Time-Dependent Multi-Group Multi-Dimensional Relativistic Radiative Transfer Code Based on Spherical Harmonic Discrete Ordinate Method

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., gammaray 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. 6 The emission from a relativistic flow is also interesting for, e.g., active galactic nuclei (AGN).

General Relativistic Implicit Monte Carlo Radiation-hydrodynamics

“…Decades of progress have seen the field of computational physics advance from relatively simple N-body and hydrodynamics simulations to the point where relativistic magnetohydrodynamics (MHD) together with radiation treatments beyond the diffusion approximation have become commonplace (a far from complete list includes such works as Farris et al 2008;Müller et al 2010;Shibata et al 2011;Zanotti et al 2011;Saḑowski et al 2013;McKinney et al 2014;Tominaga et al 2015;Kuroda et al 2016;Ryan & Dolence 2020). A historical perspective of this progress is exemplified by our own contributions with the Cosmos ++ code, which grew in sophistication from a modest start in Newtonian hydrodynamics and flux-limited (gray) diffusion (Anninos et al 2003) to eventually incorporate general relativistic magneto-hydrodynamics on unstructured, adaptively refined grids (Anninos et al 2005).…”

General Relativistic Implicit Monte Carlo Radiation-Hydrodynamics

“…Decades of progress has seen the field of computational physics advance from relatively simple N-body and hydrodynamics simulations to the point where relativistic magneto-hydrodynamics (MHD) together with radiation treatments beyond the diffusion approximation have become common place (a far from incomplete list includes Farris et al 2008;Müller et al 2010;Shibata et al 2011;Zanotti et al 2011;Sadowski et al 2013;McKinney et al 2014;Tominaga et al 2015;Kuroda et al 2016;Ryan & Dolence 2020). A historical perspective of this progress is exemplified by our own contributions with the Cosmos++ code, which grew in sophistication from a modest start in Newtonian hydrodynamics and flux-limited (grey) diffusion (Anninos et al 2003), to eventually incorporate general relativistic magneto-hydrodynamics on unstructured, adaptively refined grids (Anninos et al 2005).…”

Numerical problems in coupling photon momentum (radiation pressure) to gas

“…As such, a great deal of literature has focused on numerical methods for solving (or approximately solving) the radiative transfer equation (RTE) on-the-fly in simulations (for some recent examples, see e.g. Hopkins et al 2011;Davis et al 2012;Kuiper et al 2012;Bate 2012;Wise et al 2012;Kolb et al 2013;Rosdahl et al 2013;Davis et al 2014;González et al 2015;Roth & Kasen 2015;Tominaga et al 2015;Buntemeyer et al 2016;Zhang & Davis 2017;Rosen et al 2017;Kim et al 2017;Foucart 2018) But comparably little attention has been paid to how, given a solution to the RTE, radiation pressure forces are coupled onto the gas or fluid (although see e.g. Lowrie et al 1999).…”