Magnetic amplification in premerger neutron stars through resonance-induced magnetorotational instabilities

TL;DR

This paper explores how tidal resonances in neutron star binaries can induce magnetorotational instabilities, amplifying magnetic fields before merger and potentially explaining observed gamma-ray precursors.

Contribution

It introduces a mechanism where resonant oscillations trigger magnetic field amplification via magnetorotational instabilities in premerger neutron stars.

Findings

Resonant pulsations can generate magnetic fields >10^{13} G.

Magnetic amplification occurs in stars with spin frequencies >30 Hz.

Premerger magnetic growth influences postmerger magnetic energy.

Abstract

Tidal resonances in the final seconds of a binary neutron-star inspiral can excite oscillation modes in one or both of the constituents to large amplitudes. Under favorable circumstances, resonant pulsations can overstrain the stellar crust and unleash a torrent of magnetoelastic energy that manifests as a gamma-ray ``precursor flare.'' We show that for realistic, stratified stars rotating with a spin frequency of $\gtrsim30\,$Hz, the fundamental $g$ or its first overtone can also execute a differential rotation in the crust such that a magnetic field of strength $\gtrsim10^{13}\,$G is generated via magnetorotational instabilities. This may help to explain observed precursor rates and their luminosities. Premerger magnetic growth would also provide seed magnetic energy for the postmerger remnant.