Detection of ~100 days periodicity in the gamma-ray light curve of the BL Lac 4FGL 2022.7+4216

Abstract

Study of quasi-periodic oscillations (QPO) in blazars is one of the crucial methods for gaining insights into the workings of the central engines of active galactic nuclei. QPOs with various characteristic time scales have been observed in the multi-wavelength emission of blazars, ranging from the radio to gamma-ray frequency bands. In this study, we carry out a comprehensive variability analysis of the BL Lac object 4FGL 2022.7+4216 detected by the \textit{Fermi-}LAT, over a period of more than three years, from April 27, 2019 to August 09, 2022. By utilizing multiple widely-used methods of time-series analyses, we detect the presence of quasi-periodic fluctuations with a period of $\sim$100 days with a confidence level exceeding $4\sigma$. This is the first time such a variability feature pertaining to this source is being reported. We propose that the observed QPO 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. However, for a decisive conclusion on the physical origin of such fluctuation, further multi-wavelength complementary observations, especially Very Long Baseline Interferometric observations, would be required.