Solar impulsive soft X–ray brightenings and their connection with footpoint hard X–ray emission sources

Free access article

Issue		A&A Volume 415, Number 1, February III 2004


Page(s)		377 - 389
Section		The Sun
DOI		http://dx.doi.org/10.1051/0004-6361:20034598

A&A 415, 377-389 (2004)
DOI: 10.1051/0004-6361:20034598

Solar impulsive soft X-ray brightenings and their connection with footpoint hard X-ray emission sources

T. Mrozek and M. Tomczak

Astronomical Institute, University of Wroclaw, ul. Kopernika 11, 51-622 Wroclaw, Poland
(Received 25 April 2003 / Accepted 5 September 2003)

Abstract
We have investigated 46 solar flares showing impulsive soft X-ray brightenings in footpoints. To obtain their main observational characteristics we used the Yohkoh /SXT images. The results are presented in the form of normalized histograms showing the distribution of the characteristics. For 18 flares it has been possible to make a quantitative comparison between the footpoint response in soft X-ray images and in hard X-ray images. The latter have been derived from the Yohkoh/HXT and reconstructed using the MEM procedure. The evident correlation between these two kinds of response, as well as between the deposited energies, strongly supports a common physical cause, namely non-thermal electron beams. We present evidence that in the impulsive phase the chromospheric evaporation is driven mainly by low-energy non-thermal electrons. We show that the low-energy cut-off energy in hard X-ray photon fluxes may vary from flare to flare and may even vary during a given flare.

Key words: Sun: corona -- flares -- X-rays, gamma rays

Offprint request: T. Mrozek, mrozek@astro.uni.wroc.pl

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