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J.F. Liu, J.N. Bregman, P. Seitzer, J.A. Irwin (University of Michigan)
Ultra-luminous X-ray sources (ULXs) are off-nuclear X-ray point sources observed in other galaxies with luminosities of 1e39 - 1e41 erg/sec. These sources could be powered by accretion onto intermediate mass black holes of a few thousand solar masses, or powered by accretion onto stellar mass black holes with special mechanisms to emit the apparent super-Eddington luminosities. An essential step to solve the mystery is to study them in other wavelengths, especially the optical. Here we present our studies of ULXs in nearby galaxies with the Hubble Space Telescope and the Magellan/Baade 6.4m telescope. The optical imaging and spectroscopic observations have deepened our understanding about the environments of the ULXs, and enabled identifications of the secondaries of the ULX systems. Further spectroscopic observations of these identified bright secondaries will be able to determine the mass of the central black holes in the ULX systems.
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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.