HR: 1340h
AN: SH53A-1062    [Abstracts]
TI: Spectral Hardening of Large Solar Flares
AU: * Grigis, P C
EM: pgrigis@cfa.harvard.edu
AF: ETH Zurich, Institute of Astronomy Schecuhzerstr. 7, Zurich, 8092, Switzerland
AU: Benz, A O
EM: benz@astro.phys.ethz.ch
AF: ETH Zurich, Institute of Astronomy Schecuhzerstr. 7, Zurich, 8092, Switzerland
AB: We present quantitative studies of the hard X-ray spectral evolution of large solar flares featuring hardening trends, using RHESSI high cadence spectroscopy observations. The temporal evolution of the spectra is compared with the configuration and motion of the hard X-ray sources in RHESSI images. Both soft-hard-soft (impulsive) phases and hardening (gradual) phases are observed during the events and are well described by piecewise linear dependence of the spectral index on the logarithm of the flux. In particular, we investigate whether two different acceleration mechanisms are responsible for the impulsive and gradual phases, finding evidence that points toward a single acceleration mechanism acting in the two phases, rather than two different separated mechanisms, because the impulsive and gradual phases are closely interconnected in time and space.
DE: 7509 Corona
DE: 7519 Flares
DE: 7554 X-rays, gamma rays, and neutrinos
SC: SPA-Solar and Heliospheric Physics [SH]
MN: 2007 Fall Meeting