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
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Rossi x-ray timing explorer monitoring of the anomalous x-ray pulsar 1e 1048.1 – 5937: long-term variability and the 2007 march event
TL;DR: The Rossi X-ray Pulsar 1E 1048.1 - 5937 (RXTE) was reactivated in 2007 March 26 (MJD 54185.9), contemporaneous with the onset of a pulsed-flux flare.
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The Anomalous X-ray Pulsar 4U 0142+61: Variability in the infrared and a spectral break in the optical
TL;DR: In this article, the authors present new optical and infrared observations of the counterpart to the anomalous X-ray Pulsar (AXP) 4U 0142+61 taken with the Keck I telescope.
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Post-outburst observations of the magnetically active pulsar J1846-0258. a new braking index, increased timing noise, and radiative recovery
Margaret A. Livingstone,Cherry Ng,Victoria M. Kaspi,Fotis P. Gavriil,Fotis P. Gavriil,Eric V. Gotthelf +5 more
TL;DR: In this article, the Rossi X-ray Timing Explorer was used to measure the braking index of the pulsar J1846-0258, which was found to be 2.16+/-0.13, a decrease of 18+/-5%.
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The Quiescent Counterpart of the Soft Gamma-Ray Repeater SGR 0526–66
Shrinivas R. Kulkarni,David L. Kaplan,Herman L. Marshall,Dale A. Frail,Toshio Murakami,Daisuke Yonetoku +5 more
TL;DR: In this article, Chandra observations of RX J052600.3� 660433, the quiescent X-ray counterpart of SGR 0526� 66, famous for the intense burst of 1979 March 5, were used to find evidence for a similar periodicity in two epochs of data obtained 20 months apart.
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An XMM-Newton View of the Soft Gamma Repeater SGR 1806-20: Long-Term Variability in the Pre-Giant Flare Epoch
Sandro Mereghetti,Andrea Tiengo,Andrea Tiengo,Paolo Esposito,Paolo Esposito,D. Götz,Luigi Stella,G. L. Israel,Nanda Rea,Nanda Rea,Marco Feroci,Roberto Turolla,Silvia Zane +12 more
TL;DR: In this article, the low-energy X-ray emission of the soft gamma repeater SGR 1806-20 has been studied by means of four XMM-Newton observations carried out in the last two years, the latest performed in response to a strong sequence of hard Xray bursts observed on 2004 October 5, the source was caught in different states of activity; over the 2003-2004 period, the 2-10 keV flux doubled with respect to the historical level observed previously.
References
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