Detection of a quasi-periodic oscillation in the optical light curve of the remarkable blazar AO 0235+164

We present a long term optical $R$ band light curve analysis of the gravitationally lensed blazar AO 0235+164 in the time span 1982 - 2019. Several methods of analysis lead to the result that there is a periodicity of ~8.13 years present in these data. In addition, each of these five major flares are apparently double-peaked, with the secondary peak following the primary one by ~2 years. Along with the well known system, OJ 287, our finding constitutes one of the most secure cases of long term quasi-periodic optical behaviour in a blazar ever found. A binary supermassive black hole system appears to provide a good explanation for these results.Comment: 7 pages, 3 figures, 1 table, Accepted for publication in MNRA