γ-Ray burst observations from the UCB/LASL experiment on ISEE-3

Abstract

Since the discovery of the intense bursts of γ rays by Klebesadel et al.¹ in 1973, little progress has been made in the identification of the sources of the bursts. The initial observations provided directions to several sources with sufficient accuracy to establish the approximate isotropic distribution of the sources², but not to provide a basis for association with any known objects, γ-ray burst astronomy entered a new phase in 1976 with the launch of Helios 2 and Solrad 11 containing the first experiments designed expressly for that purpose^3,4. It then became possible to derive several error boxes that were very narrow in one dimension^3,5. Using these data it was determined that the bursts are not associated with any type of object that has previously been recognized as a high energy astrophysical source—for example, X-ray sources. In 1978 a true interplanetary network of burst detectors was established with the launch of instruments on Pioneer Venus Orbiter⁶, ISEE 3^7–9 and Venera 11 and 12^10,11. With baseline separations that can exceed 1 AU, this network provides a basis for the location of the γ burst sources with an accuracy sufficient for optical identifications. We briefly describe here one of these instruments, a joint Berkeley/Los Alamos experiment on the ISEE 3 spacecraft, and present some initial results from that experiment. These results are currently being combined with those from the other experiments to obtain accurate burst locations to be reported elsewhere.