Electromagnetic Counterparts Powered by Kicked Remnants of Black Hole Binary Mergers in AGN Disks

Abstract

The disk of an active galactic nucleus (AGN) is widely regarded as a prominent formation channel of binary black hole (BBH) mergers that can be detected through gravitational waves (GWs). Besides, the presence of dense environmental gas offers the potential for an embedded BBH merger to produce electromagnetic (EM) counterparts. In this paper, we investigate EM emission powered by the kicked remnant of a BBH merger occurring within the AGN disk. The remnant BH will launch a jet via the accretion of a magnetized medium as it traverses the disk. The resulting jet will decelerate and dissipate energy into a lateral cocoon as it propagates. We explore three radiation mechanisms of the jet–cocoon system—jet breakout emission, disk cocoon cooling emission, and jet cocoon cooling emission—and find that the jet cocoon cooling emission is likely to be detected in its own frequency bands. We predict a soft X-ray transient, lasting for O(103) s, to serve as an EM counterpart, of which the time delay O(10) days after the GW trigger contributes to follow-up observations. Consequently, BBH mergers in the AGN disk represent a novel multimessenger source. In the future, enhanced precision in measuring and localizing GWs, coupled with diligent searches for such associated EM signals, will effectively validate or restrict the origin of BBH mergers in the AGN disk.

Accretion-modified Stars in Accretion Disks of Active Galactic Nuclei: Observational Characteristics in Different Regions of the Disks

“…Numerous compact objects in the AGN disk inevitably form binary systems (Tagawa et al 2020;Rowan et al 2023;Wang et al 2024) via Jacobi capture (Wang et al 2021b), GW emission (Rom et al 2024), dynamical friction (Qian et al 2024), or the collision of their circumsingle disks (J. . Simulations of BBH evolution show that the complex interactions between the BBH and AGN disk induce the contraction of the BBH separation Li & Lai 2022;Dittmann et al 2024), leading to BBH mergers (Bartos et al 2017;Yang et al 2019;Yi & Cheng 2019;McKernan et al 2020;Samsing et al 2022), often followed by electromagnetic flares (Wang et al 2021b;Chen & Dai 2024;Tagawa et al 2023c), such as GRBs ( Perna et al 2021a;Lazzati et al 2022;Yuan et al 2022;Ray et al 2023) and GRB afterglow (Wang et al 2022). Additionally, WD collisions (Luo et al 2023;Zhang et al 2023) and kilonova emission from NS-NS/BH-NS mergers (Zhu et al 2021b;Ren et al 2022;Kathirgamaraju et al 2023) are also important probes for studying compact objects in AGN disks.…”

High-energy Neutrinos from Outflows Powered by the Kicked Remnants of Binary Black Hole Mergers in Active Galactic Nucleus Accretion Disks

“…Especially, among these compact object mergers in AGN disks, BBH mergers have attracted the most attention since they have been prime targets for Earth-based gravitational wave (GW) detectors. Another important point is that BBH mergers embedded in AGN disks can potentially power their electromagnetic (EM) counterparts by accreting the abundant disk gas (Kimura et al 2021;Wang et al 2021;Tagawa et al 2022;Chen & Dai 2024), while in normal environment, accompanying EM radiation from BBH mergers is not expected because there is no accretion material to power a jet. Recently, seven AGN flares have been suggested to have a statistical association with LIGO/ Virgo BBH merging events (Graham et al 2023).…”