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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Time Resolved Spectroscopy of SGR J1550-5418 Bursts Detected with Fermi/Gamma-Ray Burst Monitor
George Younes,Chryssa Kouveliotou,A. J. van der Horst,Matthew G. Baring,J. Granot,Anna L. Watts,P. N. Bhat,A. C. Collazzi,N. Gehrels,N. Gorgone,Ersin Gogus,David Gruber,S. Grunblatt,Daniela Huppenkothen,Yuki Kaneko,A. von Kienlin,M. van der Klis,Lin Lin,Julie McEnery,T. van Putten,Ralph A. M. J. Wijers +20 more
TL;DR: In this paper, a time-resolved spectroscopy of the 63 brightest bursts of SGR J1550-5418, detected with the Fermi/Gamma-ray Burst Monitor during its 2008-2009 intense bursting episode, was performed down to 4ms timescales to characterize the spectral evolution of the bursts.
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On the excitation of f modes and torsional modes by magnetar giant flares
TL;DR: In this paper, an estimate of the initial post-flare amplitudes of the torsional modes in the magnetar crust and of the global vibrational modes of neutron stars was derived.
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Physics in Very Strong Magnetic Fields
TL;DR: In this paper, the authors provide an introduction to a number of astrophysics problems related to strong magnetic fields, including atoms, condensed matter and high-energy processes in very strong magnetic field, and how these issues influence various aspects of neutron star astrophysics.
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XMM-Newton discovery of 2.6 s pulsations in the soft gamma-ray repeater SGR 1627-41
Paolo Esposito,Paolo Esposito,Andrea Tiengo,Sandro Mereghetti,G. L. Israel,A. De Luca,A. De Luca,Diego Götz,Nanda Rea,Roberto Turolla,Roberto Turolla,Silvia Zane +11 more
TL;DR: In this article, the soft gamma-ray repeater SGR 1627-41 reactivated on 2008 May 28 with a bursting episode followed by a slowly decaying enhancement of its persistent emission.
References
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An X-ray pulsar with a superstrong magnetic field in the soft γ-ray repeater SGR1806 − 20
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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.