We have searched for ultraluminous X-ray sources ( ULXs ) in a sample of 28 elliptical and S0 galaxies observed with Chandra .
We find that the number of X-ray sources detected at a flux level that would correspond to a 0.3–10 keV X-ray luminosity of \sim 2 \times 10 ^ { 39 } ergs s ^ { -1 } or greater ( for which we have used the designation very ultraluminous X-ray sources ; VULXs ) at the distance of each galaxy is equal to the number of expected foreground/background objects .
In addition , the VULXs are uniformly distributed over the Chandra field of view rather than distributed like the optical light of the galaxies , strengthening the argument that the high flux sources are unassociated with the galaxies .
We have also taken the VULX candidate list of Colbert and Ptak and determined the spatial distribution of VULXs in early-type galaxies and late-type galaxies separately .
While the spiral galaxy VULXs are clearly concentrated toward the centers of the galaxies , the early-type galaxy VULXs are distributed randomly over the ROSAT HRI field of view , again indicating that they are not associated with the galaxies themselves .
We conclude that with the exception of two rare high luminosity objects within globular clusters of the elliptical galaxy NGC 1399 , VULXs are generally not found within old stellar systems .
However , we do find a significant population of sources with luminosities of 1 - 2 \times 10 ^ { 39 } ergs s ^ { -1 } that reside within the sample galaxies that can be explained by accretion onto 10–20 M _ { \odot } 
black holes .
Given our results , we propose that ULXs be defined as X-ray sources with L _ { X } ( 0.3–10 keV ) > 2 \times 10 ^ { 39 } ergs s ^ { -1 } .