Gamma-Ray Bursts and Binary Neutron Star Mergers

Neutron star binaries, such as the one observed in the famous binary pulsar PSR 1916+13, end their life in a catastrophic merge event (denoted here NS$^2$M). The merger releases $\approx 5 \cdot 10^{53}$ergs, mostly as neutrinos and gravitational radiation. A small fraction of this energy suffices to power $\gamma$-ray bursts (GRBs) at cosmological distances. Cosmological GRBs must pass, however, an optically thick fireball phase and the observed $\gamma$-rays emerge only at the end of this phase. Hence, it is difficult to determine the nature of the source from present observations (the agreement between the rates of GRBs and NS$^2$Ms being only an indirect evidence for this model). In the future a coinciding detection of a GRB and a gravitational radiation signal could confirm this model.