A search for cosmic gamma-ray bursts with a balloon-borne NaI(T1) scintillation crystal

A search has been made for gamma-ray bursts in 15 hours of data obtained from a balloonborne gamma-ray detector on 10 October and 21 October, 1970. The event rate for photon energy losses in the 0.1–0.4 MeV range from the 13-in. diameter by 6-in. thick NaI(T1) scintillation crystal was examined for statistically significant fluctuations as an indication of gamma-ray bursts. Searches of the data were made with time resolutions varying from 2 ms to 64 s. Four statistically significant bursts were detected and are considered as possible cosmic gamma-ray burst events. The characteristic duration of all four of the observed events is 100 ms. Similar events can be generated in the laboratory following an extremely large (10³ GeV) thirty ns X-ray energy deposition in the NaI(T1) crystal. The implications of these short duration, low intensity events, if valid gamma-ray bursts, are discussed.Paper presented at the COSPAR Symposium on Fast Transients in X- and Gamma-Rays, held at Varna, Bulgaria, 29–31 May, 1975.