Hard and Soft X‐Ray Observations of Occulted and Nonocculted Solar Limb Flares

Abstract

Using observations from the Yohkoh Bragg Crystal Spectrometer (BCS), the Soft X-Ray Telescope, and the Hard X-Ray Telescope, we have examined the properties of 45 limb flares. Twenty-eight of the flares appear to have most or all of their footpoints occulted by the solar limb, leaving only soft X-ray emission from a looptop source visible. The remaining 17 flares have exposed footpoints. In most observational characteristics, occulted limb flares are indistinguishable from nonocculted limb flares. There does appear to be some evidence that the peak temperature observed in the BCS Ca XIX channel is lower by 2-3 MK in the occulted flares. We also see some tendency for the hard X-ray spectra averaged over the entire event to exhibit a softer spectral index in the occulted limb flares. Most of the flares for which it is possible to measure a peak in the Ca XIX nonthermal broadening velocity as a function of time show that the peak in the nonthermal broadening velocity occurs after the first significant hard X-ray peak.