Hyperactive Magnetar Eruptions: Giant Flares, Baryon Ejections, and Fast Radio Bursts

TL;DR

This paper models hyperactive magnetar eruptions driven by internal magnetic field evolution, explaining giant flares, ejecta, and potential links to fast radio bursts through relativistic shocks.

Contribution

It introduces a numerical simulation of magnetic eruptions in young magnetars, connecting internal magnetic diffusion to observable high-energy and radio phenomena.

Findings

Magnetic loops are ejected from the star during eruptions.

Eruptions produce giant gamma-ray flares and neutron-rich ejecta.

Eruptions may explain observed giant flares and fast radio bursts.

Abstract

Young neutron stars born with magnetic fields $B\gtrsim 10^{16}$ G become hyperactive as the field inside the star evolves through ambipolar diffusion on a timescale $\sim 10^9$ s. We simulate this process numerically and find that it can eject magnetic loops from the star. The internal magnetic field first diffuses to the crust surrounding the liquid core and then erupts from the surface, taking a significant amount of crustal material with it. The eruption involves magnetic reconnection, generating a giant gamma-ray flare. A significant fraction of the eruption energy is carried by the neutron-rich crustal material, which must go through a phase of decompression and nuclear heating. The massive ejecta should produce additional emission components after the giant flare, including radioactively powered gamma-rays, optical emission, and much later a radio afterglow. The predicted eruptions may rarely happen in observed magnetars in our galaxy, which are relatively old and rarely produce giant flares. The model can, however, explain the extremely powerful flare from SGR 1806-20 in December 2004, its ejecta mass, and afterglow. More active, younger magnetars may produce frequent crustal eruptions and form unusual nebulae. Such hyperactive magnetars are candidates for the central engines of cosmological fast radio bursts (FRBs). We argue that each eruption launches an ultrarelativistic magnetosonic pulse leading the ejecta and steepening into a relativistic shock capable of emitting an FRB.