Properties of Neutrino-driven Ejecta from the Remnant of Binary Neutron Star Merger : Purely Radiation Hydrodynamics Case

We performed general relativistic, long-term, axisymmetric neutrino radiation hydrodynamics simulations for the remnant formed after the binary neutron star merger, which consist of a massive neutron star and a torus surrounding it. As an initial condition, we employ the result derived in a three-dimensional, numerical relativity simulation for the binary neutron star merger. We investigate the properties of neutrino-driven ejecta. Due to the pair-annihilation heating, the dynamics of the neutrino-driven ejecta is significantly modified. The kinetic energy of the ejecta is about two times larger than that in the absence of the pair-annihilation heating. This suggests that the pair-annihilation heating plays an important role in the evolution of the merger remnants. The relativistic outflow, which is required for driving gamma-ray bursts, is not observed because the specific heating rate around the rotational axis is not sufficiently high due to the baryon loading caused by the neutrino-driven ejecta from the massive neutron star. We discuss the condition for launching the relativistic outflow and the nucleosynthesis in the ejecta.