Coalescing neutron stars { a step towards physical models II. Neutrino emission, neutron tori, and gamma-ray bursts

Three-dimensionalhydrodynamical,Newtoniancal- culations of the coalescence of equal-mass binary neutron stars are performed with the \Piecewise Parabolic Method". The properties of neutron star matter are described by the equa- tion of state of Lattimer & Swesty (1991) which allows us to includetheemissionofneutrinosandtoevaluateourmodelsfor the -annihilation in the vicinity of the merging stars. When the stars have merged into one rapidly spinning massive body, a hottoroidalcloudofgaswithamassofabout0.1-0:2M forms around the wobbling and pulsating central 3M object. At that time the total neutrino luminosity climbs to a maximum value of 1-1:5 10 53 erg/s of which 90-95% originate from the toroidal gas cloud surrounding the very dense core. The mean energies of e , e, and heavy-lepton neutrinos x are around 12 MeV, 20 MeV, and 27 MeV, respectively. The characteris- tics of the neutrino emission are very similar to the emission from type-II supernovae, except for the e luminosity from the merged neutron stars which is a factor 3-6 higher than the lu- minosities of the other neutrino species. Whentheneutrinoluminositiesarehighest,-annihilation deposits about 0.2-0.3% of the emitted neutrino energy in the immediate neighborhood of the merger, and the maximum in- tegral energy deposition rate is 3-410 50 erg/s. Since the 3M 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 reball is insufcient by a factor of about 1000 to explain -ray bursts at cosmological distances with an energy of the order of 10 51 =(4) erg/steradian. Analytical estimates show that the additional energy provided by the annihilation of pairs emitted from a possible accretion torus of 0:1M around the central black hole is still more than a factor of 10 too small, unless focussing of the reball into a jet-like expansion