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

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 $M_{N}S=2.35\pm 0.11M_{\odot }$. 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 $2.5\sigma$ 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_{\mathrm{T}\mathrm{O}\mathrm{V}}>2.27M_{\odot }$$(2.12M_{\odot })$ at $1\sigma$$(3\sigma )$ 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.