Early evolution of newly born magnetars with a strong toroidal field

TL;DR

This paper models the early evolution of newly born magnetars with strong toroidal magnetic fields, exploring their gravitational wave emissions, magnetic field decay, and implications for detection with future GW observatories.

Contribution

It introduces a comprehensive scenario for magnetar evolution post-formation, linking magnetic field decay, gravitational wave emission, and observational constraints.

Findings

GW signals from magnetars could be detectable up to Virgo cluster distances.

Magnetic field decay couples with cooling, maintaining strong fields for over 1000 years.

Electromagnetic energy input constraints align with observations of SNRs around AXPs and SGRs.

Abstract

We present a state-of-the-art scenario for newly born magnetars as strong sources of Gravitational Waves (GWs)in the early days after formation. We address several aspects of the astrophysics of rapidly rotating, ultramagnetized neutron stars (NSs), including early cooling before transition to superfluidity, the effects of the magnetic field on the equilibrium shape of NSs, the internal dynamical state of a fully degenerate, oblique rotator and the strength of the electromagnetic torque on the newly born NS. We show that our scenario is consistent with recent studies of SNRs surrounding AXPs and SGRs in the Galaxy that constrain the electromagnetic energy input from the central NS to be <= 10^51 erg. We further show that if this condition is met, then the GW signal from such sources is potentially detectable with the forthcoming generation of GW detectors up to Virgo cluster distances where an event rate <= 1/yr can be estimated. Finally, we point out that the decay of an internal magnetic field in the 10^16 G range couples strongly to the NS cooling at very early stages, thus significantly slowing down both processes: the field can remain this strong for at least 10^3 yrs, during which the core temperature stays higher than several times 10^8 K.