Radiation Magnetohydrodynamics for Black Hole-Torus System in Full General Relativity: A Step toward Physical Simulation

A radiation-magnetohydrodynamic simulation for the black hole-torus system is performed in the framework of full general relativity for the first time. A truncated moment formalism is employed for a general relativistic neutrino radiation transport. Several systems in which the black hole mass is M-BH = 3 or 6M(circle dot), the black hole spin is zero, and the torus mass is approximate to 0.14-0.38M(circle dot) are evolved as models of the remnant formed after the merger of binary neutron stars or black hole-neutron star binaries. The equation of state and microphysics for the high-density and high-temperature matter are phenomenologically taken into account in a semi-quantitative manner. It is found that the temperature in the inner region of the torus reaches greater than or similar to 10 MeV which enhances a high luminosity of neutrinos similar to 10(51) ergs/s for M-BH = 6M(circle dot) and similar to 10(52) ergs/s for M-BH = 3M(circle dot). It is shown that neutrinos are likely to be emitted primarily toward the outward direction in the vicinity of the rotational axis and their energy density may be high enough to launch a low-energy short gamma-ray burst via the neutrino-antineutrino pair-annihilation process with the total energy deposition similar to 10(47)-10(49) ergs. It is also shown in our model that for M-BH = 3M(circle dot), the neutrino luminosity is larger than the electromagnetic luminosity while for M-BH = 6M(circle dot), the neutrino luminosity is comparable to or slightly smaller than the electromagnetic luminosity.