HARD AND SOFT X-RAY OBSERVATIONS OF SOLAR LIMB FLARES

摘要

Using observations from the Yohkoh Bragg Crystal Spectrometer, hard X-ray telescope, and soft X-ray telescope, we have examined eight limb flares. Four of the flares have the footpoints occulted by the solar limb. We find that the occulted flares generally have softer hard X-ray spectra and smaller peak values of the nonthermal broadening velocity than nonocculted flares. All other physical parameters show no differences between occulted flares and nonocculted flares. The hard X-ray spectra support a model in which the footpoint emission is due to thick-target sources, while the looptop emission is due to thin-target sources. High spectral resolution hard X-ray observations should thus show a break in the hard X-ray spectrum of the looptop source. We can find no obvious explanation for the differences in nonthermal broadening velocity.