X-ray emission from solar flares (original) (raw)
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The Fe-Line Feature in the X-Ray Spectrum of Solar Flares: First Results from the SOXS Mission
Solar Physics, 2006
We present the first results from the "Low Energy Detector" payload of the "Solar X-ray Spectrometer (SOXS)" mission, which was launched onboard the GSAT-2 Indian spacecraft on 08 May 2003 by the GSLV-D2 rocket to study solar flares. The SOXS Low Energy Detector (SLD) payload was designed, developed, and fabricated by the Physical Research Laboratory (PRL) in collaboration with the Space Application Centre (SAC), Ahmedabad and the ISRO Satellite Centre (ISAC), Bangalore of Indian Space Research Organization (ISRO). The SLD payload employs state-of-the-art, solid-state detectors viz. Si PIN and Cadmium-Zinc-Telluride (CZT) devices that operate at near room temperature (-20 °C). The energy ranges of the Si PIN and CZT detectors are 4-25 keV and 4-56 keV respectively. The Si PIN provides sub-keV energy resolution while the CZT reveals ~1.7 keV energy resolution throughout the energy range. The high sensitivity and sub-keV energy resolution of the Si PIN detector allows measuring the intensity, peak energy, and the equivalent width of the Fe-line complex at approximately 6.7 keV as a function of time in all ten M-class flares studied in this investigation. The peak energy (E p) of the Fe-line feature varies between 6.4 and 6.7 keV with increasing in temperature from 9 to 58 MK. We found that the equivalent width (w) of the Fe-line feature increases exponentially with temperature up to 30 MK and then increases very slowly up to 40 Mk. It remains between 3.5 and 4 keV in the temperature range of 30-45 MK. We compare our measurements of w with calculations made earlier by various investigators and propose that these measurements may improve theoretical models. We interpret the variation of both E p and w with temperature as due to the changes in the ionization and recombination conditions in the plasma during the flare interval and as a consequence the contribution from different ionic emission lines also varies.
Solar X-ray Spectrometer (SOXS) mission: Observations and new results
Proceedings of the ILWS …, 2006
We present the observations and recently obtained new results from the "Solar X-ray Spectrometer (SOXS)" mission, which was launched onboard GSAT-2 Indian spacecraft on 08 May 2003 by GSLV-D2 rocket to study the solar flares. The state-of-the-art solid state detectors viz. Si PIN and Cadmium-Zinc-Telluride (CZT) were employed that operate at near room temperature (-20 0 C). The dynamic energy range of the Si PIN and CZT detectors are 4-25 keV and 4-56 keV, respectively. The Si PIN has sub-keV energy resolution while the CZT has about 1.7 keV energy resolutions throughout the dynamic range. The high sensitivity and sub-keV energy resolution of Si PIN detector allows for measuring the intensity, and equivalent width (w) of the Fe-line and Fe/Ni-line complexes at approximately 6.7 and 8.0 keV as a function of time. We present the results related to the Fe-line complex obtained from the study of 10 M-class flares observed by the SOXS mission. We found that the equivalent width (w) of the Fe-line feature increases exponentially with temperature up to 25 MK but later it increases very slowly up to 35 Mk and then it remains constant up to 45 MK. We compare our measurements of w of the Fe line feature with calculations made earlier by various investigators and propose that these measurements may improve theoretical models. We interpret the variation of w with temperature as the changes in the ionization and recombination conditions in the plasma during the flare interval, and, as a consequence, the contribution from different ionic emission lines also varies.
Solar Physics, 1979
Results are presented of an investigation of solar flare X-ray spectra in the region 1.70-1.95 ~, 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/~ the identification of lines due to 18 transitions of 2p + 1 s 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 ~. 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.
The thermal X-ray spectrum of the 2003 April 26 solar flare
Advances in Space Research, 2005
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 5to5 to 5to50 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.
Hot X-ray onsets of solar flares
Monthly Notices of the Royal Astronomical Society, 2020
The study of the localized plasma conditions before the impulsive phase of a solar flare can help us understand the physical processes that occur leading up to the main flare energy release. Here, we present evidence of a hot X-ray ‘onset’ interval of enhanced isothermal plasma temperatures in the range of 10–15 MK over a period of time prior to the flare’s impulsive phase. This ‘hot onset’ interval occurs during the initial soft X-ray increase and definitely before any detectable hard X-ray emission. The isothermal temperatures, estimated by the Geostationary Operational Environmental Satellite X-ray sensor, and confirmed with data from the Reuven Ramaty High Energy Solar Spectroscopic Imager, show no signs of gradual increase, and the ‘hot onset’ phenomenon occurs regardless of flare classification or configuration. In a small sample of four representative flare events, we tentatively identify this early hot onset soft X-ray emission to occur within footpoint and low-lying loop re...
The Astrophysical Journal Supplement Series, 1997
We present Ñuxes, temperatures, and emission measures for nine solar Ñares, using data from both the Fe XXV and Ca XIX channels of the Bragg Crystal Spectrometer (BCS) experiment on the Yohkoh satellite and from the wide-band soft X-ray spectrometers on the GOES spacecraft. We also present hard X-ray Ñuxes from the Hard X-ray Telescope (HXT) on Yohkoh and the BATSE spectrometer on the Compton Gamma-Ray Observatory (CGRO). All events occurred during 1992 and ranged in size from GOES class C5 to M2. Three of the events occurred near the solar limb. For each Ñare we give two sets of plots. The Ðrst set shows Ñux, electron temperature, and emission measures for Fe XXV, Ca XIX, and GOES as functions of time. The second set of plots gives log electron temperature as functions of log (emission measure)1@2 for these three wavelength ranges ; we refer to these plots as E1@2-T diagrams. Hard X-ray Ñux information is included in both sets of plots. Our observations indicate that (1) cooler plasmas are located along the legs of, or are evenly distributed along, the Ñaring loops, while hotter plasmas are concentrated near the loop tops, (2) peaks in temperature in each of the wavelength bands are closely associated with hard X-ray enhancements, and (3) the emission from both relatively hot and relatively cool Ñaring plasmas emanates from the same loop or from closely related loops.
Solar flares with similar soft but different hard X-ray emissions: case and statistical studies
From the RHESSI catalog we select events, which have approximately the same GOES class (high C-low M or 500-1200 counts/s within the RHESSI 6-12 keV energy band), but with different maximal energies of detected hard X-rays. The selected events are subdivided into two groups: 1) flares with X-ray emissions observed by Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) up to only 50 keV and 2) flares with hard Xray emission observed also above 50 keV. The main task is to understand observational peculiarities of these two flare groups. We use RHESSI X-ray data to obtain spectral and spatial information in order to find differences between selected groups. Spectra and images are analyzed in details for six events (case-study). For a larger number of samples (85 and 28 flares in the low-energy and the high-energy groups respectively) we make only some generalizations. In spectral analysis we use thick-target model for hard X-ray emission and one temperature assumption for thermal soft X-ray emission. RHESSI X-ray images are used for determination of flare region sizes. Although thermal and spatial properties of these two groups of flares are not easily distinguishable, power law indices of hard X-rays show significant differences. Events from the high-energy group generally have a harder spectrum. Therefore, the efficiency of chromospheric evaporation is not sensitive to the hardness of nonthermal electron spectra but rather depends on the total energy flux of nonthermal electrons. 1 INTRODUCTION Solar flares involve highly sophisticated processes, such as particle acceleration (revealed by nonthermal HXR and radio emissions), plasma heating up to extremely high temperatures (observed as SXR emissions), and plasma motions with velocities up to supersonic and super-alfvenic values. A big variety of flares are observed due to the complexity of the magnetic field topology and the irregularity of the plasma properties. One of the flare characteristics is an intensity peak observed within 1-8Å band-the X-ray flare importance which is determined by the X-ray detectors of Geostationary Operational Environmental Satellite (GOES). However, flares of the same GOES importance could have different HXR intensities and spectra properties.
Solar x-ray spectrometer (SOXS) mission – Low energy payload – First results
Journal of Astrophysics and Astronomy, 2006
We present the first results from the 'Low Energy Detector' payload of 'Solar X-ray Spectrometer (SOXS)' mission, which was launched onboard GSAT-2 Indian spacecraft on 08 May 2003 by GSLV-D2 rocket to study the solar flares. The SOXS Low Energy Detector (SLD) payload was designed, developed and fabricated by Physical Research Laboratory (PRL) in collaboration with Space Application Centre (SAC), Ahmedabad and ISRO Satellite Centre (ISAC), Bangalore of the Indian Space Research Organization (ISRO). The SLD payload employs the state-of-the-art solid state detectors viz., Si PIN and Cadmium-Zinc-Telluride (CZT) devices that operate at near room temperature (−20 • C). The dynamic energy range of Si PIN and CZT detectors are 4-25 keV and 4-56 keV respectively. The Si PIN provides sub-keV energy resolution while CZT reveals ∼1.7 keV energy resolution throughout the dynamic range. The high sensitivity and sub-keV energy resolution of Si PIN detector allows the measuring of the intensity, peak energy and equivalent width of the Fe-line complex at approximately 6.7 keV as a function of time in all 8 M-class flares studied in this investigation. The peak energy (E p) of Fe-line feature varies between 6.4 and 6.8 keV with increase in temperature from 9 to 34 MK. We found that the equivalent width (w) of Fe-line feature increases exponentially with temperature up to 20 MK but later it increases very slowly up to 28 MK and then it remains uniform around 1.55 keV up to 34 MK. We compare our measurements of w with calculations made earlier by various investigators and propose that these measurements may improve theoretical models. We interpret the variation of both E p and w with temperature as the changes in the ionization and recombination conditions in the plasma during the flare interval and as a consequence the contribution from different ionic emission lines also varies.
Investigation of flare heating based on X-ray observations
Advances in Space Research, 1986
Al ST RA CT tjsing X-ray data recorded by the Solar Maximum Mission Hard. X-ray Imaging Spectrometer we have investigated. flare evolution in a (I , N)-diagram, where T is the maximum temoerature 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 lOO~5o 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 (T~,, 0)-diagram. The diagnostics allows us to determine the time evolution ot~'the flare heating function, Eu(t), which gives the rate of thermal energy release, per unit volume. For thh flares which achieve the quasi-steady-state branch it gives a ne;; valuable method of estimation of the electron density in the flare loops 0-______ 6. O.L.
X-Ray Spectrometers On-Board Aditya-L1 for Solar Flare Studies
Current Science, 2017
Aditya-L1 mission will carry two high-spectral resolution X-ray spectrometers to study solar flares. The soft X-ray spectrometer will cover the energy range from 1 to 30 keV, while the hard X-ray spectrometer will cover from 10 to 150 keV. These two instruments together will provide opportunities to study the plasma parameters during solar flares as well as acceleration mechanisms of energetic particles during the flaring time.