data analysis
Title: Lines in the range 3.2 6.1 Å observed in RESIK spectra
Authors: Sylwester, B.; Sylwester, J.; Siarkowski, M.; Phillips,
K. J. H.; Culhane, J. L.; Lang, J.; Brown, C.; Kuznetsov, V. D.
Bibcode: 2006AdSpR..38.1534S
Altcode:
RESIK is a Bragg bent crystal X-ray spectrometer on board the CORONAS-F
satellite. Between 24 August 2002 and 22 May 2003 RESIK collected
a large number of solar X-ray spectra in four energy bands covering
the range 3.2 6.1 Å. A recent absolute calibration has allowed us to
make detailed identification of observed spectral features, and from
observed line and continuum fluxes to get temperature, emission measure,
etc. The lines were identified using spectra averaged over periods of
various solar activity levels. These averaged spectra contain a number
of strong lines with transitions in H- and He-like ions of K, Ar, S
and Si. Some of them are resonance parent lines and their satellites
which were observed with other spectrometers and have been described
elsewhere. Here, we report detection of several lines not previously
observed in solar spectra, including lines of H-like and He-like S
and Si ions with transitions 1s np and 1s2 1snp, n up to
10. In addition we provide identification of the He-like Cl (Cl XVI)
triplet in the range 4.43 4.45 Å. The feature at 4.182 Å, which is
the wavelength of the H-like Cl (Cl XVII) Lyα line, is probably a
blend of S XIV satellites from cooler plasma.
Title: Wrocław in Space: X-ray Diagnostics of Solar Corona
Authors: Siarkowski, M.; Kȩpa, A.; Sylwester, B.; Sylwester, J.
Bibcode: 2006AIPC..812..393S
Altcode:
X-ray observations of the solar corona have been undertaken in Solar
Physics Division (Space Research Centre of the Polish Academy of
Sciences, Wrocław) for more than 35 years. Short history of these
observations is presented. We focus mainly on the results from the
latest experiments. These are hard X-ray photometer onboard the
INTERBALL-Tail Probe and two Bragg crystal spectrometers recording
solar X-ray spectra from CORONAS-F satellite. Such observations provide
useful information on solar coronal plasma heated up to temperatures
of several 106 - 107 K.
Title: Determination of K, Ar, Cl, S and Si flare abundances from
RESIK soft X-ray spectra
Authors: Sylwester, J.; Sylwester, B.; Landi, E.; Phillips, K. J. H.;
Kuznetsov, V. D.
Bibcode: 2006cosp...36.2871S
Altcode: 2006cosp.meet.2871S
We investigate possible variability of coronal plasma composition
during flares based on the analysis of spectra measured by RESIK bent
crystal spectrometer aboard the CORONAS-F solar mission We fit the
measured spectra with synthesized theoretical ones in the vicinity of
the observed He-like ions The spectral synthesis is performed based on
CHIANTI v5 1 spectral code in so-called locally isothermal approximation
with the aim to reproduce observed line-to-continuum ratios Influence
of possible multitemperaure plasma structure is considered and discussed
based on respective differential emission measure calculations
Title: Differential emission measure distributions in X-ray
solarflares
Authors: Kepa, A.; Sylwester, B.; Siarkowski, M.; Sylwester, J.
Bibcode: 2006cosp...36.1295K
Altcode: 2006cosp.meet.1295K
X-ray spectrometer RESIK has observed spectra in the four wavelength
bands from 3 3 AA to 6 1 AA This spectral range contains many emission
lines of H- and He-like ions for Si S Ar and K These lines are formed
in plasma of coronal temperatures T 3 MK Analysis of their intensities
allows studying differential emission measure distributions DEM in
temperature range roughly between 3 MK and 30 MK The aim of present
study was to check whether any relationship exists between the
character of DEM distribution and the X-ray flare class To do this we
have calculated the DEM distributions for a set of flares belonging to
different GOES classes from the range B4 to X1 The DEM distributions
have been calculated using Withbroe - Sylwester multiplicative maximum
likelihood iterative algorithm As the input fluxes for DEM calculations
we have used absolute fluxes observed in several individual lines and
spectral bands observed by RESIK Respective emission functions have
been calculated using the CHIANTI v 5 1 atomic data package
Title: Temperature-sensitive line ratio diagnostics based on Si
satellite-to-resonance line ratios for 1s2 1snp transitions
Authors: Phillips, K. J. H.; Dubau, J.; Sylwester, J.; Sylwester,
B.; Culhane, J. L.; Doschek, G. A.; Lang, J.
Bibcode: 2006AdSpR..38.1543P
Altcode:
Dielectronic satellite lines due to 1s2n‧l‧ 1snpn‧l‧
(n = 3, 4) transitions in Li-like Si (Si XII) occur at 5.818 and
5.565 Å, on the long wavelength side of the He-like Si (Si XIII)
1s2 1s3p and 1s2 1s4p lines at 5.681 and 5.384 Å,
respectively. They have been extensively observed with the RESIK crystal
spectrometer on the Russian spacecraft CORONAS-F. As with corresponding
satellites 1s2nl 1s2pnl on the long-wavelength side of
the Si XIII 1s2 1s2p resonance line, there is an inverse
temperature dependence of the intensity ratio of the satellites to the
He-like ion lines (Isat/IHe). New atomic data
are used to calculate the Si XII satellite line intensities and thus
the Isat/IHe ratio. RESIK observations of the
ratio in solar flares, together with temperatures from the ratio of
the two GOES X-ray channels, are compared with theoretical variation
of the ratio with temperature. The good agreement indicates this to
be a valuable temperature diagnostic for solar flares and laboratory
plasmas such as tokamaks. There are implications for similar satellites
in Fe line spectra which are observed with broad-band resolution by
the RHESSI solar flare mission.
Title: Observations of 1s2 1s np and 1s np lines in RESIK
soft X-ray spectra
Authors: Kepa, A.; Sylwester, J.; Sylwester, B.; Siarkowski, M.;
Phillips, K. J. H.; Kuznetsov, V. D.
Bibcode: 2006AdSpR..38.1538K
Altcode:
RESIK is the X-ray bent crystal spectrometer on the CORONAS-F
satellite. Between 2002 and 2003, RESIK collected numerous spectra
of active regions and flares in the wavelength range from 3.37
to 6.09 Å. This range includes many strong emission lines due to
transitions 1s2 1s np and 1s np, in He-like and H-like ions,
respectively; the n = 2 and 3 lines are routinely observed for Si,
S and Ar ions. For some flares RESIK has observed enhanced emission
in spectral features coinciding with lines due to transitions for n up
to 9 or 10. Identifications of these features, not previously observed
in astrophysical spectra, are presented in this paper. Their observed
intensities are compared with those from theory.
Title: Analysis of potassium abundance in a large number of flares
Authors: Sylwester, J.; Sylwester, B.; Phillips, K. J. H.; Culhane,
J. L.; Brown, C.; Lang, J.; Stepanov, A. I.
Bibcode: 2006AdSpR..38.1490S
Altcode:
An initial study of spectra observed in the shortest wavelength
channel (3.40-3.80 Å) of the RESIK X-ray spectrometer on CORONAS-F
indicates the presence of substantial flare-to-flare variations in
the line-to-continuum ratio of several lines, in particular He-like
potassium (K XVIII) lines, occurring in the range 3.53-3.57 Å. The
observed variations are larger than those expected from temperature
variations. This has motivated a study of possible variations in
the potassium abundance in the observed spectra. With a new RESIK
calibration available, we have obtained absolute fluxes of the K
XVIII resonance line as well as the continuum and lines observed in
other RESIK channels (3.40-6.05 Å) for some 1163 intervals observed
early in 2003. Analysis of these observations allowed us to determine
the average absolute potassium abundance for the period studied and
investigate the variability of abundance. The results obtained are
presented and discussed.
Title: Dem Distributions for Short and Long Duration Flares as
Determined from Resiksoft X-Ray Spectra
Authors: Kepa, A.; Sylwester, J.; Sylwester, B.; Siarkowski, M.;
Kuznetsov, V.
Bibcode: 2005ESASP.600E..87K
Altcode: 2005dysu.confE..87K; 2005ESPM...11...87K
No abstract at ADS
Title: Evolution of Flaring Plasma Components on Diagnostic Diagrams
Authors: Sylwester, J.; Sylwester, B.; Phillips, K. J. H.; Kepa, A.
Bibcode: 2005ESASP.600E.143S
Altcode: 2005ESPM...11..143S; 2005dysu.confE.143S
No abstract at ADS
Title: Plasma Kernels in Homologous (?) Flares
Authors: Sylwester, Barbara; Sylwester, J.; Kepa, A.
Bibcode: 2005ESASP.600E.169S
Altcode: 2005ESPM...11..169S; 2005dysu.confE.169S
No abstract at ADS
Title: Observations of Solar X-ray Spectra by the DIOGENESS and
RESIK Spectrometers Onboard the CORONAS-F Satellite
Authors: Sylwester, J.; Sylwester, B.; Kordylewski, Z.; Phillips,
K. J. H.; Kuznetsov, V. D.; Boldyrev, S. I.
Bibcode: 2005SoSyR..39..479S
Altcode:
The first scientific results of the analysis of the X-ray spectra of
flares and active regions in the solar corona obtained by Polish-led
spectrometers RESIK and DIOGENESS onboard the CORONAS-F satellite
are presented. The instruments were designed and made in the Solar
Physics Division of the Space Research Center of the Polish Academy
of Sciences (SRC PAS, Wroclaw, Poland). The Institute of Terrestrial
Magnetism, Ionosphere, and Radio Wave Propagation (IZMIRAN, Russia)
and the Astronomical Institute of the Czech Academy of Sciences also
participated in designing the DIOGENESS spectrometer, while IZMIRAN
(Russia), Mullard Space Science Laboratory (MSSL, Great Britain),
Rutherford Appleton Laboratory (RAL, Great Britain), and Naval Research
Laboratory (NRL, United States) contributed to the development of the
RESIK spectrometer. In the paper, we give spectra obtained in a number
of previously unstudied spectral ranges and a preliminary identification
of new spectral lines. The results for the shifts of the X-ray spectral
lines observed with the use of a so-called dopplerometer configuration
are also presented. Methods for determining the abundances of the rare
elements in the solar corona, including chlorine, potassium, and argon,
are described.
Title: Dielectronic Satellites Near the 1s2 - 1snp (n >
2) Lines of He-like Ions in Solar X-ray Spectra
Authors: Landi, E.; Phillips, K. J. H.; Sylwester, J.; Sylwester,
B.; Dennis, B. R.; Dubau, J.
Bibcode: 2005AIPC..774..173L
Altcode:
We discuss the importance of dielectronic satellites with transitions
1s22l - 1s2l3p on the long-wavelength side of He-like ion
lines 1s2 - 1snp (n > 2). Their intensity ratios with
the He-like ion lines have an inverse temperature dependence, making
them useful as diagnostics. This is examined in the case of Si and
Fe satellites.
Title: Si XII X-ray Satellite Lines in Solar Flare Spectra
Authors: Phillips, K. J.; Sylwester, J.; Sylwester, B.; Dubau, J.
Bibcode: 2005AGUSMSP23B..08P
Altcode:
We demonstrate the temperature dependence of the intensity ratio of
dielectronic satellite lines due to Li-like Si (Si XII) to nearby
He-like Si (Si XIII) 1s2 - 1snp(n=3, 4, 5) lines emitted in solar
flare X-ray spectra. These lines, which occur in the wavelength
range 5.253~Å--5.818~Å, have been observed by the RESIK bent crystal
spectrometer on the Russian CORONAS-F solar mission. Line features made
up of several strong satellites with transitions 1s2 n'l' - 1s n'l'
nl lie near the `parent' Si XIII lines, transition 1s2 1S0 - 1snp 1P1;
thus, the feature at 5.818~Å is made up of several blended Si XII
satellites with `spectator' electrons n'l'=2s or 2p and nl=3p or 3d,
and lies on the long-wavelength side of the Si XIII 1s2 - 1s3p line
at 5.681~Å. A similar n=4 satellite feature at 5.565~Å is on the
long-wavelength side of the Si XIII 1s2 - 1s4p line at 5.384~Å. The
Si XII satellites are formed by dielectronic recombination and direct
(inner-shell) excitation. The ratio Is/IHe (Is = Si XII satellite
line flux, IHe = Si XIII line flux) depends on electron temperature
approximately as Te-1. The atomic data needed to calculate Is/IHe for
individual n=3 and n=4 Si XII satellite lines have been calculated
and will be presented in this paper; excitation mechanisms including
those by dielectronic recombination and inner-shell excitation were
included using the SUPERSTRUCTURE and Distorted Wave formalisms. With
these and theoretical fluxes of the Si XIII lines, synthetic spectra
were calculated and compared with RESIK solar flare spectra. Values
of Is/IHe measured from RESIK spectra during the decay of four
long-duration solar flares, together with temperatures estimated
both from the ratio of the GOES channels and from the ratio of total
fluxes in two of the four RESIK channels, enable a comparison to
be made with theoretical curves. The agreement with the theoretical
curve based on synthetic spectra is within expected uncertainties,
and the Te-1 dependence is confirmed. Satellites for other Li-like
ions are expected to have a similar temperature sensitivity, in
particular the Li-like Fe satellites near He-like Fe lines. Although
these lines have not been seen with high-resolution spectrometers,
the RHESSI mission observes the whole complex during solar flares
as the so-called Fe/Ni line feature; addition of these satellites to
theoretical spectra from the CHIANTI code have reduced a long-standing
discrepancy with intensities observed by RHESSI. KJHP acknowledges
an NRC Research Associateship, and JS and BS acknowledge support from
grants (2.P03D.002.22 and PBZ-KBN-054/P03/2001) of the Polish Committee
for Scientific Research. RESIK is a joint project between NRL (USA),
MSSL, and RAL (UK), IZMIRAN (Russia), and SRC (Poland). The CORONAS-F
mission is led by the IZMIRAN Institute.
Title: The thermal X-ray spectrum of the 2003 April 26 solar flare
Authors: Dennis, B. R.; Phillips, K. J. H.; Sylwester, J.; Sylwester,
B.; Schwartz, R. A.; Tolbert, A. K.
Bibcode: 2005AdSpR..35.1723D
Altcode:
Observations and their analysis of the thermal X-ray spectrum of the
M2 flare on 2003 April 26 are described. The spectrum observed by the
RHESSI mission cover the energy range from ∼5 to ∼50 keV. With
its ∼1-keV spectral resolution, intensities and equivalent widths
of two line complexes, the Fe line group at 6.7 keV (mostly due to Fe
XXV lines and Fe XXIV satellites) and the Fe/Ni line group at 8 keV
(mostly due to higher-excitation Fe XXV lines and Ni XXVII lines)
were obtained as a function of time through a number of flares. The
abundance of Fe can also be determined from RHESSI spectra; it appears
to be consistent with a coronal value for at least some times during
the flare. Comparisons of RHESSI spectra with those from the RESIK
crystal spectrometer on CORONAS-F show very satisfactory agreement,
giving much confidence in the intensity calibration of both instruments.
Title: Multi-wavelength study of a strong impulsive solar limb flare
on 2002 August 3
Authors: Gburek, S.; Sylwester, J.; Sylwester, B.; Dennis, B. R.;
Phillips, K. J. H.
Bibcode: 2005AdSpR..35.1728G
Altcode:
We made a detailed study of the impulsive solar flare of GOES class
X1.0 which occurred near the west limb on 2002 August 3, peak time
19:07 UT. There is particularly good data coverage of this event, with
simultaneous observations in EUV, soft and hard X-rays available. We
used TRACE 171 Å images to study the morphology and evolution of this
event. Soft X-ray spectra in the wavelength range 3.34-6.05 Å measured
by the RESIK Bragg crystal spectrometer on CORONAS-F were used for
determination of the evolution of the flare plasma temperature. Data
from the RHESSI instrument were used to investigate properties of the
higher-temperature plasma during the flare.
Title: Resik: A Bent Crystal X-ray Spectrometer for Studies of Solar
Coronal Plasma Composition
Authors: Sylwester, J.; Gaicki, I.; Kordylewski, Z.; Kowaliński,
M.; Nowak, S.; Płocieniak, S.; Siarkowski, M.; Sylwester, B.;
Trzebiński, W.; Bakała, J.; Culhane, J. L.; Whyndham, M.; Bentley,
R. D.; Guttridge, P. R.; Phillips, K. J. H.; Lang, J.; Brown, C. M.;
Doschek, G. A.; Kuznetsov, V. D.; Oraevsky, V. N.; Stepanov, A. I.;
Lisin, D. V.
Bibcode: 2005SoPh..226...45S
Altcode:
We describe the RESIK (REntgenovsky Spektrometr s Izognutymi Kristalami)
instrument, consisting of two double-channel X-ray spectrometers,
designed to observe solar active region and flare plasmas. RESIK is
one of the instruments making up the scientific payload of the Russian
CORONAS-F solar mission. The uncollimated spectrometer uses two silicon
and two quartz bent crystals observing flare, active region and coronal
spectra in four wavelength bands with a resolving power (λ/Δ λ)
of ∼1000. The wavelength coverage, 3.3-6.1 Å, includes emission
lines of Si, S, Cl, Ar, and K and in the third diffraction order,
the wavelength range includes He-like Fe lines (1.85 Å) and Ni lines
(1.55 Å) with dielectronic satellites, emitted during intense, hot
flares. The instrument is believed to be the best calibrated space-borne
crystal spectrometer flown to date. The spectrometer dynamically adjusts
the data gathering intervals from 1 s to 5 minutes, depending on the
level of solar X-ray emission at the time of observation. The principal
aims of RESIK are the measurements of relative and absolute element
abundances in the emitting plasma and the temperature distribution of
plasma (differential emission measure) over the temperature interval 3
and 50 MK. This paper summarizes the scientific objectives of RESIK
and describes the design, characteristics, and performance of the
instrument.
Title: RHESSI, RESIK, and GOES Observations of the Solar Flare
Thermal Spectrum
Authors: Phillips, K. J. H.; Dennis, B. R.; Sylwester, J.; Sylwester,
B.
Bibcode: 2004AAS...204.8701P
Altcode: 2004BAAS...36..818P
The bulk of the thermal spectrum of solar X-ray flares extends from
very soft X-rays (<<1 keV) to beyond 10 keV. We present results
from three instruments detecting this spectrum: RHESSI, GOES, and
the Polish-led RESIK crystal spectrometer on the Russian Coronas-F
mission. RHESSI makes imaging and spectral observations at energies
above ∼ 5 keV; RESIK operates in a first-order diffraction mode
with energy range 2.0 to 3.7 keV and, for selected stronger flares,
in a third-order mode with energy range 6.1 to 8.6 keV; GOES makes
flux measurements in two wide energy bands between ∼ 1.5 and ∼
25 keV. Simultaneous observations by all three instruments were made
of an M2 flare on 2003 April 26, with RESIK in its first-order mode
at the beginning and decay portions of the flare and in third-order
during an 8-minute interval at the flare peak. Comparison of RHESSI
and both first-order and third-order RESIK spectra indicate agreement
to within the expected uncertainties of ∼ 25%. Both instruments
observe the continuum emission and the Fe line feature (mostly Fe XXV
lines and satellites) at 6.7 keV. The Fe/Ni line feature at 7.9 keV
(Fe XXV and Ni XXVII lines) is less certainly detected. The thermal
spectra derived from the GOES channel ratios agree closely with RESIK
and RHESSI spectra. Measurements of the equivalent width of the Fe
line feature and other lines in the RESIK first-order range allow
absolute element abundances to be determined during the flare for
comparison with standard photospheric values. KJHP acknowledges
an NRC Research Associateship, and JS and BS acknowledge support from
grants (2.P03D.002.22 and PBZ-KBN-054/P03/2001) of the Polish Committee
for Scientific Research. RESIK is a joint project between NRL (USA),
MSSL and RAL (UK), IZMIRAN (Russia), and SRC (Poland). The Coronas-F
mission is led by the IZMIRAN Institute.
Title: First Determinations of Differential Emission Measure
Distribution from RESIK X-ray Spectra
Authors: Kepa, A.; Sylwester, J.; Sylwester, B.; Siarkowski, M.
Bibcode: 2004IAUS..223..461K
Altcode: 2005IAUS..223..461K
RESIK Bragg spectrometer aboard CORONAS-F solar observatory collected
spectra of hundreds of solar flares in the unique spectral range between
3.3 Å and 6.1 Å. The instrument's absolute and relative calibrations
are now finished which allows for the first time to interpret the
observations in terms of the differential emission measure (DEM)
distribution. With known DEM shape it is possible to derive and study
in detail flaring plasma composition and energy balance. Here we report
results of using an improved Maximum Likelihood iterative algorithm
(Withbroe-Sylwester) for determination of the DEM distributions for
7 January 2003 flare at 23:30 UT. The study is based on the absolute
flux values observed in a number of strong H- and He-like transitions
of K xviii, Ar xviii, Ar xvii, S xvi, S xv, Si xiv and Si xiii ions. In
this respect, we use line and continuum X-ray emissivities as provided
by CHIANTI package from SolarSoft.
Title: Abundances of Potassium, Argon, and Sulphur in Solar Flares
Authors: Phillips, K. J. H.; Sylwester, J.; Sylwester, B.; Landi, E.
Bibcode: 2004IAUS..219..176P
Altcode:
No abstract at ADS
Title: Connectivity pattern in the corona
Authors: Sylwester, J.; Sylwester, B.
Bibcode: 2004HvaOB..28...71S
Altcode:
We present images of the structures indicative for the existence
of hierarchical, self-similar organization of global connections
in the solar atmosphere. We discuss a geometrical model of the basic
building block, the atmosphere is envisaged to be made of. The important
elements of the proposed building block are the plasma kernels and the
connections between them. It appears that the concept of hierarchical
organization is generally applicable to the solar atmosphere from
the base of the photosphere towards the interplanetary space. If so,
we point out profound consequences of such a hierarchical system for
transport of energy and dynamics within the solar atmosphere. Possible
scenarios for the plasma dynamics and acceleration mechanisms are
also outlined.
Title: Identification of Lines in the Range 3.35 A - 6.1 A Observed
in RESIK Spectra
Authors: Sylwester, B.; Sylwester, J.; Siarkowski, M.; Phillips,
K. J. H.; Culhane, J. L.; Lang, J.; Brown, C.; Kuznetsov, V. D.
Bibcode: 2004cosp...35.2663S
Altcode: 2004cosp.meet.2663S
RESIK is the Bragg bent crystal X-ray spectrometer on board CORONAS-F
satellite. Between August 24, 2002 and May 22, 2003, the instrument
collected a large database of solar X-ray spectra in four energy bands
covering the range 3.35 Å - 6.1 Å. We have recently calibrated the
spectra in order to determine an absolute wavelength scale and absolute
photon fluxes. This has allowed us to make detailed indentifications
of observed spectral features, and to interpret the observed line
and continuum fluxes in terms of basic plasma characteristics
like temperature and emission measure. Our line identifications
have been made using spectra averaged over periods of various solar
activity levels, e.g. flare rise and decay phases, non-flaring active
regions and quiet Sun. The spectra contain a number of strong lines
corresponding to the transitions in H- and He-like ions of K, Ar, S
and Si. Some of these lines are resonance lines and their satellites
which have already been noted by previous authors using data from
other spectrometers, but several lines have never been observed in
solar spectra before. These include lines of H-like and He-like S and
Si corresponding to transitions 1s - np and 1s^2 -1s np with n up to
∼10. In addition we provide indentification of the H-like Cl (Cl
XVII) Ly-alpha lines at 4.182 Å, and He-like Cl (Cl XVI) triplet in
the range 4.43 Å,- 4.45 Å, never before observed simultaneously. We
will present detailed identifications of these lines in this paper.
Title: Detection of H- and He-like resonance lines of chlorine in
solar flare spectra
Authors: Sylwester, B.; Sylwester, J.; Siarkowski, M.; Phillips,
K. J. H.; Landi, E.
Bibcode: 2004IAUS..223..671S
Altcode: 2005IAUS..223..671S
Preliminary analysis of spectra collected with the RESIK Bragg bent
crystal X-ray spectrometer aboard CORONAS-F indicates the presence
of many spectral features which until recently were unidentified. We
present RESIK spectra in which the H-like Cl XVII Lyalpha line at 4.182
Å and He-like Cl XVI triplet components in the range 4.43 Å-4.45 Å
are identified.
Title: Analysis of Potassium Abundance Variability in Selected
Solar Flares
Authors: Sylwester, J.; Sylwester, B.; Phillips, K. J. H.; Culhane,
J. L.; Brown, C.; Lang, J.; Stepanov, A. I.
Bibcode: 2004cosp...35.2639S
Altcode: 2004cosp.meet.2639S
A quick-look inspection of spectra observed in the shortwavelength
channel (3.35 Å,- 3.8 Å) of the RESIK X-ray spectrometer on Coronas-F
indicates the presence of substantial flare-to-flare variations in
the line-to-continuum ratio of several lines, in particular He-like
potassium (K XVIII) lines, occurring at 3.53 Å,- 3.57 Å. The
observed variations are larger those expected from temperature
variations. This has motivated a detailed study of possible variations
in the flare-to-flare potassium abundance. With newly calibrated RESIK
spectra, we have obtained absolute fluxes of the K XVIII resonance,
intercombination and forbidden lines as well as the continuum and
lines observed in other RESIK channels (3.35 Å,- 6.1 Å). These
data have allowed us to determine the absolute potassium abundance
for a selection of flares, mostly short-lived with a range of X-ray
importance. The results obtained are presented and discussed.
Title: Observations of 1s^2-1s(np) and 1s-(np) Lines in RESIK Soft
X-ray Spectra
Authors: Kepa, A.; Sylwester, B.; Sylwester, J.; Phillips, K. J. H.;
Kuznetsov, V. D.
Bibcode: 2004cosp...35.2574K
Altcode: 2004cosp.meet.2574K
RESIK is the X-ray bent crystal spectrometer on the CORONAS-F satellite,
launched on 2001 July 31. Between 2002 and 2003, RESIK has collected
numerous spectra of active regions and flares in the wavelength range
3.37 Å to 6.09 Å. This range includes many strong emission lines
due to transitions 1s^2-1snp and 1s-np in He-like and H-like ions
respectively; the n = 2 and 3 lines are routinely observed for Si,
S and Ar ions. For some flares we have observed enhanced emission
in spectral features coinciding with these transitions for n up to
9 or 10. Identification of these features, not previously observed
in astrophysical spectra, are presented in this paper, as is their
diagnostic importance. Respective observed line series decrements are
determined and discussed in this paper.
Title: Analysis of physical plasma properties within flare kernels
from EUV/X-ray observations
Authors: Gburek, S.; Sylwester, J.; Sylwester, B.; Kowalinski, M.
Bibcode: 2004IAUS..223..455G
Altcode: 2005IAUS..223..455G
We performed the study of a solar flare of GOES class X1.0 which
occurred on 2002 August 21, peak time 05:34 UT. A new method was
applied for temperature determination of the plasma seen in TRACE
images. This method makes use of the detailed knowledge of the TRACE
point spread function (PSF) function. Substantial dependence of TRACE
PSF on wavelength allows for determination of temperature from a single
TRACE image even in these portions of the image which are saturated. We
also determined the average temperature of this flare from the soft
X-ray spectra measured by RESIK Bragg spectrometer aboard CORONAS-F
satellite. The results obtained from TARCE and RESIK data are compared.
Title: Temperature-sensitive Line Ratios Diagnostics of the
non-flaring Corona based on Satellite-to-Resonance Line Ratios for
1s^2-1s(np) Transitions
Authors: Phillips, K. J. H.; Dubau, J.; Sylwester, J.; Sylwester,
B.; Kordylewski, Z.; Culhane, J. L.; Doschek, G. A.; Lang, J.
Bibcode: 2004cosp...35.2579P
Altcode: 2004cosp.meet.2579P
One of the most convenient electron temperature diagnostics of
hot astrophysical plasmas is the intensity ratio of dielectronic
satellite lines to resonance lines in the X-ray region. Until now,
this diagnostic has been applied to satellites near the 1s-2p lines of
H-like ions or the 1s^2 - 1s2p lines of He-like ions, these lines being
extensively observed with crystal spectrometers during flares. However,
satellites near the 1s^2 - 1snp (n>2) lines of He-like ions,
unlike those near the 1s^2 - 1s2p lines, have the important advantage
of being well separated from their parent lines and unblended with
other lines. Spectra from the RESIK spectrometer on Coronas-F,
covering the wavelength range 3.4 Å,- 6.1 Å, are highly suited
for observation of these satellites, due to transitions from the n =
3, 4 and 5 levels to the n = 1 level, near corresponding resonance
lines of H-like and He-like Si (Si XIII, Si XIV) and S (S XV, S XVI)
ions. New calculations of satellite intensity factors presented in
this paper enable temperatures to be calculated from observed ratios
of Li-like Si (Si XII) 1s^2 2p ^2P1/2,3/2 - 1s 2p (^3P) 3p
^2D3/2,5/2 satellite complex (5.816 Å) near He-like Si (Si
XIII) 1s^2 ^1S_0 - 1s 3p ^1P_1} resonance (5.681 Å) line. These lines
are well observed in recent quiet and non-flaring active region RESIK
X-ray spectra, and therefore provide the most sensitive temperature
diagnostic tool for physical conditions in weakly active corona.
Title: Thermal and nonthermal contributions to the solar flare
x-ray flux
Authors: Dennis, B.; Phillips, K.; Sylwester, J.; Sylwester, B.;
Schwartz, R.; Tolbert, K.
Bibcode: 2004cosp...35.1284D
Altcode: 2004cosp.meet.1284D
The relative thermal and nonthermal contributions to the total energy
budget of a solar flare are being determined through analysis of
RHESSI X-ray imaging and spectral observations in the energy range
from ∼ 5 to ∼ 50 keV. The classic ways of differentiating between
the thermal and nonthermal components -- exponential vs. power-law
spectra, impulsive vs. gradually varying flux, compact vs. extended
sources -- can now be combined for individual flares. In addition,
RHESSI's sensitivity down to ∼ 4 keV and energy resolution of
∼ 1 keV FWHM allow the intensities and equivalent widths of the
complex of highly ionized iron lines at ∼ 6.7 keV and the complex of
highly ionized iron and nickel lines at ∼ 8 keV to be measured as a
function of time. Using the spectral line and continuum intensities
from the Chianti (version 4.2) atomic code, the thermal component
of the total flare emission can be more reliably separated from the
nonthermal component in the measured X-ray spectrum (Phillips, ApJ
2004, in press). The abundance of iron can also be determined from
RHESSI line-to-continuum measurements as a function of time during
larger flares. Results will be shown of the intensity and equivalent
widths of these line complexes for several flares and the temperatures,
emission measures, and iron abundances derived from them. Comparisons
will be made with 6.7-keV Fe-line fluxes measured with the RESIK bent
crystal spectrometer on the Coronas-F spacecraft operating in third
order during the peak times of three flares (2002 May 31 at 00:12 UT,
2002 December 2 at 19:26 UT, and 2003 April 26 at 03:00 UT). During
the rise and decay of these flares, RESIK was operating in first order
allowing the continuum flux to be measured between 2.9 and 3.7 keV
for comparison with RHESSI fluxes at its low-energy end.
Title: Multi-Wavelength Study of a Strong Impulsive Solar Limb Flare
on 2002 August 3.
Authors: Gburek, S.; Sylwester, J.; Sylwester, B.; Dennis, B.;
Phillips, K. J. H.
Bibcode: 2004cosp...35.1080G
Altcode: 2004cosp.meet.1080G
We have made a detailed study of an impulsive solar flare with GOES
class X1.0 which occurred near the west limb on 2002 August 3, peak
time 19:07 UT. There is particularly good coverage of this event, with
simultaneous observations in EUV, soft and hard X-rays available. We
used TRACE 171 A images to study the morphology and evolution of the
event. Soft X-ray spectra between 2.0 and 3.7 keV (wavelengths 3.4 -
6.1 A) measured by the RESIK Bragg crystal spectrometer on Coronas-F
have been used for differential emission measure calculations of the
thermal plasma. Imaging and spectral data from RHESSI with energies
between ~3 and 100 keV have been used to derive characteristics of the
higher-temperature plasma and nonthermal electrons accelerated during
the flare. Comparison of these data sets enable valuable insight into
the heating and particle acceleration during this well observed event.
Title: Analysis of Yohkoh-observed limb flares accompanying CME events
Authors: Sylwester, B.; Sylwester, J.
Bibcode: 2003ESASP.535..483S
Altcode: 2003iscs.symp..483S
We have made the literature/web search in order to find well observed
limb flares seen by Yohkoh instruments. For the purpose of this study
we have looked for flares associated with CME counterparts. Only few
such events have been found and analysed (including compact and arcade
type flares as seen on SXT images). In this contribution we present
results illustrating several aspects of selected flare evolution. The
results shown concern the morphology (SXT deconvolved images, HXT
reconstructed images) and the flaring plasma dynamics as seen in
transversal (from image cadences) and radial directions (from BCS
spectral analysis). As the selected event has been observed over the
limb, detailed investigation of vertical motions of the hot plasma
is possible.
Title: Patterns of X-ray line emission variability as observed by
the RESIK Bragg spectrometer
Authors: Sylwester, J.; Sylwester, B.; Culhane, J. L.; Doschek, G. A.;
Oraevsky, V. N.; Phillips, K. J. H.
Bibcode: 2003ESASP.535..733S
Altcode: 2003iscs.symp..733S
RESIK is a unique Bragg bent crystal spectrometer operating continuously
since August 2001. By now, it has collected ~10 GB of solar flare and
active region spectra in a very much unexplored spectral region between
3.2 Å and 6.1 Å. In this paper we present a number of representative
observations covering periods of various solar activity: from the most
active level (M+ flares) to exceptionally quiet corona. We present also
a tentative list of the spectral features observed. In the wavelength
range observed by RESIK there are a number of strong emission lines
corresponding to H- and He-like resonance transitions of Si, S, Ar and K
ions. These lines are formed by thermal plasma of temperature between
5 and 50 MK, and therefore their analysis reveal the distribution
of hot plasma over this interval. RESIK sees lines from a number of
different elements, so it is possible to do abundance analyses. The
elements concerned have a wide range of first ionisation potentials
(FIPs) so it has been possible to examine the dependence of coronal or
flare abundances on FIP. We have observed substantial variations of
the K/Ar line ratio, and respective line/continuum ratios, which can
be best explained by allowing for changes in the chemical composition
of the coronal plasma
Title: Solar Flare Abundances of Potassium, Argon, and Sulphur
Authors: Phillips, K. J. H.; Sylwester, J.; Sylwester, B.; Landi, E.
Bibcode: 2003ApJ...589L.113P
Altcode:
The absolute abundance of potassium has been determined for the first
time from X-ray solar flare line and continuum spectra. The absolute
and relative abundances of Ar and S have also been determined. Assuming
that the flare plasma is coronal, and since potassium has the lowest
first ionization potential (FIP) of any common element on the Sun,
this determination is of importance in the continuing debate concerning
the nature of the coronal/photospheric element abundance ratios, which
are widely considered to depend on the FIP. The measurements were made
with the RESIK crystal spectrometer on the Coronas-F spacecraft. A
differential emission measure DEM~exp(-βTe) was found to
be the most consistent with the data of three models considered. We
find that the K/H abundance ratio is (3.7+/-1.0)×10-7,
a factor of 3 times photospheric. Our measured values of the
Ar/H ratio, (2.8+/-0.2)×10-6, and of the S/H ratio,
(2.2+/-0.4)×10-5, are equal to previous coronal and
photospheric determinations to within uncertainties. These measurements
therefore fit a pattern in which low-FIP elements are enriched in
the corona by a factor 3 and in which high-FIP elements (including S)
have equal coronal and photospheric abundances.
Title: Solar Flare Abundances of Potassium, Argon, and Sulphur
Authors: Phillips, K. J. H.; Sylwester, J.; Sylwester, B.; Landi, E.
Bibcode: 2003SPD....34.1622P
Altcode: 2003BAAS...35..837P
The absolute coronal abundances of potassium, argon, and sulphur
are determined from X-ray solar flare spectra using the RESIK
bent crystal spectrometer on the Coronas-F space observatory. A
differential emission measure of the form exp(-α Te) was
found to be appropriate for describing the fluxes of the lines due
to K XVIII (λ 3.53Å), Ar XVIII (λ 3.73Å), Ar XVII (λ 3.95Å),
S XV (λ λ 4.09, 4.30Å), Si XIV (λ 5.22Å), and Si XIII (λ λ
5.40, 5.68Å) which are observed by RESIK over a period of several
hours in four long-duration flares. The continuum in two of the four
RESIK channels appears to be uncontaminated by crystal fluorescence
or other instrumental effects, allowing abundances relative to H to
be determined. We estimate the following abundances relative to H:
[K/H] = 4.7 X 10-7; [S/H] = 2.9 X 10-5; [Ar/H] =
2.0 X 10-6. These values agree with a pattern that depends
on the first ionization potential (FIP) of an element in which the
coronal abundances of low-FIP elements (like K) are enhanced over
their photospheric abundances by a factor 3 and high-FIP elements
(like Ar) are depleted by a factor 2. The coronal abundance of sulphur
(medium-FIP) is slightly enhanced (factor of 1.5) compared with its
photospheric abundance. The exponential temperature dependence of the
differential emission measure is applied to simultaneous X-ray data
from the RHESSI mission which sees a thermal spectrum (continuum plus
Fe lines at 6.7 keV) for some of these flares. Results of this will
be discussed. We acknowledge support for this research from the
National Research Council (KJHP), Polish Committee for Scientific
Research (JS, BS), and from the Office of Naval Research (EL).
Title: Multitemperature analysis of selected limb-occulted flares
lines in solar flares
Authors: Sylwester, B.; Sylwester, J.
Bibcode: 2002ESASP.506..769S
Altcode: 2002ESPM...10..769S; 2002svco.conf..769S
The aim of this contribution was to compare the so-called "quasi"
differential emission measure distributions (qDEM) with "classical"
DEM distributions. The qDEM distributions for the flaring region have
been derived from the maps of "isothermal" temperatures and emission
measures for the flaring region. The temperature and emission measure
maps have been derived based on the deconvolved Yohkoh SXT images. The
deconvolution has been performed in order to increase the spatial
resolution. Next the images have been overlaid precisely using the
position of the occulting solar disc as a reference. The high accuracy
of coalignment allowed to derive the temperature maps with spatial
resolution down to ~1 arcsec. From the other side the DEM distributions
have been determined for a flare as a whole, based on integral flare
fluxes measured by SXT and GOES using maximum likelihood iterative
algorithm. In principle such a comparison of qDEM and DEM shapes should
allow to investigate which part of DEM is related to the bright kernels
observed on SXT images.
Title: Comparison of trace and deconvolved SXT images for solar flares
Authors: Sylwester, B.; Sylwester, J.
Bibcode: 2002ESASP.506..773S
Altcode: 2002svco.conf..773S; 2002ESPM...10..773S
In this research we have studied the relationship between thermal
flaring plasma seen on TRACE and on Yohkoh SXT images. Before the
comparison we have performed the deconvolution (with oversampling) of
SXT images using ANDRIL algorithm. This effectively brought to scale
the spatial resolution on SXT and TRACE images. For the comparison
we selected events partly occulted by the limb in order to use its
apparent position for fine adjustment of images obtained in soft X-ray
and EUV ranges. Based on the performed comparison we have confirmed
that EUV and soft X-ray emissions do NOT exactly match. However, the
overall appearance of patterns suggests presence of correspondence
between plasma contributing to both emissions.
Title: RESIK observations of highly ionized argon and potassium
X-ray emission lines in solar flares
Authors: Sylwester, J.; Culhane, J. L.; Doschek, G. A.; Oraevsky,
V. N.; Phillips, K. J. H.; Sylwester, B.
Bibcode: 2002ESASP.506..765S
Altcode: 2002svco.conf..765S; 2002ESPM...10..765S
The first detailed solar X-ray spectra obtained by the RESIK bent
crystal spectrometer aboard the CORONAS-F obervatory are presented
and instrument performance discussed. RESIK is a bent crystal
spectrometer covering four soft X-ray spectral ranges (3.369-3.879 Å,
3.821-4.326 Å, 4.307-4.890 Å 4.960-6.086 Å), some of which have
not been well covered by previous instruments. RESIK forms spectra
in each of these ranges in 250 bins simultaneously in intervals
of 10 s or so. Many flares, including several of GOES X-class,
and bright active regions have now been observed in detail. (See
http://www.cbk.pan.wroc.pl/2002.htm for examples.) In this paper,
observations of spectral lines due to K XVIII, Ar XVIII, Ar XVII, S XV,
Si XIV and Si XIII ions will be shown and the time evolution of their
intensities will be discussed. These observations will eventually
allow for precise determination of differential emission measure
(DEM) and chemical composition of the hot flare plasma, and should,
alongside data from the RHESSI, TRACE, and SOHO spacecraft, enable
new and detailed insight into solar flare mechanisms.
Title: Determination of wavelengths and line shifts based on X-ray
spectra from Diogeness
Authors: Plocieniak, S.; Sylwester, J.; Kordylewski, Z.; Sylwester, B.
Bibcode: 2002ESASP.506..963P
Altcode: 2002svco.conf..963P; 2002ESPM...10..963P
Diogeness is the uncollimated scanning flat crystal spectrometer
observing flare X-ray spectra in four narrow wavelength bands in the
vicinity of Ca XIX, S XV and Si XIII He-like "triplets" around 3.18
Å, 5.04 Å and 6.65 Å. In two spectral channels, the same emission
lines (around Ca XIX w resonance line, λ = 3.177 Å) are scanned
in opposite directions. The X-rays are reflected from precisely
adjusted identical Quartz monocrystals mounted on the common shaft in
so-called Dopplerometer configuration. This novel spectrometer design
allows for highly accurate determinations of wavelengths and precise
determination of line Doppler shifts. We explain the concept of the
X-ray Dopplerometer and present results of analysis of the Doppler line
shifts for the spectra collected during 25 August 2001 X5.3 flare. We
compare derived line of sight plasma velocities with those measured
by Yohkoh BCS.
Title: Thermodynamics of partly occulted limb flares
Authors: Sylwester, Barbara; Sylwester, Janusz
Bibcode: 2002ESASP.477..171S
Altcode: 2002scsw.conf..171S
We have studied time variations of the thermodynamic parameters for
several flares which have been partly occulted by solar disc. The data
consist mainly of deconvolved Yohkoh Soft X-ray Telescope (SXT) images
coaligned to sub-arcsec accuracy using specially designed method. At
first in our analysis we have followed the maximum brightness location
for pronounced flare kernels emission seen on deconvolved images. The
analysis of the data reveals systematic variations of the brightest
kernel position. Spatial resolution achieved on the deconvolved images
allows to derive the maps of temperature and emission measure within
unocculated portion of the flaring structures (kernels) with the
resolution below ~1 arcsec. It is possible to estimate the electron
density of plasma confined within individual kernels based on their
spatial dimensions. Our analysis indicates that the hottest regions
within the flaring kernels are these with the smaller density. As
a rule the cooler regions are related with the denser plasma. It is
typical that some amount of plasma with temperatures T >= 20 MK
is present within the flaring region during the rise phase. Derived
patterns of maximum brightness location as observed on A101, A112
and Be119 filter images have been cross-compared with the location
of hard X-ray emission centers as seen on the MEM-reconstructed Hard
X-ray Telescope (HXT) images.
Title: Modeling of X-Ray Source Occultation by the Solar Disk
Authors: Sylwester, J.; Sylwester, B.
Bibcode: 2002mwoc.conf..409S
Altcode:
It is known, that the application of filter ratio (Al12/Be119)
technique into the analysis of SXT images requires a precise image
coalignment. The coalignment problems are even more serious in the
case of analysis of deconvolved images with oversampling. In order to
achieve the necessary alignment accuracy in this case, we have used
the occulting solar limb position as a reference. The limb's position,
as seen on images taken using individual SXT filters, may depend on the
source temperature and the filter transmission. We have investigated
this dependence using VAL model of the photosphere/chromosphere
transition region. We have found a difference of 0.3 arcsec (200
km) of the limb location as seen on images taken with Be119 and the
other SXT filters. The difference is even larger for individual HXT
channels. Results of the analysis allow us to coalign the Al12 and
Be119 deconvolved images to the required accuracy. In parallel, we
also discuss implications of the occultation phenomenon on the shape
of X-ray lightcurves for kernels evanescent from behind the limb. By
applying filter ratio (Al12/Be119) technique to deconvolved images
we have studied the evolution of temperature and emission measure
of flaring kernels with 1 arcsec resolution for behind the limb
sources. Obtained high resolution temperature and emission measure
maps we have compared with the maps of hard X-ray brightness (HXT). We
discuss physical implications of the results obtained.
Title: Physical conditions within flare kernels
Authors: Sylwester, B.; Sylwester, J.
Bibcode: 2002AdSpR..30..617S
Altcode:
We have investigated the distribution of temperature and emission
measure (T, EM) within flare coronal kernels. The data used consist of
the soft and hard X-ray images of flares obtained onboard the Yohkoh
using Soft and Hard X-ray Telescopes (SXT and HXT). The analysed maps
of temperature and emission measure have been obtained using a pair
of Al12 and Be119 images which signal ratio is the most sensitive to
temperature for the flaring plasma. The SXT images have been deconvolved
using the ANDRIL routine and the HXT images have been reconstructed
using standard maximum entropy method (MEM). The flares selected for
the analysis have been simple, behind the limb events for which we
can undoubtably identify the isolated kernels located in the corona,
partly occulted by the limb. We present the analysis of 5 th
October 1992 flare as an example. The importance of precise image
coalignment is emphasised and the method of making the adjustment for
limb occulted flares is presented.
Title: High Resolution Observations of Solar Flares [Invited]
Authors: Sylwester, B.
Bibcode: 2002mwoc.conf..209S
Altcode:
The most suitable data set available for investigation of flares has
been accumulated by the Yohkoh instruments. The SXT collected a wealth
of solar X-ray images including thousands of flare sequences. Over
several past years, our team in Space Research Center (SRC) of Polish
Academy of Sciences in Wroclaw has been interested in developing the
numerical image enhancement techniques with the aim of increasing the
resolution on SXT flare images. The algorithm has been worked out which
allows for the image deblurring with oversampling. The code (ANDRIL)
is available in the public domain (SolarSoft). The application of this
algorithm allows to increase the resolution on the SXT images to the
level of 1 arc sec. We performed the deconvolution of large number
of flare sequences using ANDRIL algorithm. The analysis of these data
allowed to study the morphology of million degree flaring plasma with
the resolution comparable to TRACE. The main results will be presented
in the review. In order to infer the thermodynamic parameters of the
plasma from the analysis of deconvolved images their precise coalignment
is required. Techniques which have been developed at SRC to achieve
high accuracy of image coalignment will be presented. The application
of filter ratio (Al12/Be119) technique to the deconvolved and coaligned
images allows to study temperature and emission measure distributions
in great details. These maps better resolve flare kernels located both
at the summits and foot points of flaring loop structures. We have
studied the thermodynamic properties of kernels and related them with
the corresponding characteristics derived from the analysis of BCS and
HXT data. Performed analysis improved considerably our understanding
of solar flares. Many of the results and theoretical ideas presented
in this review have been obtained in cooperation with the team from
the Astronomical Institute of Wroclaw University.
Title: Evolution of White-Light Flares Observed by YOHKOH
Authors: Sylwester, Barbara; Sylwester, Janusz
Bibcode: 2000SoPh..194..305S
Altcode:
We consider in detail the evolutionary patterns of few white-light
flares observed by Yohkoh. The following data have been used in the
analysis: sequences of de-convolved SXT images in X-ray and optical
filters, MEM reconstructed HXT images and the other supporting data. The
resolution in the de-convolved images is below 1 arc sec. Working with
sequences of de-convolved images makes it also possible to investigate
the dynamics of these structures with high spatial accuracy. Comparison
of the morphology of flare brightenings as observed in hard, soft
and optical ranges reveals that these emissions are not co-spatial
and are most probably related to different plasma volumes at any
instant. These observations cannot be easily accommodated within
standard flare scenarios. Traditionally, the hard and optical flare
emissions are expected to be co-spatial and the soft X-ray emission
is presumed to fill the coronal portion of flaring loop(s) during rise
phase. Present observations do not easily fit to such scenario.
Title: The Properties of Flares Produced Within AR 6919
Authors: Sylwester, B.; Sylwester, J.
Bibcode: 1999ESASP.448..895S
Altcode: 1999mfsp.conf..895S; 1999ESPM....9..895S
No abstract at ADS
Title: Transversal and Radial Motions of Flaring Kernels for 11
August 2992 Event
Authors: Sylwester, J.; Sylwester, B.
Bibcode: 1999ESASP.446..639S
Altcode: 1999soho....8..639S
We have studied time variations of the maximum brightness location
for pronounced flare emission kernels as seen on deconvolved Yohkoh
Soft X-ray Telescope images. Spatial resolution achieved on the
deconvolved images was +- 0.5 arcsec. Derived patterns of spatial
displacements observed on Al01, Al12 and Be119 filter images have
been intercompared. This comparison revealed systematic pattern of
variations for kernels located within the footpoint and summit flare
regions. We have found that the time variations of maximum brightness
location are typical for all flare kernels investigated. We have related
this transversal position changes with soft X-ray line displacements
as determined from Yohkoh Bent Crystal Spectrometer for SXV, Ca XIX
and Fe XXV ion spectra (radial velocity component). We have noticed
definite time correspondence between transversal motions of kernels,
spectral line displacements and the details of flare hard X-ray
flux variability. This correspondence is especially well pronounced
during the initial phase for many disc and limb events. We discuss
the importance of the noticed pattern on possible flare scenarios.
Title: Reconstruction of Images with Poisson Noise
Authors: Sylwester, J.; Sylwester, B.
Bibcode: 1999AcA....49..189S
Altcode:
This paper addresses quantitatively the problem of influence
of statistical uncertainties embedded in the recorded image on
uncertainties of the reconstructed image. In the analysis we use
iterative maximum likelihood algorithm ANDRIL (described by Sylwester
and Sylwester 1998) developed for massive deconvolution of flare images
obtained by the Soft X-ray Telescope (SXT) on Yohkoh. We illustrate
the "ill-conditioned" nature of the image reconstruction problem and
suggest the ways to reduce, at least partly, propagation of noise to
the reconstructed image.
Title: Flaring Structures Observed in Deconvolved SXT Images
Authors: Sylwester, B.; Sylwester, J.
Bibcode: 1999AcA....49...85S
Altcode:
We present and discuss evolution of flaring structures morphology
as observed in deconvolved soft X-ray images. The X-ray images have
been obtained using the Soft X-ray Telescope (SXT) on Yohkoh. The
deconvolution has been made using the iterative maximum likelihood
algorithm Andril. In the reconstructed images it is possible to study
the position of individual fine structures for the first time with
the resolution superior to the SXT pixel size. We show example of
the analysis of deconvolved images for one disc flare on July 11,
1992 at 15:25 UT. Corresponding figures and animations for two other
flares are available at the address www.cbk.pan.wroc.pl and at the
Acta Astronomica Archive (see second cover page for details). These
flares occurred on November 19, 1991 and on January 13, 1992 and have
been located near/at the limb. We conclude about the differences of
physical conditions of the flaring plasma confined in compact bright
regions (kernels) located in the footpoint and summit areas.
Title: Dynamics of coronal flux tubes in flares.
Authors: Sylwester, J.; Sylwester, B.
Bibcode: 1999joso.proc...93S
Altcode:
The authors address the problem of dynamics of the soft X-ray coronal
structures being excited during flares. The investigation of this
problem has been possible thanks to development of dedicated Yohkoh
SXT image deconvolution algorithm ANDRIL which allows to remove the
instrumental blurring and increase spatial resolution on the images
below ≡1 arcsec.
Title: The Gradual Phase of Flares
Authors: Svestka, Z. F.; Poletto, G.; Fontenla, J.; Hick, P.; Kopp,
R. A.; Sylwester, B.; Sylwester, J.
Bibcode: 1999mfs..conf..409S
Altcode:
Heating and Cooling in the Gradual Phase Emission Measure-Temperature
Diagrams Flaring Arches Gradual Phase of Eruptive Flares Postflare
Giant Arches Giant Arches: Modeling and Interpretation
Title: Reconstruction of coronal magnetic fields from deconvolved
SXT images.
Authors: Sylwester, B.; Sylwester, J.
Bibcode: 1999joso.proc..105S
Altcode:
The authors reconstruct the coronal magnetic field topology based
on analysis of deconvolved SXT images. In the analysis they use
the deconvolved SXT images and their earlier findings regarding the
differences of thermodynamic parameters (temperature, emission measure)
for plasma confined within footpoint and summit kernels. Additionally
MEM reconstructed HXT L channel data have been used.
Title: ANDRIL - Maximum Likelihood Algorithm for Deconvolution of
SXT Images
Authors: Sylwester, J.; Sylwester, B.
Bibcode: 1998AcA....48..519S
Altcode:
We present an iterative deconvolution algorithm called ANDRIL
devoted for advanced processing of images obtained by the Soft X-ray
Telescope (SXT) on Yohkoh. The algorithm is based on maximum likelihood
approach. We introduced several modifications to this algorithm in order
to optimize its properties. The goal of the algorithm is to remove
numerically the image blurring due to the instrument point spread
function (PSF) and increase the image resolution. The application
of the algorithm allows to resolve soft X-ray structures in the SXT
images on the angular scales down to 1arcsec. Presented algorithm has
been recently used for analysis of detailed morphology and physical
conditions in the plasma of flaring structures.
Title: Evolution of Flaring Structures
Authors: Sylwester, Janusz; Sylwester, Barbara
Bibcode: 1998ASPC..155..381S
Altcode: 1998sasp.conf..381S
No abstract at ADS
Title: Analysis of the flare evolution in the emission measure -
temperature diagrams for selected events observed by SMM (abstract)
Authors: Sylwester, B.; Sylwester, J.; Siarkowski, M.; Fludra, A.;
Serio, S.
Bibcode: 1998PAICz..88...94S
Altcode:
No abstract at ADS
Title: Physical conditions in flaring loops.
Authors: Sylwester, B.; Sylwester, J.
Bibcode: 1998joso.proc..155S
Altcode:
The authors present results of the analysis of physical conditions in
flaring limb X-ray coronal structures as observed on deconvolved Yohkoh
Soft X-ray Telescope (SXT) images. The results obtained indicate that
bright foot-point areas are cooler by 2-3 MK relative to the kernels
observed higher in the corona. This property may allow to distinguish
between the location (foot-point/coronal) of bright flare kernels
observed on the disc flares.
Title: Footpoint Structures of Flare Loops
Authors: Sylwester, J.; Sylwester, B.
Bibcode: 1997ESASP.404..697S
Altcode: 1997cswn.conf..697S
No abstract at ADS
Title: Structures in vicinity of sunspots as seen on deconvolved
SXT images.
Authors: Sylwester, B.; Sylwester, J.
Bibcode: 1997joso.proc...97S
Altcode:
No abstract at ADS
Title: The Analysis of Energy Release in Solar Flares Based on
X-Ray Observations
Authors: Sylwester, Barbara
Bibcode: 1996SSRv...76..319S
Altcode:
Extended review of selected papers which deal with the problem of
flare heating in solar coronal loops is presented. Discussed methods
of the analysis of flare heating based on the X-ray observations have
been worked out using the Palermo-Harvard hydrodynamic code. The case
is presented when the assumption of the uniform heating across the
loop is made. The existence of multiple elementary heating episodes
is postulated as well. Next the possibility of the non-uniform
heating across the loop is assumed and its manifestation in the X-ray
observations is investigated. The application of proposed methods of
the analysis to the observations of solar flares in X-rays is presented.
Title: ANDRIL Algorithm for Deconvolution of SXT Images
Authors: Sylwester, J.; Sylwester, B.; Siarkowski, M.
Bibcode: 1996ASPC..111..244S
Altcode: 1997ASPC..111..244S
The authors present an iterative SXT image deconvolution algorithm
based on the Richardson (1972), Lucy (1974) and Withbroe (1975) methods.
Title: Thermodynamic signatures of proton flares.
Authors: Sylwester, B.; Sylwester, J.; Garcia, H. A.
Bibcode: 1996joso.proc..161S
Altcode:
No abstract at ADS
Title: Fine Structures Observed on Deconvolved SXT Images
Authors: Sylwester, B.; Sylwester, J.; Siarkowski, M.
Bibcode: 1996ASPC..111..249S
Altcode: 1997ASPC..111..249S
The authors present prompt results of SXT image deconvolution obtained
using the ANDRIL algorithm worked out in Wroclaw. Using this algorithm
it is possible to study the morphology of individual fine structures
with the resolution superior to the SXT pixel size. The authors show
examples of deconvolved images for two selected flares.
Title: Quantitative interpretation of GOES soft X-ray
measurements. I. The isothermal approximation: application of various
atomic data.
Authors: Sylwester, J.; Garcia, H. A.; Sylwester, B.
Bibcode: 1995A&A...293..577S
Altcode:
The most temporally complete set of solar soft X-ray flux
measurements available at the present time is contained in the
archive record of 0.5-4A and 1-8A broad-band ion chamber observations
from the Geostationary Operational Environmental Satellite (GOES)
spacecraft. The archive contains a nearly continuous record of the soft
X-ray observations since 1974. Physical analyses of these measurements
are often carried out under the isothermal plasma approximation. In
this paper we present calculations of the ion chamber current ratio -
temperature relationship for soft X-ray detectors onboard four GOES
satellites whose data comprise the main historical X-ray record. The
present calculations update and extend results obtained by Thomas et
al. for the GOES-1 detectors. Our analysis has been performed using two
modern sets of theoretical X-ray spectra calculated by Mewe et al. and
by Raymond. Comparisons of the detector responses obtained for each of
the above theoretical spectra are performed. These analyses indicate
that both Mewe et al. and Raymond X-ray spectra provide mutually
consistent interpretations of measured GOES X-ray data. Deficiencies in
the physical interpretation of a mixture of low-temperature (active
region) and high-temperature (flare) plasmas resulting from the
isothermal approximation are pointed out and discussed. It is shown
that the so called flare "thermodynamic measure", defined here and
derived from GOES measurements, compares well with co-temporal values
obtained from the analysis of the Yohkoh BCS spectra. It is proposed
that the presented method of a thermodynamic measure analysis may be
useful in the interpretation of global flare thermodynamics.
Title: Manifestation of Multiple Energy Release on the Evolution of
Flares in the Diagnostic Diagrams
Authors: Sylwester, B.; Sylwester, J.; Reale, F.; Serio, S.
Bibcode: 1994scs..conf..257S
Altcode: 1994IAUCo.144..257S
The authors advance the investigation of evolution of flares in the
emission measure-temperature diagrams. Models are considered in which
the flare heating consists of a pair of elementary heating episodes
taking place in separate loops within flaring region.
Title: Estimation of equivalent flaring loop geometry based on
broadband soft x-ray observations
Authors: Sylwester, J.; Sylwester, B.; Jakimiec, J.; Garcia, H. A.;
Serio, S.; Reale, F.
Bibcode: 1993AdSpR..13i.307S
Altcode: 1993AdSpR..13..307S
Hydrodynamic models of a simple flaring loop, obtained using the
Palermo-Harvard code have been used to consider the flare global energy
balance. During the heating phase the time variations of the total
thermal energy contained in the coronal portion of the loop is well
represented by a simple analytical formula with parameters depending
on the flaring loop geometry. The loop geometry parameters are the
loop semi-length and the cross-sectional area. A method is introduced
which allows to estimate values of these parameters from a fit to the
measurements. We have applied this method to the interpretation of
GOES soft X-ray data for the flare on 11 September 1989, for which
high-resolution XUV images were available from the NIXT experiment.
Title: Properties of SMM Flares
Authors: Sylwester, J.; Sylwester, B.
Bibcode: 1993ASSL..183..139S
Altcode: 1993pssc.symp..139S
No abstract at ADS
Title: Analysis of Flare Evolution in the Emission Measure-Temperature
Diagram for Three Events Observed by SMM
Authors: Sylwester, B.; Sylwester, J.; Siarkowski, M.; Serio, S.;
Reale, F.
Bibcode: 1993ASSL..183..147S
Altcode: 1993pssc.symp..147S
No abstract at ADS
Title: Dynamics of flaring loops. III - Interpretation of flare
evolution in the emission measure-temperature diagram
Authors: Sylwester, B.; Sylwester, J.; Serio, S.; Reale, F.; Bentley,
R. D.; Fludra, A.
Bibcode: 1993A&A...267..586S
Altcode:
The aim of the paper is to illustrate the application of the
density-temperature diagrams discussed by Jakimiec (1992) to
interpretation of soft X-ray measurements, namely, calcium spectra
recorded by the Solar Maximum Mission Bent Crystal Spectrometer. Using
the emission measure and the temperature values derived for a set
of hydrodynamic flare models discussed in previous papers, we have
obtained and analyzed the (sq rt epsilon-T) counterparts of the (N-T)
diagrams. Inspection of these diagrams reveals that they qualitatively
resemble the (N-T) diagrams. The inclinations of the decay trajectories
make the main difference. Next, we have performed a comparison of the
modeled and observed flare evolutionary trajectories. This comparison
allowed us to identify characteristic cases of evolution during the
decay phase. We have discussed time variations of the heating rate
for selected observed flares. The results of this paper illustrate
how to use the diagnostic diagrams in the interpretation of flare soft
X-ray measurements.
Title: Dynamics of flaring loops. II - Flare evolution in the
density-temperature diagram
Authors: Jakimiec, J.; Sylwester, B.; Sylwester, J.; Serio, S.; Peres,
G.; Reale, F.
Bibcode: 1992A&A...253..269J
Altcode:
The evolution of basic thermodynamic parameters of a single flaring
solar loop has been investigated in terms of density-temperature (N-T)
diagram. A grid of hydrodynamic models has been calculated for this
purpose, using the Palermo-Harvard code. The calculated models differ
in their initial conditions and the form of the energy imput (i.e., the
heating rate value, the heating duration, the assumed time profile). The
consequences of variation of these model parameters on the evolutionary
paths in the density-temperature diagrams is considered; over a
substantial duration, the decay occurs along a T varies as N-squared
trajectory when the impulsive flare heating function is switched-off
abruptly. The results obtained can be very useful as diagnostics of
the flare heating process, based on soft X-ray observations.
Title: Thermodynamic decay scaling laws in solar loop flares
Authors: Serio, S.; Reale, F.; Peres, G.; Jakimiec, J.; Sylwester,
B.; Sylwester, J.
Bibcode: 1992MmSAI..63..763S
Altcode:
Results of numerical calculations are used, together with analytical
considerations, as a guide to set up diagnostic tools for the flare
decay phase in terms of the temperature-density (n-T) diagram. The
decaying loop was modeled as a hydrodynamic process in a rigid
semicircular tube. It is shown that the trajectory on the n-T plane
has a slope of about 2 for a wide set of peak model flare conditions.
Title: Flare Evolution in the Density - Temperature Diagram
Authors: Serio, S.; Reale, F.; Peres, G.; Jakimiec, J.; Sylwester,
B.; Sylwester, J.
Bibcode: 1992LNP...399..135S
Altcode: 1992esf..coll..135S; 1992IAUCo.133..135S
No abstract at ADS
Title: Thermondynamic Evolution of Flares
Authors: Sylwester, B.; Sylwester, J.; Jakimiec, J.; Serio, S.;
Reale, F.
Bibcode: 1991LNP...387..188S
Altcode: 1991fpsa.conf..188S
No abstract at ADS
Title: Dynamics of flaring loops. I - Thermodynamic decay scaling laws
Authors: Serio, S.; Reale, F.; Jakimiec, J.; Sylwester, B.;
Sylwester, J.
Bibcode: 1991A&A...241..197S
Altcode:
A simple analytical approximate solution for the hydrodynamic equations
describing the decay of a flaring loop is derived. It is found that,
independent of chemical composition of the plasma, the entropy per
particle at the top of the loop undergoes an initial phase of linear
decay, with a slope related to the initial loop conditions. The
characteristic decay time is shorter than conductive or radiative
times for typical solar flare conditions. The analytical solution
is compared with numerical solutions of the full set of hydrodynamic
equations for loop flares, and it is shown that its validity extends
over a large fraction of the decay. Also the decay times of temperature,
density and pressure are related to the entropy decay time.
Title: Investigation of non-uniform heating during the decay phase
of solar flares
Authors: Sylwester, B.; Sylwester, J.; Bentley, R. D.; Fludra, A.
Bibcode: 1990SoPh..126..177S
Altcode:
We have analysed X-ray spectra of 13 solar flares as obtained
by the Bent Crystal Spectrometer (BCS) on the Solar Maximum
Mission. In particular, we have examined the observed ratio of
TFe/TCa where TFe and TCa
are the temperatures obtained from the FeXXV and CaXIX spectra,
respectively. In order to simplify the investigation we have analysed
only flares which reach quasi-steady-state during the decay. It
turned out that the observed ratios cannot be explained by a model
consisting of a single, uniformly heated loop, with a constant or
variable cross-sectional area. We propose that this problem may be
solved by introducing some distribution of the heating function across
the flaring loop. This model has been tested by detailed calculations.
Title: Study of Non-Uniform Heating in Solar Flares
Authors: Sylwester, B.; Sylwester, J.; Jakimiec, J.; Serio, S.; Reale,
F.; Bentley, R. D.; Fludra, A.
Bibcode: 1990PDHO....7..255S
Altcode: 1990ESPM....6..255S; 1990dysu.conf..255S
The authors have analyzed the ratios of the temperatures derived from Fe
and Ca spectra (TFe/TCa) for the rising phase of
11 solar flares. Corresponding hydrodynamic models have been calculated
and the obtained results are compared with the observational data for
selected flares.
Title: Results of the LEBAN diagnostic procedure applied to two
SMM-observedflares.
Authors: Sylwester, B.; Sylwester, J.; Jakimiec, J.
Bibcode: 1988JPhys..49..309S
Altcode: 1988IAUCo.102..309S
In a previous paper (B. Sylwester et al., 1986) the authors proposed a
new procedure called LEBAN (Loop Energy Balance Analysis) for deriving
the basic geometrical parameters of flaring loops. In the present
paper they apply the LEBAN method to two well observed solar flares.
Title: Influence of the energy calibration of broad-band X-ray
detectors on determination of the plasma parameters
Authors: Sylwester, B.; Farnik, F.; Sylwester, J.
Bibcode: 1988AdSpR...8k.267S
Altcode: 1988AdSpR...8..267S
Standard broad-band measurements of the solar soft X-ray spectra
are used to derive averaged values of parameters characterizing
flaring plasmas i.e. the temperature and emission measure. Derived
values of these parameters may be used as a basis for estimating the
thermal energy content, densities and other thermodynamic properties of
flares. These derived numerical values are subject to errors inherent in
the uncertainties of the energy calibration, filter transmission etc.,
of the measuring device. In this paper we investigate the influence of
the uncertainties of the detector's energy calibration on the accuracy
of the derived physical characteristics of solar flares. This analysis
is based on data obtained from the X-ray photometer flown aboard the
Prognoz-10 (Intershock) satellit
Title: Variation in Calcium Abundance during Flares
Authors: Sylwester, J.; Lemen, J. R.; Mewe, R.; Bentley, R. D.;
Sylwester, B.
Bibcode: 1987sman.work..123S
Altcode:
The authors discuss the variation of the line-to-continuum ratio
throughout the entire flare including the temperature rise phase.
Title: LEBAN diagnostic for basic flaring loop parameters.
Authors: Sylwester, B.; Sylwester, J.; Jakimiec, J.; Fludra, A.;
Peres, G.; Serio, S.
Bibcode: 1987PAICz..66..229S
Altcode: 1987eram....1..229S
The authors describe the diagnostic procedure called LEBAN which may
be helpful in deriving basic geometrical loop parameters. "Palermo
Code" hydrodynamic flare model calculations have been used to test
reliability of the procedure.
Title: High-Temperature Plasma Diagnostics of Solar Flares and
Comparison with Model Calculations
Authors: Jakimiec, J.; Sylwester, B.; Sylwester, J.; Lemen, J. R.;
Mewe, R.; Bentley, R. D.; Peres, G.; Serio, S.; Schrijver, J.
Bibcode: 1987sman.work...91J
Altcode:
The present state of flare diagnostics from X-ray spectra is briefly
outlined. The authors discuss how improved diagnostic results can be
used in flare heating process investigations.
Title: Erratum - Investigation of the Maxii 8.42A Doublet in Solar
Flare Spectra
Authors: Sylwester, B.; Faucher, P.; Jakimiec, J.; Korneev, V. V.;
Krutov, V. V.; McWhirter, R. W. P.; Sylwester, J.; Tomczak, M.;
Volonte, S.; Zhitnik, I. A.
Bibcode: 1986SoPh..105..429S
Altcode:
No abstract at ADS
Title: Investigation of flare heating based on X-ray observations
Authors: Jakimiec, J.; Sylwester, B.; Sylwester, J.; Mewe, R.; Peres,
G.; Serio, S.; Schrijver, J.
Bibcode: 1986CoSka..15..123J
Altcode:
Using X-ray data recorded by the Solar Maximum Mission Hard X-ray
Imaging Spectrometer the authors have investigated flare evolution
in a (Tm, N)-diagram, where Tm is the maximum
temperature and N is the mean density in the flare volume. This
flare diagnostics allows one to show that most large flares achieve a
quasi-steady-state during their decay, which means that the cooling
is then so slow that a flare evolves along the line of steady-state
loops in the (Tm, N)-diagram. The diagnostics allows one
to determine the time evolution of the flare heating function, which
gives the rate of thermal energy release, per unit volume.
Title: Flare evolution from Prognos 9 data
Authors: Fárník, F.; Sylwester, B.; Sylwester, J.; Jakimiec, J.;
Valníček, B.
Bibcode: 1986CoSka..15..121F
Altcode:
No abstract at ADS
Title: Investigation of the Mg XII 8.42 Å doublet in solar flare
spectra
Authors: Sylwester, B.; Faucher, P.; Jakimiec, J.; Krutov, V. V.;
McWhirter, R. W. P.; Sylwester, J.; Tomczak, M.; Volonté, S.; Zhitnik,
I. A.
Bibcode: 1986SoPh..103...67S
Altcode:
The intensity ratio of the components of the Mg XII 8.42
Å (1s2S1/2 − 2p2P1/2,
3/2) doublet in solar flare spectra has been investigated using
observations recorded from the Intercosmos 7 satellite. The observed
values of the ratio fall within the interval 0.38-0.66 and have been
compared with recent theoretical predictions based on an optically
thin collisional-radiative model. It has been found that for the
flare plasma the low values of the ratio cannot be explained since
they fall below the smallest theoretical value. The highest values
on the other hand require that an unacceptably high electron density
be postulated. It is suggested that both high and low values may be
caused by the resonance line scattering of the Mg XII quanta in the
flare volume, provided that the volume is elongated and not spherical.
Title: Physical conditions in a large flare loop on Nov. 1980 derived
from SMM observations
Authors: Sylwester, B.; Sylwester, J.; Jakimiec, J.; Fludra, A.;
Bentley, R. D.; Schrijver, J.
Bibcode: 1986CoSka..15..145S
Altcode:
The authors present the study of a large X-ray loop related to the
H-alpha 2N flare close to the center of the solar disc. Data from Solar
Maximum Mission have been used in the analysis. The authors have derived
the temperatures, densities and the geometrical parameters (length,
diameter) for a hot core and for a cooler envelope of the flaring loop.
Title: Flare diagnostics based on Prognoz 9 X-ray data
Authors: Sylwester, B.; Fárník, F.; Sylwester, J.; Jakimiec, J.;
Valníček, B.
Bibcode: 1986AdSpR...6f.233S
Altcode: 1986AdSpR...6..233S
The X-ray fluxes measured aboard the Prognoz 9 satellite in the energy
range 2-160 keV have been analysed for several big flares which occurred
during 1983. A new method of analysis called LEBAN (Loop Energy Balance
Analysis) has been applied. The LEBAN method allows us to estimate the
effective length and volume of the flaring loop under the assumption
of single constant-cross-section geometry. Results of the analysis
provide the necessary information to investigate in detail the time
behaviour of individual terms comprising the energy balance equation
for the hot (T > 4MK) flaring plasma. The LEBAN method is described
and the flare parameters derived for eight flares are presented.
Title: Investigation of flare heating based on X-ray observations
Authors: Jakiemiec, J.; Sylwester, B.; Sylwester, J.; Mewe, R.; Peres,
G.; Serio, S.; Schrijver, J.
Bibcode: 1986AdSpR...6f.237J
Altcode: 1986AdSpR...6..237J
Using X-ray data recorded by the Solar Maximum Mission Hard X-ray
Imaging Spectrometer we have investigated flare evolution in a
(Tm, N)-diagram, where Tm is the maximum
temperature and N is the mean density in the flare volume. It is
important that the behaviour of a flare in such a diagram does not
depend significantly on details of the flare geometry and therefore
can be effectively compared with simplified model calculations of
flare loops. This flare diagnostics allows us to show that most large
flares achieve a quasi-steady-state during their decay, which means
that the cooling is then so slow that a flare evolves along the line of
steady-state loops in the (Tm, N)-diagram. The diagnostics
allows us to determine the time evolution of the flare heating function,
EH(t), which gives the rate of thermal energy release,
per unit volume. For the flares which achieve the quasi-steady-state
branch it gives a new valuable method of estimation of the electron
density in the flare loops.
Title: The Atmosphere of a Sunspot Based on Observations in the
X-Ray Extreme Ultraviolet Optical and Radio Ranges
Authors: Staude, J.; Furstenberg, F.; Hildebrandt, J.; Kruger,
A.; Jakimiec, J.; Obridko, V. N.; Siarkowski, M.; Sylwester, B.;
Sylwester, J.
Bibcode: 1984SvA....28..557S
Altcode:
No abstract at ADS
Title: The atmosphere of a sunspot based on observations in the X-ray,
extreme ultraviolet, optical, and radio ranges
Authors: Staude, J.; Furstenberg, F.; Hildebrandt, J.; Kruger,
A.; Jakimiec, J.; Obridko, V. N.; Siarkowski, M.; Sylwester, B.;
Sylwester, J.
Bibcode: 1984AZh....61..956S
Altcode:
A model of the solar atmosphere above a sunspot umbra is developed on
the basis of published X-ray, EUV, optical, and radio observations,
summarizing the findings of working conferences held at Wroclaw in
November-December 1979 (Bromboszcz et al. 1981) and at Ondrejov in
September-October 1981 (Bromboszcz et al., 1982). A lower-chromosphere
model like that of Teplitskaya et al. (1977 and 1978) is extended
upward by applying a strong temperature gradient, with T = 40,000 K
and n(e) = 4 x 10 to the 10th/cu cm at z = 2000 km above the umbral
chromosphere. At z = 3000-5000 km, cool loops with T = (1-100) x 10
to the 4th k are surrounded by hot (1.8 x 10 to the 6th K) coronal
matter with a narrow transition layer and n(e) = 5 x 10 to the 8th/cu
cm which occupies 0.8-0.9 of the total volume.
Title: Comparison of energy calibration of Prognoz 5, 6, 7 and 8,
and other hard X-ray solar photometers.
Authors: Farnik, F.; Valnicek, B.; Sylwester, B.; Sylwester, J.;
Jakimiec, J.
Bibcode: 1984BAICz..35..158F
Altcode:
The data obtained by the Prognoz 5, 6, 7, and 8 hard-X-ray photometers
are compared with the measurements carried out by similar instruments
aboard Solrad 11, ISEE 3, SMM, and Hinotori satellites. Using the
method of relative-amplitude analysis, the apparent disagreement in
the energy-discrimination-level calibration between the instruments
is pointed out. The results of the comparison and possible sources of
disagreement are given. An international effort to develop a system
of uniform prelaunch calibration of photometers based on a reference
calibration source is suggested.
Title: Differential emission measure analysis of hot-flare plasma
from solar-maximum mission X-ray data
Authors: Jakimiec, J.; Sylwester, J.; Lemen, J. R.; Mewe, R.; Bentley,
R. D.; Fludra, A.; Schrijver, J.; Sylwester, B.
Bibcode: 1984AdSpR...4g.203J
Altcode: 1984AdSpR...4..203J
We have investigated differential emission measure (DEM) distribution
of hot flare plasma (T>10 MK) using SMM X-ray data from Bent Crystal
Spectrometer (BCS) and Hard X-ray Imaging Spectrometer (HXIS). We have
found that the analysis provide a very sensitive test of consistency
of observational data coming from different instruments or different
channels of the same instrument. This has allowed to eliminate some
systematic differences contained in the analysed data. Typical
examples of the DEM distribution are discussed. It is stressed that
these improvements in the multitemperature flare diagnostics are very
important for the discussion of flare energetics.
Title: Analysis of Intensity Ratio for MG XII LY Components from
Intercosmos 7 Observations (short Abstract)
Authors: Sylwester, J.; Sylwester, B.; Jakimiec, J.; Tomczak, M.;
Mandelstam, S. L.; Zhitnik, I. A.; Korneev, V. V.
Bibcode: 1984uxsa.coll..154S
Altcode: 1984IAUCo..86..154S; 1984uxsa.conf..154S
No abstract at ADS
Title: Organisation of a unified system of energetic calibration of
X-ray experiments
Authors: Valnicek, B.; Farnik, F.; Sylwester, B.; Sylwester, J.
Bibcode: 1984AdSpR...4g.121V
Altcode: 1984AdSpR...4..121V
X-ray data obtained by the Prognoz 5,6,7 and 8 hard X-ray photometers
are compared with the measurements carried out by similar instruments
aboard the Solrad 11, ISEE 3, SMM and Hinotori satellites. Using the
method of relative amplitude analysis, the apparent disagreement in
the energy discrimination level calibration between the instruments
is pointed out. The results of the comparison and the possible sources
of disagreement are given. We suggest an international effort be made
to develop a system of uniform pre-launch calibration of photometers
based on a reference calibration source.
Title: A working model of sunspot structure in photosphere,
chromosphere and corona, derived from X-ray, EUV, optical and radio
observations
Authors: Staude, J.; Hildebrandt, J.; Fuerstenberg, F.; Krueger,
A.; Jakimiec, J.; Obridko, V. N.; Siarkowski, M.; Sylwester, B.;
Sylwester, J.
Bibcode: 1983AcA....33..441S
Altcode:
The presented sunspot model consists of several parts which have been
consistently put together: the umbral model describing the spatial
distribution of thermodynamic quantities up to the transition region as
derived from EUV and optical observations, the magnetic field model,
the model of X-ray emission, and the S-component emission model. The
model assumptions have been tested and corroborated by recently
published observations with high spatial resolution obtained in the
X-ray and EUV spectral range from Skylab, HRTS, and SMM, at centimeter
wavelengths from RATAN, VLA, and WSRT, and by ground-based magnetograms.
Title: Time variation of the differential emission measure of hot
flare plasma.
Authors: Jakimiec, J.; Mewe, R.; Schrijver, J.; Sylwester, J.;
Sylwester, B.
Bibcode: 1983PDHO....5..127J
Altcode: 1984PDHO....5..127J
The authors have investigated details of the time evolution of
the flare differential emission measure (DEM) distribution in the
temperature range 10 - 50 MK using high-resolution X-ray spectra
recorded by the Bent Crystal Spectrometer aboard the Solar Maximum
Mission satellite. It has been found that for big flares the local
maximum in the DEM distribution is systematically broader during the
phase of flare increase than during the phase of decay. It is shown
that this systematic effect is a result of development of a hot "wing"
of the DEM local maximum during flare increase and its disappearance
during flare decay.
Title: SMM flat crystal spectrometer data analysis of 7 April
1980 flare.
Authors: Sylwester, B.; Sylwester, J.; Jakimiec, J.; Mewe, R.; Bentley,
R. D.
Bibcode: 1983PDHO....5...85S
Altcode: 1984PDHO....5...85S
The authors have analysed soft X-ray images of the 1B/M4 flare of 7
April 1980 recorded by Flat Crystal Spectrometer aboard Solar Maximum
Mission satellite. The X-ray flare consisted of two patches about 1
arcmin apart. A comparison with magnetograms and white light images
indicates that the two soft X-ray patches originate from two different
loops or systems of loops. For two selected resolution elements of
the X-ray pictures a detailed differential emission measure analysis
has been carried out and time evolution of the mean electron density
and thermal energy content has been investigated.
Title: Multi-temperature Analysis of Hard X-Ray Spectra Measured
aboard the Prognoz 5 Satellite
Authors: Sylwester, B.; Sylwester, J.; Jakimiec, J.; Valnicek, B.;
Farnik, F.
Bibcode: 1983BAICz..34...40S
Altcode:
Following the method of multi-temperature analysis of hard X-ray
spectra presented by B. Sylwester et al. (1981), in the present
paper the authors analyse the hard X-ray radiation measured aboard
the Prognoz 5 satellite by means of a Czechoslovak photometer. The
analysis concerns the Feb. 11, 1977 flare event. Using the fluxes
measured in 4 energy bands they have calculated the differential
emission measure distributions for selected moments during the rise,
maximum and decay phases of the flare development. The results of the
analysis show that, in the case of the flare in question, the hard
X-ray radiation from 6 to 60 keV could have been produced by purely
thermal, multi-temperature plasma.
Title: Analysis of the physical conditions in a strong X-ray flare
Authors: Sylwester, B.; Sylwester, J.; Jakimiec, J.; Valnicek, B.
Bibcode: 1981AdSpR...1m.239S
Altcode: 1981AdSpR...1..239S
The temperature distribution of the hot plasma emission measure in
a large but slowly developing flare has been investigated using the
following data obtained from the INTERCOSMOS 4 satellite: (1) the X -
ray spectra in the range 1.7 - 1.9 Å, (2) the hard X - ray fluxes
in the range 10 - 40 keV. It has been found that all the data can be
explained by a consistent thermal model of the emitting region.
Title: Analysis of the physical conditions in a strong X-ray flare.
Authors: Sylwester, B.; Jakimiec, J.; Sylwester, J.; Valnícek, B.
Bibcode: 1981hea..conf..239S
Altcode:
No abstract at ADS
Title: Solar Flare X-Ray Spectra - Part Three - Initial and Final
Phase
Authors: Korneev, V. V.; Krutov, V. V.; Mandelshtam, S. L.; Tindo,
I. P.; Urnov, A. M.; Zhitnik, I. A.; Sylwester, B.; Valnicek, B.
Bibcode: 1980SoPh...68..381K
Altcode:
Spectra of 3 large flares on 24 Oct., 5 Nov. and 16 Nov. 1970 in the
region λ = 1.75-1.95 Å, obtained with the help of the `Intercosmos-4'
satellite during solar activity maximum are given. The physical
conditions at the initial and final (decaying) phases are mainly
studied. The line spectra are compared with hard continuum in the
region 8-80 keV and results of polarization measurements, obtained
simultaneously aboard the same satellite.
Title: Analysis of X-ray spectra emitted by the 24 October 1970 flare.
Authors: Sylwester, B.; Sylwester, J.; Jakimiec, J.; Korneev, V. V.;
Mandelstam, S. L.; Zhitnik, I. A.; Valnicek, B.
Bibcode: 1980PoAst..28..237S
Altcode:
In the present paper, high-resolution X-ray spectra obtained near 1.9
A with a quartz-crystal Bragg spectrometer, carried by the Intercosmos
4 satellite, are analyzed. The temperature dependence of the radiation
during the growth and main phases of the flare is determined.
Title: Solar flare X-ray spectra. I: Wavelengths of Fe XXIV - XXV
lines in the region lambda = 1.85 - 1.87 Å.
Authors: Korneev, V. V.; Krutov, V. V.; Mandelshtam, S. L.; Urnov,
A. M.; Zhitnik, I. A.; Kononov, A. Ia.; Golts, E. Ia.; Sidelnikov,
Iu. V.; Sylwester, B.; Sylwester, J.
Bibcode: 1979SoPh...63..319K
Altcode:
Results are presented of an investigation of solar flare X-ray spectra
in the region 1.70-1.95 Å, obtained aboard the `Intercosmos-4'
satellite during the maximum of solar activity (October-November,
1970). With the use of 6 high resolution spectra in the region 1.85-1.87
Å the identification of lines due to 18 transitions of 2p → 1s type,
consisting of the resonance, intercombination and forbidden Fe XXV ion
lines and the satellite Fe XXIV lines has been performed. With the use
of the recent laboratory data the averaged wavelengths of the lines were
obtained confirming the theoretically calculated ones with an accuracy
about ± 0.0004 Å. A variable Doppler shift of the Fe XXV resonance
lines was observed for the flare of November 16, 1970, which points
to hot plasma motions with velocities up to 400 km s-1.
Title: Discussion of the methods of determining the temperature
models of coronal active regions from the X-ray spectra.
Authors: Sylwester, J.; Sylwester, B.
Bibcode: 1977PDHO....3...75S
Altcode:
No abstract at ADS
Title: Analysis of behaviour of the Mg XII resonance line in solar
flares, from INTERCOSMOS-7 satellite observations.
Authors: Jakimiec, J.; Zhitnik, I. A.; Korneev, V. V.; Krutov, V. V.;
Sylwester, B.; Sylwester, J.
Bibcode: 1977PDHO....3...57J
Altcode:
No abstract at ADS
Title: Time variations of high-temperature plasma in solar flares.
Authors: Sylwester, B.; Zhitnik, I. A.; Korneev, V. V.; Krutov, V. V.;
Sylwester, J.; Jakimiec, J.
Bibcode: 1977PDHO....3...65S
Altcode:
No abstract at ADS
Title: Observations of a soft X-ray flare on the solar limb.
Authors: Jakimiec, J.; Sylwester, B.; Sylwester, J.
Bibcode: 1976viao.conf...20J
Altcode:
No abstract at ADS
Title: Analysis of formation of resonance lines in the X-ray spectrum
of coronal condensations.
Authors: Sylwester, B.
Bibcode: 1976str..book..143S
Altcode:
No abstract at ADS
Title: X-ray spectrum of a coronal condensation and a flare.
Authors: Jakimiec, J.; Krutov, V. V.; Mandel'Shtam, S. L.; Mandelshtam,
S. L.; Sylwester, B.; Sylwester, J.; Zhitnik, I. A.
Bibcode: 1976str..book..151J
Altcode:
No abstract at ADS
Title: Analysis of resonance line formation in the X-ray spectrum
of coronal condensations
Authors: Sylwester, B.
Bibcode: 1976CoSka...6..143S
Altcode:
No abstract at ADS
Title: X-ray spectrum of a coronal condensation and a flare
Authors: Jakimiec, J.; Krutov, V. V.; Mandelshtam, S. L.; Sylwester,
B.; Sylwester, J.; Zhitnik, I. A.
Bibcode: 1976CoSka...6..151J
Altcode:
No abstract at ADS
Title: Physical conditions in a flare region.
Authors: Bejgman, I. L.; Vajnshtejn, L. A.; Korneev, V. V.; Krutov,
V. V.; Mandel'Shtam, S. L.; Sylwester, B.; Sylwester, J.; Urnov, A. M.
Bibcode: 1976viao.conf...16B
Altcode:
No abstract at ADS
Title: Analysis of the intensities and profiles of the spectral line
Mg XII 8.42 å in the solar X-ray spectrum
Authors: Jakimiec, J.; Korneev, V. V.; Krutov, V. V.; Zhitnik, I. A.;
Plocieniak, S.; Sylwester, B.; Sylwester, J.
Bibcode: 1975SoPh...44..391J
Altcode:
High resolution profiles of the Mg XII 8.42 å line in the solar
X-ray spectrum were recorded from the Intercosmos 7 satellite. The Mg
XII line intensity provides a sensitive indicator of the hot plasma
content (T ≳ 3 × 106 K) in coronal condensations and X-ray
flare volumes. The ratio of the line intensity to the intensity of the
adjacent continuum has been used to compute approximate thermal models
of the emitting regions. For all the investigated coronal condensations
the temperature distribution of plasma has been found to be a function
monotonically decreasing with temperature. But for some X-ray bursts
there occurred a distinct excess of the hot plasma of temperature
between 6-10 × 106K. FWHM values of the Mg XII line profiles
have been used to estimate ion temperature in the emitting regions.
Title: The Analysis of Resonance Line Formation in the X-ray Spectrum
of Coronal Condensation
Authors: Sylwester, B. M.
Bibcode: 1974AcA....24..285S
Altcode:
The values of the X-ray radiation fluxes in several resonance lines,
which are formed in coronal condensations, have been calculated. The
calculations were performed making use of the coronal condensation
model worked out by Landini and Monsignori Fossi. A comparison of
the obtained theoretical values of the fluxes with observational data
was made in order to test the model. The analysis indicates that the
coronal condensation model given by Landini and Monsignori Fossi does
not describe the real structure of such a region adequately.
Title: Analysis of the solar X-ray spectrum of 20 August 1971.
Authors: Jakimiec, J.; Krutov, V. V.; Mandel'Stam, S. L.; Sylwester,
B.; Sylwester, J.; Zhitnik, I. A.
Bibcode: 1974spre.conf..425J
Altcode:
No abstract at ADS
Title: Observations of the X-ray emission of solar active regions
on 28 November 1970 and 20 August 1971.
Authors: Kordylewski, Z.; Mergentaler, J.; Jakimiec, J.; Sylwester,
B.; Sylwester, J.
Bibcode: 1973spre.conf..787K
Altcode: 1973spre....2..787K
No abstract at ADS