2026ApJ...998..332L

PSR J2032+4127 is the only gamma-ray binary that exhibits pulsations in gamma rays. Previous research has indicated that the pulsar and the Be star MT91 213 orbit each other in a highly eccentric orbit with an extremely long period, with the pulsar reaching its periastron on 2017 November 13. Since its launch, the Fermi satellite has been monitoring this pulsar for 16 yr, covering the 8 yr before and the 8 yr after the pulsar passed its periastron. Using these data, we present an analysis of pulse arrival times and precisely determine the orbital parameters for the first time: the orbital period of P_orb ∼ 52.3 yr, the eccentricity of e ∼ 0.98, the semimajor axis of asini ∼ 25.3 au, and the orbital inclination of ∼47$\mathop{.}\limits^{\unicode{x000b0}}$1-55$\mathop{.}\limits^{\unicode{x000b0}}$1. We also reveal another small glitch occurred in 2021, MJD ∼ 59500.