Rapid rotational crust-core relaxation in magnetars

TL;DR

This paper investigates how extremely strong magnetic fields in magnetars cause rapid coupling between the crust and core, challenging previous models and affecting observable phenomena like oscillations and precession.

Contribution

It introduces a new mechanism for fast crust-core relaxation in magnetars due to magnetic field-induced unpairing of proton superconductors and neutron superfluid coupling.

Findings

Crust-core coupling timescale ranges from minutes to seconds.

Rapid coupling conflicts with models assuming core-superfluid decoupling.

Magnetar precession is damped unless continuously excited.

Abstract

If a magnetar interior $B$-field exceeds $10^{15}$~G, it will unpair the proton superconductor in the stellar core by inducing diamagnetic currents that destroy the Cooper pair coherence. Then, the $P$-wave neutron superfluid in these non-superconducting regions will couple to the stellar plasma by scattering of protons off the quasiparticles that are confined in the cores of neutron vortices by the strong (nuclear) force. The dynamical timescales associated with this interaction span from several minutes at the crust-core interface to a few seconds in the deep core. We show that (a) the rapid crust-core coupling is incompatible with oscillation models of magnetars that completely decouple the core superfluid from the crust and (b) magnetar precession is damped by the coupling of normal fluids to the superfluid core and, if observed, needs to be forced or continuously excited by seismic activity.