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

Journal Article · Thu Jan 16 00:00:00 EST 2020 · Monthly Notices of the Royal Astronomical Society

DOI:https://doi.org/10.1093/mnras/staa134· OSTI ID:1598907

Otero-Santos, J.  ^[1]; Acosta-Pulido, J. A. ^[1]; Becerra González, J. ^[1]; Raiteri, C. M.  ^[2]; Larionov, V. M.  ^[3]; Peñil, P. ^[4]; Smith, P. S. ^[5]; Ballester Niebla, C. ^[6]; Borman, G. A. ^[7]; Carnerero, M. I. ^[2]; Castro Segura, N. ^[8]; Grishina, T. S. ^[9]; Kopatskaya, E. N. ^[9]; Larionova, E. G. ^[9]; Morozova, D. A. ^[9]; Nikiforova, A. A. ^[3]; Savchenko, S. S. ^[9]; Troitskaya, Yu V. ^[9]; Troitsky, I. S. ^[9]; Vasilyev, A. A. ^[9] ; Villata, M. ^[2]

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1. Instituto de Astrofísica de Canarias (IAC), E-38200 La Laguna, Tenerife, Spain, Departamento de Astrofísica, Universidad de La Laguna (ULL), E-38206 La Laguna, Tenerife, Spain
2. INAF-Osservatorio Astrofisico di Torino, via Osservatorio 20, I-10025 Pino Torinese, Italy
3. Astronomical Institute, St Petersburg State University, Universitetskij Pr. 28, Petrodvorets, 198504 St Petersburg, Russia, Pulkovo Astronomical Observatory of RAS, Pulkovskoye shosse 60, 196149 St Petersburg, Russia
4. IPARCOS and Department of EMFTEL, Universidad Complutense de Madrid, E-28040 Madrid, Spain
5. Steward Observatory, University of Arizona, Tucson, AZ 85721, USA
6. Facultad de Ciencias, Universidad de La Laguna (ULL), E-38206 La Laguna, Tenerife, Spain
7. Crimean Astrophysical Observatory, P/O Nauchny, 298409 Crimea
8. Departamento de Astrofísica, Universidad de La Laguna (ULL), E-38206 La Laguna, Tenerife, Spain, School of Physics & Astronomy, University of Southampton, Highfield, SO17 1BJ Southampton, UK
9. Astronomical Institute, St Petersburg State University, Universitetskij Pr. 28, Petrodvorets, 198504 St Petersburg, Russia

ABSTRACT 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.

• Sponsoring Organization: USDOE
• Grant/Contract Number: AC02-76SF00515; NNX08AW56G; NNX09AU10G; NNX12AO93G; NNX15AU81G
• OSTI ID: 1598907
• Journal Information: Monthly Notices of the Royal Astronomical Society, Journal Name: Monthly Notices of the Royal Astronomical Society Vol. 492 Journal Issue: 4; ISSN 0035-8711
• Publisher: Oxford University Press
• Country of Publication: United Kingdom
• Language: English