Three-dimensional Dynamics of Strongly Twisted Magnetar Magnetospheres: Kinking Flux Tubes and Global Eruptions

Abstract

The origins of the various outbursts of hard X-rays from magnetars (highly magnetized neutron stars) are still unknown. We identify instabilities in relativistic magnetospheres that can explain a range of X-ray flare luminosities. Crustal surface motions can twist the magnetar magnetosphere by shifting the frozen-in footpoints of magnetic field lines in current-carrying flux bundles. Axisymmetric (2D) magnetospheres exhibit strong eruptive dynamics, i.e., catastrophic lateral instabilities triggered by a critical footpoint displacement of ψ crit ≳ π. In contrast, our new three-dimensional (3D) twist models with finite surface extension capture important non-axisymmetric dynamics of twisted force-free flux bundles in dipolar magnetospheres. Besides the well-established global eruption resulting (as in 2D) from lateral instabilities, such 3D structures can develop helical, kink-like dynamics, and dissipate energy locally (confined eruptions). Up to 25% of the induced twist energy is dissipated and available to power X-ray flares in powerful global eruptions, with most of our models showing an energy release in the range of the most common X-ray outbursts, ≲1043 erg. Such events occur when significant energy builds up while deeply buried in the dipole magnetosphere. Less energetic outbursts likely precede powerful flares, due to intermittent instabilities and confined eruptions of a continuously twisting flux tube. Upon reaching a critical state, global eruptions produce the necessary Poynting-flux-dominated outflows required by models prescribing the fast radio burst production in the magnetar wind—for example, via relativistic magnetic reconnection or shocks.

Electromagnetic Precursors to Black Hole–Neutron Star Gravitational Wave Events: Flares and Reconnection-powered Fast Radio Transients from the Late Inspiral

“…This situation is loosely similar to the polar flaring dynamics of magnetar explosions (Parfrey et al 2013;Carrasco et al 2019). For these, Mahlmann et al (2023) have recently shown that depending on the latitude of the footpoint of the twisted flux tube, it will either flare or become kink unstable, thereby dissipating part of the twist. The distinction between the two states directly results from the different locations inside the magnetosphere that experience the twist.…”

Monster Radiative Shocks in the Perturbed Magnetospheres of Neutron Stars

“…In addition to sudden quakes, the crust may flow plastically and slowly twist a magnetospheric flux bundle to an instability threshold. Three-dimensional simulations of this process demonstrate that relaxation of the unstable flux bundle generates fast magnetosonic waves in the magnetosphere (Mahlmann et al 2023).…”

A Unified Picture of Short and Long Gamma-Ray Bursts from Compact Binary Mergers

“…In the hybrid scenario, Most & Quataert (2023) demonstrated how the differentially rotating HMNS builds loops with footpoints at different latitudes on its surface. The resultant twist in the loop causes it to become unstable, inflate, and buoyantly rise, forming a bubble that is entirely detached from the HMNS surface and erupts after reconnecting (e.g., Carrasco et al 2019;Mahlmann et al 2023;Most & Quataert 2023). This behavior powers quasiperiodic flares prior to the jet formation.…”