Role of strongly magnetized crusts in torsional shear modes of magnetars

TL;DR

This paper investigates how strong magnetic fields in magnetar crusts influence torsional shear mode oscillations, revealing significant effects on overtone frequencies and aligning theoretical models with observed quasi-periodic oscillations.

Contribution

It introduces the impact of Landau quantisation on magnetised crusts and demonstrates its effect on torsional shear mode frequencies, especially overtones, in magnetars.

Findings

Overtone frequencies are significantly affected by strong magnetic fields.

Frequencies of torsional shear modes with magnetised crusts match observed QPOs.

Fundamental mode frequencies remain largely unchanged.

Abstract

We study the influence of magnetised crusts on torsional shear mode oscillations of magnetars. In this context, we employ magnetised crusts whose ground state properties are affected by Landau quantisation of electrons. The shear modulus of magnetised crusts is enhanced in strong magnetic fields $\geq 10^{17}$ G. Though we do not find any appreciable change in frequencies of fundamental torsional shear modes, frequencies of first overtones are significantly affected in strong magnetic fields. Furthermore, frequencies of torsional shear modes calculated with magnetised crusts are in good agreement with frequencies of observed quasi-periodic oscillations.