(ed.). Gravitational waves (IOP, 2001)(422s).

Recent results obtained with the resonant detectors 99Table 8.2. Sensitivity of the resonant detectors in operation.Resonance ˜h = √ S h Frequency Minimum h Minimum hfrequency(at resonance)bandwidth for 1 ms for continuous Minimum(Hz)√ 1δ f (Hz) bursts waves Hz900–700 3–20 × 10 −22 0.5–1 4× 10 −19 2 × 10 −25 0.1Table 8.3. Target sensitivity for Auriga and Nautilus.˜h = √ S h Frequency Minimum h Minimum hat(resonance)bandwidth for 1 ms for continuous Minimum√ 1δ f (Hz) bursts waves Hz2 × 10 −22 50 3 × 10 −21 2 × 10 −26 10 −48.3 Recent results obtained with the resonant detectorsThe present five cryogenic bars in operation [1–5] (Allegro, Auriga, Explorer,Nautilus and Niobe) have roughly the same experimental sensitivity as given intable 8.2.Niobe, made with niobium, has a resonance frequency of 700 Hz, the otherones with aluminium, have resonance frequencies near 900 Hz. These minimumvalues for monochromatic waves and for the quantity have been estimated byconsidering one year of integration time (for we suppose to use the crosscorrelationof two identical antennae).The burst sensitivity for all bars can be increased by improving the transducerand associated electronics. It has been estimated that these improvements canincrease the frequency bandwidth up to 50 Hz.In addition to increasing the bandwidth, Auriga and Nautilus can improve(see table 8.3) their spectral sensitivity by making full use of their capabilityto go down in temperature to T = 0.10 K. At present the major difficulty isdue to excess noise, sometimes of unknown origin, and work is in progress foreliminating this noise.The search for signals due to GW bursts is done after the raw data havebeen filtered with optimum filter algorithms [13, 14]. These algorithms may havevarious expressions but they all have in common an optimum integration timethat is roughly the inverse of the detector bandwidth and all give approximatelythe same value of T eff (all algorithms being optimal filters for short bursts).The data recorded by the various detectors are now being analysed,searching, in particular, for coincidences above the background. The coincidence