Quasi-periodic Oscillation Analysis for the BL Lacertae Object 1823+568

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 similar or equal to 1.92 x 10(9) M-circle dot to 3.43 x 10(9) M-circle dot.