HR: 16:15h
AN: SH24A-02    [Abstracts]
TI: The hard X-ray spectral structure of flare ribbons
AU: * Hudson, H
EM: hhudson@ssl.berkeley.edu
AF: SSL/UCB, 7 Gauss Way, Berkeley, CA 94720-7450 United States
AU: Fletcher, L
EM: lyndsay@astro.gla.ac.uk
AF: SSL/UCB, 7 Gauss Way, Berkeley, CA 94720-7450 United States
AU: Fletcher, L
EM: lyndsay@astro.gla.ac.uk
AF: University of Glasgow, Astronomy & Astrophysics group Kelvin Building, Glasgow, G12 8QQ United Kingdom
AU: Krucker, S
EM: krucker@ssl.berkeley.edu
AF: SSL/UCB, 7 Gauss Way, Berkeley, CA 94720-7450 United States
AU: Pollock, J
EM: lyndsay@astro.gla.ac.uk
AF: University of Glasgow, Astronomy & Astrophysics group Kelvin Building, Glasgow, G12 8QQ United Kingdom
AB: 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.
DE: 7509 Corona
DE: 7519 Flares
DE: 7554 X rays, gamma rays, and neutrinos
SC: SPA-Solar and Heliospheric Physics [SH]
MN: 2004 AGU Fall Meeting