34th Solar Physics Division Meeting, June 2003
Session 14 RHESSI Results I
Oral, Wednesday, June 18, 2003, 9:00am-12:00noon, Auditorium

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[14.05] Electron Bremsstrahlung Hard X-Ray Spectra, Electron Distributions and Energetics in the 2002 July 23 Solar Flare

G. D. Holman (NASA/GSFC), L. Sui (CUA), R. A. Schwartz (SSAI), A. G. Emslie (UAH)

We present and analyze the first high-resolution hard X-ray spectra from a solar flare observed in both X-ray/\gamma-ray continuum and \gamma-ray lines. The 2002 July 23 flare was observed by the Ramaty High Energy Solar Spectroscopic Imager (RHESSI). The spatially integrated photon flux spectra are well fitted between 10 and 300 keV by the combination of an isothermal component and a double power law. The flare plasma temperature peaks at 40 MK around the time of peak hard X-ray emission and remains above 20 MK 37 min later. We derive the evolution of the nonthermal mean electron flux distribution by directly fitting the RHESSI X-ray spectra with the thin-target bremsstrahlung from a double power-law electron distribution with a low-energy cutoff. We also derive the evolution of the electron flux distribution on the assumption that the emission is thick-target bremsstrahlung. We find that the injected nonthermal electrons are well described throughout the flare by this double power-law distribution with a low-energy cutoff that is typically between 20 - 40 keV. Using our thick-target results, we compare the energy contained in the nonthermal electrons with the energy content of the thermal flare plasma observed by RHESSI and GOES. We find that the minimum total energy deposited into the flare plasma by nonthermal electrons, 2.6 x 1031 erg, is on the order of and possibly less than the energy in the thermal plasma. However, these fits do not rule out the possibility that the energy in nonthermal electrons exceeds the energy in the thermal plasma.

This work was supported in part by the RHESSI Project and the NASA Sun-Earth Connection program.

The author(s) of this abstract have provided an email address for comments about the abstract: holman@stars.gsfc.nasa.gov

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© 2003. The American Astronomical Soceity.