DETERMINING THE GAMMA-RAY BURST DISTANCE SCALE - OBSERVATIONAL PROSPECTS

The BATSE instrument on the Compton Gamma-Ray Observatory has demonstr ated that we live near the center of an isotropic but bounded distribu tion of gamma-ray burst sources but has left unsettled whether the bur sts occur in our own Galaxy or at cosmological distances. Because a di stance and energy scale is crucial to constraining burst models, this distance ambiguity must be resolved. The key experiment that would dis tinguish the possibilities is a search for bursts from the halo of M31 or other nearby galaxies. We discuss the observational prospects for this test, showing that no telescope now in orbit or scheduled for lau nch can settle the debate, but that an experiment could be done with a low-cost, dedicated instrument.