An Observational Study on Coronal Hard X-ray Sources in Flares

Observational studies on solar flares with footpoints partially occulted by the solar limb provide an important method for diagnostics of coronal hard X-ray emissions. The statistics of hard X-ray sources in 71 such flares observed by RHESSI (Reuven Ramaty High-Energy Solar Spectroscopic Imager) show that the two kinds of hard X-ray sources proposed in previous studies (i.e., the sources with respectively a smaller and larger spatial separations between the thermal and non-thermal sources of coronal hard X-ray emissions) have no evident difference in the aspects of their photon spectra, images, light curves, GOES durations, etc. The area of the radiation region, the flare's total thermal energy and GOES duration are well correlated with the distance of separation. These results support some unified models of solar flares proposed in recent years, and indicate that the Masuda flare is only a kind of special event, which does not possess the general features of coronal hard X-ray emissions