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  • Gamma-ray and optical oscil...
    Sandrinelli, A.; Covino, S.; Treves, A.; Lindfors, E.; Raiteri, C. M.; Nilsson, K.; Takalo, L. O.; Reinthal, R.; Berdyugin, A.; Fallah Ramazani, V.; Kadenius, V.; Tuominen, T.; Kehusmaa, P.; Bachev, R.; Strigachev, A.

    Astronomy & astrophysics, 04/2017, Volume: 600
    Journal Article

    We examine the 2008–2016 γ-ray and optical light curves of three bright BL Lac objects, 0716+714, MRK 421, 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 ~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 γ-ray and optical periodicities of about one year time scale are proposed in four bright γ-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.