Thermal and non-thermal emission from supermassive black hole circumbinary disks: Disks, Coronae, Streams, and Cavities
Abstract
The search for electromagnetic signals from supermassive black hole (SMBH) binary systems is one of the cornerstones of multi-messenger astrophysics, complementing gravitational wave observations of such systems by pulsar timing arrays and LISA. Although extensive simulations have been run to understand the time variability of the bolometric luminosity from accreting binary SMBH systems, comparatively few spectral predictions have been made, and none that go beyond simple emission models. In this paper, we post-process a \texttt{HARM3D} simulation snapshot of a binary at $20 M$ separation accreting at 0.01 Eddington. For black hole masses 106, 107, and 108 M⊙, we self-consistently solve for the radiated spectrum on the basis of time-steady radiation transfer, thermal balance, and ionization equilibrium, including all relevant relativistic effects as well as emission and absorption processes. Although most of the bolometric luminosity is radiated thermally by the disk, the low density regions evacuated by the binary's quadrupole moment produce copious X-rays, with ∼40% of the observed luminosity in a soft X-ray power law (Γ= 2.3). We identify two modes of observed azimuthal variation. The X-ray continuum varies by ∼10% due to an underlying asymmetry in the gas temperature of spiral shocks in the disk. The Fe~Kα equivalent width dips by ∼25% when the line of sight to the inner disk is partially obscured by the lump. These two effects share the same period and are ∼ π/2 out of phase; the period is order days to weeks for typical AGN masses and a 20M separation.
Related
- Radio component of the multi-messenger emission from the anticipated T Coronae Borealis outburst
- JWST/MIRI Spectroscopy of the Quiescent Black Hole X-ray Binary XTE J1118+480: Constraints on Jet and Circumbinary Dust Contributions to the Mid-infrared Emission
- Electromagnetic Emission and Orbital Evolution of Eccentric Supermassive Black Hole Binaries in Retrograde Disks
- The thermal emission for knot A of radio galaxy M87 by Chandra
- Non-thermal emission in jets and winds: Expected emission and spectral index distributions
BibTeX
@misc{nagele2026thermal,
title = {{Thermal and non-thermal emission from supermassive black hole circumbinary disks: Disks, Coronae, Streams, and Cavities}},
author = {Chris Nagele and Julian H. Krolik and Brooks E. Kinch and Jeremy D. Schnittman and Scott C. Noble},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.03140},
eprint = {2609.03140},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.03140},
}
RIS
TY - UNPB
TI - Thermal and non-thermal emission from supermassive black hole circumbinary disks: Disks, Coronae, Streams, and Cavities
AU - Chris Nagele
AU - Julian H. Krolik
AU - Brooks E. Kinch
AU - Jeremy D. Schnittman
AU - Scott C. Noble
PY - 2026
DA - 2026/09/21
PB - arXiv
DO - 10.48550/arxiv.2609.03140
UR - https://arxiv.org/abs/2609.03140
AB - The search for electromagnetic signals from supermassive black hole (SMBH) binary systems is one of the cornerstones of multi-messenger astrophysics, complementing gravitational wave observations of such systems by pulsar timing arrays and LISA. Although extensive simulations have been run to understand the time variability of the bolometric luminosity from accreting binary SMBH systems, comparatively few spectral predictions have been made, and none that go beyond simple emission models. In this paper, we post-process a \texttt{HARM3D} simulation snapshot of a binary at $20 M$ separation accreting at 0.01 Eddington. For black hole masses 10^6, 10^7, and 10^8 M_⊙, we self-consistently solve for the radiated spectrum on the basis of time-steady radiation transfer, thermal balance, and ionization equilibrium, including all relevant relativistic effects as well as emission and absorption processes. Although most of the bolometric luminosity is radiated thermally by the disk, the low density regions evacuated by the binary's quadrupole moment produce copious X-rays, with ∼40% of the observed luminosity in a soft X-ray power law (Γ= 2.3). We identify two modes of observed azimuthal variation. The X-ray continuum varies by ∼10% due to an underlying asymmetry in the gas temperature of spiral shocks in the disk. The Fe~Kα equivalent width dips by ∼25% when the line of sight to the inner disk is partially obscured by the lump. These two effects share the same period and are ∼ π/2 out of phase; the period is order days to weeks for typical AGN masses and a 20M separation.
ER -