Altitude Dependence of Hard X-Ray Spectra in Solar Flares

Abstract

We investigate the altitude dependence of hard X-ray (HXR) spectra in solar flares, i.e., whether the HXR spectra are related to the altitudes of reconnection sites. We assume that the reconnection altitude can be scaled by the distance between the two conjugate HXR footpoints in the flare. By searching the RHESSI flare list from 2002 to 2004, we find 42 solar flares below X-class that have enhanced 50-100 keV HXR emission and two well-resolved HXR footpoints at the nonthermal peak time. The preliminary results show that there is a weak correlation (∼ -0.31) between the HXR spectral index and the HXR footpoint distance. We further discuss the possible implications.