About 300 days Optical Quasi-periodic Oscillations in the Long-term Light Curves of the Blazar PKS 2155-304

Based on the long-term light curves collected from the Catalina Sky Survey (CSS) (from 2005 to 2013) and the All-Sky Automated Survey for Supernovae (ASAS-SN) (from 2014 to 2018), optical quasi-periodic oscillations (QPOs) about 300 days can be well determined in the well-known blazar PKS 2155-304 through four different methods: the generalized Lomb-Scargle periodogram (GLSP) method, the weighted wavelet Z-transform technique, the epoch-folded method and the redfit method. The GLSP determined significance level for the periodicity is higher than 99.9999% based on a false alarm probability. The redfit provided confidence level for the periodicity is higher than 99% in the ASAS-SN light curve, after considering the effects of red noise. Based on continuous autoregressive process created artificial light curves, the probability of detecting fake QPOs is lower than 0.8%. The determined optical periodicity of 300 days from the CSS and ASAS-SN light curves is well consistent with the reported optical periodicity in the literature. Moreover, three possible models are discussed to explain the optical QPOs in PKS 2155-304: the relativistic frame-dragging effect, the binary black hole model and the jet precession model.