MG13 - Talk detail

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Anomalous X-ray Pulsars (AXPs) and Soft Gamma-ray Repeaters (SGRs) constitute a special class of young neutron stars, which are thought to be magnetars, i.e. neutron stars with superstrong magnetic fields (>10e14 G). Undoubtedly, the strong superEddington bursts and giant flares must be powered by the decay of strong magnetic fields. However, the quiescent X-ray emission having typical luminosities of ~10e35 erg/s may be produced by the accretion of matter from a fall-back disk, that has been formed in the supernova explosion. In our model the required dipole field strengths are normal (10e12-10e13 G), while the sources of bursts and giant flares are located in localized superstrong multipole fields and triggered by crustal shifts. The accretion scenario is supported by the recent discovery of an AXP having a modest magnetic dipole field (< 7x10e12 G). I will discuss a model explaining the detailed spectral characteristics and energy dependent pulse profiles of the AXP 4U 0142+61. In this model the wide band X-ray emission (0.8-150 keV) is explained by thermal and bulk Comptonization in the accretion column leading to a fan beam and soft blackbody emission from the hot polar cap. This model explains why the temperature of the polar cap is much higher than those of other young neutron stars and provides evidence for a cyclotron resonance scattering feature, requiring a polar magnetic field of ~(7-8)x10e12 G.

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