PSR J0952-0607: Tightening a Record-high Neutron Star Mass

Abstract We report on new orbit-minimum photometry and revised radial-velocity fitting that provide an improved measurement of the mass of the neutron star (NS) in pulsar PSR J0952−0607 at M NS = 2.35 ± 0.11 M ⊙ . With its fast spin and unusually low magnetic field, this NS has evidently experienced unusual evolution, likely connected with its high mass, which is now 2.5 σ above that of the heaviest pulsar with a white dwarf companion, as measured by Shapiro delay techniques. By tightening the mass measurement, we also raise the maximum (commonly called Tolman–Oppenheimer–Volkoff) NS mass to M TOV > 2.27 M ⊙ (2.12 M ⊙ ) at 1 σ (3 σ ) confidence, which improves bounds on the dense-matter equation of state. While the statistical error decreases and systematic issues should be modest, uncertainties remain; we comment briefly on these factors and prospects for further improvement.