Supermassive Objects as Gamma-Ray Bursters

We propose that the gravitational collapse of supermassive objects ($ M\ga10^4 M_\odot$), either as relativistic star clusters or as single supermassivestars (which may result from stellar mergers in dense star clusters), could bea cosmological source of $\gamma$-ray bursts. These events could provide theseeds of the supermassive black holes observed at the center of many galaxies.Collapsing supermassive objects will release a fraction of their hugegravitational binding energy as thermal neutrino pairs. We show that theaccompanying neutrino/antineutrino annihilation-induced heating could driveelectron/positron ``fireball'' formation, relativistic expansion, andassociated $\gamma$-ray emission. The major advantage of this model is itsenergetics: supermassive object collapses are far more energetic than solarmass-scale compact object mergers; therefore, the conversion of gravitationalenergy to fireball kinetic energy in the supermassive object scenario need notbe highly efficient, nor is it necessary to invoke directional beaming. Themajor weakness of this model is difficulty in avoiding a baryon loading problemfor one dimensional collapse scenarios.Comment: latex 16 pages, 1 figure, accepted by Ap