GRAVITATIONAL LENSING ORIGIN FOR A POSSIBLE GAMMA-RAY BURST REPEATER

One observational consequence of a cosmological distribution of gamma- ray bursts is that some recurrent bursts, due to gravitational lensing , should be seen during the Lifetime of the Compton Gamma-Ray Observat ory. These would be identifiable by their spatial coincidence and by t heir identical time profiles and spectra. The COMPTEL experiment, onbo ard the Compton Gamma-Ray Observatory, has imaged two gamma-ray bursts (GRB 930704 and GRB 940301) with coincident locations, separated in t ime by eight months. We report here on the spectral and temporal analy sis of these two events in order to establish whether they are gravita tionally lensed images of the same burst. We conclude that although th e envelopes of the time profiles are similar, they are sufficiently di fferent on short timescales to rule out the standard lensing hypothesi s. Furthermore, spectral dissimilarities between the pair mitigate aga inst the possibility that the differences in time profiles could have arisen through microlensing. Since lensing is ruled out, the remaining possibilities are an accidental coincidence of unrelated bursts or a true repeating burst source. The latter would severely constrain cosmo logical burst models.