Frequency of fast, narrow γ-ray bursts

Early studies of the time histories of the γ-ray burst events reported by the Vela satellites led to the suggestion that very brief, ~ 0.1 s, bursts formed a class distinct from the longer, highly structured bursts¹. Results of the KONUS experiments on Veneras 11, 12, 13 and 14 argue for the existence of a separate class of short-duration γ-ray bursts², revealing that many of the short bursts exhibit much softer spectra ( ~ 30 keV) than the more familiar complex bursts. Although this correlation is not completely clear and the observations are in some cases contradictory^2-6, the existence of two γ-ray burst populations is suggested by Fig. 1, showing a duration histogram for 24 events detected by our ISEE-3 experiment. Figure 1 also shows the distribution of 123 Venera 13 and 14 events (60 detected by both spacecraft) and suggests two γ-ray burst populations in each experiment sample, the domains separated with a minimum near 1 or 2s. Here we point out that the results of the Goddard ISEE-3 γ-ray burst spectrometer actually enhance the appearance of two burst populations suggested in the Venera data.