An Accretion Model for Anomalous X‐Ray Pulsars

We present a model for the anomalous X-ray pulsars (AXPs) in which theemission is powered by accretion from a fossil disk, established from matterfalling back onto the neutron star following its birth. The time-dependentaccretion drives the neutron star towards a ``tracking'' solution in which therotation period of the star increases slowly, in tandem with the decliningaccretion rate. For appropriate choices of disk mass, neutron star magneticfield strength and initial spin period, we demonstrate that a rapidly rotatingneutron star can be spun down to periods characteristic of AXPs on timescalescomparable to the estimated ages of these sources. In other cases, accretiononto the neutron star switches off after a short time, and the star becomes anordinary radio pulsar. Thus, in our picture, radio pulsars and AXPs are drawnfrom the same underlying population, in contrast to models involving neutronstars with ultrastrong magnetic fields, which require a new population of starswith very different properties.Comment: 15 pages and 3 Postscript figure