# General Relativistic Radiation Magnetohydrodynamic Simulations of Thin Magnetically Arrested Disks

## TL;DR

This study uses advanced 3D general relativistic radiative magnetohydrodynamic simulations to explore how strong magnetic fields influence the efficiency and radiation of thin accretion disks around black holes, revealing that winds carry most of the accretion energy.

## Contribution

First fully global GRRMHD simulations of a thin, magnetically arrested disk with self-consistent radiation transport, analyzing the impact of magnetic fields on radiative efficiency and outflows.

## Key findings

- Magnetically driven winds carry most of the accretion energy (~13% efficiency).
- Radiative efficiency is slightly lower than classical predictions, contrary to previous simulations.
- The disk remains thin and magnetically arrested out to ~16 gravitational radii.

## Abstract

The classical, relativistic thin-disk theory of Novikov and Thorne (NT) predicts a maximum accretion efficiency of 40% for an optically thick, radiatively efficient accretion disk around a maximally spinning black hole (BH). However, when a strong magnetic field is introduced to numerical simulations of thin disks, large deviations in efficiency are observed, in part due to mass and energy carried by jets and winds launched by the disk or BH spin. The total efficiency of accretion can be significantly enhanced beyond that predicted by NT but it has remained unclear how the radiative component is affected. In order to study the effect of a dynamically relevant large-scale magnetic field on radiatively efficient accretion, we have performed numerical 3D general relativistic - radiative - magnetohydroynamic (GRRMHD) simulations of a disk with scale height to radius ratio of $H/R~0.1$ around a moderately spinning BH (a=0.5) using the code HARMRAD. Our simulations are fully global and allow us to measure the jet, wind, and radiative properties of a magnetically arrested disk (MAD) that is kept thin via self-consistent transport of energy by radiation using the M1 closure scheme. Our fiducial disk is MAD out to a radius of ~16R_g and the majority of the total ~13\% efficiency of the accretion flow is carried by a magnetically driven wind. We find that the radiative efficiency is slightly suppressed compared to NT, contrary to prior MAD GRMHD simulations with an ad hoc cooling function, but it is unclear how much of the radiation and thermal energy trapped in the outflows could ultimately escape.