What are ultraluminous X-ray sources?
Tim Roberts, University of Leicester, UK
Debate continues to rage over the underlying nature of ultraluminous
X-ray sources (ULXs). Each new result intensifies the controversy
over whether they are powered by accretion onto a new class of 100 -
100000 solar mass ("intermediate-mass") black holes, or whether they
are the extreme high-accretion rate manifestation of "ordinary" (~10
solar mass) black hole X-ray binaries. In this seminar I will present
the work we have been undertaking at Leicester to clarify the
underlying nature of these remarkable X-ray emitters, both directly
through the study of their X-ray emission using the excellent
capabilities of Chandra and XMM-Newton, and indirectly through the use
of optical follow-up to search for counterparts and to study their
effect on their immediate environment. A broad range of complex
phenomena are revealed by these studies, which are offering a new and
exciting perspective on the actual nature of the ULXs.