Incompatibility of long-period neutron star precession with creeping neutron vortices

Abstract

Aims: To determine whether ``vortex creep'' in neutron stars, the slow motion of neutron vortices with respect to pinning sites in the core or inner crust, is consistent with observations of long-period precession. Methods: Using the concept of vortex drag, I discuss the precession dynamics of a star with imperfectly-pinned (i.e., "creeping'') vortices. Results: The precession frequency is far too high to be consistent with observations, indicating that the standard picture of the outer core (superfluid neutrons in co-existence with type II, superconducting protons) should be reconsidered. There is a slow precession mode, but it is highly over-damped and cannot complete even a single cycle. Moreover, the vortices of the inner crust must be able to move with little dissipation with respect to the solid.