How can newly born rapidly rotating neutron stars become magnetars?

TL;DR

This paper proposes a mechanism by which newly born, rapidly rotating neutron stars can develop into magnetars within a few minutes through r-mode instability-driven dynamo processes, magnetic field amplification, and spin-down via gravitational waves.

Contribution

It introduces a novel dynamo scenario involving r-mode instability, Tayler instability, and magnetic field evolution leading to magnetar formation in young neutron stars.

Findings

Neutron stars can generate ultra-strong magnetic fields (~10^{17} G) within 100-300 seconds.

The process can spin down the star to ~5 ms period due to gravitational wave emission.

This mechanism explains the formation of millisecond magnetars in gamma-ray bursts and superluminous supernovae.

Abstract

In a newly born (high-temperature and Keplerian rotating) neutron star, r-mode instability can lead to stellar differential rotation, which winds the seed poloidal magnetic field ($\sim 10^{11}$ G) to generate an ultra-high ($\sim 10^{17}$ G) toroidal field component. Subsequently, by succumbing to the Tayler instability, the toroidal field could be partially transformed into a new poloidal field. Through such dynamo processes, the newly born neutron star with sufficiently rapid rotation could become a magnetar on a timescale of $\sim 10^{2-3}$ s, with a surface dipolar magnetic field of $\sim10^{15}$ G. Accompanying the field amplification, the star could spin down to a period of $\sim5$ ms through gravitational wave radiation due to the r-mode instability and, in particular, the non-axisymmetric stellar deformation caused by the toroidal field. This scenario provides a possible explanation for why the remnant neutron stars formed in gamma-ray bursts and superluminous supernovae could be millisecond magnetars.