A 1.05 $M_\odot$ Companion to PSR J2222-0137: The Coolest Known White Dwarf?

Understand

The recycled pulsar PSR J2222-0137 is one of the closest known neutron stars, with a parallax distance of $267_{-0.9}^{+1.2}\,$pc and an edge-on orbit.

• We measure the Shapiro delay in the system through pulsar timing with the Green Bank Telescope, deriving a low pulsar mass ($1.20\pm0.14$ $M_\odot$) and a high companion mass ($1.05\pm0.06$ $M_\odot$) consistent with either a low-mass neutron star or a high-mass white dwarf.
• We can largely reject the neutron star hypothesis on the basis of the system's extremely low eccentricity (3e-4) - too low to have been the product of two supernovae under normal circumstances.
• However, despite deep optical and near-infrared searches with SOAR and the Keck telescopes we have not discovered the optical counterpart of the system.