Constraining the neutron star radius with joint gravitational-wave and short gamma-ray burst observations of neutron star–black hole coalescing binaries

Coalescing neutron star (NS)–black hole (BH) binaries are promising sources of gravitational-waves (GWs) that are predicted to be detected within the next few years by current GW observatories. If the NS is tidally disrupted outside the BH innermost stable circular orbit, an accretion torus may form, and this could eventually power a short gamma-ray burst (SGRB). The observation of an SGRB in coincidence with gravitational radiation from an NS–BH coalescence would confirm the association between the two phenomena and also give us new insights into NS physics. We present here a new method to measure NS radii and thus constrain the NS equation of state using joint SGRB and GW observations of NS–BH mergers. We show that in the event of a joint detection with a realistic GW signal-to-noise ratio of 10, the NS radius can be constrained to <\lesssim>20% accuracy at 90% confidence