Virgo is a kilometer-length interferometer for gravitationnal waves detection located near Pisa. Its first science run, VSR1, occured from May to October 2007. The aims of the calibration are to ...measure the detector sensitivity and to reconstruct the time series of the gravitationnal wave strain h(t). The absolute length calibration is based on an original non-linear reconstruction of the differential arm length variations in free swinging Michelson configurations. It uses the laser wavelength as length standard. This method is used to calibrate the frequency dependent response of the Virgo mirror actuators and derive the detector in-loop response and sensitivity within ~ 5%. The principle of the strain reconstruction is highlighted and the h(t) systematic errors are estimated. A photon calibrator is used to check the sign of h(t). The reconstructed h(t) during VSR1 is valid from 10 Hz up to 10 kHz with systematic errors estimated to 6% in amplitude. The phase error is estimated to be 70 mrad below 1.9 kHz and 6 μs above.
Le détecteur d'ondes gravitationnelles Virgo est un interféromètre laser dont les bras font trois kilomètres de long. Cet interféromètre est actuellement dans une phase de réglages et d'ajustements ...ayant pour but d'amener l'instrument à sa sensibilité nominale. Il est pour cela nécessaire de réduire les bruits instrumentaux qui limitent la sensibilité pendant cette phase. Le travail décrit dans ce mémoire est consacré à l'analyse des bruits instrumentaux.
Une description des bruits que l'on sait susceptibles de limiter la sensibilité de l'interféromètre est d'abord présentée, ainsi que leur mécanisme de propagation. La méthode ayant permis d'analyser les bruits instrumentaux est ensuite exposée. Elle consiste tout d'abord à identifier les sources de bruit potentielles par la recherche de cohérence entre les signaux de l'interféromètre. Il est ensuite utile de comprendre le mécanisme par lequel ces bruits se propagent dans l'interféromètre en élaborant des modèles analytiques. Cette analyse, appliquée aux données de l'interféromètre, a été complétée par des études utilisant une simulation du détecteur.
Entre fin 2003 et fin 2005, les progrès de la mise en route de Virgo ont été ponctués par sept prises de données techniques, qui ont permis de vérifier l'évolution des performances du détecteur. Les résultats de l'analyse des bruits limitant la sensibilité de l'interféromètre au cours de chacune de ces prises de données techniques sont présentés dans ce mémoire. L'impact des améliorations techniques apportées à l'interféromètre pour éliminer l'effet de ces bruits est également discuté.
The Advanced Virgo detector uses two monolithic optical cavities at its output port to suppress higher order modes and radio frequency sidebands from the carrier light used for gravitational wave ...detection. These two cavities in series form the output mode cleaner. We present a measured upper limit on the length noise of these cavities that is consistent with the thermo-refractive noise prediction of \(8 \times 10^{-16}\,\textrm{m/Hz}^{1/2}\) at 15 Hz. The cavity length is controlled using Peltier cells and piezo-electric actuators to maintain resonance on the incoming light. A length lock precision of \(3.5 \times 10^{-13}\,\textrm{m}\) is achieved. These two results are combined to demonstrate that the broadband length noise of the output mode cleaner in the 10-60 Hz band is at least a factor 10 below other expected noise sources in the Advanced Virgo detector design configuration.
The LIGO Scientific Collaboration (LSC) is developing and running analysis pipelines to search for gravitational-wave transients emitted by astrophysical events such as compact binary mergers or ...core-collapse supernovae. However, because of the non-Gaussian, non-stationary nature of the noise exhibited by the LIGO detectors, residual false alarms might be found at the end of the pipelines. A critical aspect of the search is then to assess our confidence for gravitational waves and to distinguish them from those false alarms. Both the 'Compact Binary Coalescence' and the 'Burst' working groups have been developing a detection checklist for the validation of candidate-events, consisting of a series of tests which aim to corroborate a detection or to eliminate a false alarm. These tests include for example data quality checks, analysis of the candidate appearance, parameter consistency studies and coherent analysis. In this paper, the general methodology used for candidate validation is presented. The method is illustrated with an example of simulated gravitational-wave signal and a false alarm.
The Virgo gravitational wave detector is an interferometer (ITF) with 3km
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 interferometer 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 (AdV) 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
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 10m to 100m. An attempt is made to measure the attenuation of
emitted noise at the ITF and correlate it to the distance from the source and
to seismic attenuation models in soil.
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