Characteristics of cosmic x-ray bursts observed with the OGO-5 satellite

Observations of 11 cosmic x-ray bursts made with the University of California, Berkeley, solar x-ray spectrometer aboard the OGO-5 satellite are presented. Their identification as cosmic events is based on good time coincidence with the observations of cosmic γ-ray bursts reported in the literature. The OGO-5 experiment is most sensitive to cosmic x-ray sources located in the sunward hemisphere. When this condition was satisfied and the OGO-5 experiment was operating normally, almost every cosmic γ-ray burst reported by other observers was detected by the OGO-5 experiment at x-ray energies approximately-greater-than32 keV. In three events the spectrum was observed down to about 10 keV. Each cosmic event consisted of one or more x-ray maxima. As many as four maxima were present in one event (1969 October 7). This was also the event with the longest duration (approx.104 s) and steepest 10--130 keV x-ray spectrum which varied with time during the event. Two intense events (1971 March 15 and March 18) were observed with 0.288 s time resolution, and large time variations were observed to occur in times approximately-less-than0.3 s. We find evidence that most cosmic γ-ray bursts have photon spectra extending down to approx.10 keV. The photon flux always increases with the decrease in photon energy. The origin of these cosmic events in processes similar to those believed to occur in solar flares is briefly examined. We find that, because of the large energy and particle requirements, white dwarfs and/or stars similar to the Sun and located at a distance approximately-greater-than10 pc are not likely to produce such events