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H. Matsumoto (MIT), T.G. Tsuru, T. Harashima, F. Iwamuro, T. Maihara (Kyoto), S. Matsushita (Harvard-Smithsonian CfA), R. Kawabe (NAOJ)
[1] We had found an X-ray luminous variable source in M82 with ASCA. We discovered with CXO that the source is located not at the galactic center but at the off-center position although its luminosity reaches the AGN class. We concluded that the source is an Intermediate-mass black hole (IMBH).
[2] The X-ray spectrum of the IMBH obtained with Ginga is not described with a power law model but with a thermal bremsstrahlung model. We found with ASCA that its temperature has no correlation with the luminosity. It suggests the standard optically thick and geometrically thin accretion disk models can not explain the emission mechanism of the IMBH. They are quite different from the characteristics of the ULXs that Makishima et. al. (2000) has been discussing.
[3] We discovered an energetic molecular superbubble expanding at ~100km/s with the Nobeyama Millimeter Array. It has a size of 140\times 210~pc. The expanding energy reaches ~1055~ergs which is one of the most energetic expanding molecular bubble ever observed in extra galactic sources. The bubble was created by a large explosion ~106~yr ago. We also discovered that the IMBH is located at the center of the superbubble, which is a direct evidence suggesting that the IMBH was born in an energetic explosion forming the superbubble.
[4] We successfully identified a star cluster with the IMBH from our SUBARU CISCO observation in NIR band. From the photometric and spectroscopic observation in NIR-band, the age and mass of the star cluster were determined.
[Ref.] Matsumoto et. al. 2001, ApJ, 547, L25; Matsushita et. al. 2001, ApJ, 545, L107; Tsuru 1992, Ph.D thesis Univ. of Tokyo; Tsuru et. al. 1997, PASJ, 49, 619; Matsumoto and Tsuru 1999, PASJ, 51, 321.