AVS-F observations of γ-ray emission during January 20, 2005 solar flare up to 140MeV (original) (raw)
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Advances in Space Research, 2009
By the data on intensity-time profiles of the neutron capture line of 2.223 MeV we have studied some characteristics of two solar flares, 28 October 2003 and 20 January 2005 (INTEGRAL and CORONAS-F observations, respectively). The SINP code was applied making allowance for the main processes of neutron interactions and deceleration in the solar plasma, character of neutron source, losses of neutrons and density model of the solar atmosphere. Comparison of the computed time profiles of 2.223 MeV line with observed ones for the flare of 28 October 2003 confirms the results obtained earlier for three other flares. Namely, the effect of density enhancement (EDE) in the sub-flare region, as well as the variations (hardening) of accelerated particle spectrum in the course of the event have been confirmed. The usual modeling procedure by the SINP code, however, seems to be inapplicable to the event of 20 January 2005. Possible causes of density enhancements during some flares and peculiarities of the 20 January 2005 flare are discussed.
Advances in Space Research, 2009
The count rate temporal profiles and energy spectra of the solar flares January 15, 17, 20 2005 in hard X-ray and gamma energy bands by data of AVS-F apparatus onboard CORONAS-F satellite are discussed. The energy spectra of these solar flares contain positron line and neutron capture line. Solar flares of January 17 and 20 spectra also contain some nuclear lines. Thin structure with characteristic timescales of 33-92 s is presented on flares temporal profiles in energy bands corresponding to the observed spectral features, which are confirmed by periodogram analysis (confidence level is 99%).
Journal of Physics: Conference Series, 2013
Basing on the data of AVS-F apparatus from SONG-D detector onboard CORONAS-F satellite, we have studied the extreme solar event of January 20, 2005 used the 2.223 MeV, 4.44 MeV and 6.13 MeV -lines temporal profiles. By the statistical modeling method we calculated the temporal profile of 2.223 MeV line. Calculations were performed in assumption of Bessel type of accelerated particles energy spectrum, different 3 He content in the region of nuclear reactions and several density models of the solar atmosphere. Comparison of the results of modeling with observational 2.223 MeV data reveals the increasing of the ratio of 3 He concentration to 1 H one during the flare from 210-5 at the rise phase of the gamma-ray flux up to 210-4 at the decay one. During the same period the spectrum became harder, spectral index changed from αT=0.005 up to 0.1, and the density of solar atmosphere increased too. Averaged over full time of 2.223 MeV -emission, concentration ratio of 3 He/ 1 H is equal to (1.40±0.15)10-4 , the spectral index of accelerated protons αT=0.1 for the energy interval of 0.1-100 MeV and the density model with enlarged density up to 210 17 cm-3 in the lower chromosphere and through the whole photosphere is realized.. Using the AVS-F/SONG-D/CORONAS-F gamma-ray spectral data in the wide range up to 140 MeV, we have estimated the spectral index as s≈2.5 in the case of power law spectrum of accelerated particles for energies more than 300 MeV.
Extended γ-ray emission in solar flares
AIP Conference Proceedings, 1996
During the solar are events on 11 and 15 June 1991, COMPTEL measured extended emission in the neutron capture line for about 5 hours after the impulsive phase. The time pro les can be described by a double exponential decay with decay constants on the order of 10 min for the fast and 200 min for the slow component. Within the statistical uncertainty both ares show the same long-term behaviour. The spectrum during the extended phase is signi cantly harder than during the impulsive phase and pions are not produced in signi cant numbers before the beginning of the extended emission. Our results with the measurements of others allow us to rule out long-term trapping of particles in non-turbulent loops to explain the extended emission of these two ares and our data favour models based on continued acceleration.
The hard X-rays and gamma rays from solar flares
The Astrophysical Journal, 1990
Radiation of energies from 10 keV to greater than 10 MeV has been observed during solar flares, and is interpreted to be due to bremsstrahlung by relativistic electrons. A complete treatment of this problem requires solution of the kinetic equation for relativistic electrons and inclusion of synchrotron energy losses. Using the elctron distributions obtained from numerical solutions of this equation the bremsstrahlung spectra in the impulsive X-ray and y-ray regimes are calculated, and the variation of these spectral indices and directivities with energy and observation angle are described. The dependences of these characteristics of the radiation of changes in the solar atmospheric model, including the convergence of the magnetic field, the injected electron spectral index, and most importantly, in the anisotropy of the injected electrons and the of convergence of the magnetic field are also described. The model results are compared with stereoscopic observations of individual flares and the constraints that this data sets on the models are discussed.
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.
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.
FIRST DETECTION OF >100 MeV GAMMA-RAYS ASSOCIATED WITH A BEHIND-THE-LIMB SOLAR FLARE
The Astrophysical Journal, 2015
We report the first detection of >100 MeV gamma rays associated with a behind-the-limb solar flare, which presents a unique opportunity to probe the underlying physics of high-energy flare emission and particle acceleration. On 2013 October 11 a GOES M1.5 class solar flare occurred ∼ 9 • .9 behind the solar limb as observed by STEREO-B. RHESSI observed hard X-ray emission above the limb, most likely from the flare loop-top, as the footpoints were occulted. Surprisingly, the Fermi Large Area Telescope (LAT) detected >100 MeV gamma-rays for ∼30 minutes with energies up to 3 GeV. The LAT emission centroid is consistent with the RHESSI hard X-ray source, but its uncertainty does not constrain the source to be located there. The gamma-ray spectra can be adequately described by bremsstrahlung radiation from relativistic electrons having a relatively hard power-law spectrum with a high-energy exponential cutoff, or by the decay of pions produced by accelerated protons and ions with an isotropic pitch-angle distribution and a power-law spectrum with a number index of ∼3.8. We show that high optical depths rule out the gamma rays originating from the flare site and a high-corona trap model requires very unusual conditions, so a scenario in which some of the particles accelerated by the CME shock travel to the visible side of the Sun to produce the observed gamma rays may be at work.