Massimo Cerdonio
INFN Section and Department
of Physics, University of Padua, Italy
Five bar detectors are presently active, oriented with parallel axis, and searches for impulsive signals are correlated within IGEC. Spectral strain noises can be as low as 2 10-22 Hz-1/2 at the modes resonant frequencies and not larger than 3 10-21 Hz-1/2 within few tens of Hz of the modes. Three of them show energy sensitivities to short pulses close or even somewhat below Teff=1 mK. With one of the detectors it has been found that the noise, in optimal filtering for short pulses, for part of the "on " time appears dominated by a modeled quasi-stationary gaussian component with Teff as above, to which the filter easily adapts, plus an unmodeled higher energy component of some 100 events/day; a significant fraction, tens %, of this componenent can be vetoed as spuria by a chisqure-test. If one restricts to such periods of better understood noise behaviour the duty cycle, it lowers to some 50%, in contrast with the about 90% of the "on" time after cryogenic mantainance, common to all detectors.
A review will be given of: