2022MNRAS.513L..68G

The long-period (P = 1091 s) of the recently discovered pulsar GLEAM-X J162759.5-523504.3 can be attained by neutron stars evolving with fallback discs and magnetic dipole moments of a few 10³⁰ G cm³ at ages greater than ∼2 x 10⁵yr consistently with the observational upper limits to the period derivative, {dot}P, and the X-ray luminosity, L_X, of the source. The current upper limits for {dot}P allow two alternative present states: (1) The disc is still active with ongoing accretion at a low rate such that the accretion luminosity is much less than the neutron star's cooling luminosity, which in turn is below the upper limit for L_X. In this scenario, the spin-down will continue at {dot}P∼10^–10 s s^–1 until the disc becomes inactive; the final period will be P ∼ a few 10³ s. (2) The disc is already inactive, there is no accretion. In this case, the period evolution has levelled off to the observed value in the final period range. The remaining, very weak, dipole torque sustains asymptotic spin-down at {dot}P∼4 ×10^–18 s s^–1. Long periods P ∼ a few 10³ s were predicted for the final states of soft gamma repeaters and anomalous X-ray pulsars with relatively strong dipole fields in earlier work with the fallback disc model.