Diagnostics of non-thermal distributions in solar flare spectra observed by RESIK and RHESSI

TL;DR

This study investigates non-thermal electron distributions in solar flare spectra using RESIK and RHESSI data, revealing consistent non-thermal components in the 2-5 keV range through independent diagnostics.

Contribution

It introduces a combined analysis of line ratios and bremsstrahlung spectra to identify non-thermal electron distributions in solar flares, demonstrating their presence in multiple energy ranges.

Findings

Non-thermal n-distributions are detected in the 2-4 keV range.

RHESSI bremsstrahlung spectra correlate with the n-distribution.

Non-thermal components are associated with radio bursts.

Abstract

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.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. 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.