The Identification of the White Dwarf Companion to the Millisecond Pulsar J2317+1439

We report the identification of the optical counterpart to the companion of the millisecond pulsar J2317+1439. At the timing position of the pulsar, we find an object with $g=22.96\pm 0.05$, $r=22.86\pm 0.04$, and $i=22.82\pm 0.05$. The magnitudes and colors of the object are consistent with a white dwarf (WD). Compared with WD cooling models, we estimate that it has a mass of ${0.39}_{-0.10}^{+0.13}$ $M_{\odot }$, an effective temperature of ${8077}_{-470}^{+550}$ K, and a cooling age of 10.9 ± 0.3 Gyr. Combining our results with published constraints on the orbital parameters obtained through pulsar timing, we estimate the pulsar mass to be ${3.4}_{-1.1}^{+1.4}$ $M_{\odot }$. Although the constraint on the pulsar mass is still weak, there is a significant possibility that the pulsar could be more massive than two solar masses.