Gamma-ray and optical oscillations of 0716+714, MRK 421, and BL Lacertae

: Sandrinelli A, Covino S, Treves A, Lindfors E, Raiteri CM, Nilsson K, Takalo LO, Reinthal R, Berdyugin A, Ramazani VF, Kadenius V, Tuominen T, Kehusmaa P, Bachev R, Strigachev A

Publisher: EDP SCIENCES S A

: 2017

Astronomy and Astrophysics

: ASTRONOMY & ASTROPHYSICS

: ASTRON ASTROPHYS

: ARTN A132

: 600

: 7

: 1432-0746

DOI: https://doi.org/10.1051/0004-6361/201630288

: https://arxiv.org/abs/1701.04454

We examine the 2008-2016 gamma-ray and optical light curves of three bright BL Lac objects, 0716+714, MRK421, BL Lac, which exhibit large structured variability. We searched for periodicities by using a fully Bayesian approach. For two out of three sources investigated, no significant periodic variability was found. In the case of BL Lac, we detected a periodicity of similar to 680 days. Although the signal related to this is modest, the coincidence of the periods in both gamma and optical bands is indicative of a physical relevance. Taking into consideration previous literature results, possibly related gamma-ray and optical periodicities of about one year time scale are proposed in four bright gamma-ray blazars out of the ten examined in detail. Compared with results from periodicity search of optical archives of quasars, the presence of quasi-periodicities in blazars may be more frequent by a large factor. This suggests the intriguing possibility that the basic conditions for their observability are related to the relativistic jet in the observer direction, but the overall picture remains uncertain.

BL Lacertae objects: general, BL Lacertae objects: individual: BL Lac, BL Lacertae objects: individual: Mrk 421, BL Lacertae objects: individual: PKS 0716+71, gamma rays: galaxies