A possible tidal disruption event candidate in the black hole binary system of OJ 287

TL;DR

This paper reports a potential tidal disruption event in the black hole binary system OJ 287, characterized by a unique multi-wavelength outburst with decay patterns consistent with TDEs, suggesting a new interpretation of the system's activity.

Contribution

The study presents evidence supporting a tidal disruption event as the cause of an unusual outburst in OJ 287, offering new insights into the system's complex physics and outburst mechanisms.

Findings

Soft X-ray luminosity decayed as t^{-5/3}, typical of TDEs.

Enhanced helium and oxygen emission lines post-outburst.

Outburst likely caused by a tidal disruption event.

Abstract

The BL Lacertae OJ 287 is a supermassive black holes binary (SMBHB) system with complex physics of its irregular flares. During 2016 October -- 2017 April period, a surprising outburst in the X-ray, UV and optical bands was detected, while no variability was seen in the $\gamma$-ray light curve. During the outburst, the X-ray light curves were dominated by the soft X-rays, whose peak in the luminosity was $\sim$ $10^{46}\text{erg}~\text{s}^{-1}$ -- more than 10 times higher than the mean level before the outburst -- and a "softer-when-brighter" phenomenon was exhibited. These above phenomena have been reported by some previous works. The hardness ratio showed negligible evolution with flare time and soft X-ray luminosity. Critically, the luminosity of the soft X-rays decayed following a power law of $t^{-5/3}$ which occurs in most tidal disruption events (TDEs), and similar trend can be seen in UV and optical bands during the soft X-ray declining period. Helium and oxygen narrow emission lines are strengthened prominently in the optical spectra of postoutburst epochs, that could be attributed to the surrounding gas appeared due to TDE. We discuss three possible origins of the event, including the jet's precession, the aftereffect of the black hole-disk impaction and the TDE. Our results show that the TDE is the more likely scenario to explain the outburst.