2010MNRAS.406.1116P

The Cartwheel galaxy harbours more ultraluminous X-ray sources (ULXs) than any other galaxy observed so far, and as such it is a particularly interesting target to study them. In this paper, we analyse the three Chandra observations of the brightest ULX (N10) in the Cartwheel galaxy, in light of current theoretical models suggested to explain such still elusive objects. For each model, we derive the relevant spectral parameters. Based on self-consistency arguments, we can interpret N10 as an accreting binary system powered by an ∼ 100 M_☉ black hole. A young supernova strongly interacting with its surroundings is a likely alternative that can be discarded only with the evidence of a flux increase from future observations.