The Gravitational Wave Detector NAUTILUS Operating at T=0.1 K

We report on the ultralow�??temperature resonant�??mass gravitational�??wave detector NAUTILUS, operating at the Frascati INFN Laboratories. The present aim of this detector is to achieve a sensitivity sufficient to detect bursts of gravitational radiation from sources located in our Galaxy and in the local group. Progress in transducer technology is likely to lead to sensitivities that will enable us to observe events from sources as far away as the Virgo cluster of galaxies. We describe the cryogenic apparatus, readout system, cosmic�??ray veto system, and give first results obtained during one year of continuous operation at T=0.1K. In particular the Brownian noise of the detector at T=0.1 K was measured. The measured strain sensitivity was |6 10�??22 Hz�??1/2 at the frequencies of the two modes, 908 Hz and 924 Hz, with bandwidths of about 1 Hz.