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

Abstract

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 MBH = 3 or 6M⊙, the black hole spin is zero, and the torus mass is ≈ 0.14–0.38M⊙ 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 ≳ 10 MeV which enhances a high luminosity of neutrinos ∼ 1051 ergs/s for MBH = 6M⊙ and ∼ 1052 ergs/s for MBH = 3M⊙. 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 ∼ 1047–1049 ergs. It is also shown in our model that for MBH = 3M⊙, the neutrino luminosity is larger than the electromagnetic luminosity while for MBH = 6M⊙, the neutrino luminosity is comparable to or slightly smaller than the electromagnetic luminosity.