Pulsar timing constraints on the Fermi massive black hole binary blazar population

A. Miguel Holgado, Alberto Sesana, Angela Sandrinelli, Stefano Covino, Aldo Treves, Xin Liu, Paul Milton Ricker

Research output: Contribution to journalArticlepeer-review


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 flatspectrum radio quasars. Using mock populations informed by the luminosity functions for BL Lacertae objects and flat-spectrum radio quasarswith 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.

Original languageEnglish (US)
Pages (from-to)L74-L78
Number of pages5
JournalMonthly Notices of the Royal Astronomical Society: Letters
Issue number1
StatePublished - Nov 21 2018


  • BL Lacertae objects: general
  • Galaxies: active
  • Gravitational waves
  • Pulsars:general
  • Quasars: supermassive black holes

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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