Towards Understanding Ultraluminous X-ray Sources in Nearby Galaxies

One of the unsolved questions in contemporary astrophysics is the nature of thebright nonnuclear Xray sources which appear to surpass by large margins theEddington luminosity of a stellarmass compact object. We have recentlydiscovered extended emission nebulae around several ultraluminous sources (ULX)in nearby galaxies which are partly photoionized by their XUV radiation; extentand expansion velocity suggest that these ULX were formed in energetic eventssome 1E6 years ago. Here we propose to observe a sample of bright ULX in nearbygalaxies with the goal to understand their Xray spectra and to test currentideas of accretion physics in ULX. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]