Coalescing neutron stars -- a step towards physical models. II. 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\mathrm{/}s\mathrm{.}Sincethe$3,M_{\odot}$ 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 ${10}^{51}\mathrm{/}(4\pi )$~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 $\sim 0.1M_{\odot }$ 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.