XMM-Newton Observations of CXOU J010043.1-721134: The First Deep Look at the Soft X-Ray Emission of a Magnetar

Abstract

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^∞_{BB 1} = 12.1^{+ 2.1}_-1.4 km and R^∞_{BB 2} = 1.7^{+ 0.6}_-0.5 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, 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.

Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA.