Triggering magnetar outbursts in 3D force-free simulations. (arXiv:1901.08889v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Carrasco_F/0/1/0/all/0/1">Federico Carrasco</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Vigano_D/0/1/0/all/0/1">Daniele Vigan&#xf2;</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Palenzuela_C/0/1/0/all/0/1">Carlos Palenzuela</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Pons_J/0/1/0/all/0/1">Jose A. Pons</a>

In this letter, we present the first 3D force-free general relativity
simulations of the magnetosphere dynamics related to the magnetar
outburst/flare phenomenology. Starting from an initial dipole configuration, we
adiabatically increase the helicity by twisting the footprints of a spot on the
stellar surface and follow the succession of quasi-equilibrium states until a
critical twist is reached. Twisting beyond that point triggers instabilities
that results in the rapid expansion of magnetic field lines, followed by
reconnection, as observed in previous axi-symmetric simulations. If the
injection of magnetic helicity goes on, the process is recurrent, periodically
releasing a similar amount of energy, of the order of a few % of the total
magnetic energy. From our current distribution, we estimate the local
temperature assuming that dissipation occurs mainly in the highly resistive
outermost layer of the neutron star. We find that the temperature smoothly
increases with injected twist, being larger for spots located in the tropical
regions than in polar regions, and rather independent of their sizes. After the
injection of helicity ceases, the magnetosphere relaxes to a new stable state,
in which the persistent currents maintain the footprints area slightly hotter
than before the onset of the instability.

In this letter, we present the first 3D force-free general relativity
simulations of the magnetosphere dynamics related to the magnetar
outburst/flare phenomenology. Starting from an initial dipole configuration, we
adiabatically increase the helicity by twisting the footprints of a spot on the
stellar surface and follow the succession of quasi-equilibrium states until a
critical twist is reached. Twisting beyond that point triggers instabilities
that results in the rapid expansion of magnetic field lines, followed by
reconnection, as observed in previous axi-symmetric simulations. If the
injection of magnetic helicity goes on, the process is recurrent, periodically
releasing a similar amount of energy, of the order of a few % of the total
magnetic energy. From our current distribution, we estimate the local
temperature assuming that dissipation occurs mainly in the highly resistive
outermost layer of the neutron star. We find that the temperature smoothly
increases with injected twist, being larger for spots located in the tropical
regions than in polar regions, and rather independent of their sizes. After the
injection of helicity ceases, the magnetosphere relaxes to a new stable state,
in which the persistent currents maintain the footprints area slightly hotter
than before the onset of the instability.

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