Unlocking the nature of ultraluminous X-ray sources using their X-ray   spectra
  We explore the nature of ultraluminous X-ray sources through detailed investigations of their spectral shape using some of the highest quality data available in the XMM-Newton public archives. Phenomenological models allow us to characterise their spectra, while more 'physically-motivated' models enable us to explore the physical processes underlying these characteristics. These physical models imply the presence of extreme (probably super-Eddington) accretion on to stellar mass black holes. 
Jeanette C. Gladstone, Timothy P. Roberts and Chris Done
astro-ph.HE