X-Ray Reflection Signatures of Supermassive Black Hole Binaries

Malewicz J, Ballantyne DR, Bogdanović T, Brenneman L, Dauser T (2025)

Publication Type: Journal article

Publication year: 2025

Journal

Astrophysical Journal American Astronomical Society

Book Volume: 989

Article Number: 190

Journal Issue: 2

DOI: 10.3847/1538-4357/adea75

Abstract

We investigate the presence of supermassive black hole (SMBH) binary signatures and the feasibility of identifying them through X-ray reflection spectra. The X-ray emitting region is modeled as a set of two mini-disks bound to the individual SMBHs separated by 100 GM/c2 and the spectra calculated as a function of the mass, mass ratio, and total accretion rate of the binary. The X-ray reflection features are strongly influenced by the accretion-inversion phenomenon expected in SMBH binaries, which results in a wide range of ionization conditions in the two mini-disks. These are imprinted in the resulting composite spectra and the double-peaked and time-variable relativistic Fe Kα line profiles. To test whether these features can be used as evidence for the presence of an SMBH binary, we fit mock 100 ks observations with a single active galactic nucleus (AGN) model. For a 109 M⊙ binary targeted by pulsar timing arrays (PTAs), at z = 0.1, the single AGN model clearly fails to fit the data, while at z = 1, the fit is acceptable but unable to converge on the SMBH spin. For a 106 M⊙ binary, a progenitor of a Laser Interferometer Space Antenna (LISA) source, spectral fitting is only possible at z = 0.1, with the outcomes similar to the PTA binary at z = 1. We also find that PTA binaries can be expected to show a distinct X-ray spectral variability in multiepoch observations, whereas for LISA precursors, orbital averaging results in the loss of spectral variability signatures.

Authors with CRIS profile

Thomas Dauser Dr.Karl-Remeis-Sternwarte Bamberg, Astronomisches Institut

Involved external institutions

Georgia Institute of Technology US United States (USA) (US) Smithsonian Institution US United States (USA) (US)

How to cite

APA:

Malewicz, J., Ballantyne, D.R., Bogdanović, T., Brenneman, L., & Dauser, T. (2025). X-Ray Reflection Signatures of Supermassive Black Hole Binaries. Astrophysical Journal, 989(2). https://doi.org/10.3847/1538-4357/adea75

MLA:

Malewicz, Julie, et al. "X-Ray Reflection Signatures of Supermassive Black Hole Binaries." Astrophysical Journal 989.2 (2025).

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