3D dynamics of magnetar magnetospheres: Kinked fluxtubes and global eruptions

The origin of outbursts of hard X-rays from highly magnetized neutron stars is still unknown, yet the release of magnetic energy through kink and tearing instabilities in magnetar magnetospheres can explain such flaring activity. Crustal surface motions twist the magnetar magnetosphere by shifting frozen-in footpoints of magnetic field lines. 2D axisymmetric magnetospheres develop catastrophic instabilities when their displacement angle along the magnetar surface exceeds 180 degrees. The release of strong toroidal fields buried deep inside the magnetosphere can power events up to the observed energetics of giant flares, $10^47$ erg. However, 2D models are dimensionally restricted, and important non-axisymmetric dynamics are not captured. Thus, we model the full 3D dynamics of twisted force-free flux bundles in dipolar magnetospheres. In this 3D setup, a slowly rotating disc on the stellar surface (hotspot) gradually twists an extended flux tube. For varying hotspot locations and extent, the flux bundle develops different instabilities. While twists applied at higher latitudes quickly open up the dipole magnetosphere, the kink instability can develop closer to the star and dissipate magnetic energy locally along closed field lines. We discuss criteria for the development of different instabilities and how they can be distinguished in X-ray flare observations by the amount of released energy.