2020ApJ...893..146A

The post-merger product of the first binary neutron star merger event detected in gravitational waves, GW170817, depends on neutron star equation of state (EoS) and is not well determined. We generally discuss the constraints one may pose on the maximum mass of a non-spinning neutron star, M_TOV, based on the observations and some EoS-independent universal relations of rapidly spinning neutron stars. If the merger product is a black hole after a brief hypermassive neutron star (HMNS) phase, we derive M_TOV< 2.09_–0.09^+0.11(_–0.04^+0.06)M_☉ at the 2σ (1σ) level. The cases for a massive neutron star (MNS), neither a supramassive neutron star (SMNS) nor even a stable neutron star (SNS) are also allowed by the data. We derive 2.09_–0.09^+0.11(_–0.04^+0.06M_☉)≤ M_TOV< 2.43_–0.08^+0.10(_–0.04^+0.06)M_☉ for the SMNS case and M_TOV≥ 2.43_–0.08^+0.10(_–0.04^+0.06)M_☉ for the SNS case, at the 2σ (1σ) confidence level. In the MNS cases, we also discuss the constraints on the neutron star parameters (the dipolar magnetic field strength at the surface B_p and the ellipticity ε) that affect the spin down history, by considering different MNS survival times, e.g., 300 s, 1 day, and 155 days after the merger, as suggested by various observational arguments. We find that once an SMNS is formed, without violating the electromagnetic observational constraints, there always exist a set of (B_p,ε) parameters that allow the SMNS to survive for 300 s, 1 day, 155 days, or even longer.