Revisiting the Constraint on Equation of State of Neutron Star based on the Binary Neutron Star Mergers

Abstract: The merger of neutron star (NS)-NS binary can form different production of the compact remnant, among which the supramassive NS (SMNS) could create an internal plateau and the followed steep decay marks the collapse of the SMNS. The proportion of SMNS and the corresponding collapse-time are often used to constrain the NS equation of state (EoS). This paper revisits this topic by considering the effect of an accretion disk on the compact remnant, which is not considered in previous works. Compared with previous works, the collapse-time distribution (peaks $\sim$100 s) of the SMNSs formed from NS-NS merger is almost unaffected by the initial surface magnetic ($B_{{\rm s},i}$) of NS, but the total energy output of the magnetic dipole radiation from the SMNSs depends on $B_{{\rm s},i}$ significantly. Coupling the constraints from the SMNS fraction, we exclude some EoSs and obtain three candidate EoSs, i.e., DD2, ENG, and MPA1. By comparing the distributions of the collapse-time and the luminosity of the internal plateau (in the short gamma-ray bursts) for those from observations with those obtained based on the three candidate EoSs, it is shown that only the EoS of ENG is favored. Our sample based on the ENG EOS and a mass distribution motivated by Galactic systems suggests that approximately $99\%$ of NS-NS mergers collapse to form a black hole within $10^7$s. This includes scenarios forming a BH promptly ($36.5\%$), a SMNS ($60.7\%$), or a stable NS that transitions into a BH or a SMNS following accretion ($2.1\%$). It also indicates that the remnants for GW170817 and GW190425, and the second object of GW190814 are more likely to be BHs.