We find a class of twisted and differentially rotating neutron star magnetospheres that do not have a light cylinder, generate no wind, and thus do not spin-down. The magnetosphere is composed of embedded differentially rotating flux surfaces, with the angular velocity decreasing as Ω ∝ 1/r (equivalently, becoming smaller at the foot-points closer to the axis of rotation). For each given North–South self-similar twist profile there is a set of self-similar angular velocity profiles (limited from above) with a ‘smooth’, dipolar-like magnetic field structure extending to infinity. For spin parameters larger than some critical value, the light cylinder appears, magnetosphere opens up, and the wind is generated.
Relativistic coronal mass ejections from magnetars
We study dynamics of relativistic coronal mass ejections (CMEs), from launching by shearing of foot-points (either slowly – the ‘Solar flare’ paradigm, or suddenly – the ‘star quake’ paradigm), to propagation in the preceding magnetar wind. For slow shear, most of the energy injected into the CME is first spent on the work done on breaking through the overlaying magnetic field. At later stages, sufficiently powerful CMEs may lead to the ‘detonation’ of a CME and opening of the magnetosphere beyond some equipartition radius req, where the decreasing energy of the CME becomes larger than the decreasing external magnetospheric energy. Post-CME magnetosphere relaxes via the formation of a plasmoid-mediated current sheet, initially at ∼req, and slowly reaching the light cylinder. Both the location of the foot-point shear and the global magnetospheric configuration affect the frequent/weak versus rare/powerful CME dichotomy – to produce powerful flares, the slow shear should be limited to field lines that close in near the star. After the creation of a topologically disconnected flux tube, the tube quickly (at ∼ the light cylinder) comes into force-balance with the preceding wind and is passively advected/frozen in the wind afterward. For fast shear (a local rotational glitch), the resulting large amplitude Alfvén waves lead to the opening of the magnetosphere (which later recovers similarly to the slow shear case). At distances much larger than the light cylinder, the resulting shear Alfvén waves propagate through the wind non-dissipatively.
more » « less- NSF-PAR ID:
- 10439627
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 524
- Issue:
- 4
- ISSN:
- 0035-8711
- Page Range / eLocation ID:
- p. 6024-6051
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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