Explicit-Implicit Scheme for Relativistic Radiation Hydrodynamics

Relativistic flows appear in many high-energy astrophysical phenomena in which the magnetic field has a crucial role in dynamics. For example, magnetic fields connecting an accretion disk with a central star, or, different points of accretion disks are twisted and amplified due to the differential rotation, launching jets. Also magnetic fields play an important role in accretion disks to transport the angular momentum outward, leading to the mass accretion. Not merely the observational point of view, but the radiation field is also an important ingredient in the dynamics of relativistic phenomena. The radiation pressure force would play a key role in jet acceleration. Recently, Takeuchi, et al. [1] showed a formation of radiatively accelerated and magnetically collimated jets using non-relativistic radiation magnetohydrodynamic (RMHD) simulations. These magnetic and radiative forces would accelerate jets and outflows to the relativistic speed. But, due to the lack of numerical techniques, RMHD simulations consistently including relativistic effects have not been performed. The radiation field is described by the radiation transfer equation, which represents time evolutions of the intensity. But it is hard task to solve the transfer equation coupling with the hydrodynamic code due to its complexity and high computational costs. Recently, Farris, et al. [2] proposed numerical schemes to solve general-relativistic radiation magnetohydrodynamic equations. They solved radiation moment equations instead of solving the radiative transfer equations