The variable finesse locking technique

Virgo is a power recycled Michelson interferometer, with 3 km long Fabry-Perot cavities in the arms. The locking of the interferometer has been obtained with an original lock acquisition technique. The main idea is to lock the instrument away from its working point. Lock is obtained by misaligning the power recycling mirror and detuning the Michelson from the dark fringe. In this way, a good fraction of light escapes through the antisymmetric port and the power build-up inside the recycling cavity is extremely low. The benefit is that all the degrees of freedom are controlled when they are almost decoupled, and the linewidth of the recycling cavity is large. The interferometer is then adiabatically brought on to the dark fringe. This technique is referred to as variable finesse, since the recycling cavity is considered as a variable finesse Fabry-Perot. This technique has been widely tested and allows us to reach the dark fringe in few minutes, in an essentially deterministic way

A simple line detection algorithm applied to Virgo data

International audienceWe propose a new method for the detection of spectral lines in random noise. It mimics the processing scheme of matching filtering, i.e., a whitening procedure combined with the measurement of the correlation between the data and a template. Thanks to the original noise spectrum estimate used in the whitening procedure, the algorithm can easily be tuned to various types of noise. It can thus be applied to the data taken from a wide class of sensors. This versatility and its small computational cost make this method particularly well suited for real-time monitoring in gravitational wave experiments. We show the results of its application to Virgo C4 commissioning data

A first study of environmental noise coupling to the Virgo interferometer

International audienceDuring the commissioning of the Virgo interferometer, a search for environmental noise contributions to the dark fringe signal was undertaken. Dedicated tests have been performed to identify major sources of disturbances and to understand the coupling mechanism with the interferometer. The major effect is due to seismic/acoustic noise coupling to the laser beam before the input mode cleaner, then propagating as beam power noise to the ITF dark fringe output signal. In this paper we illustrate the tests performed and preliminary results of our investigation

A first test of a sine-Hough method for the detection of pulsars in binary systems using the E4 Virgo engineering run data

Most of the known pulsars with frequencies lying in the best sensitivity range of the Virgo/LIGO/TAMA interferometers belong to binary systems. Accordingly their frequencies are Doppler shifted in an unknown way. We investigate a new method to search for and extract the parameters of such pulsars. A first preliminary test of this method, performed on the Virgo data recorded during the E4 engineering run, is presented

Data Acquisition System of the Virgo Gravitational Waves Interferometric Detector

International audienceVirgo is an experiment aiming at the detection of gravitational waves emitted by astrophysical sources. Its detector, based on a 3km arms interferometer, is a complex setup which requires several digital control loops running up to 10kHz, an accurate and reliable central timing system and an efficient data acquisition, all of them being distributed over 3km. We overview here the main hardware and software components developed for the data acquisition system (DAQ) and its current architecture. Then, we briefly discuss its connections with interferometer's controls, especially through the automation of the interferometer's startup procedure. Then, we describe the tools used to monitor the DAQ and the performances we measured with them. Finally, are described also the tools developped for the online detector monitoring, mandatory complement of the DAQ for the commissioning of the Virgo detector

Noise budget and noise hunting in VIRGO

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Status of Virgo

International audienceThe commissioning phase of the full Virgo gravity-wave interferometric detector started in September 2003, and ended in May 2007 as the data taking phase began. This activity was intended to achieve a stable operation of the detector, at its design strain sensitivity, in the frequency bandwidth extending from about 10 Hz up to a few kHz, with a value of a few 10¡23 around 500 Hz. In September 2006 the first weekend science run (WSR 1) was held, followed by one or two more each month until WSR 10 in March 2007, The WSRs served to test the detector performance and reliability, and to prepare the transition to the long scientific data taking period which started on 18 May 2007. In this article the main features of Virgo, together with its actual status and sensitivity at the beginning of its first long science run, are presented

Interferometric detectors of gravitational waves on Earth: the next generations

International audienceThe interferometric detectors of gravitational waves of first generation are now taking data. A first detection might be possible with these instruments, but more sensitive detectors will be needed to start the gravitational wave astronomy. The interferometers of second generation will improve the sensitivity by a factor ten, allowing to explore a universe volume 1000 times larger. The technology is almost ready and the construction will start at the beginning of next decade. The community of the physicists involved in the field has also started to make plans for third generation detectors, for which a long term technology development will be required. The plans for the upgrades of the existing detectors and the scenario for the evolution of the field will be reviewed in this paper

LIGO and VIRGO: large interferometers searching for gravitational waves

International audienceThe largest interferometric detectors for gravitational waves, LIGO and Virgo, have reached (or are close to) the design sensitivity and have started taking science data. The operation of such detectors is reviewed and the expected sources and detection rates are discussed. LIGO and Virgo might make the first detection, but more advanced detectors will be needed to truly open the field of gravitational wave astronomy: the current ideas and plans for the upgrades of the existing interferometers are presented

GRB 050915a & the Virgo detector

GravitationalWaves (GWs) are expected to be emitted in association with Gamma-Ray Bursts (GRBs). In this context, we are analyzing data collected by the Virgo interferometer during 2005 to develop a method aimed to search for coincidences between GW bursts and GRBs. Our analysis is currently focused on Virgo C7 run and the long GRB 050915a, observed by the Swift satellite. The goal of such analysis is either to identify significant events around the GRB trigger time or, in the absence of such events, to set a limit on the strength of the associated GW emission. This study is a prototype for evaluating Virgo capability in constraining the GW output associated with a typical long GRB. Here we give an overview of the procedure we are following in our analysis