Keck/LRIS spectra of PSR J0952-0607

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{deg}+/-1.9{deg} and a pulsar mass M_NS_=2.35+/-0.17M_{sun}_, 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 1M_{sun}_ has been accreted; this may be connected with the especially low intrinsic dipole surface field, estimated at 6x10^7^G. Joined with reanalysis of other black widow and redback pulsars, we find that the minimum value for the maximum NS mass is M_max_>2.19M_{sun}_ (2.09M_{sun}_) at 1{sigma} (3{sigma}) confidence.