Broad-band X-ray spectra of anomalous X-ray pulsars and soft γ-ray repeaters: pulsars in a weak-accretion regime?

Abstract

We present the results from the analysis of the broad-band X-ray spectra of five anomalous X-ray pulsars (AXPs) and soft γ-ray repeaters (SGRs). We fit their Suzaku and INTEGRAL spectra with models appropriate for the X-ray emission from the accretion flow on to a pulsar. We find that their X-ray spectra can be well described with this model. In particular, we find that (a) the radius of the accretion column is ∼150-350 m resulting in a transverse optical depth of ∼1, (b) the vertical Thompson optical depth is ≈50-400, and (c) their luminosity translates in accretion rates ≈ 10¹⁵ g s^{- 1}. These results are in good agreement with the predictions from the fall-back disc model, providing further support in the interpretation of AXPs and SGRs as accreting pulsars.