The force-free twisted magnetosphere of a neutron star

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Title: The force-free twisted magnetosphere of a neutron star
Authors: Akgün, Taner | Miralles, Juan A. | Pons, José A. | Cerdá-Durán, Pablo
Research Group/s: Astrofísica Relativista
Center, Department or Service: Universidad de Alicante. Departamento de Física Aplicada
Keywords: Magnetic fields | MHD | Stars: magnetars | Stars: neutron
Knowledge Area: Astronomía y Astrofísica
Issue Date: 21-Oct-2016
Publisher: Oxford University Press
Citation: Monthly Notices of the Royal Astronomical Society. 2016, 462(2): 1894-1909. doi:10.1093/mnras/stw1762
Abstract: We present a detailed analysis of the properties of twisted, force-free magnetospheres of non-rotating neutron stars, which are of interest in the modelling of magnetar properties and evolution. In our models the magnetic field smoothly matches to a current-free (vacuum) solution at some large external radius, and they are specifically built to avoid pathological surface currents at any of the interfaces. By exploring a large range of parameters, we find a few remarkable general trends. We find that the total dipolar moment can be increased by up to 40 per cent with respect to a vacuum model with the same surface magnetic field, due to the contribution of magnetospheric currents to the global magnetic field. Thus, estimates of the surface magnetic field based on the large-scale dipolar braking torque are slightly overestimating the surface value by the same amount. Consistently, there is a moderate increase in the total energy of the model with respect to the vacuum solution of up to 25 per cent, which would be the available energy budget in the event of a fast, global magnetospheric reorganization commonly associated with magnetar flares. We have also found the interesting result of the existence of a critical twist (φmax ≲ 1.5 rad), beyond which we cannot find any more numerical solutions. Combining the models considered in this paper with the evolution of the interior of neutron stars will allow us to study the influence of the magnetosphere on the long-term magnetic, thermal, and rotational evolution.
Sponsor: This work is supported in part by the Spanish MINECO grants AYA2013-40979-P, AYA2013-42184-P, and AYA2015-66899-C2-2-P, the grant of Generalitat Valenciana PROMETEOII-2014-069, the European Union ERC Starting Grant 259276-CAMAP, and by the New Compstar COST action MP1304.
ISSN: 0035-8711 (Print) | 1365-2966 (Online)
DOI: 10.1093/mnras/stw1762
Language: eng
Type: info:eu-repo/semantics/article
Rights: © 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society
Peer Review: si
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Appears in Collections:INV - Astrofísica Relativista - Artículos de Revistas

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