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تسجيل مستخدم جديدX-ray spectra from magnetar candidates - III. Fitting SGRs/AXPs soft X-ray emission with non-relativistic Monte Carlo models
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S. Zane
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Within the magnetar scenario, the twisted magnetosphere model appears very promising in explaining the persistent X-ray emission from the Soft Gamma Repeaters and the Anomalous X-ray Pulsars (SGRs and AXPs). In the first two papers of the series, we have presented a 3D Monte Carlo code for solving radiation transport as soft, thermal photons emitted by the star surface are resonantly upscattered by the magnetospheric particles. A spectral model archive has been generated and implemented in XSPEC. Here we report on the systematic application of our spectral model to different XMM-Newton and Integral observations of SGRs and AXPs. We find that the synthetic spectra provide a very good fit to the data for the nearly all the source (and source states) we have analyzed.
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The anomalous X-ray pulsars and soft gamma-repeaters are peculiar high-energy sources believed to host a magnetar, i.e. an ultra-magnetized neutron star. Their persistent, soft X-ray emission (~1-10 keV)is usually modeled by the superposition of a bl
ackbody and a power-law tail. It has been suggested that this spectrum forms as the thermal photons emitted by the star surface traverse the magnetosphere. Magnetar magnetospheres are likely different from those of ordinary radio-pulsars, since the external magnetic field may acquire a toroidal component as a consequence of the deformation of the star crust induced by the super-strong interior field. In turn, the magnetosphere will be permeated by currents that can boost primary photons through repeated scatterings. Here we present 3D Monte Carlo simulations of photon propagation in a twisted magnetosphere. Our model is based on a simplified treatment of the charge carriers velocity distribution which, however, accounts for the particle collective motion, in addition to the thermal one. Present treatment is restricted to conservative (Thomson) scattering in the electron rest frame. The code, nonetheless, is completely general and inclusion of the relativistic QED resonant cross section, which is required in the modeling of the hard (~20-200 keV) spectral tails observed in the magnetar candidates, is under way. The properties of emerging spectra have been assessed under different conditions, by exploring the model parameter space, including effects arising from the viewing geometry. Monte Carlo runs have been collected into a spectral archive. Two tabulated XSPEC spectral models, with and without viewing angles, have been produced and applied to the 0.1-10 keV XMM-Newton EPIC-pn spectrum of the AXP CXOU J1647-4552.
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