2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/181428Soft X-ray spectra of ULXs show small deviations from a power-law model, that can be attributed to reprocessing in a fast, ionized outflow, or to thermal emission from a cool disk. If it is thermal emission, the cool peak temperature can be explained by an inner disk that radiates only a small fraction of the gravitational power, transferring the rest to an upscattering medium which is then responsible for the dominant power-law component. This scenario does not require intermediate-mass black holes: we use a phenomenological model to show that the observed X-ray luminosities and spectra of ULXs are consistent with typical masses ~ 50-100 Msun.To appear in the proceedings of "The Multicoloured Landscape of Compact Objects and their Explosive Progenitors: Theory vs Observations", Cefalu', Sicily, June 11-24, 2006 (AIP)Astrophysicstext