Twisting, reconnecting magnetospheres and magnetar spindown

TL;DR

This paper presents simulations of magnetar magnetospheres showing how twisting and reconnection events lead to X-ray flares and dramatic increases in spindown rate, potentially explaining observed giant flares.

Contribution

First simulation of evolving, strongly twisted magnetar magnetospheres including rotation and wind effects, linking magnetic reconnection to observed flares and spindown changes.

Findings

Magnetospheric expansion and reconnection cause X-ray flares.

Increasing twist dramatically enhances spindown rate.

Explosive opening of magnetic flux can explain giant flares.

Abstract

We present the first simulations of evolving, strongly twisted magnetar magnetospheres. Slow shearing of the magnetar crust is seen to lead to a series of magnetospheric expansion and reconnection events, corresponding to X-ray flares and bursts. The axisymmetric simulations include rotation of the neutron star and the magnetic wind through the light cylinder. We study how the increasing twist affects the spindown rate of the star, finding that a dramatic increase in spindown occurs. Particularly spectacular are explosive events caused by the sudden opening of large amounts of overtwisted magnetic flux, which may be associated with the observed giant flares. These events are accompanied by a short period of ultra-strong spindown, resulting in an abrupt increase in spin period, such as was observed in the giant flare of SGR 1900+14.