A1 Journal article – refereed
Gamma-ray and optical oscillations of 0716+714, MRK 421, and BL Lacertae
List of Authors: 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
Publication year: 2017
Journal: Astronomy and Astrophysics
Journal name in source: ASTRONOMY & ASTROPHYSICS
Journal acronym: ASTRON ASTROPHYS
Volume number: 600
ISSN: 1432-0746
eISSN: 1432-0746
Abstract
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.