Are All ULXs Created EqualquestionMark The Globular Cluster ULX in the S0 Galaxy NGC 1380

Most UltraLuminous Xray sources (ULXs) are now believed to be associated withstellar mass black holes (StMBHs); however, ULXs in globular clusters arenatural candidates among which to search for (the elusive) IMBHs. Our Chandraand HST observations of the S0 galaxy NGC 1380 detected the third bonafide ULXlocated in a GC that shows both large variability and persistent ULX emission.The ULX is a 5.8e39 erg/s source with atypically hard emission. Our proposed XMMobservation will accurately measure the spectrum of the source, allowing us toclassify it as a likely StMBH or IMBH. The variability will be determined,including searches for an orbital period, low frequency QPOs, a powerspectrumbreak, or a state change (associated spectral/luminosity variation), giving a mass estimate. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]