Detection of periodicity in the gamma-ray light curve of the BL Lac 4FGL J2202.7+4216

Abstract

ABSTRACT In this study, we carry out a comprehensive variability analysis of the BL Lac object 4FGL J2202.7+4216 detected by the Fermi-LAT, over a period of more than 3 yr, from 2019 April 27 to 2022 August 09. We detect the presence of quasi-periodic fluctuations with a period of ∼100 d with a confidence level exceeding 4σ. We also tentatively detect two other quasi-periodic fluctuations with a period of ∼75 and ∼50 d, which persist over the entire duration of observation. This is the first time such a variability feature pertaining to this source is being reported. We propose that the observed quasi-periodic oscillations may be related to the precession of the blazar jet with a high Lorentz factor or to the motion of a plasma blob through the helical structure of the jet. The harmonicity among the detected periodicities suggests the global p-mode oscillations of the thick disc to be a plausible mechanism as well. For a decisive conclusion on the physical origin of such fluctuation, further multiwavelength complementary observations, especially very long baseline interferometric observations, would be required.