Automatic Alignment for the first science run of the Virgo interferometer

During the past few years a network of large-scale laser interferometers, including the Virgo detector, has been developed with the aim of detecting gravitational waves. To properly operate the detectors, the longitudinal and angular positions of the suspended detector test masses, the interferometer mirrors, must be kept within a small range from the operating point. The design of the Virgo angular control system, called Automatic Alignment is based on a modified version of the Anderson-Giordano technique, a wave-front sensing scheme which uses the modulation-demodulation technique. This paper will present the theoretical background of the Virgo Automatic Alignment system, the implementation issues and the performances observed during the first Virgo science run (VSR1). A total RMS of 4 × 10−2 to 3 × 10−3 μrad for all angular degrees of freedom has been achieved

Cleaning the Virgo sampled data for the search of periodic sources of gravitational waves

International audienceThe cleaning procedure used to produce the data that we analyze for the search of periodic sources of gravitational waves is based on different steps, which are applied to both time and frequency domain data. We have recently improved the procedure, which now consists of different steps. The use of a cleaned procedure is in principle important, since it is aimed to recover at best the observation time from the data by vetoing only times where disturbances act and not entire data chunks. Clearly, the effect of the procedure depends on the nature of the data, and is thus highly related to the detector characteristics in a particular run. We will here describe the whole cleaning chain, by giving details and examples based on the C7 and WSR10 Virgo runs

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