Volume 600, April 2017
|Number of page(s)||7|
|Published online||13 April 2017|
Gamma-ray and optical oscillations of 0716+714, MRK 421, and BL Lacertae
1 Università dell’Insubria, Dipartimento di Scienza ed Alta Tecnologia, via Valleggio 11, 22100 Como, Italy
2 INAF–Istituto Nazionale di Astrofisica, Osservatorio Astronomico di Brera, via Bianchi 46, 23807 Merate (LC), Italy
3 INFN–Istituto Nazionale di Fisica Nucleare, Sezione Trieste – Udine, via Valerio 2, 34127 Trieste, Italy
4 Tuorla Observatory, Department of Physics and Astronomy, University of Turku, 20500 Turku, Finland
5 INAF–Istituto Nazionale di Astrofisica, Osservatorio Astrofisico di Torino, via Osservatorio 20, 10025 Pino Torinese, Italy
6 FINCA–Centre for Astronomy with ESO, University of Turku, 20500 Turku, Finland
7 Harlingten New Mexico Observatory, USA
8 Institute of Astronomy, Bulgarian Academy of Sciences, 72 Tsarigradsko shosse Blvd., 1784 Sofia, Bulgaria
Received: 19 December 2016
Accepted: 16 January 2017
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.
Key words: gamma rays: galaxies / BL Lacertae objects: general / galaxies: jets / BL Lacertae objects: individual: PKS 0716+71 / BL Lacertae objects: individual: MRK 421 / BL Lacertae objects: individual: BL Lac
© ESO, 2017
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