L. Bosi

Detailed comparison of LIGO and Virgo inspiral pipelines in preparation for a joint search

Presented in this paper is a detailed and direct comparison of the detection pipelines used by LIGO and Virgo in their attempt to observe gravitational waves from binary neutron star systems. In order to test the search programs, numerous inspiral signals were added to 24 h of simulated detector data. The efficiencies of the different pipelines were tested, and found to be very similar. Parameter estimation routines were also tested. We demonstrate that there are definite benefits if LIGO and Virgo conduct a joint coincident analysis; these advantages include increased detection efficiency and information on source sky location.

Low-frequency internal friction in silica glass

Precise low-frequency internal friction measurements on vitreous silica, taken over a wide temperature (4 K 160 K the loss angle develops a distinct step-like structure followed by a plateau, both independent of ν, thus signalling the onset of a competing relaxation mechanism with much higher an activation energy. Copyright c EPLA, 2007

A comparison of methods for gravitational wave burst searches from LIGO and Virgo

The search procedure for burst gravitational waves has been studied using 24 h of simulated data in a network of three interferometers (Hanford 4 km, Livingston 4 km and Virgo 3 km are the example interferometers). Several methods to detect burst events developed in the LIGO Scientific Collaboration (LSC) and Virgo Collaboration have been studied and compared. We have performed coincidence analysis of the triggers obtained in the different interferometers with and without simulated signals added to the data. The benefits of having multiple interferometers of similar sensitivity are demonstrated by comparing the detection performance of the joint coincidence analysis with LSC and Virgo only burst searches. Adding Virgo to the LIGO detector network can increase by 50% the detection efficiency for this search. Another advantage of a joint LIGO–Virgo network is the ability to reconstruct the source sky position. The reconstruction accuracy depends on the timing measurement accuracy of the events in each interferometer, and is displayed in this paper with a fixed source position example.

A parallel Beowulf-based system for the detection of gravitational waves in interferometric detectors

The detection, in a modern interferometric detector like Virgo, of a gravitational wave signal from a coalescing binary stellar system is an intensive computational task both for the on-line and off-line computer systems. A parallel computing scheme using the Message Passing Interface (MPI) is described. Performance results on a small scale cluster are reported.

Fused silica suspension for the VIRGO optics: status and perspectives

Thermal noise in mirror suspension wires is the main limitation of low-frequency sensitivity of interferometric gravitational wave detectors. In order to minimize the pendulum thermal noise, a monolithic design, using a low dissipation material, is proposed for VIRGO. High mechanical Qs and high breaking strengths have been obtained for monolithic fused silica fibres. A low-dissipation and high-strength bonding technique using potassium silicate bonding is proposed.

A first comparison of search methods for gravitational wave bursts using LIGO and Virgo simulated data

We present a comparative study of six search methods for gravitational wave bursts using simulated LIGO and Virgo noise data. The simulated data were generated according to the design sensitivity of the two 4 km LIGO interferometers and the 3 km Virgo interferometer. The searches were applied on replicas of the data sets to which eight different signals were injected. Three figures of merit were employed in this analysis: (a) receiver operator characteristic curves, (b) necessary signal-to-noise ratios for the searches to achieve 50% and 90% efficiencies and (c) variance and bias for the estimation of the arrival time of a gravitational wave burst.

Monocrystalline fibres for low thermal noise suspension in advanced gravitational wave detectors

Thermal noise in mirror suspension will be the most severe fundamental limit to the low-frequency sensitivity of future interferometric gravitational wave detectors. We propose a new type of materials to realize low thermal noise suspension in such detectors. Monocrystalline suspension fibres are good candidates both for cryogenic and for ambient temperature interferometers. Material characteristics and a production facility are described in this paper.

Mechanical quality factor of mirror substrates for VIRGO

Thermal noise in the mirror substrates is expected to be the main limit to the VIRGO sensitivity in the 50–500 Hz frequency range. The mechanical quality of the mirror substrates and the geometry of their suspension are expected to affect the noise level of the detector output. High mechanical Q have been obtained for different large fused silica substrates under VIRGO suspension conditions. Moreover, calcium fluoride substrates are shown to provide a more promising option for the design of future cryogenic, low thermal noise interferometers.

A first comparison between LIGO and Virgo inspiral search pipelines

This paper reports on a project that is the first step the LIGO Scientific Collaboration and the Virgo Collaboration have taken to prepare for a mutual search for inspiral signals. The project involved comparing the analysis pipelines of the two collaborations on data sets prepared by both sides, containing simulated noise and injected events. The ability of the pipelines to detect the injected events was checked, and a first comparison of how the parameters of the events were recovered has been completed.

Measurement of the thermoelastic properties of crystalline Si fibres

In order to reduce the thermal noise in future interferometers for gravitational wave (GW) detectors, new suspension materials with low thermal noise are under investigation. Crystalline silicon seems to be a promising material mainly at low temperature. A new technology to produce crystalline silicon fibres has been realized. Measurements of mechanical and thermal properties of the fibres at room temperature have been performed. Preliminary measurements at low temperature are presented.