NuSTAR Observations of Candidate Subparsec Binary Supermassive Black Holes

M. Lynne Saade, Murray Brightman, Daniel Stern, Thomas Connor, S. G. Djorgovski, Daniel J. D’Orazio, K. E. S. Ford, Matthew J. Graham, Zoltán Haiman, Hyunsung D. Jun, Elias Kammoun, Ralph P. Kraft, Barry McKernan, Alexei Vikhlinin, Dominic J. Walton

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We present an analysis of NuSTAR X-ray observations of three active galactic nuclei (AGN) that were identified as candidate subparsec binary supermassive black hole (SMBH) systems in the Catalina Real-Time Transient Survey based on apparent periodicity in their optical light curves. Simulations predict that close-separation accreting SMBH binaries will have different X-ray spectra than single accreting SMBHs. We previously observed these AGN with Chandra and found no differences between their low-energy X-ray properties and the larger AGN population. However, some models predict differences to be more prominent at energies higher than probed by Chandra. We find that even at the higher energies probed by NuSTAR, the spectra of these AGN are indistinguishable from the larger AGN population. This could rule out models predicting large differences in the X-ray spectra in the NuSTAR bands. Alternatively, it might mean that these three AGN are not binary SMBHs.
Original languageEnglish
Article number104
Pages (from-to)1-10
Number of pages10
JournalThe Astrophysical Journal
Issue number1
Early online date29 Apr 2024
Publication statusPublished - 1 May 2024


  • X-ray active galactic nuclei
  • Seyfert galaxies
  • Supermassive black holes
  • Quasars


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