Distinguishing the nature of comparable-mass neutron star binary systems with multimessenger observations: GW170817 case study

TL;DR

This paper develops new numerical simulations and models to distinguish between neutron star-neutron star and neutron star-black hole mergers using combined gravitational wave and electromagnetic data, applied to GW170817.

Contribution

It introduces novel GW and EM observables for NS-BH mergers with similar masses, enhancing the ability to identify the nature of compact binary systems.

Findings

Less than 40% of NS-BH parameter space matches GW170817 EM data

New numerical-relativity simulations incorporate modeling uncertainties

Joint GW and EM analysis constrains merger progenitor type

Abstract

The discovery of GW170817 with gravitational waves (GWs) and electromagnetic (EM) radiation is prompting new questions in strong-gravity astrophysics. Importantly, it remains unknown whether the progenitor of the merger comprised two neutron stars (NSs), or a NS and a black hole (BH). Using new numerical-relativity simulations and incorporating modeling uncertainties we produce novel GW and EM observables for NS-BH mergers with similar masses. A joint analysis of GW and EM measurements reveals that if GW170817 is a NS-BH merger, <40% of the binary parameters consistent with the GW data are compatible with EM observations.