@article{128f994a089f4bd4a27e478adbcbbdc4,
title = "Electron thermodynamics in GRMHD simulations of low-luminosity black hole accretion",
abstract = "Simple assumptions made regarding electron thermodynamics often limit the extent to which general relativistic magnetohydrodynamic (GRMHD) simulations can be applied to observations of low-luminosity accreting black holes. We present, implement, and test a model that self-consistently evolves an entropy equation for the electrons and takes into account the effects of spatially varying electron heating and relativistic anisotropic thermal conduction along magnetic field lines. We neglect the backreaction of electron pressure on the dynamics of the accretion flow. Our model is appropriate for systems accreting at ≪10-5 of the Eddington accretion rate, so radiative cooling by electrons can be neglected. It can be extended to higher accretion rates in the future by including electron cooling and proton-electron Coulomb collisions. We present a suite of tests showing that our method recovers the correct solution for electron heating under a range of circumstances, including strong shocks and driven turbulence. Our initial applications to axisymmetric simulations of accreting black holes show that (1) physically motivated electron heating rates that depend on the local magnetic field strength yield electron temperature distributions significantly different from the constant electron-to-proton temperature ratios assumed in previous work, with higher electron temperatures concentrated in the coronal region between the disc and the jet; (2) electron thermal conduction significantly modifies the electron temperature in the inner regions of black hole accretion flows if the effective electron mean free path is larger than the local scaleheight of the disc (at least for the initial conditions and magnetic field configurations we study). The methods developed in this work are important for producing more realistic predictions for the emission from accreting black holes such as Sagittarius A* and M87; these applications will be explored in future work.",
keywords = "Galaxies: jets, Galaxies: nuclei, Galaxy: centre, MHD, Stars: black holes",
author = "Ressler, {S. M.} and Alexander Tchekhovskoy and E. Quataert and M. Chandra and Gammie, {C. F.}",
note = "Funding Information: We thank F. Foucart for useful discussions, as well as all the members of the horizon collaboration, horizon.astro.illinois.edu, for their advice and encouragement. We also thank Dmitri Uzdensky for a useful and thorough referee report. This work was supported by NSF grant AST 13-33612 and NASA grant NNX10AD03G, and a Romano Professorial Scholar appointment to CFG. EQ is supported in part by a Simons Investigator Award from the Simons Foundation and the David and Lucile Packard Foundation. MC is supported by the Illinois Distinguished Fellowship from the University of Illinois. Support for AT was provided by NASA through Einstein Postdoctoral Fellowship grant number PF3-140131 awarded by the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory for NASA under contract NAS8-03060, and by NSF through an XSEDE computational time allocation TG-AST100040 on TACC Stampede. This work was made possible by computing time granted by UCB on the Savio cluster. Funding Information: We thank F. Foucart for useful discussions, as well as all the members of the horizon collaboration, horizon.astro.illinois.edu, for their advice and encouragement. We also thank Dmitri Uzdensky for a useful and thorough referee report. This work was supported by NSF grant AST 13-33612 and NASA grant NNX10AD03G, and a Romano Professorial Scholar appointment to CFG. EQ is supported in part by a Simons Investigator Award from the Simons Foundation and the David and Lucile Packard Foundation. MC is supported by the IllinoisDistinguished Fellowship from the University of Illinois. Support for AT was provided by NASA through Einstein Postdoctoral Fellowship grant number PF3-140131 awarded by the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory for NASA under contract NAS8-03060, and by NSF through an XSEDE computational time allocation TG-AST100040 on TACC Stampede. This work was made possible by computing time granted by UCB on the Savio cluster. Publisher Copyright: {\textcopyright} 2015 The Authors.",
year = "2015",
month = dec,
day = "1",
doi = "10.1093/mnras/stv2084",
language = "English (US)",
volume = "454",
pages = "1848--1870",
journal = "Monthly Notices of the Royal Astronomical Society",
issn = "0035-8711",
publisher = "Oxford University Press",
number = "2",
}