Extinction and Distance to Anomalous X-ray Pulsars from X-ray Scattering Halos

Abstract

We analyze the X-ray scattering halos around three Galactic Anomalous X-ray Pulsars (AXPs) in order to constrain the distance and the optical extinction of each source. We obtain surface brightness distributions from EPIC-pn data obtained with XMM-Newton, compare the profiles of different sources, and fit them with a model based on the standard theory of X-ray scattering by dust grains, both for a uniform distribution of dust along the line of sight, and for dust distributions constrained by previous measurements. Somewhat surprisingly, we find that for all three sources, the uniform distribution reproduces the observed surface brightness as well as or better than the distributions that are informed by previous constraints. Nevertheless, the inferred total dust columns are robust, and serve to confirm that previous measurements based on interstellar edges in high-resolution X-ray spectra and on modelling of broad-band X-ray spectra were reliable. Specifically, we find Av ~= 4, 6, and 8 mag for 4U 0142+61, 1E 1048.1-5937, and 1RXS J170849.0-400910, respectively. For 1E 1048.1-5937, this is well in excess of the extinction expected towards a HI bubble along the line of sight, thus casting further doubt on the suggested association with the source.

arXiv comment8 pages, 6 figures

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• X-ray and radio observations of the magnetar Swift J1834.9-0846 and its dust-scattering halo
• Long-term spectral and timing properties of the soft gamma-ray repeater SGR 1833-0832 and detection of extended X-ray emission around the radio pulsar PSR B1830-08
• Distance to the SNR CTB 109/AXP 1E 2259+586 by HI absorption and self-absorption
• SGR 1806-20 distance and dust properties in molecular clouds by analysis of a flare x-ray echoes
• The extended X-ray emission around RRAT J1819-1458
• Chandra observations of the newly discovered magnetar Swift J1818.0-1607