Quasi-periodicities of BL Lacertae objects



: Sandrinelli A, Covino S, Treves A, Holgado AM, Sesana A, Lindfors E, Ramazani VF

Publisher: EDP SCIENCES S A

: 2018

: Astronomy and Astrophysics

: ASTRONOMY & ASTROPHYSICS

: ASTRON ASTROPHYS

: ARTN A118

: 615

: 5

: 1432-0746

DOI: https://doi.org/10.1051/0004-6361/201732550

: https://research.utu.fi/converis/portal/detail/Publication/35448573


We review the reports of possible year-long quasi-periodicities of BL Lac objects in the gamma-ray and optical bands, and present a homogeneous time analysis of the light curves of PKS2155-304, PG1553+113, and BL Lac. Based on results from a survey covering the entire Fermi gamma-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 z less than or similar to 1 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.

Last updated on 2024-26-11 at 21:27