2022MNRAS.512.1003Z

In this manuscript, a 6.4-yr optical quasi-periodic oscillations (QPOs) is detected in the quasar SDSS J075217.84+193542.2 (=+SDSS J0752) at a redshift 0.117, of which 13.6-yr-long light curve from Catalina Sky Survey and All-Sky Automated Survey for Supernovae is directly described by a sinusoidal function with a periodicity 6.4 yr. The 6.4-yr QPOs can be further confirmed through the generalized Lomb-Scargle periodogram with confidence level higher than 99.99 per cent, and through the autocorrelation analysis results, and through the weighted wavelet z-transformation technique. The optical QPOs strongly indicate a central binary black hole (BBH) system in SDSS J0752. The determined two broad Gaussian components in the broad H α can lead to the BBH system with expected space separation about 0.02 pc between the expected two central BHs with determined virial BH masses about 8.8 x 10⁷ and 1.04 x 10⁹ M_☉. Meanwhile, we check the disc precessions applied to explain the optical QPOs. However, under the disc precession assumption, the determined optical emission regions from central BH have sizes about 40R_G two times smaller than sizes of the expected Near UltraViolet (NUV) emission regions through the correlation between disc size and BH mass, indicating the disc precessions are not preferred. And due to the lower radio loudness around 0.28, jet precessions can be also totally ruled out. Furthermore, only 0.08 per cent probability can determined as the QPOs misdetected through light curves randomly created by the continuous autoregressive process, reconfirming the reported optical QPOs.