Asteroseismic model of paramagnetic neutron star

TL;DR

This paper develops an asteroseismic model for non-rotating paramagnetic neutron stars, analyzing torsional vibrations caused by magnetic and elastic forces, and relates findings to observed X-ray oscillations.

Contribution

It introduces a novel magneto-solid-mechanical model for neutron star vibrations considering paramagnetic core effects and calculates spectral properties relevant to observed phenomena.

Findings

Derived spectral formulas for frequency and lifetime of torsional modes.

Linked seismic vibrations to observed quasi-periodic oscillations in X-ray flux.

Explored two scenarios of seismic vibrations influenced by magnetic and elastic forces.

Abstract

We investigate an asteroseismic model of non-rotating paramagnetic neutron star with core-crust stratification of interior pervaded by homogeneous internal and dipolar external magnetic field, presuming that neutron degenerate Fermi-matter of the star core is in the state of Pauli's paramagnetic permanent magnetization caused by polarization of spin magnetic moments of neutrons along the axis of magnetic field of collapsed massive progenitor. The magnetic cohesion between metal-like crust and permanent-magnet-like core is considered as playing a main part in the dynamics of starquake. Focus is laid on the post-quake relaxation of the star by node-free torsional vibrations of highly conducting crustal solid-state plasma, composed of nuclei embedded in the degenerate Fermi-gas of relativistic electrons, about axis of magnetic field frozen in the immobile paramagnetic core. Two scenarios of these axisymmetric seismic vibrations are examined, in first of which these are considered as maintained by combined action of Lorentz magnetic and Hooke's elastic forces and in second one by solely Lorentz force. Based on the energy variational method of magneto-solid-mechanical theory of elastic continuous medium, the spectral formulae for the frequency and lifetime of this toroidal mode are obtained and discussed in the context of theoretical treatment of recently discovered quasi-periodic oscillations of the X-ray outburst flux from SGR 1806-20 and SGR 1900+14 as being produced by above seismic vibrations.