Electrodynamics of Magnetars: Implications for the Persistent X-ray Emission and Spindown of the Soft Gamma Repeaters and Anomalous X-ray Pulsars
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In this paper, the authors considered the structure of neutron star magnetospheres threaded by large-scale electrical currents and the effect of resonant Compton scattering by the charge carriers (both electrons and ions) on the emergent X-ray spectra and pulse profiles.Abstract:
(ABBREVIATED) We consider the structure of neutron star magnetospheres threaded by large-scale electrical currents, and the effect of resonant Compton scattering by the charge carriers (both electrons and ions) on the emergent X-ray spectra and pulse profiles. In the magnetar model for the SGRs and AXPs, these currents are maintained by magnetic stresses acting deep inside the star. We construct self-similar, force-free equilibria of the current-carrying magnetosphere with a power-law dependence of magnetic field on radius, B ~ r^(-2-p), and show that a large-scale twist softens the radial dependence to p < 1. The spindown torque acting on the star is thereby increased in comparison with a vacuum dipole. We comment on the strength of the surface magnetic field in the SGR and AXP sources, and the implications of this model for the narrow measured distribution of spin periods. A magnetosphere with a strong twist, B_\phi/B_\theta = O(1) at the equator, has an optical depth ~ 1 to resonant cyclotron scattering, independent of frequency (radius), surface magnetic field strength, or charge/mass ratio of the scattering charge. When electrons and ions supply the current, the stellar surface is also heated by the impacting charges at a rate comparable to the observed X-ray output of the SGR and AXP sources, if B_{dipole} ~ 10^{14} G. Redistribution of the emerging X-ray flux at the ion and electron cyclotron resonances will significantly modify the emerging pulse profile and, through the Doppler effect, generate a non-thermal tail to the X-ray spectrum. The sudden change in the pulse profile of SGR 1900+14 after the 27 August 1998 giant flare is related to an enhanced optical depth to electron cyclotron scattering, resulting from a sudden twist imparted to the external magnetic field.read more
Citations
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The timing behavior of magnetar Swift J1822.3 1606: timing noise or a decreasing period derivative?
TL;DR: In this paper, different timing results of the magnetar Swift J1822.3−1606 are analyzed and understood theoretically, and it is noted that different timing solutions are caused not only by timing noise, but also because the period derivative is decreasing after the outburst.
Journal ArticleDOI
Force-free twisted magnetospheres of neutron stars
TL;DR: In this article, a numerical code is proposed 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.
Journal ArticleDOI
The 2001 April Burst Activation of SGR 1900+14: Pulse Properties and Torque
P. M. Woods,Chryssa Kouveliotou,Ersin Gogus,Mark H. Finger,Marco Feroci,Sandro Mereghetti,Jean H. Swank,Kevin Hurley,John Heise,D. A. Smith,Filippo Frontera,C. Guidorzi,Christopher Thompson +12 more
TL;DR: In this article, the authors measured the spindown torque on the star and confirmed earlier findings that the torque and burst activity are not directly correlated, and compared the X-ray pulse profile to the gamma-ray profile during the April 18 intermediate flare.
Journal ArticleDOI
Searching for x-ray variability in the glitching anomalous x-ray pulsar 1e 1841–045 in kes 73
Weiwei Zhu,Victoria M. Kaspi +1 more
TL;DR: In this paper, an analysis of archival X-ray data from the AXP 1E 1841-045, obtained between 1993 and 2007, has been carried out to find no evidence for glitch-correlated flux changes from this source after 1999, supporting the existence of radiatively silent glitches in AXPs.
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Axisymmetric force-free magnetosphere in the exterior of a neutron star
TL;DR: In this paper, the axisymmetric solutions for the force-free field with a power-law current model are calculated by taking into account general relativistic effects, and it is shown how the magnetic energy and helicity are accumulated along a sequence of equilibria.
References
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