Gravitationally Lensed Gamma-Ray Bursts as Probes of Dark Compact Objects

If dark matter in the form of compact objects comprises a large fraction of the mass of the universe, then gravitational lensing effects on gamma-ray bursts are expected. We utilize BATSE and Ulysses data to search for lenses of different mass ranges, which cause lensing in the milli, pico, and femto regimes. Null results are used to set weak limits on the cosmological abundance of compact objects in mass ranges from 10$^{-16}$ to 10$^{-9}$ $M_{\odot} $. A stronger limit is found for a much discussed $\Omega = 0.15$ universe dominated by black holes of masses $\sim 10^{6.5} M_{\odot}$, which is ruled out at the $\sim$ 90% confidence level.