Diagnostics of non-thermal distributions in solar flare spectra observed by RESIK and RHESSI⋆
Astronomical Institute of the Academy of Sciences of the Czech Republic, v. v. i., Fričova 298, 251 65 Ondřejov, Czech Republic
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2 Department of Astronomy, Physics of the Earth and Meteorology, Faculty of Mathematics, Physics and Informatics, Comenius University, Mlynská dolina, 842 48 Bratislava, Slovakia
3 Space Research Centre, Polish Academy of Sciences, 51-622, Kopernika 11, Wrocław, Poland
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Received: 17 February 2011
Accepted: 7 July 2011
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.
Key words: Sun: flares / Sun: X-rays, gamma rays / Sun: radio radiation / radiation mechanisms: non-thermal / methods: data analysis
Appendix A is available in electronic form at http://www.aanda.org
© ESO, 2011