Inferring Neutron Star Nuclear Properties from Gravitational-Wave and Gamma-Ray Burst Observations

Recent discoveries of long gamma-ray bursts accompanied by kilonova emission prompted interest in understanding their progenitors. If these long-duration bursts arise from neutron star mergers, similar to short gamma-ray bursts, it raises the question of which physical properties govern burst duration. The mass of the merger stands out as a key factor, strongly influencing the lifetime of the merger remnant, which in turn determines the burst duration: lighter mergers that form long-lived remnants produce short bursts, whereas more massive mergers result in short-lived remnants that collapse into black holes, powering longer bursts. In this study, we compare merger rates from gravitational-wave observations of LIGO-Virgo-KAGRA with the rates of kilonova-associated long and short gamma-ray bursts, to identify a characteristic total neutron star mass that separates the two burst classes. Our results suggest that massive neutron stars could survive an extended period after merger. Moreover, we identify a correlation between the characteristic mass and the neutron star TOV mass, allowing constraints on the characteristic mass to be directly mapped to inferences of the TOV mass. This establishes a novel, independent method for measuring the neutron star TOV mass and constraining their equation of state using gravitational-wave and gamma-ray burst observations.