The Radiative Efficiency and Spectra of Slowly Accreting Black Holes from Twotemperature GRRMHD Simulations
Abstract
We present axisymmetric numerical simulations of radiatively inefficient accretion flows onto black holes combining general relativity, magnetohydrodynamics, selfconsistent electron thermodynamics, and frequencydependent radiation transport. We investigate a range of accretion rates up to {10}^{5} {\dot{M}}_{{Edd}} onto a {10}^{8} {M}_{☉ } black hole with spin {a}_{\star }=0.5. We report on averaged flow thermodynamics as a function of accretion rate. We present the spectra of outgoing radiation and find that it varies strongly with accretion rate, from synchrotrondominated in the radio at low \dot{M} to inverseComptondominated at our highest \dot{M}. In contrast to canonical analytic models, we find that by \dot{M}≈ {10}^{5} {\dot{M}}_{{Edd}}, the flow approaches ̃ 1 % radiative efficiency, with much of the radiation due to inverseCompton scattering off Coulombheated electrons far from the black hole. These results have broad implications for modeling of accreting black holes across a large fraction of the accretion rates realized in observed systems.
 Publication:

The Astrophysical Journal
 Pub Date:
 August 2017
 DOI:
 10.3847/20418213/aa8034
 arXiv:
 arXiv:1707.04238
 Bibcode:
 2017ApJ...844L..24R
 Keywords:

 accretion;
 accretion disks;
 black hole physics;
 magnetohydrodynamics: MHD;
 methods: numerical;
 radiation: dynamics;
 Astrophysics  High Energy Astrophysical Phenomena
 EPrint:
 8 pages, 4 figures, submitted to ApJL. Comments welcome