The Spin Period, Luminosity, and Age Distributions of Anomalous X‐Ray Pulsars

Abstract

We consider the accretion model for anomalous X-ray pulsars proposed recently by Chatterjee, Hernquist, and Narayan, in which the emission is powered by accretion from a fossil disk that is formed by the fallback of material from a supernova explosion. We demonstrate that this model is able to account for the spin period, luminosity, and age distributions of the observed population of anomalous X-ray pulsars (AXPs) for reasonable and broad distributions of the free parameters of the model, namely, the surface magnetic field of the neutron star, the mass of its accretion disk, and its initial spin period. In particular, this model is able statistically to account for the puzzlingly narrow observed spin distribution of the AXPs. We show also that if the establishment of fallback accretion disks around isolated neutron stars is a universal phenomenon, then a fairly large minority (similar to 20%) of these objects become X-ray-bright AXPs or X-ray-faint systems spinning down by propeller action, while the rest become radio pulsars.