Cosmological Models of Gamma-ray Bursts

We review models of cosmological gamma-ray bursts (GRBs). The statistical and-ray transparency issues are summarized. Neutron-star and black-hole merger scenarios are described and estimates of merger rates are summarized. We review the simple reball models for GRBs and the recent work on non-simple reballs. Alternative cos-mological models, including models where GRBs are analogs of active galactic nuclei and where they are produced by high-eld, short period pulsars, are also mentioned. The value of neutrino astronomy to solve the GRB puzzle is brieey reviewed. Soon after the rst published report (Klebesadel et al., 1973) of the discovery of gamma-ray bursts (GRBs), Usov and Chibisov (1975) discussed the statistical issues. The size distribution N(> F) for GRBs produced by galac-tic disk neutron stars (NSs) bends from N(> F) / F 1 for GRB uences F(ergs cm 2) F b to N(> F) / F 3=2 for F F b , with strong accompanying anisotropy of the GRB sky distribution towards the galactic disk when F F b. For burst energies Q = 10 38 Q 38 ergs and scale heights of 300d 21 pc, the break F b in the uence size distribution occurs at F b = 10 5 Q 38 d 2 21. Two cosmological models were considered by Usov and Chibisov, and the point was made that a bend in the size distribution due to cosmological redshifting would occur for sources located at redshift z = 1, or source distances d(cm) = c=H 0 10 7 d 21 d 28. For GRBs from supernovae with Q 38 = 10 10 , a attened size distribution N(> F) / k, a constant, at low uences followed solely from expansion eeects. But with the bend in N(> F) found at uences F < F b 10 9 ergs cm 2 , it would be be quite diicult to detect due to the background galactic-ray glow. On the other hand, if Q 10 52 ergs, then F b 10 5 ergs cm 2. The proposed model for this incredible energy release was the collapse of magnetic supermassive stars with masses M 10 5-10 6 M , which was then being considered (Ozernoi and Usov, 1973; Prilutskii and Usov, 1975) as a model for the engine of active galactic nuclei (AGNs). In 1983, van den Bergh published an early (the rst?) Aitoo projection of the sky distribution of 46 GRBs. From their apparent …