Radiative Properties of Magnetically-Arrested Disks

TL;DR

This study uses magnetohydrodynamic simulations to compare the radiative properties of magnetically-arrested disks (MADs) and standard accretion flows, revealing that MADs are generally brighter but have similar spectra to SANEs, with implications for black hole systems.

Contribution

The paper develops a method to analyze radiative properties of MADs using simulations, comparing them systematically to SANEs across different magnetic flux configurations.

Findings

MADs are systematically brighter than SANEs at the same accretion rates.

Spectral similarities make it difficult to distinguish MADs from SANEs observationally.

Maximum luminosity of MADs is comparable but slightly lower than SANEs.

Abstract

Magnetically-arrested disks (MADs) appear when accretion flows are supplied with a sufficient amount of magnetic flux. In this work, we use results of magnetohydrodynamic simulations to set the configuration of the magnetic field and investigate the dynamics and radiative properties of the resulting accretion flow (i.e., without that of the jet) of MAD. The method developed here is applied to both the MAD and the standard and normal evolution (SANE) accretion flow with or without large scale magnetic fields. For the radiative processes, we include synchrotron, bremsstrahlung and Compton scattering. We find that, in general, MAD accretion flows have similar spectra to those of the SANE, which complicates the task of distinguishing MADs from SANEs. At the same accretion rates, MADs are systematically brighter than SANEs. However, the critical accretion rate above which the hot solution ceases to exist is lower in MAD. Consequently, the maximum luminosity the MAD can reach is comparable but slightly lower than that of SANE, and the dependence on the magnetic flux is weak. We then discuss implications of our results for active galactic nuclei and accreting black-hole binaries.