SEARCHING GAMMA-RAY BURSTS FOR GRAVITATIONAL LENSING ECHOES - IMPLICATIONS FOR COMPACT DARK-MATTER

The first available 44 gamma-ray bursts (GRBs) detected by the Burst a nd Transient Source Experiment on board the Compton Gamma-Ray Observat ory have been inspected for echo signals following shortly after the m ain signal. No significant echoes have been found. Echoes would have b een expected were the GRBs distant enough and the universe populated w ith a sufficient density of compact objects composing the dark matter. Constraints on dark matter abundance and GRB redshifts from the prese nt data are presented and discussed. Based on these preliminary result s, a universe filled to critical density of compact objects between 10 (6.5) M. and 10(8.1) M. are now marginally excluded, or the most likel y cosmological distance paradigm for GRBs is not correct. We expect fu ture constraints to be able either to test currently popular cosmologi cal dark matter paradigms or to indicate that GRBs do not lie at cosmo logical distances.