Damping of neutron star shear modes by superfluid friction

Abstract

The forced motion of superfluid vortices in shear oscillations of rotating solid neutron star matter produces damping of the mode. A simple model of the unpinning and repinning processes is described, with numerical calculations of the consequent energy decay times. These are of the order of 1 s for typical anomalous X-ray pulsars with rotational angular velocity Ω ≈ as 1 rad s-1 but become very short for radio pulsars with Ω ≈ 10-100 rad s-1. The superfluid friction processes considered here may also be significant for the damping of r modes in rapidly rotating neutron stars.