PSR J0952-0607: The Fastest and Heaviest Known Galactic Neutron Star

TL;DR

This study measures the mass of the fastest spinning known galactic neutron star, PSR J0952-0607, finding it to be the heaviest with a well-measured mass of about 2.35 solar masses, providing new constraints on neutron star maximum mass.

Contribution

The paper presents the first detailed optical modeling of the companion to PSR J0952-0607, leading to a precise neutron star mass measurement and improved limits on the maximum neutron star mass.

Findings

Neutron star mass measured at 2.35 solar masses.

Minimum maximum neutron star mass exceeds 2.19 solar masses.

The neutron star has accreted nearly 1 solar mass from its companion.

Abstract

We describe Keck-telescope spectrophotometry and imaging of the companion of the ``black widow" pulsar PSR~J0952$-$0607, the fastest known spinning neutron star (NS) in the disk of the Milky Way. The companion is very faint at minimum brightness, presenting observational challenges, but we have measured multicolor light curves and obtained radial velocities over the illuminated ``day" half of the orbit. The model fits indicate system inclination $i=59.8\pm 1.9^\circ$ and a pulsar mass $M_{NS} = 2.35\pm 0.17 M_\odot$, the largest well-measured mass found to date. Modeling uncertainties are small, since the heating is not extreme; the companion lies well within its Roche lobe and a simple direct-heating model provides the best fit. If the NS started at a typical pulsar birth mass, nearly $1 M_\odot$ has been accreted; this may be connected with the especially low intrinsic dipole surface field, estimated at $6\times 10^7$G. Joined with reanalysis of other black widow and redback pulsars, we find that the minimum value for the maximum NS mass is $M_{\rm max} > 2.19 M_\odot$$(2.09 M_\odot)$ at $1\sigma$$(3\sigma)$ confidence. This is $\sim 0.15 M_\odot$ heavier than the lower limit on $M_{\rm max}$ implied by the white-dwarf--pulsar binaries measured via radio Shapiro-delay techniques.