Pulsar timing constraints on the Fermi massive black hole binary blazar population. (30th August 2018)

• Record Type: Journal Article
• Authors: Holgado, A Miguel; Sesana, Alberto; Sandrinelli, Angela; Covino, Stefano; Treves, Aldo; Liu, Xin; Ricker, Paul
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 481:Number 1(2018:Nov.)
• Page Start: 74
• Page End: 78
• Publication Date: 2018-08-30
• Subjects: gravitational waves -- BL Lacertae objects: general -- galaxies: active -- pulsars:general -- quasars: supermassive black holes; Astronomy -- Research -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnrasl/sly158
• Languages: English
• ISSNs: 1745-3933

Abstract

ABSTRACT: Blazars are a subpopulation of quasars whose jets are nearly aligned with the line of sight, which tend to exhibit multiwavelength variability on a variety of time-scales. Quasi-periodic variability on year-like time-scales has been detected in a number of bright sources, and has been connected to the orbital motion of a putative massive black hole binary. If this were indeed the case, those blazar binaries would contribute to the nanohertz gravitational-wave stochastic background. We test the binary hypothesis for the blazar population observed by the Fermi Gamma-Ray Space Telescope, which consists of BL Lacertae objects and flat-spectrum radio quasars. Using mock populations informed by the luminosity functions for BL Lacertae objects and flat-spectrum radio quasars with redshifts z ≤ 2, we calculate the expected gravitational-wave background and compare it to recent pulsar timing array upper limits. The two are consistent only if a fraction ≲10 −3 of blazars hosts a binary with orbital periods <5 yr. We therefore conclude that binarity cannot significantly explain year-like quasi-periodicity in blazars.