Magnetar bursts due to Alfv\'{e}n wave nonlinear breakout

TL;DR

This paper proposes a model where Alfvén waves from magnetar quakes cause bursts and potentially FRBs by forming ultra-relativistic ejecta that trigger magnetic reconnection, explaining observed X-ray and radio phenomena.

Contribution

It introduces a 3D force-free electrodynamics simulation demonstrating how magnetar quakes can produce bursts and FRBs through nonlinear Alfvén wave breakout and ejecta formation.

Findings

Ejecta can be ultra-relativistic and cause magnetic reconnection.

The angular size of ejecta depends on the quake region size.

The model links magnetar quakes to observed X-ray bursts and FRBs.

Abstract

The most common form of magnetar activity is short X-ray bursts, with durations from milliseconds to seconds, and luminosities ranging from $10^{36}$ to $10^{43}\ {\rm erg}\,{\rm s}^{-1}$. Recently, an X-ray burst from the galactic magnetar SGR 1935+2154 was detected to be coincident with two fast radio burst (FRB) like events from the same source, providing evidence that FRBs may be linked to magnetar bursts. Using fully 3D force-free electrodynamics simulations, we show that such magnetar bursts may be produced by Alfv\'{e}n waves launched from localized magnetar quakes: a wave packet propagates to the outer magnetosphere, becomes nonlinear, and escapes the magnetosphere, forming an ultra-relativistic ejecta. The ejecta pushes open the magnetospheric field lines, creating current sheets behind it. Magnetic reconnection can happen at these current sheets, leading to plasma energization and X-ray emission. The angular size of the ejecta can be compact, $\lesssim 1$ sr if the quake launching region is small, $\lesssim 0.01$ sr at the stellar surface. We discuss implications for the FRBs and the coincident X-ray burst from SGR 1935+2154.