Optical follow-up of the tick-tock massive black hole binary candidate

TL;DR

This study presents optical follow-up observations of a candidate massive black hole binary showing decreasing luminosity, challenging the binary interpretation and suggesting alternative explanations like relativistic precession.

Contribution

It provides new optical data on the tick-tock candidate and discusses alternative models to explain its light curve beyond the binary black hole scenario.

Findings

Observed decreasing luminosity in follow-up data.

Challenges binary scenario explanation.

Proposes relativistic precession as alternative.

Abstract

The observation of a population of massive black hole binaries (MBHBs) is key for our complete understanding of galaxy mergers and for the characterization of the expected gravitational waves (GWs) signal. However, MBHBs still remain elusive with only a few candidates proposed to date. Among these, SDSSJ143016.05+230344.4 ('tick-tock' hereafter) is the only candidate with a remarkably well sampled light curve showing a clear reduction of the modulation period and amplitude over three years of observations. This particular feature has been recently claimed to be the signature of a MBHB that is about to merge. In this paper, we provide an optical follow-up of the tick-tock source using the Rapid Eye Mount (REM) telescope. The decreasing luminosity observed in our follow up is hardly explained within the binary scenario. We speculate about an alternative scenario that might explain the observed light curve through relativistic Lense-Thirring precession of an accretion disc around a single massive black hole.