RHESSI line and continuum observations of super-hot flare plasma

Abstract

We use RHESSI high-resolution imaging and spectroscopy observations from ∼5 to 100 keV to characterize the hot thermal plasma during the 2002 July 23 X4.8 flare. These measurements of the steeply falling thermal X-ray continuum are well fit throughout the flare by two distinct isothermal components: a super-hot (Te > 30 MK) component that peaks at ∼44 MK and a lower-altitude hot (Te ≲ 25 MK) component whose temperature and emission measure closely track those derived from GOES measurements. The two components appear to be spatially distinct, and their evolution suggests that the super-hot plasma originates in the corona, while the GOES plasma results from chromospheric evaporation. Throughout the flare, the measured fluxes and ratio of the Fe and Fe-Ni excitation line complexes at ∼6.7 and ∼8 keV show a close dependence on the super-hot continuum temperature. During the pre-impulsive phase, when the coronal thermal and non-thermal continua overlap both spectrally and spatially, we use this relationship to obtain limits on the thermal and non-thermal emission. © 2010 The American Astronomical Society. All rights reserved.