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

Journal
Date Issued
2020
Author(s)
Otero-Santos, J.
•
Acosta-Pulido, J. A.
•
Becerra González, J.
•
•
Larionov, V. M.
•
Peñil, P.
•
Smith, P. S.
•
Ballester Niebla, C.
•
Borman, G. A.
•
•
Castro Segura, N.
•
Grishina, T. S.
•
Kopatskaya, E. N.
•
Larionova, E. G.
•
Morozova, D. A.
•
Nikiforova, A. A.
•
Savchenko, S. S.
•
Troitskaya, Yu V.
•
Troitsky, I. S.
•
Vasilyev, A. A.
•
DOI
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.
Volume
492
Issue
4
Start page
5524
Uri
Url
Issn Identifier
0035-8711
Ads BibCode
2020MNRAS.492.5524O
Rights
open.access
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