The X–ray Source at the Center of the Cassiopeia A Supernova Remnant

We present the first results of an XMM-Newton observation of the central X– ray source in the Cas A supernova remnant. The spectrum can be fit equally well with an absorbed steep power law (αph=3.01 +0.27 −0.24, NH=(1.64 +0.29 −0.24)×10 22 cm) or with a blackbody of temperature kT= 0.70±0.05 keV and column density NH=(0.53 +0.14 −0.12)×10 22 cm. A search for pulsations for periods longer than 150 ms gave negative results. The 3σ upper limits on the pulsed fraction are ∼13% for P>0.3 s and ∼7% for P>3 s. The overall properties of the central X–ray source in Cas A are difficult to explain in terms of a rapidly spinning neutron star with a canonical magnetic field of ∼10 G, and are more similar to those of slowly rotating neutron stars such as the Anomalous X–ray Pulsars. Subject headings: Stars: neutron; X–ray: stars; Supernovae: individual (Cas A)