XMM-Newton Observations of an Intermediate X-Ray Object in NGC 2276

Abstract

We present the results from a ~53 ks XMM-Newton observation of NGC 2276. This galaxy has an unusual optical morphology with the disk of this spiral appearing to be truncated along the western edge. This XMM-Newton observation shows that the X-ray source at the western edge is a bright intermediate X-ray object (IXO). Its spectrum is well fitted by a multicolor disk blackbody model used to fit optically thick standard accretion disks around black holes. The luminosity derived for this IXO is 1.1×10⁴¹ ergs s^-1 in the 0.5-10 keV band, making it one of the most luminous discovered to date. The large source luminosity implies a large-mass black hole if the source is radiating at the Eddington rate. On the other hand, the inner-disk temperature determined here is too high for such a massive object given the standard accretion disk model. In addition to the IXO, we find that the nuclear source in this galaxy has dimmed by at least a factor of several thousand in the 8 years since the ROSAT HRI observations.