IGEC2: A 17-month search for gravitational wave bursts in 2005–2007

Abstract

We present here the results of a 515 day search for short burst of gravitational waves by the IGEC2 observatory. This network included 4 cryogenic resonant-bar detectors: AURIGA, EXPLORER and NAUTILUS in Europe, and ALLEGRO in America. These results cover the time period from Nov 6 2005 until Apr 15 2007, partly overlapping the first long term observations by the LIGO interferometeric detectors. The observatory operated with high duty cycle, namely 57% for 4-fold coincident observations, and 94% for 3-fold observations. The sensitivity was the best ever obtained by a bar network: we could detect impulsive events with a burst strain amplitude hrss ∼ 1 · 10with an efficiency ¿50%. The network data analysis was based on time coincidence searches over at least three detectors, used a blind search technique and was tuned to achieve a false alarm rate of 1/century. When the blinding was removed, no gravitational wave candidate was found.PACS numbers: 04.80. Nn, 95.30.Sf, 95.85.Sz

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

“…The event times of one detector were delayed, with respect to the other ones, 10,000 times in steps of 1.5 seconds (i.e., between AE7; 500 s, excluding the zero time shift). This value is larger than the dead time [20] inserted by the event finder. The search of coincidences in each of the 10,000 cases, performed with a time window of 15 ms as discussed in Sec.…”

“…The filter is designed and optimized for delta-like signals, but it works equally well [20] for a wider class of short bursts, like e.g., damped sinusoids with decay time < 5 ms.…”

“…We found that a coincidence window of AE15 ms assures an efficiency very close to 1 for delta-like signals, even at the lowest injected amplitude: indeed, the measured probability of missing a coincident event with the chosen window of 15 ms is less than 1 Â 10 À4 . Besides, the chosen window is sufficiently wide to also accommodate, without significant losses of efficiency, other classes of signals [20] for which the detectors time response might be different.…”

SGR 1806-20 and the gravitational wave detectors EXPLORER and NAUTILUS

“…The metric perturbation hðtÞ can either be a millisecond pulse, a signal made by a few millisecond cycles, or a damped sinusoid signal. In the hypothesis of a signal sweeping in frequency through the detector resonances, with small decay times ( < 50 ms), the filter maintains good detection capability [32][33][34]. For a short signal of duration time g and frequency f g $ f 0 , the spectral amplitude,…”