# Multi-messenger prospects for black hole - neutron star mergers in the O4 and O5 runs

**Authors:** Alberto Colombo, Raphaël Duqué, Om Sharan Salafia, Floor S. Broekgaarden, Francesco Iacovelli, Michele Mancarella, Igor Andreoni, Francesco Gabrielli, Fabio Ragosta, Giancarlo Ghirlanda, Tassos Fragos, Andrew J. Levan, Silvia Piranomonte, Andrea Melandri, Bruno Giacomazzo, Monica Colpi  
**arXiv:** [2310.16894](https://arxiv.org/abs/2310.16894)  
**Date:** 2023-10-25  
**Summary page:** https://www.summarizepaper.com/en/paper/2310.16894v1/

## Key points

- Study focuses on multi-messenger prospects for black hole-neutron star mergers during O4 and O5 observing runs of LIGO-Virgo-KAGRA GW detector network
- Merging BHNS binaries confirmed through GW signals, but no definitive EM emission associated
- Aim is to provide detailed predictions to enhance observational efforts and extract scientific information
- Methodology includes population synthesis approach and modeling various aspects such as GW signal, sky localization, KN light curves, GRB prompt emission, and afterglow light curves
- MM detections of BHNS mergers during O4 not promising with a GW detection rate of $15.0^{+15.4}_{-8.8}$ yr$^{−1}$
- Joint MM rates estimated to be around $\sim 10^{−1}$ yr$^{−1}$ for KN emission and $\sim 10^{−2}$ yr$^{−1}$ for jet related emission in O5
- Expected overall increase in detection rates by approximately an order of magnitude in O5 due to enhanced sensitivity of GW detector network and upcoming EM facilities
- Discussion on direct searches for GRB radio afterglow as a potential follow-up strategy considering dimming prospects for KN detection
- Detailed predictions offer insights into BH spin distribution, neutron star equation of state, and heavy element production rates suggesting increased detection rates in O5 and proposing alternative follow-up strategies

## Summary

This study focuses on the multi-messenger (MM) prospects for black hole-neutron star (BHNS) mergers during the fourth (O4) and fifth (O5) observing runs of the LIGO-Virgo-KAGRA gravitational wave (GW) detector network. While the existence of merging BHNS binaries has been confirmed through GW signals, no definitive electromagnetic (EM) emission has been associated with these mergers. The authors aim to provide detailed predictions that can enhance observational efforts and extract valuable scientific information from these events. The methodology employed in this study is based on a population synthesis approach which includes modeling various aspects such as the signal-to-noise ratio of the GW signal in the detectors, sky localization of the source inferred from GW data, kilonova (KN) optical and near-infrared light curves, relativistic jet gamma-ray burst (GRB) prompt emission peak photon flux, and GRB afterglow light curves in radio, optical, and X-ray bands. The results indicate that MM detections of BHNS mergers during O4 are not promising with a GW detection rate of $15.0^{+15.4}_{-8.8}$ yr$^{−1}$. However, joint MM rates are estimated to be around $\sim 10^{−1}$ yr$^{−1}$ for KN emission and $\sim 10^{−2}$ yr$^{−1}$ for jet related emission. In O5 an overall increase in expected detection rates by approximately an order of magnitude is projected due to enhanced sensitivity of the GW detector network and upcoming EM facilities. Additionally, direct searches for GRB radio afterglow using large field of view instruments as a potential follow up strategy considering dimming prospects for KN detection are discussed. This study provides detailed predictions for MM emission during O4 and O5 runs offering insights into BH spin distribution neutron star equation of state and heavy element production rates suggesting an increase in detection rates in O5 and proposing alternative follow up strategies for future observations.