Letter to the Editor

Kappa distribution and hard X-ray emission of solar flares

Astronomický ústav AV ČR, v.v.i., Fričova 298, 251 65 Ondřejov, Czech Republic e-mail: kasparov@asu.cas.cz

Received: 20 February 2009
Accepted: 5 March 2009

Abstract

Aims. 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.

Methods. Using Ramaty High Energy Solar Spectroscopic imager (RHESSI) flare data we fit spatially- and feature-integrated spectra, assuming a kappa distribution for the mean electron flux spectrum.

Results. 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.