Long-period Pulsars as Possible Outcomes of Supernova Fallback Accretion

Abstract

For about half a century the radio pulsar population was observed to spin in the ~0.002-12s range, with different pulsar classes having a spin-period evolution that differs substantially depending on their magnetic fields or past accretion history. The recent detection of several slowly rotating pulsars has re-opened the long-standing question of the exact physics, and observational biases, driving the upper bound of the period range of the pulsar population. In this work, we perform a parameter study of the spin-period evolution of pulsars interacting with supernova fallback matter and specifically look at the fallback accretion disk scenario. Depending on the initial conditions at formation, this evolution can differ substantially from the typical dipolar spin-down, resulting in pulsars that show spin periods longer than their coeval peers. By using general assumptions for the pulsar spin period and magnetic field at birth, initial fallback accretion rates and including magnetic field decay, we find that very long spin periods (>100s) can be reached in the presence of strong, magnetar-like magnetic fields (>10^{14}G) and moderate initial fallback accretion rates (~10^{22-27} g s^{-1}). In addition, we study the cases of two recently discovered periodic radio sources, the pulsar PSR J0901-4046 (P = 75.9 s) and the radio transient GLEAM-X\,J162759.5-523504.3 (P = 1091 s), in light of our model. We conclude that the supernova fallback scenario could represent a viable channel to produce a population of long-period isolated pulsars that only recent observation campaigns are starting to unveil.