Multiband optical photometric variability of the blazar OJ 287 from 2015 to 2025

Abstract

We present the most densely sampled multiband optical photometric observations of the peculiar BL Lacertae object OJ 287 from 2015 to 2025 with a focus on its optical activity on diverse timescales. We present a total of 2296, 10,927, 11,484, and 2982 data points in B, V, R, and I bands, respectively. The densely sampled observations allow us to keep track of the source evolution that it has exhibited since the start of the predicted major optical flaring activity at the end of 2015. The study reveals clear and persistent bluer-when-brighter trends in both the long-term and short-term variations. Different bands were cross-correlated with discrete correlation functions, which peak at zero lag, implying cospatial emission. Using eight optical spectra in the low-flux states of OJ 287 taken from 2017 October 21 to 2017 November 22, from Steward Observatory, we estimate the central black hole mass to be at least 3.89 × 109 M⊙ from the [O III] line width. The emission mechanism of the binary black hole blazar, and its possible implication in various aspects of multimessenger astronomy, are briefly discussed.