Abstract:
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 yr 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 yr.
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.
