Search for coincident excitation of the widely spaced resonant gravitational wave detectors EXPLORER, NAUTILUS and NIOBE

We report the search for coincidences among three resonant mass detectors: EXPLORER at CERN and NAUTILUS in Frascati of the Rome group and NIOBE in Perth of the UWA group. The three detectors have a sensitivity for short bursts of GW in the h approximate to 10(-18) range, about one thousand times better in energy than Weber's original detectors. The analysis is based on the comparison of candidate event lists recorded by the detectors in the period December 1994 through October 1996. The events have been obtained by applying a pulse detection filter to the raw data and using a predetermined threshold. Due to the different periods of data taking it was not possible to search for triple coincidences. We searched for coincidences between EXPLORER and NAUTILUS during the years 1995 and 1996 for a total time coverage of 1372 hours and between EXPLORER and NIOBE in 1995 for a coverage of 1362 hours. The results have been: a weak indication of a coincidence excess with respect to the accidental ones between EXPLORER and NAUTILUS and no coincidence excess between EXPLORER and NIOBE. (C) 1998 Elsevier Science B.V.