Outflow Bubbles from Compact Binary Mergers Embedded in Active Galactic Nuclei: Cavity Formation and the Impact on Electromagnetic Counterparts

TL;DR

This paper explores how outflows from compact binary mergers in AGN disks create cavities that suppress electromagnetic counterparts, but under certain conditions, bright X-ray emissions from cavity breakouts could be observable.

Contribution

It introduces a new scenario where outflow cavities formed by mergers in AGN disks affect EM counterpart detectability and discusses conditions for observable breakout emissions.

Findings

Outflows form cavities in AGN disks before mergers.

Cavities reduce the likelihood of EM counterparts.

Cavity breakouts can produce detectable X-ray signals.

Abstract

We propose a novel scenario for possible electromagnetic (EM) emission by compact binary mergers in the accretion disks of active galactic nuclei (AGNs). Nuclear star clusters in AGNs are a plausible formation site of compact-stellar binaries (CSBs) whose coalescences can be detected through gravitational waves (GWs). We investigate the accretion onto and outflows from CSBs embedded in AGN disks. We show that these outflows are likely to create outflow "cavities" in the AGN disks before the binaries merge, which makes EM or neutrino counterparts much less common than would otherwise be expected. We discuss the necessary conditions for detectable EM counterparts to mergers inside the outflow cavities. If the merger remnant black hole experiences a high recoil velocity and can enter the AGN disk, it can accrete gas with a super-Eddington rate, newly forming a cavity-like structure. This bubble can break out of the disk within a day to a week after the merger. Such breakout emission can be bright enough to be detectable by current soft X-ray instruments, such as Swift-XRT and Chandra.