Solar flares release a large fraction of their energy into non-thermal electrons, but it is not clear where and how. Bremsstrahlung X-rays are observed from the corona (coronal or looptop source) and chromosphere (footpoints).
The spectral time evolution of the sources and the relations between them reflect the geometry and constrict the configuration of the flare.
We studied solar flares of GOES class larger than M1 with three hard X-ray sources observed simultaneously in the course of the flare. The events where selected from observations with the X-ray satellite RHESSI from February 2002 until July 2005.
We used imaging spectroscopy methods to determine the spectral time evolution of each source in each event. The images of all of the five events show two sources visible only at high energies (footpoints) and one source only
visible at low energies (coronal source).
We find soft-hard-soft behavior in both, coronal source and footpoints. This is a strong indication, that soft-hard-soft is a feature of the acceleration mechanism rather than a transport effect.
The coronal source is nearly always softer than the footpoints. The footpoint spectra differ significantly only in one event out of five.
Authors: Marina Battaglia & Arnold O. Benz
Publication Status: A&A (in press)
Last Modified: 2006-06-16 11:07