2008ApJ...680L.133T

We present the analysis of six XMM-Newton observations of the anomalous X-ray pulsar CXOU J010043.1-721134, the magnetar candidate characterized by the lowest interstellar absorption. In contrast with all the other magnetar candidates, its X-ray spectrum cannot be fitted by an absorbed power-law plus blackbody model. The sum of two (absorbed) blackbody components with kT₁=0.30±0.02 keV and kT₂=0.7±0.1 keV gives an acceptable fit, and the radii of the corresponding blackbody emission regions are R^∞_BB1=12.1^+2.1_–1.4 km and R^∞_BB2=1.7^+0.6_–0.5km. The former value is consistent with emission from a large fraction of a neutron star surface, and given the well-known distance of CXOU J010043.1-721134, which is located in the Small Magellanic Cloud, it provides the most constraining lower limit to a magnetar radius ever obtained. A more physical model, where resonant cyclotron scattering in the magnetar magnetosphere is taken into account, has also been successfully applied to this source.