Coalescing neutron stars: a step towards physical models; 2, neutrino emission, neutron tori, and $\gamma$-ray bursts

Three-dimensional hydrodynamical, Newtonian calculations of the coalescence of equal-mass binary neutron stars are performed, including a physical high-density equation of state and a treatment of the neutrino emission of the heated matter. The total neutrino luminosity climbs to a maximum value of 1--1.5\cdot 10^{53}~erg/s of which 90--95\% originate from the toroidal gas cloud surrounding the very dense core formed after the merging. When the neutrino luminosities are highest, \nu\bar\nu-annihilation deposits about 0.2--0.3\% of the emitted neutrino energy in the immediate neighborhood of the merger, and the maximum integral energy deposition rate is 3--4\cdot 10^{50}~erg/s. Since the 3\,M_{\odot} core of the merged object will most likely collapse into a black hole within milliseconds the energy that can be pumped into a pair-photon fireball is insufficient by a factor of about 1000 to explain \gamma-ray bursts at cosmological distances with an energy of the order of 10^{51}/(4\pi)~erg/steradian. Analytical estimates show that the additional energy provided by the annihilation of \nu\bar\nu pairs emitted from a possible accretion torus of \sim 0.1\,M_{\odot} around the central black hole is still more than a factor of 10 too small, unless focussing of the fireball into a jet-like expansion plays an important role. About 10^{-4}--10^{-3}~M_\odot of material lost during the neutron star merging and swept out from the system in a neutrino-driven wind might be a site for nucleosythesis. Aspects of a possible r-processing in these ejecta are discussed