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arXiv · 1610.10036

Particle-in-cell simulations of the twisted magnetospheres of magnetars

Alexander Y. Chen·Andrei M. Beloborodov
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Abstract

The magnetospheres of magnetars are believed to be filled with electron-positron plasma generated by electric discharge. We present a first direct numerical experiment showing how the plasma is created in an axisymmetric closed magnetosphere. The $e^\pm$ discharge occurs in response to twisting of the magnetic field lines by a shear deformation of the magnetar surface, which launches electric currents into the magnetosphere. The simulation shows the formation of an electric "gap" with unscreened electric field ($\mathbf{E}\cdot \mathbf{B}\neq 0$) that continually accelerates particles along the magnetic field lines and sustains pair creation. The accelerating voltage is self-regulated to the threshold of the $e^\pm$ discharge. It controls the rate of energy release and the lifetime of the magnetic twist. The simulation follows the global evolution of the twisted magnetosphere over a long time and demonstrates its gradual resistive untwisting. A vacuum cavity forms near the star and expands, gradually erasing magnetospheric electric currents $j$. The active j-bundle shrinks with time and its footprints form shrinking hot spots on the magnetar surface bombarded by the created particles.

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Alexander Y. Chen, Andrei M. Beloborodov. 2016-10-31. Particle-in-cell simulations of the twisted magnetospheres of magnetars. https://doi.org/10.3847/1538-4357%2Faa7a57

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