Five fake ultra-luminous X-ray sources

Context. The nature of ultra-luminous X-ray (ULX) sources is still a matter of debate. Studies of their counterparts in other spectral ranges will help to clarify the nature of those sources. Aims. Our goal was to identify and characterize the optical counterparts of five sources catalogued as ULXs. Methods. We obtained optical imaging and intermediate resolution spectroscopy of these optical counterparts. Results. We demonstrate that five sources previously catalogued as ULXs, two are foreground stars in our galaxy and three are background active galactic nuclei.