The force-free twisted magnetosphere of a neutron star – II. Degeneracies of the Grad–Shafranov equation

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Title: The force-free twisted magnetosphere of a neutron star – II. Degeneracies of the Grad–Shafranov equation
Authors: Akgün, Taner | Cerdá-Durán, Pablo | Miralles, Juan A. | Pons, José A.
Research Group/s: Astrofísica Relativista
Center, Department or Service: Universidad de Alicante. Departamento de Física Aplicada
Keywords: Magnetic fields | MHD | Stars: magnetars | Stars: magnetic field | Stars: neutron
Knowledge Area: Astronomía y Astrofísica
Issue Date: 11-Feb-2018
Publisher: Oxford University Press
Citation: Monthly Notices of the Royal Astronomical Society. 2018, 474(1): 625-635. doi:10.1093/mnras/stx2814
Abstract: We extend our previous study of equilibrium solutions of non-rotating force-free magnetospheres of neutron stars. We show that multiple solutions exist for the same sets of parameters, implying that the solutions are degenerate. We are able to obtain configurations with disconnected field lines, however, in nearly all cases these correspond to degenerate higher energy solutions. We carry out a wide parametric search in order to understand the properties of the solutions. We confirm our previous results that the lower energy solutions have up to ∼ 25 per cent more energy than the vacuum case, helicity of the order of ∼5 (in some defined units), maximum twist of ∼1.5 rad and a dipole strength that is up to ∼ 40 per cent larger than the vacuum dipole. Including the degenerate higher energy solutions allows for larger theoretical limits of up to ∼ 80 per cent more energy with respect to the vacuum case, helicity of the order of ∼8 and a dipole strength that can now be up to four times that of the vacuum dipole, while the twist can be significantly larger and even diverge for configurations with disconnected domains. The higher energy solutions are probably unstable, therefore, it is unlikely that such magnetospheres exist under normal conditions in magnetars and high magnetic field pulsars.
Sponsor: This work is supported in part by the Spanish MINECO/FEDER grants AYA2015-66899-C2-1-P, AYA2015-66899-C2-2-P, the grant of Generalitat Valenciana PROMETEOII-2014-069, and by the New Compstar COST action MP1304.
URI: http://hdl.handle.net/10045/75268
ISSN: 0035-8711 (Print) | 1365-2966 (Online)
DOI: 10.1093/mnras/stx2814
Language: eng
Type: info:eu-repo/semantics/article
Rights: © 2017 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society
Peer Review: si
Publisher version: https://doi.org/10.1093/mnras/stx2814
Appears in Collections:INV - Astrofísica Relativista - Artículos de Revistas

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