# Multi-messenger Bayesian parameter inference of a binary neutron-star merger

## TL;DR

This paper presents a pioneering Bayesian multi-messenger analysis combining gravitational wave and electromagnetic data from a neutron-star merger to tightly constrain key astrophysical parameters and the neutron star equation of state.

## Contribution

It introduces the first Bayesian parameter estimation that jointly uses GW and EM data for a neutron-star merger, utilizing new phenomenological models from numerical relativity.

## Key findings

- Tidal deformability constrained to [302,860] at 90% confidence
- Total binary mass constrained to [2.722,2.751] solar masses
- Neutron star radius constrained to [11.3,13.5] km

## Abstract

The combined detection of a binary neutron-star merger in both gravitational waves (GWs) and electromagnetic (EM) radiation spanning the entire spectrum -- GW170817 / AT2017gfo / GRB170817A -- marks a breakthrough in the field of multi-messenger astronomy. Between the plethora of modeling and observations, the rich synergy that exists among the available data sets creates a unique opportunity to constrain the binary parameters, the equation of state of supranuclear density matter, and the physical processes at work during the kilonova and gamma-ray burst. We report, for the first time, Bayesian parameter estimation combining information from GW170817, AT2017gfo, GRB170817 to obtain truly multi-messenger constraints on the tidal deformability $\tilde{\Lambda} \in [302,860]$, total binary mass $M \in [2.722,2.751] M_\odot$, the radius of a $1.4$ solar mass neutron star $R \in [11.3,13.5] \rm km$ (with additional $0.2\ \rm km$ systematic uncertainty), and an upper bound on the mass ratio of $q \leq 1.27$, all at 90% confidence. Our joint novel analysis makes use of new phenomenological descriptions of the dynamical ejecta, debris disk mass, and remnant black hole properties, all derived from a large suite of numerical relativity simulations.