AAS 204th Meeting, June 2004
Session 49 X-ray Binary and ULX Populations in Nearby Galaxies
Topical Session, Wednesday, June 2, 2004, 8:30-10:00am, 10:45am-12:30pm, 2:30-4:00pm, 4:15-6:00pm, 601

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[49.10] Spectral classifications and transitions of ULXs in comparison with Galactic black-hole binaries

K. Makishima (Department of Physics, University of Tokyo, Japan), S. Ebisuzaki (RIKEN, Saitama, Japan), A. Kubota (Institute of Space & Astronautical Science, Japan), R. Miyawaki (Department of Physics, University of Toky, Japan), T. Mizuno (Department of Physical Science, Hiroshima University, Japan), M. Namiki (Osaka University, Osaka, Japan), M. Sugiho (NEC-Toshiba Space System, Co. Ltd., Japan), T. Tanaka (Institute of Space & Astronautical Science, Japan), N. Tsunoda (Tokyo Science University, Japan)

Since the first clear indication obtained with ASCA (Makishima et al. 2000), increasing pieces of evidence suggest that ULXs are accreting black holes (BHs) with relatively large masses. By combining ASCA, XMM-Newton and Chandra data, we attempt to interpret their spectral properties and spectral transitions in close comparison with those of Galactic BH binaries. The scenario allows us to constract a unified picture of mass-accreting BHs invoking four spectral regimes; low/hard state, soft/standard state, Compton-disk state, and slim-disk state, in the order of increasing mass accretion rate. We specifically suggest that ULXs with power-law type spectra are in the Compton-disk state, whereas those with multi-color-disk type spectra are in the slim disk state. The suggested intermediate-mass BH in ULXS may be produceed throgh runaway mergers of massive stars (Ebisuzaki et al. 2001). We also report on our optical search, using Subaru, for the counterpart to M81 X-6.

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