AAS 204th Meeting, June 2004
Session 54 Solar Flares
SPD Poster, Wednesday, June 2, 2004, 10:00am-7:00pm, Ballroom

## [54.03] The hard X-ray spectral structure of flare ribbons

L. Fletcher (University of Glasgow), H. S. Hudson, S. Krucker (SSL/UCB), J. A. Pollock (University of Glasgow)

We examine the spatial distribution of hard X-ray spectral parameters in flares exhibiting the classic two-ribbon structure using RHESSI observations. The flares studied include July~15 and July~17, 2002, and October~29, 2003. We confirm the existence of a tendency for the localization of the hard X-ray sources into dominant bright footpoint'' regions which do not show ribbon structure as extensive as that seen in H\alpha or UV~images. As a part of the study we characterize the ribbons photometrically in the EUV as observed by TRACE, confirming earlier results that find complicated relationships between EUV and hard X-rays. We seek an empirical explanation for the restricted hard X-ray footpoints in terms of a spatial analog of the well-known soft-hard-soft'' morphology: the regions of weaker hard X-ray emission correspond to steeper X-ray energy spectra and hence to softer electron precipitation spectra. This relationship may be as predicted by the 1D radiation hydrodynamics models of flaring loops.

Bulletin of the American Astronomical Society, 36 #2
© YEAR. The American Astronomical Soceity.