Relativistic radiation hydrodynamics for accretion

Accretion flow in general involves relativistic motions, radiative interaction, and strong gravity, all of which demand accurate relativistic treatment. I use the covariant tensor formalism to show how to derive the general radiation hydrodynamic equations for arbitrary coordinates or spacetimes. Frequency-integrated radiation moments defined in given tetrad frames are transformed to covariant forms. Interactions between radiation and matter are to be evaluated in the tetrad comoving with the gas while the hydrodynamic and radiation moment equations are written in covariant forms. This mixed-frame covariant approach is more straightforward to apply to accretion problems. The closure relation for inherently incomplete radiation moment equations is also discussed.