Kappa distribution and hard X-ray emission of solar flares

TL;DR

This study assesses whether the kappa distribution can model electron populations responsible for hard X-ray emissions in solar flares, finding it suitable for some coronal sources but not for combined footpoint and coronal emissions.

Contribution

It demonstrates the applicability and limitations of the kappa distribution in modeling solar flare electron spectra using RHESSI data.

Findings

Kappa distribution fits some coronal source spectra.

Single kappa distribution cannot describe combined footpoint and coronal emissions.

Kappa distribution is inconsistent with certain spatially integrated spectra.

Abstract

We investigate whether the so-called kappa distribution, often used to fit electron distributions detected in-situ in the solar wind, can describe electrons producing the hard X-ray emission in solar flares. Using Ramaty High Energy Solar Spectroscopic imager (RHESSI) flare data we fit spatially- and feature-integrated spectra, assuming kappa distribution for the mean electron flux spectrum. We show that a single kappa distribution generally cannot describe spatially integrated X-ray emission composed of both footpoint and coronal sources. In contrast, the kappa distribution is consistent with mean electron spectra producing hard X-ray emission in some coronal sources.