8th HEAD Meeting, 8-11 September, 2004
Session 20 Black Hole Binaries and Intermediate Mass Black Holes
Oral, Thursday, September 9, 2004, 2:00-3:38pm

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[20.01] Are Ultraluminous X-ray Sources in Nearby Galaxies Intermediate Mass Black Holes?

J. A. Irwin (University of Michigan)

The presence of non-nuclear variable ultraluminous (>1039 ergs s-1) X-ray sources (ULXs) within nearby galaxies has spawned a flurry of debate regarding the nature of these objects. The X-ray luminosities of the brightest ULXs exceed the Eddington luminosity onto a neutron star by over two orders of magnitude. Taken at face value and assuming the X-ray emission is isotropic, this implies a mass of at least several hundred solar masses for the accreting object -- the much-sought-after intermediate mass black hole (IMBH). However, difficulty in creating a black hole in this mass range has led others to develop alternative descriptions of ULXs involving a black hole of mass ~10 solar masses, in which the high X-ray luminosities are accounted for by anisotropic beaming or super-Eddington accretion. In this talk I will review the properties of ULXs, as well as discuss the pros and cons of the major ULX models.

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Bulletin of the American Astronomical Society, 36 #3
© 2004. The American Astronomical Soceity.