Moving-mesh radiation-hydrodynamic simulations of wind-reprocessed transients

TL;DR

This paper introduces advanced moving-mesh radiation-hydrodynamic simulations to model how winds reprocess radiation from central sources in transient astrophysical events, providing insights into radiation diffusion and isotropization.

Contribution

The authors develop a new coupled moving-mesh hydrodynamics and radiation module enabling self-consistent multi-dimensional simulations over large scales, confirming analytic reprocessing stages.

Findings

Confirmed stages of radiation trapping and diffusion in winds.

Reprocessed radiation becomes isotropic after about one lateral diffusion time.

Moderate cone opening angles reduce early flux along certain sightlines.

Abstract

Motivated by recent theoretical work on tidal disruption events and other peculiar transients, we present moving-mesh radiation-hydrodynamic simulations of radiative luminosity emitted by a central source being reprocessed by a wind-like outflow. We couple the moving-mesh hydrodynamic code JET with our newly-developed radiation module based on mixed-frame grey flux-limited diffusion with implicit timestep update. This allows us to study the self-consistent multi-dimensional radiation-hydrodynamic evolution over more than ten orders of magnitude in both space and time in a single run. We simulate an optically-thick spherical wind with constant or evolving mass-loss rate, which is irradiated by a central isotropic or angularly-dependent radiation source. Our spherically-symmetric simulations confirm previous analytic results by identifying different stages of radiation reprocessing: radiation trapped in the wind, diffusing out through the wind, and reaching constant maximum attenuation. We find that confining the central radiation source in a cone with moderate opening angles decrease up to one order of magnitude the early flux along sightlines oriented away from the direction of radiation injection but that the reprocessed radiation becomes isotropic roughly after one lateral diffusion time through the ejecta. We discuss further applications and guidelines for the use of our novel radiation-hydrodynamics tool in the context of transient modelling.