The Radiative Efficiency and Spectra of Slowly Accreting Black Holes from Two-temperature GRRMHD Simulations
Abstract
We present axisymmetric numerical simulations of radiatively inefficient accretion flows onto black holes combining general relativity, magnetohydrodynamics, self-consistent electron thermodynamics, and frequency-dependent 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 synchrotron-dominated in the radio at low \dot{M} to inverse-Compton-dominated 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 inverse-Compton scattering off Coulomb-heated 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:
- 10.3847/2041-8213/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
- E-Print:
- 8 pages, 4 figures, submitted to ApJL. Comments welcome