Precursor flares in OJ 287
  We have studied three most recent precursor flares in the light curve of the blazar OJ 287 while invoking the presence of a precessing binary black hole in the system to explain the nature of these flares. Precursor flare timings from the historical light curves are compared with theoretical predictions from our model that incorporate effects of an accretion disk and post-Newtonian description for the binary black hole orbit. We find that the precursor flares coincide with the secondary black hole descending towards the accretion disk of the primary black hole from the observed side, with a mean z-component of approximately z_c = 4000 AU. We use this model of precursor flares to predict that precursor flare of similar nature should happen around 2020.96 before the next major outburst in 2022. 
P. Pihajoki, M. Valtonen, S. Zola, A. Liakos, M. Drozdz, M. Winiarski,   W. Ogloza, D. Koziel-Wierzbowska, J. Provencal, K. ...
astro-ph.HE