The BAT AGN spectroscopic survey – XVIII. Searching for supermassive black hole binaries in the x-rays

Tingting Liu, Michael Koss, Laura Blecha, Claudio Ricci, Benny Trakhtenbrot, Richard Mushotzky, Fiona Harrison, Kohei Ichikawa, Darshan Kakkad, Kyuseok Oh, Meredith Powell, George C. Privon, Kevin Schawinski, T. Taro Shimizu, Krista Lynne Smith, Daniel Stern, Ezequiel Treister, C. Megan Urry

Research output: Contribution to journalArticlepeer-review


Theory predicts that a supermassive black hole binary (SMBHB) could be observed as a luminous active galactic nucleus (AGN) that periodically varies on the order of its orbital timescale. In X-rays, periodic variations could be caused by mechanisms including relativistic Doppler boosting and shocks. Here we present the first systematic search for periodic AGNs using 941 hard X-ray light curves (14–195 keV) from the first 105 months of the Swift Burst Alert Telescope (BAT) survey (2004-2013). While we do not find evidence for periodic AGNs in Swift-BAT, we have investigated the detectability of SMBHBs in the context of the eROSITA survey by adopting prescriptions for AGN X-ray variability and the periodic variability from a population of SMBHBs and assuming weekly and monthly temporal sampling rates. Even under generous assumptions about the binary population in AGNs, the detectable fraction is modest due to the challenge of distinguishing the periodic signal from normal AGN variability. Due to this effect of “red noise”, we instead find that the search for SMBHBs would greatly benefit from sampling a large number of AGNs at lower cadence.

Original languageEnglish
JournalUnknown Journal
Publication statusPublished - 2019 Dec 5


  • Active galaxies
  • Surveys
  • X-ray sources

ASJC Scopus subject areas

  • General

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