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

TL;DR

This study identifies a significant ~8.13-year quasi-periodic oscillation in the optical light curve of the blazar AO 0235+164, supporting the binary black hole model as a plausible explanation.

Contribution

It provides one of the most secure detections of long-term quasi-periodic behavior in a blazar, using extensive data analysis over several decades.

Findings

Detected ~8.13-year periodicity in optical light curve

Observed double-peaked major flares with ~2-year separation

Supports binary supermassive black hole system hypothesis

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 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.