Magnetic Reconnection Instabilities in Soft-Gamma Repeaters

TL;DR

This paper proposes a model where shearing motions in magnetospheres trigger magnetic reconnection, leading to giant flares in soft gamma-ray repeaters, with the thinning of current layers playing a key role.

Contribution

It introduces a reconnection model linking footpoint shearing to impulsive Hall reconnection in SGR giant flares, highlighting the role of current layer thinning.

Findings

Precursor activity can initiate the main flare.

Thinning time of current layers matches pre-flare quiescent periods.

Hall reconnection triggers the impulsive energy release.

Abstract

We examine an external trigger mechanism that gives rise to the intense soft gamma-ray repeater (SGR) giant flares. Out of the three giant flares, two showcased the existence of a precursor, which we show to have had initiated the main flare. We develop a reconnection model based on the hypothesis that shearing motion of the footpoints causes the materialization of a Sweet-Parker current layer in the magnetosphere. The thinning of this macroscopic layer due to the development of an embedded super-hot turbulent current layer switches on the impulsive Hall reconnection, which powers the giant flare. We show that the thinning time is on the order of the pre-flare quiescent time.