General Relativistic Implicit Monte Carlo Radiation-Hydrodynamics

TL;DR

This paper introduces a new implicit Monte Carlo radiation transport method integrated into a general relativistic radiation-magnetohydrodynamics code, capable of handling complex interactions in curved spacetime.

Contribution

It develops a generalized IMC approach for relativistic regimes, including novel estimators for radiation moments in curved spacetime within a multi-reference frame framework.

Findings

Validated against flat and curved spacetime test problems.

Successfully modeled radiation-matter interactions including Comptonization.

Demonstrated accurate geodesic transport of photon packets.

Abstract

We report on a new capability added to our general relativistic radiation-magnetohydrodynamics code, Cosmos++: an implicit Monte Carlo (IMC) treatment for radiation transport. The method is based on a Fleck-type implicit discretization of the radiation-hydrodynamics equations, but generalized for both Newtonian and relativistic regimes. A multiple reference frame approach is used to geodesically transport photon packets (and solve the hydrodynamics equations) in the coordinate frame, while radiation-matter interactions are handled either in the fluid or electron frames then communicated via Lorentz boosts and orthonormal tetrad bases attached to the fluid. We describe a method for constructing estimators of radiation moments using path-weighting that generalizes to arbitrary coordinate systems in flat or curved spacetime. Absorption, emission, scattering, and relativistic Comptonization are among the matter interactions considered in this report. We discuss our formulations and numerical methods, and validate our models against a suite of radiation and coupled radiation-hydrodynamics test problems in both flat and curved spacetimes.