A&A 419, 365-373 (2004)
DOI: 10.1051/0004-6361:20035817

High-frequency slowly drifting structures and X-ray sources observed by RHESSI

M. Karlický¹, F. Fárník¹ and S. Krucker<sup>2

1</sup>  Astronomical Institute of the Academy of Sciences of the Czech Republic, 25165 Ondrejov, Czech Republic
²  Space Sciences Lab. University of California, Berkeley, USA

(Received 7 December 2003 / Accepted 10 February 2004)

Abstract
Three solar flares (April 4, 2002, May 17, 2002, and August 30, 2002) with the 0.4-2.0 GHz slowly drifting structures were selected and analyzed together with RHESSI X-ray observations. Two events (April 4, 2002 and May 17, 2002) were observed above and one event (August 30, 2002) close to the solar limb. While in April 4, 2002 and August 30, 2002 the radio drifting structures with relatively high frequency drifts (-32- -25 MHz s ^-1) were recorded at times of the start of a motion of the X-ray flare source, in May 17, 2002 event a splitting of the X-ray source into two sources was observed before observation of the 0.8-1.8 GHz radio structure drifting with very slow frequency drift ( -0.4 MHz s ^-1). The X-ray source of the May 17, 2002 was much softer ( <40 keV) than those in April 4, 2002 and August 30, 2002 ( >100 keV). Velocities of the X-ray sources in the image plane were estimated as 12 km s ^-1 for April 4, 2002 and 10 km s ^-1 for August 30, 2002. Analyzing GOES data and X-ray RHESSI spectra of the May 17, 2002 flare the plasma thermal and non-thermal electron densities in the X-ray sources were determined. For two cases (April 4, 2002 and May 17, 2002) it was found that the plasma density in the coronal X-ray source is higher than maximum one derived from the radio drifting structure. The cross-correlation of the radio drifting structure and hard X-ray flux for the August 30, 2002 event reveals that the hard X-ray emission is delayed 0.5-0.7 s after the radio and it is partly correlated with an enhanced background of the drifting structure. All these results are discussed and interpreted considering the flare model with the plasmoid ejection.

Key words: Sun: flares -- Sun: radio radiation -- Sun: X-rays, gamma rays

Offprint request: M. Karlický, karlicky@asu.cas.cz

© ESO 2004

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