Weiner filters for gravitational-wave antennas: Characteristics and applications

Summary We report on the application of Wiener filters to the data of Weber-type gravitational-wave antennas, with particular reference to data processed by means of lock-in amplifiers driven at the frequencies of the modes of the detector. After a review of some basic results concerning the filtering of the data, we briefly examine the relationship between Wiener filters and matched filters. The discussion that follows is centred on various aspects related to the practical application of Wiener filters as well as on their limitations, also addressing the dependence of their performance on the values of their parameters. Finally, we consider some applications of non-optimal Wiener filters: by reducing the filter smoothing time constant, the time resolution can be increased; by increasing it, the filter becomes an estimator of the Brownian motion.     

Wide-band measurement of gravitational waves: the VIRGO project

Summary To detect gravitational waves (GW) in a frequency range between 10 Hz and few kHz a ground-based antenna was designed by the French-Italian collaboration VIRGO. The antenna is a 3 km long interferometer with special suspensions for the optical components, planned to reduce the seismic noise in order to reach the low-frequency region. Results on the seismic isolation devices are given together with some preliminary results on the use of permanent magnets on the VIRGO suspensions. Paper presented at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990.     

Gravitational-wave research with resonant antennas

Summary A brief historical survey of the GW experiments is presented. In particular, the experiments with resonant detectors are illustrated and the problems arising when comparing data of different detectors for the search of coincidences are discussed. The experimental results so far obtained are shown, among them the correlation during the SN1987A with various GW and neutrino detectors. Finally a warning for the long times needed to improve the sensitivity of the GW detectors is given and the improvements expected with spherical resonant detectors are mentioned.     

The gravitational wave antenna in Frascati

Summary We report on the cryogenic gravitational detector operating at 1763 Hz in Frascati. The antenna was equipped with a resonant capacitive transducer and a d.c. SQUID as an amplifier. After a test run in 1987, the detector was cooled again in the present configuration and took data for nearly two months in June and July 1988. A preliminary data analysis shows a noise temperature of 115 mK, but we expect to lower it further by applying improved filtering tecniques. During the same period two other cryogenic antennae were operating, and we plan to undertake a correlation analysis between the output of the three detectors. To speed up publication, the proofs were not sent to the authors and were supervised by the Scientific Committee.     

Upper limit on the flux of gravitational wave bursts

Summary The data obtained with three highly sensitive gravitational wave antennas have been used to establish an improved observational upper limit on the flux of impulsive gravitational waves. Preliminary results under the assumption of a source located in the center of the Galaxy are also reported. To speed up publication, the proofs were not sent to the authors and were superised by the Scientific Committee.     

SN 1987 A: Correlations between the Maryland and Rome gravitational wave detector data and the Mont Blanc and Kamiokande neutrino detector data

Summary The author reports on the analysis of the data obtained with the detectors given in the title in the period 12h of February 22, 1987 to 6h of February 23, 1987, that includes the time of the ν observation with the Mont Blanc detector during SN 1987a. A very significant correlation has been observed among the data of the above detectors in a period of one or two hours which includes the time of the Mont Blanc 5ν observation. The correlation between the g.w. data and the Kamiokande data is found if a time of 7.8s is added to the Kamioka recorded time; this is very close to the time difference, 6.2s, between the IMB and Kamioka large ν bursts observed at ≈7h 35 min. To speed up publication, the proofs were not sent to the authors and were supervised by the Scientific Committee.     

Data analysis for a gravitational wave antenna with resonant capacitive transducer

Summary We present here a new approach which simplifies considerably the data analysis for gravitational-wave antennas equipped with resonant transducer, based on the representation of the antenna as two independent oscillators. In fact, we can apply to each of the two modes of these antennas the same data analysis procedures already in use for antennas with nonresonant transducer and then compute the coincidences between the outputs of the two modes. The results deduced by such a procedure are in good agreement with the experimental results from the data collected in March 1984 with our 2270 kg 5056 Al bar cooled at liquid-helium temperature (T=4.2 K). The performances of the algorithms are presented in terms of the effective noise temperatures and sensitivity to short bursts of gravitational waves. With our experimental values, obtained by using a FET amplifier, we get an instrumental sensitivityF(v) of 6 J/m² Hz. We have also evaluated the sensitivity of the detector for monochromatic gravitational waves with frequencies in bandwidths of ≏0.4 Hz around the frequenciesv ₋ andv ₊, for one month of observation:h ₀≏3·10⁻²³.

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Riassunto Si presenta un nuovo approccio che semplifica notevolmente l’analisi dei dati per antenne gravitazionali con trasduttore risonante, basato sulla rappresentazione dell’antenna come due oscillatori indipendenti. A ciascuno dei modi di tali antenne si applicano le procedure di analisi dei dati già usati per le antenne con trasduttore risonante e si calcolano quindi le coincidenze tra le uscite dei due modi. I risultati dedotti mediante tale procedura sono in buon accordo con i risultati sperimentali relativi ai dati raccolti nel marzo 1984 con la nostra sbarra di Al 5056 da 2270 kg raffreddata alla temperatura dell’elio liquido (T=4.2 K). Si presentano le prestazioni degli algoritmi in termini delle temperature efficaci di rumore e della sensibilità per brevi fiotti di onde gravitazionali. Con i nostri valori sperimentali, ottenuti usando un amplificatore a FET, si ha una sensibilità strumentaleF(v) di 6 J/m² Hz. Si è anche calcolata la sensibilità del rivelatore per onde gravitazionali monocromatiche in bande di frequenza di circa 0.4 Hz attorno alle frequenzev ₋ ev ₊, per un mese di ossevazione:h ₀≏3.·10⁻²³.

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Резюме Предлагается новый подход, котрый значительно упрощает анализ данных для антенн гравитационных волн с резонансным емкостным датчиком, основанный на представлении антенны в виде двух независимых осцилляторов. Мы можем применить к каждой из двух мод этих антенн процедуры анализа данных, которые ыже использовались для антенн с нерезонансными датчиками, а затем вычислить совпадения между результатами на выходе для двух мод. Результаты, полученные с помощью такой процедуры, хорошо согласуются с экспериментальными результатами, собранными в марте 1984 года с помощью 2270 кг 5056 Al антенны, охлажденной до температуры жидкого гелия (T=4.2 К). Описываются алгоритмы анализа, исходя из эффективных температур шума и чувствительности к коротким вспышкам гравитационных волн. Используя экспериментальные значения, полученные с помощью FET усилителя, мы определяем инструментальную чувствительностьF(v)≈6Дж/M² Гц. Мы также оцениваем чувствительность детектора для монохроматических гравитационных волн в полосе частот 0.4 Гц вблизи частот,v ₋ иv ₊ для одного месяца наблюдения:h ₀≏3·10⁻²³.

     

Noise measurements on a tunnel junction d.c. SQUID for a gravitational radiation detector at ultralow temperature

Summary We present noise measurements made at temperatures down to 200 mK on a tunnel junction d.c. SQUID, to be used as amplifier for the gravitational-wave experiment Nautilus of the Rome group. We find that the flux noise decreases with temperature, as expected, with a best measured value of at 0.2 K. The presence of an excess noise term independent of temperature is discussed.     

An adaptive filter for gravitational-wave antennas

Summary We report on the development of an adaptive optimum filter for processing the data of a resonant bar gravitational-wave detector. This filter, based on the matched-filter theory, is adaptive in the sense that the function it realizes is derived from the actual noise spectrum of the data being analysed (instead from an idealized model of the noise). Its implementation is mostly based on frequency domain techniques. We also report on the application of the new filter to the data of the cryogenic antenna Explorer of the Rome group, with particular reference to the comparison between its performance and that of an otpimum filter with fixed values of the parameters.     

Lagrangian formalism for resonant capacitive transducers for gravitational-wave antennas

Summary A general analysis of the characteristics of a resonant transducer for gravitational-wave antennas whose resonator has a general mode of vibration has been made using a Lagrangian formalism. The method has been applied to investigate the characteristics of the resonant capacitive transducer developed at the University of Rome and mounted on the cryogenic gravitational-wave antenna built at CERN, finding results in good agreement with the experimental behaviour.

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Riassunto Si usa il formalismo lagrangiano per svolgere un'analisi delle caratteristiche di un trasduttore risonante per antenne gravitazionali nel caso generale in cui il risuonatore utilizzato abbia un modo di vibrazione di forma qualunque. Il metodo è applicato allo studio delle caratteristiche del trasduttore risonante capacitivo sviluppato alla I Università di Roma e montato sull'antenna gravitazionale criogenica realizzata al CERN, trovando risultati in buon accordo con i valori sperimentali.

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Резюме Используя Лагранжев формализм, проводится обший анализ характеристик резонансного датчика для антенн гравитационных волх. Предложенный метод применяется для исследования характеристик резонансного емкостного датчика, разработанного в Римском Университете и смонтированного на криогенной антенне гравитационных волн в ЦЕРНе. Полученные результаты хорошо согласуются с экспериментальными данными.

     

Correlation between gravitational-wave detectors and particle detectors during SN1987A

Summary A review of the correlations between gravitational-wave detectors and particle detectors during SN1987A is given. The correlation between the Maryland and Rome g.w. detectors with the Mont Blanc neutrino detector is illustrated. This correlation extends during a period of one or two hours centred at 2∶45 UT of 23 February 1987, with the ?neutrino? signals delayed by (1.1±0.5) s and with a probability of the order of 10⁻⁵ to be accidental. Using the data obtained with the Kamiokande and IMB detectors, with the same statistical choices and procedures for the data analysis used previously, the above result is confirmed with a probability of the order of 10⁻³ or 10⁻⁴ that the additional correlation be accidental. Paper presented at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990.     

Coincidences among the data recorded by the baksan, kamioka and mont blanc underground neutrino detectors, and by the Maryland and Rome gravitational-wave detectors during Supernova 1987 A

Summary The data recorded with the neutrino detectors at Mont Blanc, Kamioka, Baksan and with the gravitational-wave detectors in Maryland and Rome have been analysed searching for correlations associated with SN 1987 A, without presuming or excluding hypotheses for correlations due to neutrinos and gravitational waves. The statistical analysis has been based on a previous analysis that showed a correlation among Maryland, Rome and Mont Blanc with a probability to be accidental less than 10⁻⁵. Independent correlations are found during a period of one or two hours, around the Mont Blanc 5ν burst (2h 52 min 36 s UT), among the various sets of data: Mont Blanc-Baksan with a probability to be accidental of the order ofp∼4·10⁻³, Mont Blanc-Kamioka withp∼4·10⁻³, Maryland-Rome-Kamioka withp∼5·10⁻⁴, Maryland-Rome-Baksan withp∼5·10⁻². It is remarkable that the events from all the neutrino detectors follow the signals from the g.w. detectors by a time of the order of 1/2 or 1 s. At present we will not give a physical interpretation of the observed correlations which have strong statistical significance. Professor Edoardo Amaldi died on December 5, 1989.     

Testing deviations from the inverse square law with a freely falling gravity gradiometer at balloon altitudes

Summary We discuss a null experiment to search for the fifth force at ranges around 10 km. It is proposed to use a three-axis gravity gradiometer to measure the trace of the Earth gravity tensor from a freely falling elevator dropped by a balloon. The main error sources are considered to some extent. Paper presented at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990.     

Application to other fields of techniques used for gravity wave detection

Summary The experimental techniques developed to build a sensitive gravitational wave antenna can find application in many different fields of research. In the present paper we discuss briefly two experiments that we are developing in the Istituto Fisica Spazio Interplanetario of C.N.R. More precisely, a noncryogenic gravity gradiometer to be flown on the subsatellite of the TSS and a cryogenic force sensor which will be used to verify some recent results on the interaction of neutrino with matter are described. To speed up publication the proofs were not sent to the authors and were superivised by the Scientific Committee.     

Effect of baffle on gravity-gradient-excited slosh waves and spacecraft moment and angular-momentum fluctuations in microgravity

Summary The dynamical behavior of fluids affected by the asymmetric gravity gradient acceleration has been investigated. In particular, the effects of surface tension on partially filled rotating fluids applicable to a full-scale Gravity Probe-B Spacecraft dewar tank with and without baffles are studied. Results of slosh wave excitation along the liquid-vapor interface induced by gravity gradient acceleration indicate that the gravity gradient acceleration is equivalent to the combined effect of a twisting force and a torsional moment acting on the spacecraft. The results are clearly seen from one-up one-down and one-down one-up oscillations in the cross-section profiles of two bubbles in the vertical (r, z)-plane of the rotating dewar, and from the eccentric contour of the bubble rotating around the axis of the dewar in a horizontal (r, θ)-plane. As the viscous force, between liquid and solid interface, greatly contributes to the damping of slosh wave excitation, a rotating dewar with baffles provides more areas of liquid-solid interface than that of a rotating dewar without baffles. Results show that the damping effect provided by the baffles reduces the amplitude of slosh wave excitation and lowers the degree of asymmetry in liquid-vapor distribution. Fluctuations of angular momentum and fluid moment caused by the slosh wave excited by gravity gradient acceleration with and without baffle boards are also investigated. It is also shown that the damping effect provided by the baffles greatly reduces the amplitudes of angular momentum and fluid moment fluctuations.     

General relativistic measurements with satellite laser ranging, lunar laser ranging and very long baseline interferometry

Summary After a brief discussion on the experimental tests of general relativity, we describe three new measurements of Einstein theory. The first, already performed, is the test of the De Sitter or geodetic effect, for the Earth-Moon system. The second will be realized with the launch of the laser ranged satellite, LAGEOS III, and will test the existence of the, never measured, gravitomagnetic field. The third, currently being performed, is the measurement of the LAGEOS relativistic perigee advance. To speed up publication, the proofs were not sent to the authors and were supervised by the Scientific Committee.     

The abnormal influence of the partial solar eclipse on December 24th, 1992, on the time comparisons between atomic clocks

Summary During the partial solar eclipse on Dec. 24th, 1992, time comparisons between atomic clocks were made: direct comparisons between different clocks at one and the same station, clock transport comparisons, GPS comparisons and LOC comparisons. And it is concluded from the observations that solar eclipse exerts an influence on the rate of atomic clocks. Project Supported by the State Science and Technology Commission of China and by the National Natural Foundation of China.     

Sensitivity improvement of a two-mode gravitational-radiation detector through the use of a transducer not perfectly tuned to the antenna

Summary The detailed analysis of the behaviour of a gravitational-wave antenna coupled to a passive resonant transducer has been performed for short bursts of gravitational radiation. An expression for the noise temperature of the system is given for the general case of a transducer with resonant frequency and mechanical quality factor different from those of the antenna. The analysis of the optimum noise temperature obtainable for a given system shows that the optimum performance is obtained when the frequency of the transducer is slightly different from that of the antenna. The main point of this paper has been presented byC. Cosmelli at theSecond Workshop on Precision Measurements on Relativistic Effects in Astrophysical Systems, held in Rome, 11–13 July 1983.     

The ALTAIR cryogenic gravitational-wave experiment

Summary We report on the experimental results obtained with the cryogenic Gravitational-Wave resonant detector ALTAIR located in Frascati (Italy) at the Istituto di Fisica dello Spazio Interplanetario of Consiglio Nazionale delle Ricerche. The peculiarity of this experiment is its working frequency. The first longitudinal mode of resonance of the antenna is at 1.8 kHz. The antenna, now equipped with a resonant capacitive transducer and a d.c. SQUID preamplifier, after a first test in November 1989, has operated almost continuously from May 1990. The best sensitivity, recently reached, expressed in terms of the effective noise temperatureT _eff, is 20 mK, corresponding, for a short pulse of gravitational wave, to a metric perturbationh of 3×10⁻¹⁸. In the last period of measurements (from April 1991 to March 1992) two other antennas were operating: the Explorer antenna (2300 kg,T=2.0 K) at CERN in Geneva and the LSU antenna (2500 kg,T=4.2 K) at Louisiana State University in USA, both having a resonant frequency below 1 kHz. The data of these three detectors can be remote observed, in real time, by the international computer network. Coincidence analysis between the data of these three detectors is in progress. Paper presented at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990 (updated version).     

Test of the equivalence principle in space

Summary Any violation of the equivalence principle (EP) between test masses in the near-Earth orbit is about 500 times bigger than on the ground, which makes the case for a space experiment very strong. Indeed, ESA and NASA (the European Space Agency and the American National Aeronautics and Space Administration) are currently studying at Phase A level the space mission STEP, whose main goal is to test the universality of free fall to 1 part in 10¹⁷ by means of a combination of very advanced technologies (drag free with proportional thrusters, superfluid-He temperature, SQUID sensors). We discuss the key features of STEP as well as some novel ideas about the possibility of testing the equivalence principle at room temperature in a non-drag-free satellite. Paper presented at the 6th Cosmic Physics National Conference, Palermo, 3–7 November 1992.