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

We present results from a search for gravitational-wave bursts in the data collected by the LIGO and Virgo detectors between July 7, 2009 and October 20, 2010: data are analyzed when at least two of the three LIGO-Virgo detectors are in coincident operation, with a total observation time of 207 days. The analysis searches for transients of duration < 1 s over the frequency band 64-5000 Hz, without other assumptions on the signal waveform, polarization, direction or occurrence time. All identified events are consistent with the expected accidental background. We set frequentist upper limits on the rate of gravitational-wave bursts by combining this search with the previous LIGO-Virgo search on the data collected between November 2005 and October 2007. The upper limit on the rate of strong gravitational-wave bursts at the Earth is 1.3 events per year at 90% confidence. We also present upper limits on source rate density per year and Mpc^3 for sample populations of standard-candle sources. As in the previous joint run, typical sensitivities of the search in terms of the root-sum-squared strain amplitude for these waveforms lie in the range 5 10^-22 Hz^-1/2 to 1 10^-20 Hz^-1/2. The combination of the two joint runs entails the most sensitive all-sky search for generic gravitational-wave bursts and synthesizes the results achieved by the initial generation of interferometric detectors.Comment: 15 pages, 7 figures: data for plots and archived public version at https://dcc.ligo.org/cgi-bin/DocDB/ShowDocument?docid=70814&version=19, see also the public announcement at http://www.ligo.org/science/Publication-S6BurstAllSky

The seismic Superattenuators of the Virgo gravitational waves interferometer

The Virgo experiment, located near Pisa, Italy, is a large laser Michelson interferometer aiming at the first direct detection of gravitational waves. The interferometer monitors the relative distance of its mirrors placed at the ends of two 3 km-long perpendicular arms. The goal is to measure spectral differential variations of the arm lengths of 10(-18) m/Hz(1/2) in the frequency range from 10 Hz to 10 kHz. Avoiding spurious motions of the optical components is therefore essential to detect gravitational waves. Since the ground motion is 9 orders of magnitude larger than the arm length variations induced by gravitational waves, the seismic noise is the dominant low frequency noise source for terrestrial gravitational wave interferometers. The seismic isolation is obtained suspending the mirrors by an 8-meter tall chain of cascaded mechanical filters, called "Superattenuator" (SA). The Superattenuator is a passive device acting as a low pass filter in all six degrees of freedom, capable of attenuating the ground motion by more than 10 orders of magnitude, starting from a few Hz. To further reduce the seismic disturbances, the filter chain is suspended from an actively stabilized platform that compensates for low frequency and large amplitude oscillations caused by the mechanical resonances of the chain. In this article we describe the Superattenuator together with its control system, and we report about its performance

Status of the Virgo project

We describe the present state and future evolution of the Virgo gravitational wave detector, realized by the Virgo Collaboration at the European Gravitational Observatory, in Cascina near Pisa in Italy. We summarize basic principles of the operation and the design features of the Virgo detector. We present the sensitivity evolution due to a series of intermediate upgrades called Virgo+ which is being completed this year and includes new monolithic suspensions. We describe the present scientific potential of the detector. Finally we discuss the plans for the second generation of the detector, called Advanced Virgo, introducing its new features, the expected sensitivity evolution and the scientific potential

Status of the Commissioning of the Virgo Interferometer

Long baseline optical interferometry is a promising technique for the detection of gravitational waves [1], [2], [3], [4]. The French-Italian detector Virgo is a Michelson interferometer with 3 km arms, equipped with high storage time Fabry-Perot cavities. In this kind of detectors, the passage of gravitational waves would be sensed as a differential length variation of the arms. After the end of the second Virgo Science Run, lasting from July 2009 to the beginning of January 2010, some important upgrades have been carried out; in particular, the mirrors of the Fabry-Perot cavities, which act as test masses of the detector, have been replaced by new ones with an higher reflectivity, which should increase by three times the finesse of the cavities; moreover the mirrors are now suspended by silica fibers in a monolithic assembly expected to significantly lower the thermal noise. Finally, the digital signal processing electronics and the global control system have been largely improved. We will present the status of the commissioning of the Virgo interferometer

Characterization of the Virgo seismic environment

The Virgo gravitational wave detector is an interferometer (ITF) with 3 km arms located in Pisa, Italy. From July to October 2010, Virgo performed its third science run (VSR3) in coincidence with the LIGO detectors. Despite several techniques adopted to isolate the ITF from the environment, seismic noise remains an important issue for Virgo. Vibrations produced by the detector infrastructure (such as air conditioning units, water chillers/heaters, pumps) are found to affect Virgo's sensitivity, with the main coupling mechanisms being through beam jitter and scattered light processes. The Advanced Virgo design seeks to reduce ITF couplings to environmental noise by having most vibration-sensitive components suspended and in vacuum, as well as muffle and relocate loud machines. During the months of June and July in 2010, a Guralp-3TD seismometer was stationed at various locations around the Virgo site hosting major infrastructure machines. Seismic data were examined using spectral and coherence analysis with seismic probes close to the detector. The primary aim of this study was to identify noisy machines which seismically affect the ITF environment and thus require mitigation attention. Analyzed machines are located at various distances from the experimental halls, ranging from 10 to 100 m. An attempt is made to measure the attenuation of emitted noise at the ITF and correlate it with the distance from the source and with seismic attenuation models in soil

Search for gravitational waves from binary black hole inspiral, merger, and ringdown

We present the first modeled search for gravitational waves using the complete binary black-hole gravitational waveform from inspiral through the merger and ringdown for binaries with negligible component spin. We searched approximately 2 years of LIGO data, taken between November 2005 and September 2007, for systems with component masses of 1–99M⊙ and total masses of 25–100M⊙. We did not detect any plausible gravitational-wave signals but we do place upper limits on the merger rate of binary black holes as a function of the component masses in this range. We constrain the rate of mergers for 19M⊙≤m1, m2≤28M⊙ binary black-hole systems with negligible spin to be no more than 2.0  Mpc−3 Myr−1 at 90% confidence