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 $M_{\rm BH}=3$or$6M_{\odot}$,theblackholespiniszero,andthetorusmassis$\approx 0.14$--$0.38M_{\odot}$ 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 $\text{agt}10$ MeV which enhances a high luminosity of neutrinos $\sim {10}^{51}$ ergs/s for $M_{\mathrm{B}\mathrm{H}}=6M_{\odot }$ and $\sim {10}^{52}$ ergs/s for $M_{\mathrm{B}\mathrm{H}}=3M_{\odot }$. 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 $\sim 10^{47}$--$10^{49}$ergs\mathrm{.}Itisalsoshowninourmodelthatfor$M_{\rm BH}=3M_{\odot}$, the neutrino luminosity is larger than the electromagnetic luminosity while for $M_{\mathrm{B}\mathrm{H}}=6M_{\odot }$, the neutrino luminosity is comparable to or slightly smaller than the electromagnetic luminosity.