X-ray Reflection as Diagnostic of Supermassive Black Hole Binary Properties
Abstract
We investigate correlations between prominent features in the relativistic X-ray reflection spectrum emitted by an accreting supermassive black hole (SMBH) binary with the underlying properties of the binary system. Model-independent measurements of the relativistic Fe Kα line (∼6.4 keV) and the Compton reflection hump (∼20-30 keV) are shown to be useful in constraining binary parameters. We compute 24,570 X-ray reflection spectra from two mini-disks attached to SMBHs at a fixed separation of 100 GM/c2 on circular orbits, by varying its mass ratio, spin parameters, inclination, orbital phase and total mass accretion rate. We find that the location of the blue peak in the relativistic Fe Kα is a relatively robust diagnostic of the binary inclination, which could be obtained from a single-epoch X-ray spectrum. Given a few epochs of spectra, one may be able to determine the orbital phase of the binary and place constraints on its mass ratio by monitoring the Fe Kα centroid. Of all parameters, SMBH spin effects are most subtle and prone to measurement degeneracies. Some markers of high SMBH spin may nevertheless surface in the composite spectrum due to increased radiative efficiency. The approach developed here can be used to place preliminary constraints on binary parameters before a full parametrized X-ray spectral fitting method is available. It complements gravitational wave measurements by the Pulsar Timing Arrays (PTAs) and the Laser Interferometer Space Antenna by providing independent constraints on binary parameters that may be prone to degeneracy (inclination), or otherwise inaccessible (spin for PTAs).
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BibTeX
@misc{malewicz2026xray,
title = {{X-ray Reflection as Diagnostic of Supermassive Black Hole Binary Properties}},
author = {Julie Malewicz and Tamara Bogdanović and David R. Ballantyne and Laura Brenneman and Thomas Dauser},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2608.04961},
eprint = {2608.04961},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2608.04961},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - X-ray Reflection as Diagnostic of Supermassive Black Hole Binary Properties
AU - Julie Malewicz
AU - Tamara Bogdanović
AU - David R. Ballantyne
AU - Laura Brenneman
AU - Thomas Dauser
PY - 2026
DA - 2026/11/04
PB - arXiv
DO - 10.48550/arxiv.2608.04961
UR - https://arxiv.org/abs/2608.04961
AB - We investigate correlations between prominent features in the relativistic X-ray reflection spectrum emitted by an accreting supermassive black hole (SMBH) binary with the underlying properties of the binary system. Model-independent measurements of the relativistic Fe Kα line (∼6.4 keV) and the Compton reflection hump (∼20-30 keV) are shown to be useful in constraining binary parameters. We compute 24,570 X-ray reflection spectra from two mini-disks attached to SMBHs at a fixed separation of 100 GM/c^2 on circular orbits, by varying its mass ratio, spin parameters, inclination, orbital phase and total mass accretion rate. We find that the location of the blue peak in the relativistic Fe Kα is a relatively robust diagnostic of the binary inclination, which could be obtained from a single-epoch X-ray spectrum. Given a few epochs of spectra, one may be able to determine the orbital phase of the binary and place constraints on its mass ratio by monitoring the Fe Kα centroid. Of all parameters, SMBH spin effects are most subtle and prone to measurement degeneracies. Some markers of high SMBH spin may nevertheless surface in the composite spectrum due to increased radiative efficiency. The approach developed here can be used to place preliminary constraints on binary parameters before a full parametrized X-ray spectral fitting method is available. It complements gravitational wave measurements by the Pulsar Timing Arrays (PTAs) and the Laser Interferometer Space Antenna by providing independent constraints on binary parameters that may be prone to degeneracy (inclination), or otherwise inaccessible (spin for PTAs).
ER -