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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Intensity and Polarization Characteristics of Extended Neutron Star Surface Regions
TL;DR: In this article , a convolution of varied properties of Stokes parameter information at disparate surface locales with different magnetic field strengths and directions relative to the local zenith is used to define local surface anisotropy and polarization signatures.
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Magnetar signature - the U curve
Vikram Soni,Vikram Soni,Dipankar Bhattacharya,Sameer Patel,Sameer Patel,Sajal Gupta,Prasanta Bera +6 more
TL;DR: In this paper, the authors look at some definitive signatures of magnetars, in particular of period closures accompanied by a decline of X-ray radiation in two models: the dynamo model and the screened core model.
Detailed Physical Modeling Reveals the Magnetar Nature of a Transient Anomalous X-ray Pulsar
TL;DR: In this article, the surface magnetic field strength of an anomalous X-ray pulsar (AXP) has been measured and the authors demonstrate that heating occurs in the upper neutron star crust during an outburst and shed light on the transient behaviour of AXPs.
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How else can we detect Fast Radio Bursts
Maxim Lyutikov,Duncan R. Lorimer +1 more
TL;DR: In this article, the authors discuss possible electromagnetic signals accompanying Fast Radio Bursts (FRBs) that are expected in the scenario where FRBs originate in neutron star magnetospheres, and conclude that the best chances are: (i) prompt short GRB-like emission; (ii) a contemporaneous optical flash that can reach naked eye peak luminosity (but only for a few milliseconds); (iii) a high energy afterglow emission.
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What can Fermi tell us about magnetars
TL;DR: In this article, the physical implications of Fermi observations of magnetars were analyzed and it was shown that magnetars are wind-braking instead of magnetic dipole braking.
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.