SIMBAD references

Context. Quasi-periodic behavior in the light curves of blazars can help us understand the physics. The identification of the supermassive black hole binary (SMBHB) is an active topic, and the periodicity analysis of light curves is a powerful method for searching for these sources.
Aims. In this work, we aim to identify quasi-periodic oscillations (QPOs) in the optical band light curves in our sample and discuss the possible physical origins behind these targets.
Methods. In this study, we collected 155 optical band light curves from three different monitoring programs. We searched for QPOs in our sample using the generalised Lomb-Scargle (GLS) and weighted wavelet Z-transform (WWZ) methods. We simulated 10⁴ artificial light curves and evaluated the significance of the results using the Monte Carlo method.
Results. Our work reveals that 18 targets show QPOs with timescales ranging from 200 days to 1400 days. These QPOs could be explained by three scenarios, including the SMBHB, instability of thick disks and jet precession. Since the frequencies corresponding to QPOs are in the nHz regime, our work provides candidates of SMBHBs for further verification.