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 ± 0.05, r = 22.86 ± 0.04, and i = 22.82 ± 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⊙, an effective temperature of 8077-470 +550 K, and a cooling age of 10.9 ± 0.3Gyr. 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⊙. 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.