Optical Emission Model for Binary Black Hole Merger Remnants Travelling through Discs of Active Galactic Nucleus

Abstract

Active galactic nuclei (AGNs) have been proposed as plausible sites hosting a sizable fraction of the binary black hole (BBH) mergers measured through gravitational waves (GWs) by the LIGO-Virgo-Kagra (LVK) experiment. These GWs could be accompanied by radiation feedback due to the interaction of the BBH merger remnant with the AGN disc. We present a new predicted radiation signature driven by the passage of a kicked BBH remnant throughout a thin AGN disc. We analyse the situation of a merger occurring outside the thin disc, where the merger is of second or higher generation in a merging hierarchical sequence. The coalescence produces a kicked BH remnant that eventually plunges into the disc, accretes material, and inflates jet cocoons. We consider the case of a jet cocoon propagating quasi-parallel to the disc plane and study the outflow that results when the cocoon emerges from the disc. Here we focus on the long time-scale emission produced after the disc outflow expands and becomes optically thin. The bolometric luminosity of such disc outflow evolves as $L\propto t^{-7/2}$. Depending on the parameter configuration, the flare produced by the disc outflow could be comparable to or exceed the AGN background emission at near-infrared, optical, and extreme ultraviolet wavelengths appearing $\sim$[20-500] days after the GW event and lasting for $\sim$[1-200] days, accordingly.Comment: 11 pages, 8 figures. Submitted to MNRA