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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Journal ArticleDOI
Detailed X-ray spectroscopy of the magnetar 1E 2259+586
D. Pizzocaro,Andrea Tiengo,Andrea Tiengo,Sandro Mereghetti,Roberto Turolla,Roberto Turolla,Paolo Esposito,Paolo Esposito,Luigi Stella,Silvia Zane,Nanda Rea,Nanda Rea,F. Coti Zelati,G. L. Israel +13 more
TL;DR: In this article, a phase-variable absorption feature in the X-ray spectrum of SGR 0418+5729, interpreted as cyclotron resonant scattering, suggests the presence of very strong non-dipolar components in the magnetic fields of magnetars.
Journal ArticleDOI
Nonlinear force-free configurations in cylindrical geometry
TL;DR: In this paper, a new family of solutions for force-free magnetic structures in cylindrical geometry was proposed, which have radial power-law dependence and are periodic but non-harmonic in the azimuthal direction.
Journal ArticleDOI
Topology of magnetars external field. I. Axially symmetric fields
TL;DR: In this article, a general method to generate multipolar solutions of the Grad- Schluter-Shafranov equation was discussed, and the spectra and lightcurves for these multipolar, globally twisted magnetospheres were compared with those of a purely dipolar configuration.
Journal ArticleDOI
Nonlinear force-free configurations in cylindrical geometry.
TL;DR: In this article, a new family of solutions for force-free magnetic structures in cylindrical geometry was proposed, which have radial power-law dependance and are periodic but non-harmonic in azimuthal direction.
Journal ArticleDOI
Dark matter stars from beyond General Relativity models: Magnetosphere dynamics and torsion fields
TL;DR: In this article, the magnetosphere structure of compact objects is considered in the context of a theory of gravity with dynamical torsion field beyond standard General Relativity (GR) introduced previously in Cirilo-Lombardo and Minotti.
References
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An X-ray pulsar with a superstrong magnetic field in the soft γ-ray repeater SGR1806 − 20
Chryssa Kouveliotou,Chryssa Kouveliotou,S. Dieters,S. Dieters,Tod E. Strohmayer,Tod E. Strohmayer,J. van Paradijs,Gerald J. Fishman,Charles A. Meegan,Kevin Hurley,Jefferson M. Kommers,Ian Smith,Dale A. Frail,Toshio Murakami +13 more
TL;DR: In this paper, the authors reported the discovery of pulsations in the persistent X-ray flux of SGR1806-20, with a period of 7.47 s and a spindown rate of 2.6 x 10(exp -3) s/yr.