2022RAA....22e5017L

We studied the optical band periodic variability of 1823+568 using the Jurkevich method, the Lomb-Scargle periodogram and the REDFIT38 software, and found evidence of quasi-periodic oscillation. An unprecedented variability with period P = 283_–13⁺¹⁷ days was identified by three different analysis methods. This quasi-periodic variability most likely results from nonballistic helical jet motion driven by the orbital motion in a binary black hole system. Considering the light-travel time effect, the real physical period is P_d = 67.1 yr. Moreover, we estimated that the primary black hole mass is M ≃ 1.92 x 10⁹ M_☉ to 3.43 x 10⁹ M_☉.