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Title: The Radiative Efficiency and Spectra of Slowly Accreting Black Holes from Two-temperature GRRMHD Simulations

In this paper, 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 $${10}^{-5}\,{\dot{M}}_{\mathrm{Edd}}$$ onto a $${10}^{8}\,{M}_{\odot }$$ 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 $$\dot{M}\approx {10}^{-5}\,{\dot{M}}_{\mathrm{Edd}}$$, the flow approaches $$\sim 1 \% $$ radiative efficiency, with much of the radiation due to inverse-Compton scattering off Coulomb-heated electrons far from the black hole. Finally, these results have broad implications for modeling of accreting black holes across a large fraction of the accretion rates realized in observed systems.
Authors:
ORCiD logo [1] ; ORCiD logo [2] ;  [3] ;  [4] ; ORCiD logo [5] ; ORCiD logo [2]
  1. Univ. of Illinois, Urbana, IL (United States). Dept. of Astronomy
  2. Univ. of California, Berkeley, CA (United States). Dept. of Astronomy. Dept. of Physics. Theoretical Astrophysics Center
  3. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  4. Univ. of California, Berkeley, CA (United States). Dept. of Astronomy. Dept. of Physics. Theoretical Astrophysics Center; Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Northwestern Univ., Evanston, IL (United States). Center for Interdisciplinary Exploration & Research in Astrophysics (CIERA), Physics & Astronomy
  5. Univ. of Illinois, Urbana, IL (United States). Dept. of Astronomy. Dept. of Physics
Publication Date:
Report Number(s):
LA-UR-17-25079
Journal ID: ISSN 2041-8213; TRN: US1800804
Grant/Contract Number:
AC52-06NA25396; PF3-140131; NAS8-03060; TG-AST100040; AST 13-33612
Type:
Accepted Manuscript
Journal Name:
The Astrophysical Journal. Letters
Additional Journal Information:
Journal Volume: 844; Journal Issue: 2; Journal ID: ISSN 2041-8213
Publisher:
Institute of Physics (IOP)
Research Org:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Univ. of California, Berkeley, CA (United States); Univ. of Illinois at Urbana-Champaign, IL (United States)
Sponsoring Org:
USDOE National Nuclear Security Administration (NNSA); LANL Laboratory Directed Research and Development (LDRD) Program; National Aeronautic and Space Administration (NASA); National Science Foundation (NSF)
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; accretion disks; black hole physics; magnetohydrodynamics (MHD); numerical methods; radiation dynamics
OSTI Identifier:
1415406