XMM-NEWTON OBSERVATIONS OF CXOU J010043.1-721134: THE FIRST DEEP LOOK AT THE SOFT X-RAY EMISSION OF A MAGNETAR

摘要

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 kT_1 = 0.30 ± 0.02 keV and kT_2 = 0.7 ± 0.1 keV gives an acceptable fit, and the radii of the corresponding blackbody emission regions are R_(BBI)~∞ = 12.1_(-1.4)~(+2.1) km and R_(BB2)~∞ = 1.7_(-0.5)~(+0.6) 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 JO 10043.1-721134, 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.