Summary

We investigate the prospects of observing electromagnetic counterparts (γ-ray burst prompt and afterglow and kilonova) to binary neutron star and black hole-neutron star mergers observed through gravitational waves at Einstein Telescope and Cosmic Explorer. We further provide projections to optimize observational strategies and maximize scientific insights from these sources. We find that, already alone, Einstein Telescope could detect tens to hundreds of electromagnetic counterparts to BNSs, and increase by an order of magnitude the rates of multimessenger detections of NSBHs copared to current instruments.

Contribution

I took care of the gravitational wave modeling aspects of the paper, writing the relative part and producing the results of the gravitational wave observational prospects.

Abstract

The Einstein Telescope (ET), a proposed next-generation gravitational wave (GW) observatory, will expand the reach of GW astronomy of stellar-mass compact object binaries to unprecedented distances, enhancing opportunities for multi-messenger observations. Here we investigate multi-messenger emission properties of binary neutron star (NSNS) and black hole-neutron star (BHNS) mergers detectable by ET, providing projections to optimize observational strategies and maximize scientific insights from these sources. Using a synthetic population of compact binary mergers, we model each source’s GW signal-to-noise ratio, sky localization uncertainty, kilonova (KN) light curves in optical and near-infrared bands, fluence of the relativistic jet gamma-ray burst (GRB) prompt emission and afterglow light curves across radio, optical, X-ray and very high energy wavelengths. We analyze multi-messenger detectability prospects for ET as a standalone observatory with two different configurations and within a network of next-generation GW detectors. ET will detect over 10⁴ NSNS mergers annually, enabling potential observation of tens to hundreds of electromagnetic (EM) counterparts. BHNS mergers have more limited multi-messenger prospects, but joint GW-EM rates will increase by an order of magnitude compared to current-generation instruments. We quantify uncertainties due to the NS equation of state (EoS) and mass distribution of NSNSs, as well as the NS EoS and BH spin for BHNSs. While a single ET will achieve an impressive GW detection rate, the fraction of well-localized events (< 100 deg²) is orders of magnitude lower than in a network with additional detectors. This significantly limits efficient EM follow-up and science cases requiring well-characterized counterparts or early observations. The challenge is even greater for BHNS mergers due to their low EM rate. Thus, multi-messenger astronomy in the next decade will critically depend on a network of at least two detectors.

Links

arXiv: 2503.00116 [astro-ph.HE]