Thirty-five years of timing of M53A with Arecibo and FAST

Abstract: PSR B1310+18A is a 33-ms binary pulsar in a 256-day, low eccentricity orbit with a low-mass companion located in NGC 5024 (M53). In this Letter, we present the first phase-coherent timing solution for this pulsar (designated as M53A) derived from a 35-year timing baseline; this combines the archival Arecibo Observatory data with the recent observations from the Five-hundred-meter Aperture Spherical radio Telescope (FAST). We find that the spin period derivative of the pulsar is between 6.1 and $7.5 \times 10^{-19} \rm \, s\, s^{-1}$, which implies a characteristic age between 0.70 and 0.85 Gyr. The timing solution also includes a precise position and proper motion for the pulsar, enabling the identification of the companion of M53A in Hubble Space Telescope data as a Helium white dwarf (He WD) with a mass of $M_{\rm WD}=0.39^{+0.05}_{-0.07} \, \rm M_{\odot}$ and a cooling age of $0.14^{+0.04}_{-0.03}\, \rm Gyr$, confirming that the system formed recently in the history of the GC. The system resembles, in its spin and orbital characteristics, similarly wide pulsar - He WD systems in the Galactic disk. We conclude by discussing the origin of slow pulsars in globular clusters, showing that none of the slow pulsars in low-density globular clusters are as young as the systems observed in the densest known globular clusters.