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

**Authors:** Ken Chen, Zi-Gao Dai  
**arXiv:** [2311.10518](https://arxiv.org/abs/2311.10518)  
**Date:** 2023-11-17  
**Summary page:** https://www.summarizepaper.com/en/paper/2311.10518v1/

## Key points

- The disk of an active galactic nucleus (AGN) is a source of binary black hole (BBH) mergers detected through gravitational waves (GWs)
- BBH mergers in AGN disks can produce electromagnetic (EM) counterparts due to dense environmental gas
- Study investigates EM emission powered by the kicked remnant of a BBH merger within the AGN disk
- Remnant black hole launches a jet that decelerates and dissipates energy into a lateral cocoon
- Three radiation mechanisms explored: jet breakout emission, disk cocoon cooling emission, and jet cocoon cooling emission
- Jet cocoon cooling emission is most likely detection in its own frequency bands
- Predicted as soft X-ray transient lasting for approximately O($10^3$) seconds
- Time delay of around O(10) days after GW trigger before EM counterpart occurs, allowing for follow-up observations
- BBH mergers in AGN disks are a novel multimessenger source
- Properties of telescopes summarized in Table 3 of Tagawa et al.'s work from 2023a provide additional context
- Variations in observable duration and spectra discussed by Chen & Dai based on BH mass and mass distribution of jet cocoon material
- Soft X-ray telescopes like Chandra, XMM-Newton, and Swift XRT recommended for observing softer X-ray band spectra.

## Summary

The disk of an active galactic nucleus (AGN) is known to be a significant source of binary black hole (BBH) mergers that can be detected through gravitational waves (GWs). Additionally, the presence of dense environmental gas in AGN offers the potential for these mergers to produce electromagnetic (EM) counterparts. In this study, the authors investigate the electromagnetic emission powered by the kicked remnant of a BBH merger occurring within the AGN disk. The remnant black hole (BH) launches a jet as it accretes magnetized medium while traversing the disk. This jet decelerates and dissipates energy into a lateral cocoon during its propagation. The researchers explore three radiation mechanisms associated with the jet cocoon system: jet breakout emission, disk cocoon cooling emission, and jet cocoon cooling emission. Through their analysis, they find that the most likely detection in its own frequency bands is the jet cocoon cooling emission. They predict that this emission will manifest as a soft X-ray transient lasting for approximately O($10^3$) seconds. Importantly, there is a time delay of around O(10) days after the GW trigger before this EM counterpart occurs, which provides an opportunity for follow-up observations. Overall, BBH mergers in AGN disks represent a novel multimessenger source. The future enhancement in precision measuring and localizing GWs combined with diligent searches for associated EM signals will effectively validate or restrict the origin of BBH mergers in AGN disks. In terms of additional context provided by other sources, properties of various telescopes such as detection bandpass, sensitivity, and field of view are summarized in Table 3 of Tagawa et al. 's work from 2023a. Furthermore, variations in observable duration and spectra due to different parameters like BH mass and mass distribution of jet cocoon material are discussed by Chen & Dai. It is noted that soft X-ray telescopes like Chandra, XMM-Newton, and Swift XRT would be beneficial for observing softer X-ray band spectra.