Quasi-periodic behaviour in the optical and γ-ray light curves of blazars 3C 66A and B2 1633+38

J. Otero-Santos, J. A. Acosta-Pulido, J. Becerra González, C. M. Raiteri, V. M. Larionov, P. Peñil, P. S. Smith, C. Ballester Niebla, G.A. Borman, M. I. Carnerero, N. Castro Segura, T. S. Grishina, E. N. Kopatskaya, E. G. Larionova, D. A. Morozova, A. A. Nikiforova, S. S. Savchenko, Yu. V. Troitskaya, I.S. Troitsky, A. A. VasilyevM. Villata

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We report on quasi-periodic variability found in two blazars included in the Steward Observatory Blazar Monitoring data sample: the BL Lac object 3C 66A and the Flat Spectrum Radio Quasar B2 1633+38. We collect optical photometric and polarimetric data in V and R bands of these sources from different observatories: St. Petersburg University, Crimean Astrophysical Observatory, WEBT-GASP, Catalina Real-Time Transient Survey, Steward Observatory, STELLA Robotic Observatory, and Katzman Automatic Imaging Telescope. In addition, an analysis of the γ-ray light curves from Fermi-LAT is included. Three methods are used to search for any periodic behaviour in the data: the Z-transform Discrete Correlation Function, the Lomb-Scargle periodogram and the Weighted Wavelet Z-transform. We find pieces of evidence of possible quasi-periodic variability in the optical photometric data of both sources with periods of ˜3 yr for 3C 66A and ˜1.9 yr for B2 1633+38, with significances between 3σ and 5σ. Only B2 1633+38 shows evidence of this behaviour in the optical polarized data set at a confidence level of 2σ-4σ. This is the first reported evidence of quasi-periodic behaviour in the optical light curve of B2 1633+38. Also, a hint of quasi-periodic behaviour is found in the γ-ray light curve of B2 1633+38 with a confidence level ≥2σ, while no periodicity is observed for 3C 66A in this energy range. We propose different jet emission models that could explain the quasi-periodic variability and the differences found between these two sources.
Original languageEnglish
Pages (from-to)5524-5539
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Publication statusPublished - 2020

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    Otero-Santos, J., Acosta-Pulido, J. A., Becerra González, J., Raiteri, C. M., Larionov, V. M., Peñil, P., Smith, P. S., Ballester Niebla, C., Borman, G. A., Carnerero, M. I., Castro Segura, N., Grishina, T. S., Kopatskaya, E. N., Larionova, E. G., Morozova, D. A., Nikiforova, A. A., Savchenko, S. S., Troitskaya, Y. V., Troitsky, I. S., ... Villata, M. (2020). Quasi-periodic behaviour in the optical and γ-ray light curves of blazars 3C 66A and B2 1633+38. Monthly Notices of the Royal Astronomical Society, 492(4), 5524-5539. https://doi.org/10.1093/mnras/staa134