Radiative Properties of Magnetically Arrested Disks

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 MADs. 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, accretion flows of MADs 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 MADs. Consequently, the maximum luminosity an MAD can reach is comparable to but slightly lower than that of SANE, and the dependence on the magnetic flux is weak. We then discuss the implications of our results for active galactic nuclei and accreting black hole binaries.