PSR J1810+1744: Companion Darkening and a Precise High Neutron Star 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 L1 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 Kc=462.3+/-2.2km/s, this gives an accurate neutron star mass MNS=2.13+/-0.04Mo, with important implications for the dense-matter equation of state. A classic direct-heating model, ignoring the L1 gravitational darkening, would predict an unphysical MNS>3Mo. A few other ``spider" pulsar binaries have similar large heating and fill factor; thus, they should be checked for such effects.
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