Impact of nonthermal tails and nonthermal distributions on solar flare plasma diagnostics

Jaroslav Dudík (1,2), Elena Dzifčáková (2), Michal Homola (1), Marian Karlický (2), Alena Kulinová (1,2), Jana Kašparová (2)

(1) DAPEM, Faculty of Mathematics, Physics and Informatics, Comenius University, Bratislava, Slovakia.  (2) Astronomical Institute of the Academy of Sciences, Ondřejov, Czech Republic.

The presence of nonthermal, high-energy power-law tails has been observed by RHESSI for almost a decade. It is known that the power-law tails can influence line ratios, in particular ratios of the dielectronic satellite to allowed lines. We construct a realistic composed electron distribution function consisting of a thermal or nonthermal plasma bulk and a high-energy tail. We investigate the influence of the high-energy tail and nonthermal or thermal bulk of the distribution function on the flare spectra of Si. The high-energy tail significantly increases the temperature-sensitive Si XIV / Si XIII line ratio, but has only a small effect on the Si XIId / Si XIII ratios. The increase of this ratio observed by RESIK can be explained only by nonthermality of the plasma bulk, with a steep gradient in range of few keV.

Talk presented at the symposium From Atoms to Stars:the impact of Spectroscopy on Astrophysics, 26th-28th July 2011, Oxford, UK.

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