Time-dependent Multi-group Multidimensional Relativistic Radiative Transfer Code Based On Spherical Harmonic Discrete Ordinate Method

TL;DR

This paper introduces a novel time-dependent, multi-group, multidimensional relativistic radiative transfer code based on the spherical harmonic discrete ordinate method, enabling detailed simulations of radiation in relativistic astrophysical phenomena.

Contribution

The authors develop and validate a comprehensive relativistic radiative transfer code incorporating time dependence, multi-frequency, Lorentz transformations, and scattering, advancing computational tools for astrophysics.

Findings

Code accurately models intensity evolution in relativistic scenarios.

Validation confirms correct implementation of scattering and Lorentz transformations.

Enables calculation of Eddington tensor for radiation hydrodynamics.

Abstract

We develop a time-dependent multi-group multidimensional relativistic radiative transfer code, which is required to numerically investigate radiation from relativistic fluids involved in, e.g., gamma-ray bursts and active galactic nuclei. The code is based on the spherical harmonic discrete ordinate method (SHDOM) that evaluates a source function including anisotropic scattering in spherical harmonics and implicitly solves the static radiative transfer equation with a ray tracing in discrete ordinates. We implement treatments of time dependence, multi-frequency bins, Lorentz transformation, and elastic Thomson and inelastic Compton scattering to the publicly available SHDOM code. Our code adopts a mixed frame approach; the source function is evaluated in the comoving frame whereas the radiative transfer equation is solved in the laboratory frame. This implementation is validated with various test problems and comparisons with results of a relativistic Monte Carlo code. These validations confirm that the code correctly calculates intensity and its evolution in the computational domain. The code enables us to obtain an Eddington tensor that relates first and third moments of intensity (energy density and radiation pressure) and is frequently used as a closure relation in radiation hydrodynamics calculations.