A systematic search for close supermassive black hole binaries in the Catalina Real-time Transient Survey

By M. Graham, S. George Djorgovski, D. Stern, A. Drake, A. Mahabal, C. Donalek, E. Glikman, S. Larsen, E. Christensen. 2015

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Hierarchical assembly models predict a population of supermassive black hole (SMBH) binaries. These are not resolvable by direct imaging but may be detectable via periodic variability (or nanohertz frequency gravitational waves). Following our detection of a 5.2-year periodic signal in the quasar PG 1302−102, we present a novel analysis of the optical variability of 243 500 known spectroscopically confirmed quasars using data from the Catalina Real-time Transient Survey (CRTS) to look for close (<0.1 pc) SMBH systems. Looking for a strong Keplerian periodic signal with at least 1.5 cycles over a baseline of nine years, we find a sample of 111 candidate objects. This is in conservative agreement with theoretical predictions from models of binary SMBH populations. Simulated data sets, assuming stochastic variability, also produce no equivalent candidates implying a low likelihood of spurious detections. The periodicity seen is likely attributable to either jet precession, warped accretion discs or periodic accretion associated with a close SMBH binary system. We also consider how other SMBH binary candidates in the literature appear in CRTS data and show that none of these are equivalent to the identified objects. Finally, the distribution of objects found is consistent with that expected from a gravitational-wave-driven population. This implies that circumbinary gas is present at small orbital radii and is being perturbed by the black holes. None of the sources is expected to merge within at least the next century. This study opens a new unique window to study a population of close SMBH binaries that must exist according to our current understanding of galaxy and SMBH evolution.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/70d43a1db6e4e9e5b0833939ee77957ddf0525c8

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Citations in the corpus

The quest for dual and binary supermassive black holes: A multi-messenger view (2019, background): “This candidate was included in the sample of Graham et al. (2015), but was not identified as periodic.”
A Population of Short-Period Variable Quasars from PTF as Supermassive Black Hole Binary Candidates (2016, methodology): “…calibrated to Jonhson V -band (e.g., see § 3 in Drake et al. 2013), with a limiting magnitude of 19-21.5.2 A particularly compelling member of this sample, PG1302102, is a bright (median V-band mag ∼15) quasar at redshift z = 0.2784 with an observed period of 5.2± 0.2 yr (Graham et al. 2015b).”
The NANOGrav 15 yr Data Set: Constraints on Supermassive Black Hole Binaries from the Gravitational-wave Background (2023, background): “…light curves (Farris et al. 2014; D’Orazio et al. 2015; Bowen et al. 2018; D’Orazio & Di Stefano 2018) have yielded a similar number of candidates (Graham et al. 2015; Charisi et al. 2016; Liu et al. 2019), though these samples are likely to also suffer significant contamination (Vaughan et al.…”