Magnetic Field Decay and Period Evolution of Anomalous X-Ray Pulsars in the Context of Quark Stars
Abstract
We discuss a model wherein soft gamma-ray repeaters (SGRs), anomalous X-ray pulsars (AXPs), and radio quiet isolated neutron stars (RQINSs) are all compact objects exhibiting superconductivity, namely color-flavor locked quark stars. In particular we calculate the magnetic field decay due to the expulsion of spin-induced vortices from the star's superfluid-superconducting interior, and the resultant spin-down rate. We find that, for initial parameters characteristic of AXPs/SGRs (1013<B<1014~G; 3<P<12~s), the magnetic field strengths and periods remain unchanged within a factor of two for timescales of the order of 5× 105 - 5× 107~yrs given a quark star of radius 10~km. Within these timescales, we show that the observed period clustering in RQINSs can be explained by compactness, as well as calculate how the magnetic field and period evolve in a manner concurrent with RQINS observations.
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