Three-dimensional dynamics of strongly twisted magnetar magnetospheres: Kinking flux tubes and global eruptions

Creators: Mahlmann, J. F.; Philippov, A. A.; Mewes, V.; Ripperda, B.; Most, E. R.; Sironi, L.

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.

Additional Information

We are grateful for the helpful suggestions by the referee, especially regarding the analysis of outgoing fast modes from confined eruptions. The authors thank A. Beloborodov, P. Cerdá-Durán, F. Bacchini, M. Gabler, H. Hakobyan, Y. Lyubarky, K. Parfrey, E. Novoselov, A. Spitkovsky, P. Stefanou, C. Thompson, and Z. Wadiasingh for useful discussions. We thank M. Elmassry for engaging in the Princeton Writing Program and giving comments to improve our manuscript. We are grateful for the funding provided through NASA grant 80NSSC18K1099. A.A.P. and J.F.M. acknowledge support by the National Science Foundation under grant No. AST-1909458. This research was facilitated by the Multimessenger Plasma Physics Center (MPPC), NSF grant PHY-2206607. V.M. is supported by the Exascale Computing Project (17-SC-20-SC), a collaborative effort of the U.S. Department of Energy (DOE) Office of Science and the National Nuclear Security Administration. Work at Oak Ridge National Laboratory is supported under contract DE-AC05-00OR22725 with the U.S. Department of Energy. Support for this work was provided by NASA through the NASA Hubble Fellowship grant HST-HF2-51518.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. E.R.M. gratefully acknowledges support as the John A. Wheeler Fellow at the Princeton Center for Theoretical Science, the Princeton Gravity Initiative, and the Institute for Advanced Study. This research is part of the Frontera (Stanzione et al. 2020) computing project at the Texas Advanced Computing Center (LRAC-AST21006). Frontera is made possible by the National Science Foundation award OAC-1818253. The presented numerical simulations were further enabled by the MareNostrum supercomputer (Red Española de Supercomputación, AECT-2021-1-0006), and by the VSC (Flemish Supercomputer Center), funded by the Research Foundation Flanders (FWO) and the Flemish Government—department EWI. E.R.M. acknowledges support through the Extreme Science and Engineering Discovery Environment (XSEDE; Towns et al. 2014) through Expanse at SDSC and Bridges-2 at PSC through allocations PHY210053 and PHY210074. The authors further acknowledge supported by Princeton Research Computing, a consortium of groups including the Princeton Institute for Computational Science and Engineering (PICSciE) and the Office of Information Technology's High-Performance Computing Center and Visualization Laboratory at Princeton University.

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