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

TL;DR

The paper refines the mass measurement of the neutron star in PSR J0952-0607, a fast-spinning black-widow pulsar, by obtaining high-quality Keck photometry near orbital minimum and combining with prior spectroscopy. The authors perform a joint photometric and radial-velocity analysis using ICARUS with additional heating physics and Bayesian Multinest sampling, achieving a tighter mass constraint: $M_{ m NS}=2.35\pm0.11\,M_\odot$, and set a strengthened lower bound on the Tolman-Oppenheimer-Volkoff limit, $M_{ m TOV}>2.27\,M_\odot$ (1σ). The result reduces model systematics from companion heating and distance, while maintaining consistent results with previous measurements. This tighter constraint narrows the allowed dense-matter equations of state and informs the evolutionary history of spiders with low heating flux. The work demonstrates how targeted, high-quality photometry near orbital minimum can substantially improve dynamical mass determinations for pulsar binaries.

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 $M_NS = 2.35\pm 0.11 M_\odot$. 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 $2.5σ$ 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_{\rm TOV} > 2.27\,M_\odot$$(2.12\,M_\odot)$ at $1σ$$(3σ)$ 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.

Figures (1)

• Figure 1: Keck LRIS $g/i$ photometry near orbital minimum brightness.