HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Measurement of the optical parameters of the Virgo interferometer F. Acernese, P. Amico, M. Alshourbagy, F. Antonucci, S. Aoudia, P. Astone, S. Avino, D. Babusci, G. Ballardin, F. Barone, et al.

We present a search for gravitational waves from 116 known millisecond and young pulsars using data from the fifth science run of the LIGO detectors. For this search ephemerides overlapping the run period were obtained for all pulsars using radio and X-ray observations. We demonstrate an updated search method that allows for small uncertainties in the pulsar phase parameters to be included in the search. We report no signal detection from any of the targets and therefore interpret our results as upper limits on the gravitational wave signal strength. The most interesting limits are those for young pulsars. We present updated limits on gravitational radiation from the Crab pulsar, where the measured limit is now a factor of seven below the spin-down limit. This limits the power radiated via gravitational waves to be less than ~2% of the available spin-down power. For the X-ray pulsar J0537-6910 we reach the spin-down limit under the assumption that any gravitational wave signal from it stays phase locked to the X-ray pulses over timing glitches, and for pulsars J1913+1011 and J1952+3252 we are only a factor of a few above the spin-down limit. Of the recycled millisecond pulsars several of the measured upper limits are only about an order of magnitude above their spin-down limits. For these our best (lowest) upper limit on gravitational wave amplitude is 2.3x10^-26 for J1603-7202 and our best (lowest) limit on the inferred pulsar ellipticity is 7.0x10^-8 for J2124-3358.

We present the results of a search for gravitational-wave bursts associated with 137 gamma-ray bursts (GRBs) that were detected by satellite-based gamma-ray experiments during the fifth LIGO science run and first Virgo science run. The data used in this analysis were collected from 2005 November 4 to 2007 October 1, and most of the GRB triggers were from the Swift satellite. The search uses a coherent network analysis method that takes into account the different locations and orientations of the interferometers at the three LIGO-Virgo sites. We find no evidence for gravitational-wave burst signals associated with this sample of GRBs. Using simulated short-duration (<1 s) waveforms, we set upper limits on the amplitude of gravitational waves associated with each GRB. We also place lower bounds on the distance to each GRB under the assumption of a fixed energy emission in gravitational waves, with typical limits of D ~ 15 Mpc (E_GW^iso / 0.01 M_o c^2)^1/2 for emission at frequencies around 150 Hz, where the LIGO-Virgo detector network has best sensitivity. We present astrophysical interpretations and implications of these results, and prospects for corresponding searches during future LIGO-Virgo runs.

We report on the stabilization of the laser frequency for the Virgo gravitational-wave detector. We have obtained a frequency noise level, measured in loop, of 1.9x10(-7) Hz/Hz at 10 Hz for the 1064 nm laser; this value is limited by shot noise. The Allan standard deviation for relative frequency noise is 1.0x10(-21) on a 100-ms time scale. The spectral density of the laser frequency noise is negligible in the channel where gravitational waves ought to appear and meets the specifications for the target spectral resolution of the Virgo interferometer in the 10 Hz-10 kHz detection bandwidth.

The 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.

A search for gravitational wave burst events has been performed with the Virgo C7 commissioning run data that have been acquired in September 2005 over 5 days. It focused on unmodeled short duration signals in the frequency range 150 Hz to 2 kHz. A search aimed at detecting the GW emission from the merger and ring-down phases of binary black hole coalescences was also carried out. An extensive understanding of the data was required to be able to handle a burst search using the output of only one detector. A 90% confidence level upper limit on the number of expected events given the Virgo C7 sensitivity curve has been derived as a function of the signal strength, for unmodeled gravitational wave searches. The sensitivity of the analysis presented is, in terms of the root sum square strain amplitude, hrss ≃ 10−20 Hz−1/2. This can be interpreted in terms of a frequentist upper limit on the rate of detectable gravitational wave bursts at the level of 1.1 events per day at a 90% confidence level. From the binary black hole search, we obtained the distance reach at 50% and 90% efficiency as a function of the total mass of the final black hole. The maximal detection distance for non-spinning high and equal mass black hole binary system obtained by this analysis in C7 data is ≃2.9 ± 0.1 Mpc for a detection efficiency of 50% for a binary of total mass 80 M⊙.

In this paper we present the studies performed on a set of Lu3Al5O12:Pr(LuAG:Pr) crystals with praseodymium concentration between 1.5 and 10%, grown by the micro-pulling-down (mu PD) technique. The research comprises the measurements of X-ray excited emission spectra and Cs-137 gamma-ray pulse height spectra in a range from 78 to 600 K, and thermoluminescence glow curves. Based on experimental data we discuss the dependence of scintillation properties of Lu3Al5O12:Pr on praseodymium content and temperature. The main attention is focused on a distinct increase of scintillation yield with temperature, which we attribute to existence of shallow electron traps and their temperature-dependent contribution to scintillation of LuAG:Pr. An active role of traps is demonstrated by a novel experiment combining X-ray and laser excitation.

The measurement of the space-time structure variations induced by strong cosmic events (supernovae, coalescing binaries of neutron stars, etc.) requires an oscillator with a relative stability of 10−21 on time scales typically ≈100 ms. We demonstrate that the Virgo interferometer with a wavelength of 1.064 °m has a laser frequency with an in-loop stability of 1.0 × 10−21 on a 100 ms time scale, and an in-loop frequency noise of 2 × 10−7 Hz/√Hz at 10 Hz. We show that this fits the specifications. Two references successively stabilize the laser frequency. The first one is a 144 m long suspended cavity; the second one is the common mode of two perpendicular 3 km long Fabry-Perot cavities. The differential mode of the relative length variations of these two optical cavities is the port where we expect the signal for the gravitational waves; this out-of-loop measurement, less sensitive to laser frequency noise, does not show up correlations with the in-loop error signal. This is the best ever performance of short term laser frequency stabilization reported.

The first Virgo long science run (VSR1) lasted 136 days, from 18th May 2007. During the run several noise sources were identified and reduced; this significantly improved the detector sensitivity between the start and the end of the run. We describe three noise studies, showing how data monitoring programs and simple analysis tools permitted the first detection of the noise and provided useful information regarding its origin.

The Virgo collaboration has just concluded its first long science run (VSR1). In these four months the detector achieved a good duty cycle, larger than 80%, and an average horizon distance for binary neutron star system sources of about 4 Mpc. An intense commissioning activity was resumed after the run was complete to further increase the performances of the detector and to prepare the Virgo+ upgrades. The detector performances during the first science run and the last commissioning achievements are briefly discussed here.

The VIRGO interferometer is the largest ground based European gravitational wave detector operating at the EGO Laboratory in the Pisa, Italy; countryside. During the last commissioning period relevant progress have been done in approaching its design sensitivity all over the detection bandwidth. Thanks to the effort of the whole Collaboration a long scientific run has been done collecting data for more than 4 months in conjunction with the LIGO detectors. The results obtained from the detector point of view are: a very good stability and a duty-cycle as high as 81% in science mode. In this paper we present the status of the VIRGO interferometer giving an overview of the experimental apparatus together with its most relevant features.

Virgo is an experiment aiming at the detection of gravitational waves emitted by astrophysical sources. Its detector, based on a 3 km arms interferometer, is a complex setup which requires several digital control loops running up to 10 kHz, an accurate and reliable central timing system and an efficient data acquisition, all of them being distributed over 3 km. 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 developed for the online detector monitoring, mandatory complement of the DAQ for the commissioning of the Virgo detector.

F. Acernese6, P. Amico10, M. Alshourbagy11, F. Antonucci 12, S. Aoudia7, P. Astone12, S. Avino6, D. Babusci4, G. Ballardin2, F. Barone6, L. Barsotti11, M. Barsuglia8 , F. Beauville1, S. Bigotta11, S. Birindelli11, M.A. Bizouard8, C. Boccara9, F. Bondu7, L. Bosi10, C. Bradaschia11, S. Braccini11,A. Brillet7, V. Brisson8, L. Brocco12, D. Buskulic1, E. Calloni6, E. Campagna3, F. Carbognani2, F. Cavalier8, R. Cavalieri2, G. Cella11, E. Cesarini3, E. Chassande-Mottin7, N. Christensen2, C. Corda11, A. Corsi12, F. Cottone10, A.-C. Clapson8, F. Cleva7, J.-P. Coulon7, E. Cuoco2, A. Dari10, V. Dattilo2, M. Davier8, M. del Prete2, R. De Rosa6, L. Di Fiore6, A. Di Virgilio11, B. Dujardin7, A. Eleuteri6, I. Ferrante11, F. Fidecaro11, I. Fiori11, R. Flaminio1, 2, J.-D. Fournier7, O.Francois2, S. Frasca12, F. Frasconi2, 11, L. Gammaitoni10, F. Garufi6, E. Genin2, A. Gennai11, A. Giazotto11, G. Giordano4, L. Giordano6, R. Gouaty1, D. Grosjean1, G. Guidi3, S. Hebri2, H. Heitmann7, P. Hello8, S. Karkar1, S. Kreckelbergh8, P. La Penna2, M. Laval7, N. Leroy8, N. Letendre1, B. Lopez2, Lorenzini3, V. Loriette9, G. Losurdo3, J.-M. Mackowski5, E. Majorana12, C. N. Man7, M. Mantovani11, F. Marchesoni10, F. Marion1, J. Marque2, F. Martelli3, A. Masserot1, M. Mazzoni3, L. Milano6, F. Menzinger2, C. Moins2, J. Moreau9, N. Morgado5, B. Mours1, F. Nocera2, A. Pai12, C. Palomba12, F. Paoletti2, 11, S. Pardi6, A. Pasqualetti2, R. Passaquieti11, D. Passuello11, B. Perniola3, F. Piergiovanni3, L. Pinard5, R. Poggiani11, M. Punturo10, P. Puppo12, K. Qipiani6, P. Rapagnani12, V. Reita9, A. Remillieux5, F. Ricci12, I. Ricciardi6, P. Ruggi 2, G. Russo6, S. Solimeno6, A. Spallicci7, R. Stanga3, T. Marco11, M. Tonelli11, A. Toncelli11, E. Tournefier1, F. Travasso10, C. Tremola11, G. Vajente 11, D. Verkindt1, F. Vetrano3, A. Vicere3, J.-Y. Vinet7, H. Vocca10 and M. Yvert1 1Laboratoire d’Annecy-le-Vieux de Physique des Particules (LAPP), IN2P3/CNRS, Universite de Savoie, Annecy-le-Vieux, France;

In the framework of the expected association between gamma-ray bursts and gravitational waves, we present results of an analysis aimed to search for a burst of gravitational waves in coincidence with gamma-ray burst 050915a. This was a long duration gamma-ray burst detected by Swift during September 2005, when the Virgo gravitational wave detector was engaged in a commissioning run during which the best sensitivity attained in 2005 was exhibited. This offered the opportunity for Virgo's first search for a gravitational wave signal in coincidence with a gamma-ray burst. The result of our study is a set of strain amplitude upper-limits, based on the loudest event approach, for different but quite general types of burst signal waveforms. The best upper-limit strain amplitudes we obtain are h_rss=O(10^-20)Hz^-1/2 around 200-1500 Hz. These upper-limits allow us to evaluate the level up to which Virgo, when reaching nominal sensitivity, will be able to constrain the gravitational wave output associated with a long burst. Moreover, the analysis here presented plays the role of a prototype, crucial in defining a methodology for gamma-ray burst triggered searches with Virgo and opening the way for future joint analyses with LIGO.

The interferometric gravitational wave detector Virgo its completing the commissioning phase, and it is close to commencing with scientific data taking.In 2005, before a temporary shutdown of the interferometer, two commissioning runs were performed: the C6 run from July 29th to August 12th, and the C7 run from September 14th to 19th.The sensitivity of the detector during these commissioning runs was not yet at an interesting level for scientific observations.However, the bandwidth and stability of the detector is already sufficient to perform important studies in preparation for the acquisition and analysis of astrophysically important data.The data have therefore been analyzed by the Virgo physics groups, with the goal of testing the analysis pipelines and developing veto strategies.The results also allowed a better understanding of the noise sources, thus providing useful feedback to the commissioning team.

We present a methodology of network data analysis applied to the search for coincident burst excitations over a 24 h long data set collected by AURIGA, EXPLORER, NAUTILUS and Virgo detectors during September 2005. The search of candidate triggers was performed independently on each of the data sets from single detectors. We looked for two-fold time coincidences between these candidates using an algorithm optimized for a given population of sources and we calculated the efficiency of detection through injections of templated signal waveforms into the streams of data. To this end we have considered the case of signals shaped as damped sinusoids coming from the galactic center direction. Our method targets an optimal balance between high efficiency and low false alarm rate, aiming at setting confidence intervals as stringent as possible in terms of the rate of the selected source models.

Yb doped Lu3Al5O12 single crystal fibers has been grown with various Yb3+ ion concentrations: 2%, 5%, 10%, 15%, and 50% Yb doping levels. The diameter of the fibers is around 3mm and their length is up to 110mm. The fibers have been annealed in air at 1400°C for 24h to remove Yb2+ produced during the growth in the fibers. Structural characterization by x-ray diffraction method has been performed to confirm the monocrystalline phase and the orientation of the fibers. Absorption measurements have been performed on different pieces of the fibers to check the homogeneity of the distribution of Yb3+ along the fiber length. The results indicate that the distribution coefficient is close to 1. The fluorescence lifetime was measured for different Yb3+ concentrations. Results are in agreement with the literature and can be interpreted as a mixture of the radiation trapping and concentration quenching effects. The emission cross section has been calculated both from absorption spectra and from emission data. The two different independent methods give similar results, but emission data suffer from strong reabsorption effects on some of the lines. On the zero phonon line at high doping levels a central dip appears that can be interpreted with a reabsorption model.