STUDY ON GRAVITATIONAL WAVES FROM COALESCING BLACK-HOLE MACHO BINARIES

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A 20-m baseline laser interferometer gravitational wave detector was moved from Tokyo into the Kamioka mine, where the seismic noise was lower by two orders of magnitude than in Tokyo, and its sensitivity and stability were drastically improved. The obtained displacement sensitivity of 1.2 x 10^<-18> m/√<Hz> was comparable with the world best sensitivity obtained by TAMA300 gravitational wave detector. Its sensitivity was also enough to detect gravitational waves from compact binary star coalescences within 1 kpc from the Earth with S/N of 10. The stable operation, which was enabled by not only the lower seismic noise environment but also a newly installed self restart system, realized over 2000 hours observation in 2001 and the best operation rate of 99.8% in some selected 11 days. We also demonstrated the first coincidence gravitational wave observation from compact star (such as a MACHO black hole) binary inspiraling in our galaxy with TAMA300 in the summer of 2001. The data taken coincidentally totaled up to 709 hours. After selecting the gravitational waves candidates by using one step search, the coincident analysis checked arrival time, mass parameters and S/N ratio consistency. As a preliminary result, no gravitational wave signal was found. This result is expected to put a new upper limitation on gravitational wave search.