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Victoria M. Kaspi 《Astrophysics and Space Science》2007,308(1-4):1-11
I review recent observational progress on Anomalous X-ray Pulsars, with an emphasis on timing, variability, and spectra. Highlighted
results include the recent timing and flux stabilization of the notoriously unstable AXP 1E 1048.1–5937, the remarkable glitches
seen in two AXPs, and the newly recognized variety of AXP variability types, including outbursts, bursts, flares, and pulse
profile changes. I also discuss recent discoveries regarding AXP spectra, including their surprising hard X-ray and far-infrared
emission, as well as the pulsed radio emission seen in one source. Much has been learned about these enigmatic objects over
the past few years, with the pace of discoveries remaining steady. However additional work on both observational and theoretical
fronts is needed before we have a comprehensive understanding of AXPs and their place in the zoo of manifestations of young
neutron stars.
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2.
The recent discovery of high frequency oscillations during giant flares from the Soft Gamma Repeaters SGR 1806-20 and SGR
1900+14 may be the first direct detection of vibrations in a neutron star crust. If this interpretation is correct it offers
a novel means of testing the neutron star equation of state, crustal breaking strain, and magnetic field configuration. We
review the observational data on the magnetar oscillations, including new timing analysis of the SGR 1806-20 giant flare using
data from the Ramaty High Energy Solar Spectroscopic Imager and the Rossi X-ray Timing Explorer. We discuss the implications for the study of neutron star structure and crust thickness, and outline areas for future investigation.
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3.
We have presently derived the positive-energy solutions to the Dirac equation minimally coupled to a depth-dependent spatially harmonic tangential magnetostatic field to the magnetar crust, similar to the one proposed by Wareing and Hollerbach. It turns out that, for ultra-relativistic fermions and time-intervals much less the characteristic time (comparable to the average Ohmic timescale in the crust), the corresponding linearly independent modes get their depth-dependent amplitudes expressed in terms of Mathieu’s functions and therefore, non-trivial resonances arise, leading to instabilities in the system, for computable ranges of the model parameters. In order to detail these features, we have also discussed the current density components, pointing out the regions for which the particle density has a double bounded modulation. Finally as the magnetic field induction is increasing, the instability range gets larger triggering the exponential growth of the amplitudes, once the imaginary part of the Mathieu Characteristic Exponent becomes more and more dominant. 相似文献
4.
Nanda Rea Silvia Zane Maxim Lyutikov Roberto Turolla 《Astrophysics and Space Science》2007,308(1-4):61-65
The X-ray spectra of the magnetar candidates are customarily fitted with an empirical, two component model: an absorbed blackbody
and a power-law. However, the physical interpretation of these two spectral components is rarely discussed. It has been recently
proposed that the presence of a hot plasma in the magnetosphere of highly magnetized neutron stars might distort, through
efficient resonant cyclotron scattering, the thermal emission from the neutron star surface, resulting in production of non-thermal
spectra. Here we discuss the Resonant Cyclotron Scattering (RCS) model, and present its XSPEC implementation, as well as preliminary
results of its application to Anomalous X-ray Pulsars and Soft Gamma-ray Repeaters.
N.R. is supported by an NWO Post-Doctoral Fellowship. S.Z. thanks the Particle Physics and Astronomy Research Council, PPARC,
for support through an Advanced Fellowship. 相似文献
5.
Kostas Glampedakis Lars Samuelsson Nils Andersson 《Astrophysics and Space Science》2007,308(1-4):607-611
The presence of a magnetic field in a neutron star interior results in a dynamical coupling between the fluid core and the
elastic crust. We consider a simple toy-model where this coupling is taken into account and compute the system’s mode oscillations.
Our results suggest that the notion of pure torsional crust modes is not useful for the coupled system, instead all modes
excite Alfvén waves in the core. However, we also show that among a rich spectrum of global MHD modes the ones most likely
to be excited by a fractured crust are those for which the crust and the core oscillate in concert. For our simple model,
the frequencies of these modes are similar to the “pure crustal” frequencies. We advocate the significant implications of
these results for the attempted theoretical interpretation of QPOs during magnetar flares in terms of neutron star oscillations.
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