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A. Caspi (Dept. of Physics & Space Sciences Lab, UC Berkeley), S. Krucker (Space Sciences Lab, UC Berkeley), R. P. Lin (Dept. of Physics & Space Sciences Lab, UC Berkeley)
Solar flare plasmas contain both non-thermal and thermal electron populations, with the latter often reaching temperatures above ~10 MK. These high-temperature plasmas emit a characteristic line and continuum X-ray spectrum, including emission in the Fe/Ni line complexes at ~6.7 and ~8 keV. The fluxes and equivalent widths of these line complexes are strongly temperature-dependent, and thus they are a useful probe of thermal flare plasmas. The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) observes photons with energies above 3 keV, with a spectral resolution of ~1 keV FWHM, and is especially sensitive to flare plasmas above ~10 MK. In many flares, RHESSI detects emission in both of the Fe/Ni line complexes, as well as in the thermal continuum. Recent results using RHESSI for full-Sun spectroscopy show that the relationship between the 6.7- to 8-keV line flux ratio and the continuum temperature does not agree with theoretical values, and further, varies from flare to flare. RHESSI provides imaging spectroscopy, and hence the individual spectra of spatially-separated sources can be obtained and and the source morphology can be studied at different energies. We perform such an analysis on a variety of flares, including the X4.8 event on 23 July 2002 and the X1.5 event on 21 April 2002, to determine the time-varying characteristics of the multiple thermal and non-thermal electron populations. We estimate and compare the energy contained in these electron populations, and discuss the implications for heating and energy transport in solar flares.
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Bulletin of the American Astronomical Society, 36 #2
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