Neutron star mergers, disks around black holes, and gamma-ray bursts

We have performed three-dimensional hydrodynamical simulations of the coalescence of binary neutron stars taking into account the emission and backreaction of gravitational waves in the Newtonian code based on the "Piecewise Parabolic Method" The use of the physical equation of state (EOS) of Lattimer & Swesty (1991) allowed us to calculate the production of neutrinos. We evaluated our models for the efficiency of v (v) over bar annihilation in the surroundings of the coalescing neutron stars. The corresponding energy deposition prior to and during merging turned out to be 2-3 orders of magnitude too small to power a typical gamma-ray burst (GRB) with an energy output of similar to (10(51)/4 pi) erg/sterad at cosmological distances. Analytical estimates of the subsequent evolution of the disk which possibly surrounds the central black hole showed that even under the most favorable conditions the energy provided by v (v) over bar --> e(-)e(+) --> gamma gamma falls short by at least an order of magnitude. We discuss the implications of our results and speculate about possibilities how v (v) over bar annihilation might still be a viable energy source for GRBs.