PSR J1810+1744: Companion Darkening and a Precise High Neutron Star Mass

TL;DR

This study uses spectrophotometry and light-curve modeling of PSR J1810+1744's companion to determine a precise neutron star mass of 2.13 solar masses, revealing significant gravity darkening effects due to pulsar heating.

Contribution

It provides the first detailed analysis of gravity darkening effects in a spider pulsar binary, leading to a more accurate neutron star mass measurement.

Findings

Neutron star mass is 2.13±0.04 solar masses.

Gravity darkening significantly affects light-curve modeling.

Classic models ignoring gravity darkening overestimate the mass.

Abstract

Keck-telescope spectrophotometry of the companion of PSR J1810+1744 shows a flat, but asymmetric light-curve maximum and a deep, narrow minimum. The maximum indicates strong gravity darkening near the L_1 point, along with a heated pole and surface winds. The minimum indicates a low underlying temperature and substantial limb darkening. The gravity darkening is a consequence of extreme pulsar heating and the near-filling of the Roche lobe. Light-curve modeling gives a binary inclination i=65.7+/-0.4deg. With the Keck-measured radial-velocity amplitude K_c=462.3+/-2.2km/s, this gives an accurate neutron star mass M_NS=2.13+/-0.04M_o, with important implications for the dense-matter equation of state. A classic direct-heating model, ignoring the L_1 gravitational darkening, would predict an unphysical M_NS>3M_o. A few other ``spider" pulsar binaries have similar large heating and fill factor; thus, they should be checked for such effects.