Results of the IGEC-2 search for gravitational wave bursts during 2005

Abstract

The network of resonant bar detectors of gravitational waves resumed coordinated observations within the International Gravitational Event Collaboration (IGEC-2). Four detectors are taking part in this Collaboration: ALLEGRO, AURIGA, EXPLORER and NAUTILUS. We present here the results of the search for gravitational wave bursts over 6 months during 2005, when IGEC-2 was the only gravitational wave observatory in operation. The implemented network data analysis is based on a time coincidence search among AURIGA, EXPLORER and NAUTILUS; ALLEGRO data was reserved for follow-up studies. The network amplitude sensitivity to bursts improved by a factor 3 over the 1997-2000 IGEC observations; the wider sensitive band also allowed the analysis to be tuned over a larger class of waveforms. Given the higher single-detector duty factors, the analysis was based on threefold coincidence, to ensure the identification of any single candidate of gravitational waves with high statistical confidence. The false detection rate was as low as 1 per century. No candidates were found.

All-sky search for gravitational-wave bursts in the second joint LIGO-Virgo run

“…This search makes no prior assumptions on source sky location, signal arrival time, or the waveform itself. Event rate upper limits from long-term searches of this category have been derived with networks of resonant bar detectors with spectral sensitivity limited to around 900 Hz in 1997-2000 [11,12] and in 2005-2007 [13,14]. Networks of interferometric detectors set more stringent upper limits for GW bursts on a wider bandwidth using the LIGO detectors in 2005-2006 [15-17] and during the first joint observation of LIGO and Virgo detectors in 2007 [18].…”

Analysis of 3 years of data from the gravitational wave detectors EXPLORER and NAUTILUS

“…Equation (3) shows that R also depends on other parameters, so that an optimization is possible: we can vary our handles (i.e., the thresholds) until we find the minimum value among all r à . The functional dependence of R on the thresholds is due to two competing effects: by raising the thresholds, we decrease both r 0 (that decreases R) and ", i.e., (that increases R).…”

“…In fact, the analysis of simultaneous data from more detectors at different sites allows an efficient rejection of the spurious outliers, either caused by transient local disturbances or by the intrinsic noise of the detectors. Resonant GW detectors have operated for decades in several laboratories around the world, reliably staying on the air for long periods with high duty cycle [1][2][3], mainly looking for burst events. The coming of age of laser interferometer detectors [4], with much better sensitivity and bandwidth, has led to a gradual phasing out of many resonant detectors.…”

“…Both detectors have been on the air since the early 1990s, performing various joint coincidence searches [10][11][12]. In the period May 5, 2005 to April 15, 2007 they took part in the IGEC2 network [2,3] that collected and exchanged data, together with the Auriga detector at the INFN Legnaro National Labs (Italy) [13] and with the Allegro detector at LSU (USA) [14]. After that period, Allegro was shut down and data have been collected by the three surviving antennas, but never analyzed before.…”

Progress towards gravitational-wave astronomy

“…The results detailed in [5] use over 130 days of joint observation by the three detectors AURIGA, NAUTILUS and EXPLORER setting a duty factor milestone that remains unbeaten to date. The sensitivity band of LIGO extends between 50 Hz and 1500 Hz.…”