RHESSI Discovery of a Coronal Non-thermal Hard X-ray Source in the 23 July 2002 Gamma-ray Line Flare

摘要

The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) observations of the gamma-ray line flare of 2002 July 23,show that in the ~8 minute rise prior to the impulsive phase,the hard X-ray emission comes from a coronal source which has no counterpart in the simultaneous TRACE EUV images or in the Ha images.The spectrum above ~10 keV fits to a double-power-law shape with break energies at ~20-40 keV and exponents of ~5 below and ~7 above,with no obvious thermal emission above ~10 keV.This coronal non-thermal source implies that substantial energy release and electron acceleration occurs before the impulsive phase.