Multigroup Radiation Diffusion with Compton Scattering on a Moving Mesh: Implementation in RICH and Application to Tidal Disruption Events
Abstract
Compton scattering exchanges energy between radiation and hot gas and changes the spectrum in high-energy astrophysical systems such as tidal disruption events (TDEs). Because it couples all photon energies and can act faster than the hydrodynamic time step, many radiation-hydrodynamics (RHD) simulations omit its spectral redistribution or treat its energy exchange in the gray approximation. We extend the multigroup flux-limited diffusion module of the moving-mesh RHD code RICH to include Compton scattering with the exact thermal Compton kernel. In our semi-implicit scheme for the thermal radiative transfer equation, the temperature dependence of the kernel enters a generalized Fleck factor, and the group Compton operator conserves photon number and satisfies detailed balance. In equilibration tests, the scheme agrees with independent solutions, relaxes without absorption and emission to a Bose-Einstein spectrum, and remains stable for time steps that do not resolve the Compton equilibration timescale. We apply it to a three-dimensional simulation of the disruption of a 0.5 M⊙ star by a 106 M⊙ black hole. We find that during the X-ray flash, inverse Compton scattering dominates the coupling between the gas and the radiation near the nozzle shock, where it adds X-ray energy much faster than thermal emission and may affect the dynamics. Outside the X-ray thermalization radii, its instantaneous X-ray production rate during the flash is comparable to or larger than the escaping X-ray luminosity, so it may contribute substantially to the X-ray emission from TDEs.
Related
- Multigroup Implicit Monte Carlo Radiation Hydrodynamics on Moving Voronoi Meshes with STORM and RICH
- MACE: Multigroup-Multiangle Integrated Thermal Compton Scattering Kernel
- Tidal Disruption Events in Active Galactic Nuclei: Thermal Radiation and Jets
- The Magnusian generator for dissipative systems and application to leading 2.5PN radiation-reaction dynamics
- The Magnusian generator for dissipative systems and application to leading 2.5PN radiation-reaction dynamics
BibTeX
@misc{giron2026multigroup,
title = {{Multigroup Radiation Diffusion with Compton Scattering on a Moving Mesh: Implementation in RICH and Application to Tidal Disruption Events}},
author = {Itamar Giron and Menahem Krief and Elad Steinberg},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.31324},
eprint = {2610.31324},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.31324},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Multigroup Radiation Diffusion with Compton Scattering on a Moving Mesh: Implementation in RICH and Application to Tidal Disruption Events
AU - Itamar Giron
AU - Menahem Krief
AU - Elad Steinberg
PY - 2026
DA - 2026/10/22
PB - arXiv
DO - 10.48550/arxiv.2610.31324
UR - https://arxiv.org/abs/2610.31324
AB - Compton scattering exchanges energy between radiation and hot gas and changes the spectrum in high-energy astrophysical systems such as tidal disruption events (TDEs). Because it couples all photon energies and can act faster than the hydrodynamic time step, many radiation-hydrodynamics (RHD) simulations omit its spectral redistribution or treat its energy exchange in the gray approximation. We extend the multigroup flux-limited diffusion module of the moving-mesh RHD code RICH to include Compton scattering with the exact thermal Compton kernel. In our semi-implicit scheme for the thermal radiative transfer equation, the temperature dependence of the kernel enters a generalized Fleck factor, and the group Compton operator conserves photon number and satisfies detailed balance. In equilibration tests, the scheme agrees with independent solutions, relaxes without absorption and emission to a Bose-Einstein spectrum, and remains stable for time steps that do not resolve the Compton equilibration timescale. We apply it to a three-dimensional simulation of the disruption of a 0.5 M_⊙ star by a 10^6 M_⊙ black hole. We find that during the X-ray flash, inverse Compton scattering dominates the coupling between the gas and the radiation near the nozzle shock, where it adds X-ray energy much faster than thermal emission and may affect the dynamics. Outside the X-ray thermalization radii, its instantaneous X-ray production rate during the flash is comparable to or larger than the escaping X-ray luminosity, so it may contribute substantially to the X-ray emission from TDEs.
ER -