Force-free twisted magnetospheres of neutron stars


Autoria(s): Viganò, Daniele; Pons, José A.; Miralles Torres, Juan Antonio
Contribuinte(s)

Universidad de Alicante. Departamento de Física Aplicada

Astrofísica Relativista

Data(s)

12/11/2013

12/11/2013

13/09/2011

Resumo

Context. The X-ray spectra observed in the persistent emission of magnetars are evidence for the existence of a magnetosphere. The high-energy part of the spectra is explained by resonant cyclotron upscattering of soft thermal photons in a twisted magnetosphere, which has motivated an increasing number of efforts to improve and generalize existing magnetosphere models. Aims. We want to build more general configurations of twisted, force-free magnetospheres as a first step to understanding the role played by the magnetic field geometry in the observed spectra. Methods. First we reviewed and extended previous analytical works to assess the viability and limitations of semi-analytical approaches. Second, we built a numerical code able to relax an initial configuration of a nonrotating magnetosphere to a force-free geometry, provided any arbitrary form of the magnetic field at the star surface. The numerical code is based on a finite-difference time-domain, divergence-free, and conservative scheme, based of the magneto-frictional method used in other scenarios. Results. We obtain new numerical configurations of twisted magnetospheres, with distributions of twist and currents that differ from previous analytical solutions. The range of global twist of the new family of solutions is similar to the existing semi-analytical models (up to some radians), but the achieved geometry may be quite different. Conclusions. The geometry of twisted, force-free magnetospheres shows a wider variety of possibilities than previously considered. This has implications for the observed spectra and opens the possibility of implementing alternative models in simulations of radiative transfer aiming at providing spectra to be compared with observations.

This work was partly supported by CompStar, a Research Networking Program of the European Science Foundation and the Spanish grant AYA 2010-21097-C03-02. D. Viganò is supported by a fellowship from the Prometeo program for research groups of excellence of the Generalitat Valenciana.

Identificador

Astronomy & Astrophysics. 2011, 533: A125. doi:10.1051/0004-6361/201117105

0004-6361 (Print)

1432-0746 (Online)

http://hdl.handle.net/10045/33783

10.1051/0004-6361/201117105

Idioma(s)

eng

Publicador

EDP Sciences

Relação

http://dx.doi.org/10.1051/0004-6361/201117105

Direitos

© ESO, 2011

info:eu-repo/semantics/openAccess

Palavras-Chave #Stars: magnetic field #Stars: neutron #Magnetohydrodynamics (MHD) #Scattering #Astronomía y Astrofísica
Tipo

info:eu-repo/semantics/article