Magnetars oscillations in the presence of a crust

TL;DR

This paper investigates the oscillation modes of magnetars, considering the interaction between the fluid core and solid crust, to explain observed quasi-periodic oscillations and constrain stellar parameters.

Contribution

It provides a detailed analysis of coupled core-crust oscillations, confirming the existence of discrete Alfvén modes and resolving some within the continua, advancing understanding of magnetar oscillations.

Findings

Identification of discrete crustal oscillations

Confirmation of discrete Alfvén modes in the continuum gap

Constraints on magnetar mass, radius, and crust thickness

Abstract

We study axisymmetric perturbations of neutron star endowed with a strong magnetic field (magnetars), considering the coupled oscillations of the fluid core with the solid crust. We recover discrete oscillations based mainly in the crust and a continuum in the core. We also confirm the presence of "discrete Alfv\'en modes" in the gap between two contiguous continua (see Van Hooven& Levin (2011)) and, in addition, we can resolve some of them also inside the continua. Our results can explain both the lower and the higher observed quasi periodical oscillations (QPOs) in SGR 1806-20 and SGR 1900+14 and put constrains on the mass, radius and crust thickness of the two magnetars.