XMM-Newton observations of CXOU J010043.1-721134: the first deep look at   the soft X-ray emission of a magnetar
  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 fit by an absorbed power-law plus blackbody model. The sum of two (absorbed) blackbody components with kT1=0.30 keV and kT2=0.7 keV gives an acceptable fit, and the radii of the corresponding blackbody emission regions are R1=12.1 km and R2=1.7 km. 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, that 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. 
A. Tiengo (1), P. Esposito (1,2), S. Mereghetti (1) ((1) INAF-IASF   Milano, Italy (2) INFN Pavia, Italy)