| Summary: | PSR J2150+3427 is a 0.654 s pulsar discovered by the Commensal Radio Astronomy FAST Survey. From the follow-up observations, we find that the pulsar is in a highly eccentric orbit ( e = 0.601) with an orbital period of 10.592 days and a projected semimajor axis of 25.488 lt-s. Using 2.7 yr of timing data, we also measured the rate of periastron advance $\dot{\omega }$ = 0.0115(4) deg yr ^−1 . An estimate for the total mass of the system using the $\dot{\omega }$ gives M _tot = 2.59(13) M _⊙ , which is consistent with most of the known double neutron star (DNS) systems and one neutron star (NS)–white dwarf (WD) system named B2303+46. Combining $\dot{\omega }$ with the mass function of the system gives the masses of M _p < 1.67 and M _c > 0.98 M _⊙ for the pulsar and the companion star, respectively. This constraint, along with the spin period and orbital parameters, suggests that it is possibly a DNS system, and we cannot entirely rule out the possibility of an NS–WD system. Future timing observations will vastly improve the uncertainty in $\dot{\omega }$ , and are likely to allow the detection of additional relativistic effects, which can be used to modify the values of M _p and M _c . With a spin-down luminosity of $\dot{E}$ = 5.07(6) × 10 ^29 erg s ^−1 , PSR J2150+3427 is a very low-luminosity pulsar, with only the binary pulsar J2208+4610 having a smaller $\dot{E}$ .
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