RHESSI and Hinode X-Ray Observations of a Partially Occulted Solar Flare

Abstract

This Letter presents X-ray observations of a partially limb-occulted solar flare taken by the Reuven Ramaty High-Energy Solar Spectroscopic Imager and the X-ray telescope on board Hinode. Thermal emission originates from a simple loop at the western limb that rises slowly (~7 km s−1) until the flare peak time. Above 18 keV, faint nonthermal emission with a hard/flat spectrum (γ ~ 4) and fast time variations (of the order of tens of seconds) is seen that comes from a loop slightly above (~2000 km) the thermal loop, if compared at the same time. However, the nonthermal loop agrees well in altitude with the thermal flare loop seen later, at the soft X-ray peak time. This is consistent with simple flare models where nonthermal electrons in a flare loop produce thin-target hard X-ray emission in the corona as they travel to the loop footpoints. There they lose all their energy and heat chromospheric plasma that fills the loop earlier seen in nonthermal hard X-rays. This suggests that electron acceleration in solar flares occurs in the corona.