Interlinking internal and external magnetic fields of relativistically rotating neutron stars

TL;DR

This paper develops a comprehensive model linking internal and external magnetic fields of rotating neutron stars, revealing how internal twists influence magnetospheric structure and star spin-down, with implications for pulsar and magnetar behavior.

Contribution

It introduces a global solution connecting internal and external magnetic fields, highlighting the impact of internal twists and magnetospheric currents on neutron star dynamics and emissions.

Findings

Internal magnetic twist affects external field structure.

Magnetospheric currents influence internal field volume.

Transient behavior may result from magnetic field dissipation.

Abstract

This work presents a global solution for the internal and the external field of an axisymmetric rotating neutron star. It is shown that the twist of the internal field affects the external field, by increasing the number of open field lines and eventually the spin-down rate of the star. This effect is far more drastic if the toroidal field, and consequently the poloidal current flowing within the star, is allowed to populate the closed field lines of the magnetosphere, rather than if it remains confined in the star. We further remark that the internal field structure depends on the presence of a twisted magnetosphere: if the twist current is not allowed to flow in the magnetosphere it only occupied a narrow toroid at the interior of the star, whereas if the twist currents are allowed to flow in the magnetosphere the internal toroidal field may occupy a significant volume of the stellar interior. Strong magnetospheric currents may also impact the emission mechanisms, and lead to fluctuations in magnetar spin-down rates, moding and nulling of pulsars, a correlation between angular shear and twist, and the general morphology of the pulsar magnetic field leading to various observational manifestations. The magnetospheric toroidal fields may possibly dissipate, thus the system may switch from global twist to internal twist and consequently exhibit transient behavior.