Bremsstrahlung in GRMHD Models of Accreting Black Holes

Journal Article · Wed Jul 22 00:00:00 EDT 2020 · The Astrophysical Journal

DOI:https://doi.org/10.3847/1538-4357/ab9808· OSTI ID:2367477

Yarza, Ricardo ^[1]; Wong, George N. ^[1]; Ryan, Benjamin R. ^[2]; Gammie, Charles F. ^[1]

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1. Univ. of Illinois at Urbana-Champaign, IL (United States)
2. Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)

Here, the role of bremsstrahlung in the emission from hot accretion flows around slowly accreting supermassive black holes is not thoroughly understood. In order to appraise the importance of bremsstrahlung relative to other radiative processes, we compute spectral energy distributions (SEDs) of accretion disks around slowly accreting supermassive black holes including synchrotron radiation, inverse Compton scattering, and bremsstrahlung. We compute SEDs for (i) four axisymmetric radiative general relativistic magnetohydrodynamics (RadGRMHD) simulations of 10⁸M_⊙ black holes with accretion rates between 10^-8$$\dot{M}$$_Edd and 10^-5$$\dot{M}$$_Edd, (ii) four axisymmetric RadGRMHD simulations of M87* with varying dimensionless spin a$$_*$$ and black hole mass, and (iii) a 3D GRMHD simulation scaled for Sgr A*. At 10^-8$$\dot{M}$$_Edd, most of the luminosity is synchrotron radiation, while at 10^-5$$\dot{M}$$_Edd the three radiative processes have similar luminosities. In most models, bremsstrahlung dominates the SED near 512 keV. In the M87* models, bremsstrahlung dominates this part of the SED if a$$_*$$ = 0.5, but inverse Compton scattering dominates if a$$_*$$ = 0.9375. Since scattering is more variable than bremsstrahlung, this result suggests that 512 keV variability could be a diagnostic of black hole spin. In the appendix, we compare some bremsstrahlung formulæ found in the literature.

• Research Organization: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: National Science Foundation (NSF); USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: 89233218CNA000001
• OSTI ID: 2367477
• Alternate ID(s): OSTI ID: 23025137
• Report Number(s): LA-UR--19-32704
• Journal Information: The Astrophysical Journal, Journal Name: The Astrophysical Journal Journal Issue: 1 Vol. 898; ISSN 0004-637X
• Publisher: IOP Publishing
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
accretion
accretion disks
black holes
bremsstrahlung
low-luminosity active galactic nuclei
radiative processes
radiative transfer
supermassive black holes