Discovery of a Candidate Binary Supermassive Black Hole in a Periodic Quasar from Circumbinary Accretion Variability
Creators: name: Liao, Wei-Ting
name: Chen, Yu-Ching
name: Liu, Xin
name: Holgado, A. Miguel
name: Guo, Hengxiao
name: Gruendl, Robert
name: Morganson, Eric
name: Shen, Yue
name: Davis, Tamara
name: Kessler, Richard
name: Martini, Paul
name: McMahon, Richard G.
name: Allam, Sahar
name: Annis, James
name: Avila, Santiago
name: Banerji, Manda
name: Bechtol, Keith
name: Bertin, Emmanuel
name: Brooks, David
name: Buckley-Geer, Elizabeth
name: Rosell, Aurelio Carnero
name: Kind, Matias Carrasco
name: Carretero, Jorge
name: Castander, Francisco Javier
name: Cunha, Carlos
name: D'Andrea, Chris
name: da Costa, Luiz
name: Davis, Christopher
name: De Vicente, Juan
name: Desai, Shantanu
name: Diehl, H. Thomas
name: Doel, Peter
name: Eifler, Tim
name: Evrard, August
name: Flaugher, Brenna
name: Fosalba, Pablo
name: Frieman, Josh
name: Garcia-Bellido, Juan
name: Gaztanaga, Enrique
name: Glazebrook, Karl
name: Gruen, Daniel
name: Gschwend, Julia
name: Gutierrez, Gaston
name: Hartley, Will
name: Hollowood, Devon L.
name: Honscheid, Klaus
name: Hoyle, Ben
name: James, David
name: Krause, Elisabeth
name: Kuehn, Kyler
name: Lima, Marcos
name: Maia, Marcio
name: Marshall, Jennifer
name: Menanteau, Felipe
name: Miquel, Ramon
name: Malagón, Andrés Plazas
name: Roodman, Aaron
name: Sanchez, Eusebio
name: Scarpine, Vic
name: Schubnell, Michael
name: Serrano, Santiago
name: Smith, Mathew
name: Smith, R. Chris
name: Soares-Santos, Marcelle
name: Sobreira, Flavia
name: Suchyta, Eric
name: Swanson, Molly
name: Tarle, Gregory
name: Vikram, Vinu
name: Walker, Alistair
name: Collaboration, the DES
Publisher: name: arXiv
Year: 2020
Subjects: subject: Astrophysics of Galaxies (astro-ph.GA)
subject: High Energy Astrophysical Phenomena (astro-ph.HE)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: Binary supermassive black holes (BSBHs) are expected to be a generic byproduct from hierarchical galaxy formation. The final coalescence of BSBHs is thought to be the loudest gravitational wave (GW) siren, yet no confirmed BSBH is known in the GW-dominated regime. While periodic quasars have been proposed as BSBH candidates, the physical origin of the periodicity has been largely uncertain. Here we report discovery of a periodicity (P=1607$\pm$7 days) at 99.95% significance (with a global p-value of ~$10^{-3}$ accounting for the look elsewhere effect) in the optical light curves of a redshift 1.53 quasar, SDSS J025214.67-002813.7. Combining archival Sloan Digital Sky Survey data with new, sensitive imaging from the Dark Energy Survey, the total ~20-yr time baseline spans ~4.6 cycles of the observed 4.4-yr (restframe 1.7-yr) periodicity. The light curves are best fit by a bursty model predicted by hydrodynamic simulations of circumbinary accretion disks. The periodicity is likely caused by accretion rate modulation by a milli-parsec BSBH emitting GWs, dynamically coupled to the circumbinary accretion disk. A bursty hydrodynamic variability model is statistically preferred over a smooth, sinusoidal model expected from relativistic Doppler boost, a kinematic effect proposed for PG1302-102. Furthermore, the frequency dependence of the variability amplitudes disfavors Doppler boost, lending independent support to the circumbinary accretion variability hypothesis. Given our detection rate of one BSBH candidate from circumbinary accretion variability out of 625 quasars, it suggests that future large, sensitive synoptic surveys such as the Vera C. Rubin Observatory Legacy Survey of Space and Time may be able to detect hundreds to thousands of candidate BSBHs from circumbinary accretion with direct implications for Laser Interferometer Space Antenna.
description: Accepted to MNRAS, 17 pages, 9 figures