Physics
Scientific paper
Dec 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufmsh13a0285c&link_type=abstract
American Geophysical Union, Fall Meeting 2005, abstract #SH13A-0285
Physics
7509 Corona, 7519 Flares, 7554 X-Rays, Gamma Rays, And Neutrinos, 7594 Instruments And Techniques, 7845 Particle Acceleration
Scientific paper
The GOES-class X4.8 event on 23 July 2002 exhibits significant hard X-ray emission prior to the impulsive phase of the flare. Images from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) show that most of the emission appears to originate from a coronal source. Analysis of the Fe (~6.7 keV) and Fe/Ni (~8 keV) line complexes seen in RHESSI spectra suggests that there is little or no thermal continuum emission above ~15 keV, thus implying that non-thermal electron bremsstrahlung dominates the spectrum even to low energies. The X3.1 event on 24 Aug 2002 displays similar characteristics, and its position at the west limb occults the footpoints and shows that the bulk of the HXR emission unambiguously originates in the corona. Preliminary analysis shows that the pre-impulsive spectra are well-fit by a broken power-law characteristic of non-thermal emission. The spectral indices above and below the break energy differ by ~2, suggesting that we may be observing the transition between thin- and thick-target bremsstrahlung. The break energy increases with time, which suggests an average electron pitch angle of ~45°, assuming an increasing column density derived from the thermal emission measure. We analyze and compare the RHESSI X-ray spectra for the pre-impulsive phases of both 24 Aug 2002 and 23 July 2002, using the Fe and Fe/Ni line complexes to constrain the thermal parameters. We derive the time-varying characteristics of the electron populations and discuss the implications for acceleration and heating of electrons in the corona during this period.
Caspi Amir
Krucker Sa"m
Lin Robert P.
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