UCL Discovery
UCL home » Library Services » Electronic resources » UCL Discovery

Topology of magnetars external field - I. Axially symmetric fields

Pavan, L; Turolla, R; Zane, S; Nobili, L; (2009) Topology of magnetars external field - I. Axially symmetric fields. Monthly Notices of the Royal Astronomical Society , 395 (2) 753 - 763. 10.1111/j.1365-2966.2009.14600.x. Green open access

[thumbnail of 178102.pdf]
Preview
PDF
178102.pdf
Available under License : See the attached licence file.

Download (1MB)

Abstract

There is an increasing theoretical and observational evidence that the external magnetic field of magnetars may contain a toroidal component, likely of the same order of the poloidal one. Such ‘twisted magnetospheres’ are threaded by currents flowing along the closed field lines which can efficiently interact with soft thermal photons via resonant cyclotron scatterings (RCS). Actually, RCS spectral models proved quite successful in explaining the persistent ∼1–10 keV emission from the magnetar candidates, the soft γ-ray repeaters (SGRs) and the anomalous X-ray pulsars (AXPs). Moreover, it has been proposed that, in the presence of highly relativistic electrons, the same process can give rise to the observed hard X-ray spectral tails extending up to ∼200 keV. Spectral calculations have been restricted up to now to the case of a globally twisted dipolar magnetosphere, although there are indications that the twist may be confined only to a portion of the magnetosphere, and/or that the large-scale field is more complex than a simple dipole. In this paper, we investigate multipolar, force–free magnetospheres of ultramagnetized neutron stars. We first discuss a general method to generate multipolar solutions of the Grad-Schlüter-Shafranov (GSS) equation, and analyse in detail dipolar, quadrupolar and octupolar fields. The spectra and lightcurves for these multipolar, globally twisted fields are then computed using a Monte Carlo code and compared with those of a purely dipolar configuration. Finally, the phase-resolved spectra and energy-dependent lightcurves obtained with a simple model of a locally sheared field are confronted with the International Gamma-Ray Astrophysics Laboratory (INTEGRAL) observations of the AXPs 1RXS J1708−4009 and 4U 0142+61. Results support a picture in which the field in these two sources is not globally twisted.

Type: Article
Title: Topology of magnetars external field - I. Axially symmetric fields
Open access status: An open access version is available from UCL Discovery
DOI: 10.1111/j.1365-2966.2009.14600.x
Publisher version: http://dx.doi.org/10.1111/j.1365-2966.2009.14600.x
Language: English
Additional information: © 2009 RAS Definitive versions of articles pre-2013 are available at http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1365-2966, now published by http://mnras.oxfordjournals.org
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics
URI: https://discovery.ucl.ac.uk/id/eprint/178102
Downloads since deposit
104Downloads
Download activity - last month
Download activity - last 12 months
Downloads by country - last 12 months

Archive Staff Only

View Item View Item