11 research outputs found
Quasar physical pairs.
Osservatorio di Brera, Merate - Osservatorio astronomico di Padova, Padova.openopenAstronomia e AstrofisicaTREVES, ALDOSandrinelli, AngelaSandrinelli, Angel
Pulsar Timing Constraints on the Fermi Massive Black-Hole Binary Blazar Population
Blazars are a sub-population of quasars whose jets are nearly aligned with
the line-of-sight, which tend to exhibit multi-wavelength variability on a
variety of timescales. Quasi-periodic variability on year-like timescales 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 \textit{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 , 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 of blazars hosts a binary with orbital periods years. We
therefore conclude that binarity cannot significantly explain year-like
quasi-periodicity in blazars.Comment: 5 pages, 4 figures, accepted by MNRAS Letter
Quasi-periodicities of BL Lac Objects
We review the reports of possible year-long quasi-periodicities of BL Lac
objects in the -ray and optical bands, and present a homogeneous time
analysis of the light curves of PKS2155304, PG1553+113, and BL Lac. Based on
results from a survey covering the entire Fermi -ray sky we have
estimated the fraction of possible quasi-periodic BL Lac objects. We compared
the cyclical behaviour in BL Lac objects with that derived from the search of
possible optical periodicities in quasars, and find that at z1 the
cosmic density of quasi-periodic BL Lac objects is larger than that of
quasi-periodic quasars. If the BL Lac quasi-periodicities were due to a
supermassive binary black hole (SBBH) scenario, there could be a tension with
the upper limits on the gravitational wave background measured by the pulsar
timing array. The argument clearly indicates the difficulties of generally
associating quasi-periodicities of BL Lac objects with SBBHs.Comment: In publication on A&A, 6 pages, 4 figure (11 plots). Minor
corrections adde
Quasi-Periodicities at Year Time Scales in Blazars
We examine the 2008-2016 gamma-ray and optical light curves of a number of bright Fermi blazars. In a fraction of them, the periodograms show possible evidence of quasi-periodicities related in the two bands. This coincidence strengthens their physical meaning. Comparing with results from the periodicity search of quasars, the presence of quasi-periodicities in blazars suggests that the basic condition for its observability is related to the relativistic jet in the observer direction, but the overall picture remains uncertain