Holgado, A. MiguelA. MiguelHolgadoSESANA, ALBERTOALBERTOSESANASANDRINELLI, ANGELAANGELASANDRINELLICOVINO, StefanoStefanoCOVINOTreves, AldoAldoTrevesLiu, XinXinLiuRicker, PaulPaulRicker2020-10-152020-10-1520180035-8711http://hdl.handle.net/20.500.12386/27843Blazars 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<SUP>-3</SUP> of blazars hosts a binary with orbital periods <5 yr. We therefore conclude that binarity cannot significantly explain year-like quasi-periodicity in blazars.STAMPAenArticle10.1093/mnrasl/sly1582-s2.0-85054082502000451569100016https://academic.oup.com/mnrasl/article/481/1/L74/50876642018MNRAS.481L..74HFIS/05 - ASTRONOMIA E ASTROFISICAERC sectors::Physical Sciences and Engineering::PE9 Universe sciences: astro-physics/chemistry/biology; solar systems; stellar, galactic and extragalactic astronomy, planetary systems, cosmology, space science, instrumentation::PE9_13 Gravitational astronomy