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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Magnetar field evolution and crustal plasticity
TL;DR: In this paper, the authors suggest that magnetic flux transport/decay due to persistent plastic flow in the crust of a magnetar can explain the evolution of the corona of a single giant flare.
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The calm after the storm: XMM-Newton observation of SGR 1806-20 two months after the Giant Flare of 2004 December 27 ⋆
Andrea Tiengo,Paolo Esposito,Sandro Mereghetti,Nanda Rea,Nanda Rea,Luigi Stella,G. L. Israel,Roberto Turolla,Silvia Zane +8 more
TL;DR: In this article, the authors explore the possibility of descri bing the long-term spectral evolution as only due to the power-law variations and show that the spectral softening following a giant flare is caused by the increase of the relative contribution of the blackbody over the power law component.
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Sgr 0418+5729: a small inclination angle resulting in a not so low dipole magnetic field?
TL;DR: In this paper, the pulsar spin-down model of Contopoulos and Spitkovsky is applied to SGR 418+5729 and it is shown that SGR lies below the pulsars death line and its rotation-powered magnetospheric activities may therefore have stopped and the compact star is now spun down by the magnetic dipole moment perpendicular to its rotation axis.
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Low-magnetic-field magnetars
TL;DR: In this article, the authors summarize the observational status of low-magnetic-field magnetars and discuss their properties in the context of the mainstream magnetar model and its main alternatives.
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Pressure Balance and Intrabinary Shock Stability in Rotation-Powered State Redback and Transitional Millisecond Pulsar Binary Systems
TL;DR: In this paper, the pressure balance for low-mass millisecond pulsar (MSP) binaries in their rotation-powered state exhibits double-peaked X-ray orbital modulation centered at inferior pulsar conjunction.
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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