Can thin disks produce anomalous X-ray pulsars?

Abstract

We investigate whether young neutron stars with fallback disks can produce anomalous X-ray pulsars (AXPs) within timescales indicated by the ages of associated supernova remnants. The system passes through a propeller stage before emerging as an AXP or a radio pulsar. The evolution of the disk is described by a diffusion equation that has self-similar solutions with either angular momentum or total mass of the disk conserved. We associate these two types of solutions with accretor and propeller regimes, respectively. Our numerical calculations of thin-disk models with changing inner radius take into account the supercritical accretion at the early stages and electron scattering and bound-free opacities with rich metal content. Our results show that, assuming a fraction of the mass inflow is accreted onto the neutron star, the fallback disk scenario can produce AXPs for acceptable parameters.