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Abstract

Coalescing neutron star (NS)-black hole (BH) binaries are promising sources
of gravitational-waves (GWs) 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
on 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 realistic GW
signal-to-noise ratio (S/N) of 10, the NS radius can be constrained to
$\lesssim\,$20% accuracy at 90% confidence.