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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 blackbody 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.
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
Recent models of spectral formation in magnetars called renewed attention on electron-photon scattering in the presence of ultra-strong magnetic fields. Investigations presented so far mainly focussed on mildly relativistic particles and magnetic sca
Magnetars are believed to host the strongest magnetic fields in the present universe ($Bgtrsim10^{14}$ G) and the study of their persistent emission in the X-ray band offers an unprecendented opportunity to gain insight into physical processes in the
We present time-domain Monte Carlo simulations of radio emission from cosmic ray air showers in the scheme of coherent geosynchrotron radiation. Our model takes into account the important air shower characteristics such as the lateral and longitudina
Blue shifted absorption lines from highly ionised iron are seen in some high inclination X-ray binary systems, indicating the presence of an equatorial disc wind. This launch mechanism is under debate, but thermal driving should be ubiquitous. X-ray