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abstract: 'We present three-dimensional force-free electrodynamics simulations of magnetar magnetospheres that demonstrate the instability of certain degenerate, high energy equilibrium solutions of the Grad-Shafranov equation. This result indicates the existence of an unstable branch of twisted magnetospheric solutions and allows to formulate an instability criterion. The rearrangement of magnetic field lines as a consequence of this instability triggers the dissipation of up to 30% of the magnetospheric energy on a thin layer above the magnetar surface. During this process, we predict an increase of the mechanical stresses onto the stellar crust, which can potentially result in a global mechanical failure of a significant fraction of it. We find that the estimated energy release and the emission properties are compatible with the observed giant flare events. The newly identified instability is a candidate for recurrent energy dissipation, which could explain part of the phenomenology observed in magnetars.'
author:
- |
    J. F. Mahlmann$^1$[^1], T. Akgün$^2$, J. A. Pons$^2$, M.A. Aloy$^1$ and P. Cerdá-Durán$^1$[^2]\
    $^1$Departament d’Astronomia i Astrofísica, Universitat de València, 46100, Burjassot, Spain\
    $^2$Departament de Fisica Aplicada, Universitat d’Alacant, 03690, Alicante, Spain
bibliography:
- 'literature.bib'
date: 'Accepted 2019 September 25. Received 2019 September 22; in original form 2019 July 31'
