Interpreting the AXP 1E 2259 586 antiglitch as a change in internal magnetization

Abstract

The sudden spin-down event ('antiglitch') observed in AXP 1E 2259+586 on 2012 April 21 was arguably caused by a decay of its internal toroidal magnetic field component, which turns a stable prolate configuration into an unstable one. We refine previous models of this process by modelling the star's magnetic field self-consistently as a 'twisted torus' configuration in non-barotropic equilibrium (which allows us to explore a greater range of equilibrium configurations). It is shown that, if the star's magnetic field is purely dipolar, the change in the toroidal field strength required to produce an antiglitch of the observed size can be ~10 times larger than previously calculated. If the star..