Estimating the maximum gravitational mass of nonrotating neutron stars from the GW170817/GRB 170817A/AT2017gfo observation

Abstract

Assuming that the differential rotation of the massive neutron star (NS) formed in the double NS (DNS) mergers has been effectively terminated by the magnetic braking and a uniform rotation has been subsequently established (i.e., a supramassive NS is formed), we analytically derive in this work an approximated expression for the critical total gravitational mass (${M}_{\mathrm{tot},\mathrm{c}}$) to form supramassive NS (SMNS) in the DNS mergers, benefited from some equation of state (EoS) insensitive relationships. The maximum gravitational mass of the nonrotating NSs (${M}_{\mathrm{TOV}}$) as well as the dimensionless angular momentum of the remnant ($j$) play the dominant roles in modifying ${M}_{\mathrm{tot},\mathrm{c}}$, while the radius and mass differences of the premerger NSs do not. The GW170817/GRB 170817A/AT2017gfo observations have provided so far the best opportunity to quantitatively evaluate ${M}_{\mathrm{TOV}}$. Supposing the central engine for GRB 170817A is a black hole quickly formed in the collapse of an SMNS, we find ${M}_{\mathrm{TOV}}=2.1{3}_{\ensuremath{-}0.08}^{+0.09}{M}_{\ensuremath{\bigodot}}$ (68.3% credibility interval, including also the uncertainties of the EoS insensitive relationships), which is consistent with the constraints set by current NS mass measurements.