A. Roy, V.R. Chitnis, A.C. Gupta, P.J. Wiita, G.E. Romero, S.A. Cellone, A. Chatterjee, J.A. Combi, C.M. Raiteri, A. Sarkar, M. Villata

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.