AAS 204th Meeting, June 2004
Session 87 Flares
SPD Oral, Thursday, June 3, 2004, 10:30-11:30am, 704/706

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[87.01] RHESSI, RESIK, and GOES Observations of the Solar Flare Thermal Spectrum

K.J.H. Phillips (NRC Senior Research Associate, NASA Goddard Space Flight Center), B.R. Dennis (NASA Goddard Space Flight Center), J. Sylwester, B. Sylwester (Space Research Centre, Polish Academy of Sciences)

The bulk of the thermal spectrum of solar X-ray flares extends from very soft X-rays (<<1 keV) to beyond 10 keV. We present results from three instruments detecting this spectrum: RHESSI, GOES, and the Polish-led RESIK crystal spectrometer on the Russian Coronas-F mission. RHESSI makes imaging and spectral observations at energies above ~5 keV; RESIK operates in a first-order diffraction mode with energy range 2.0 to 3.7 keV and, for selected stronger flares, in a third-order mode with energy range 6.1 to 8.6 keV; GOES makes flux measurements in two wide energy bands between ~1.5 and ~25 keV. Simultaneous observations by all three instruments were made of an M2 flare on 2003 April 26, with RESIK in its first-order mode at the beginning and decay portions of the flare and in third-order during an 8-minute interval at the flare peak. Comparison of RHESSI and both first-order and third-order RESIK spectra indicate agreement to within the expected uncertainties of ~25%. Both instruments observe the continuum emission and the Fe line feature (mostly Fe XXV lines and satellites) at 6.7 keV. The Fe/Ni line feature at 7.9 keV (Fe XXV and Ni XXVII lines) is less certainly detected. The thermal spectra derived from the GOES channel ratios agree closely with RESIK and RHESSI spectra. Measurements of the equivalent width of the Fe line feature and other lines in the RESIK first-order range allow absolute element abundances to be determined during the flare for comparison with standard photospheric values.

KJHP acknowledges an NRC Research Associateship, and JS and BS acknowledge support from grants (2.P03D.002.22 and PBZ-KBN-054/P03/2001) of the Polish Committee for Scientific Research. RESIK is a joint project between NRL (USA), MSSL and RAL (UK), IZMIRAN (Russia), and SRC (Poland). The Coronas-F mission is led by the IZMIRAN Institute.

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