Search for bursts of gamma rays of energies > 1 GeV

Abstract

A ground-based experiment to detect cosmic gamma-ray bursts (GRB) in which the individual gamma-rays at the top of the atmosphere have energies in the GeV range has been in operation at Ootacamund, India, for nearly 1.5 years. Not a single event was observed, although five of the GRB seen by satellite-borne detectors in the MeV energy range were in the view of and potentially observable by our experiment. Details of the experimental results and their implications to the phenomenon of GRB are presented. The experiment also enables us to place a 99 per cent confidence level upper limit to the rate of explosions of primordial black holes (Hawking process) in the vicinity of the solar system at a value of 1.6 × 10³ or 5.7 × 10³/ (yr pc⁺³), depending on whether the explosions take place according to an elementary or a composite particle hypothesis, respectively.