Relativistic coronal mass ejections from magnetars

TL;DR

This paper models the dynamics of relativistic coronal mass ejections from magnetars, exploring their launching, propagation, and effects on the magnetosphere, with implications for fast radio bursts and magnetar flares.

Contribution

It presents a detailed theoretical framework for understanding CMEs from magnetars, including the effects of different shear rates and the resulting magnetospheric phenomena.

Findings

Powerful CMEs can open the magnetosphere beyond the equipartition radius.

Post-CME magnetosphere relaxation involves plasmoid-mediated current sheets.

Shear type influences CME strength and magnetospheric response.

Abstract

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 over-laying magnetic field. At later stages, sufficiently powerful CMEs may experience ``detonation" and lead to opening of the magnetosphere beyond some equipartition radius $r_{eq}$, where the energy of the CME becomes larger than the decreasing external magnetospheric energy. Post-CME magnetosphere relaxes via formation of a plasmoid-mediated current sheet, initially at $\sim r_{eq}$ and slowly reaching the light cylinder (this transient stage has much higher spindown rate and may produce an ``anti-glitch''). Both the location of the foot-point shear and the global magnetospheric configuration affect the frequent-and-weak versus rare-and-powerful CME dichotomy - to produce powerful flares the slow shear should be limited to field lines that close near the star. After the creation of a topologically disconnected flux tube, the tube quickly (at $\sim$ 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 Alfven waves lead to opening of the magnetosphere (which later recovers similarly to the slow shear case). At distances much larger than the light cylinder, the resulting shear Alfven waves propagate through the wind non-dissipatively. Implications to Fast Radio Bursts are discussed.