OSO-7 observations of solar x-rays in the energy range 10?100 keV

Abstract

The solar X-ray experiment on the satellite OSO-7 has provided extensive observations of hard and soft X-ray bursts. We give a general description of the hard X-ray data here, in parallel with the description of the soft X-ray data already published (Datlowe et al., 1974). The data for this study consist of 123 hard X-ray bursts which occurred between 10 October 1971 and 6 June 1972. We examine the behavior of a typical event in terms of its spectral and flux variations. For the whole data sample, we find that 2/3 of the soft X-ray bursts have detectable hard X-ray emission. We present the distributions of frequency of occurrence of peak flux, spectral index, collisional energy loss, burst duration and the duration at half maximum of the flux profile. No correlation was found between the flux and the spectral slope of an individual data sample, nor was there a correlation between the peak flux and the full width at half maximum of a burst. We have utilized Hα flare identifications to study longitude variations. No statistically significant variation was found in the relative frequency of hard or soft X-ray bursts with longitude. However, the spectral slope does exhibit a center-to-limb variation, with limb spectra tending to be softer. We have compared the growth of energy in the hot flare plasma (soft X-ray source) with the collisional energy deposition (hard X-ray source) for the entire sample. This analysis shows that collision loss within the hot plasma is not the principal source of its heating.