Do γ-ray bursts contain γ-rays of energies above 1 GeV

A ground-based experiment to detect gamma-ray bursts (g.r.b.) at gigaelectronvolt energies is being made at a depth of 800 g cm-2 in the atmosphere at Ootacamund, India. During the 1.2 years of operation of the experiment, the various satellite-borne experiments have reported observing tens of g.r.b. at megaelectronvolt energies. Of these, the source locations and times of occurrence for five g.r.b. were such that they were potentially observable in our experiment, had they contained γ-rays at gigaelectronvolt energies. None was seen. The details of the experiment and the implications of the result are presented. (author)