G. Ricigliano | Searcharxiv

arXiv2026

Prospects for optical detections from binary neutron star mergers with the next-generation multi-messenger observatories

Next-generation gravitational wave (GW) observatories, such as the Einstein Telescope (ET) and Cosmic Explorer, will observe binary neutron star (BNS) mergers across cosmic history, providing precise parameter estimates for the closest ones. Innovative wide-field observatories, such as the Vera Rubin Observatory, will quickly cover large portions of the sky with unprecedented sensitivity to detect faint transients. This study aims to assess the prospects for detecting optical emissions from BNS mergers with next-generation detectors, considering how uncertainties in neutron star (NS) population properties and microphysics may affect detection rates. Starting from BNS merger populations exploiting different NS mass distributions and equations of state (EOSs), we model the GW and kilonova (KN) signals based on source properties. We model KN ejecta through numerical-relativity informed fits, considering the effect of prompt collapse of the remnant to black hole and new fitting formulas appropriate for more massive BNS systems, like GW190425. We include optical afterglow emission from relativistic jets consistent with observed short gamma-ray bursts. We evaluate the detected mergers and the source parameter estimations for different geometries of ET, operating alone or in a network of current or next-generation GW detectors. Finally, we estimate the number of detected optical signals simulating realistic observational strategies by the Rubin Observatory. ET as a single observatory will enable the detection of about ten to a hundred KNe per year by the Rubin Observatory. This improves by a factor of about 10 already when operating in the network with current GW detectors. Detection rate uncertainties are dominated by the poorly constrained local BNS merger rate, and depend to a lesser extent on the NS mass distribution and EOS.

astro-ph.HE↗

arXiv2022

Numerical relativity simulations of the neutron star merger GW190425: microphysics and mass ratio effects

GW190425 was the second gravitational wave (GW) signal compatible with a binary neutron star (BNS) merger detected by the Advanced LIGO and Advanced Virgo detectors. Since no electromagnetic counterpart was identified, whether the associated kilonova was too dim or the localisation area too broad is still an open question. We simulate 28 BNS mergers with the chirp mass of GW190425 and mass ratio $1 \leq q \leq 1.67$, using numerical-relativity simulations with finite temperature, composition dependent nuclear equation of state (EOS) and neutrino radiation. The energy emitted in GWs is $\lesssim 0.083 M_{\odot} c^2$ with peak luminosity of $1.1-2.4 \times 10^{58} {\rm erg~s^{-1}}/(1+q)^2$. Dynamical ejecta and disc mass range between $5 \times 10^{-6} - \sim 10^{-3}~M_{\odot}$ and $10^{-5} - 0.1~M_{\odot}$, respectively. Asymmetric mergers, especially with stiff EOS, unbind more matter and to form heavier discs compared to equal mass binaries. The angular momentum of the disc is $8-10 M_{\odot}~GM_{\rm disc}/c$ over three orders of magnitude in $M_{\rm disc}$. While the nucleosynthesis shows no peculiarity, the simulated kilonovae are relatively dim compared with the GW170817 event. For distances compatible with GW190425, AB magnitudes are always dimmer than $\sim20~{\rm mag}$ for the $B$, $r$ and $K$ bands, with brighter kilonovae associated to more asymmetric binaries and stiffer EOS. We suggest that, even assuming a good coverage of GW190425's sky location, the kilonova could hardly have been detected by present wide-field surveys and no firm constraints on the binary parameters or EOS can be argued from the lack of the detection.

astro-ph.HE↗