Untwisting magnetospheres of neutron stars
Andrei M. Beloborodov (Columbia University)

TL;DR
This paper develops a model describing how twisted magnetospheres of neutron stars untwist over time, dissipate energy, and produce observable radiation, explaining behaviors of magnetars like XTE J1810-197.
Contribution
The paper derives an evolution equation for magnetospheric untwisting, identifying distinct regions and linking the process to observable features such as hot spots and radio emission.
Findings
The untwisting magnetosphere features a cavity and a j-bundle with a shrinking hot spot.
The twist amplitude can reach up to ~1 during evolution.
The model explains the behavior of magnetar XTE J1810-197.
Abstract
Magnetospheres of neutron stars are anchored in the rigid crust and can be twisted by sudden crustal motions ("starquakes"). The twisted magnetosphere does not remain static and gradually untwists, dissipating magnetic energy and producing radiation. The equation describing this evolution is derived, and its solutions are presented. Two distinct regions coexist in untwisting magnetospheres: a potential region where curl(B)=0 ("cavity") and a current-carrying bundle of field lines ("j-bundle"). The cavity has a sharp boundary, which expands with time and eventually erases all of the twist. In this process, the electric current of the j-bundle is sucked into the star. Observational appearance of the untwisting process is discussed. A hot spot forms at the footprints of the j-bundle. The spot shrinks with time toward the magnetic dipole axis, and its luminosity and temperature gradually…
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Taxonomy
TopicsPulsars and Gravitational Waves Research · Earthquake Detection and Analysis · Geophysics and Sensor Technology
