The detection of possible $γ$-ray quasi-periodic modulation with $\sim$600 days from the blazar S2 0109+22

Abstract: In this work, we analyzed the long term gamma-ray data by a Fermi Large Area Telescope (Fermi-LAT) of blazar S2 0109+22, ranging from 2008 to 2023. The quasi-periodic oscillations (QPOs) of blazars aided in investigating the physical properties of internal supermassive black holes, the nature of variability, and the underlying radiation mechanism. We employed four different methods--Weighted Wavelet Z-transform, Lomb-Scargle periodogram, REDFIT and phase folded light curve analysis, for searching QPO signals. Our analysis identified a possible QPO behavior with a periodicity of $\sim$600 days in November 2013 to January 2023 at a significance level of 3.5 $\sigma$. This QPO signal sustained $\sim$9 years, corresponding to 5.6 cycles, which was in good agreement with the previously observed of periodicity $\sim$657 days in radio. We explained this phenomenon based on the accretion model and the lighthouse effect, in a binary black hole system.