G. Pizzella

Data Recordered by the Rome Room Temperature Gravitational Wave Antenna, during the Supernova SN 1987a in the Large Magellanic Cloud

The data recorded by the Rome room temperature gravitational-wave antenna during the Supernova SN 1987a have been analysed in connection with the Mont Blanc neutrino event. An energy innovation is observed which precedes by (1.4 ± 0.5) s the first observed neutrino arrival time with the probability of being accidental of 3 per cent. An estimation of the energy emitted as g.w. distributed over 4π and a frequency bandwidth of 1 kHz gives the figure of 2400 M⊙, which is abnormal according to standard views on g.w. Under the hypothesis that the time delay δt between the antenna signal and the first neutrino detected in the Mont Blanc tunnel is due only to the neutrino mass, the following mass value is derived from the observed δt = (1.4 ± 0.5) s: mνe ≤ (7.2 ± 1.3) eV.

Sensitivity of the Rome Gravitational Wave Experiment with the Explorer Cryogenic Resonant Antenna Operating at 2 K

We report on the results obtained with a cryogenic gravitational wave antenna equipped with a d.c. SQUID, operating at 2 K. During a period of a few days in April 1989 the measured noise temperature (for short bursts of gravitational waves) was Teff 7 mK corresponding to a sensitivity of hc 710-19. This result allows to improve the previously published upper limits for the rate of gravitational wave bursts.

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

SummaryThe 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.

Q measurements down to liquid helium temperatures for a gravitational wave aluminium bar antenna

Abstract To detect gravitational waves it is necessary to separate the signals due to these waves from thermal noise in the antenna. A possible way of achieving this would be to operate at liquid helium temperatures. The behaviour of aluminium bar antenna was studied at liquid helium temperatures with particular reference to Q values.

Resonant detectors for the search for gravitational waves

An overview of the experiments for the search for gravitational waves by means of resonant detectors is given. Since 1990 cryogenic resonant antennas have been in operation and data have been recorded by Explorer, Allegro, Niobe and Nautilus. The sensitivity for pulse detection with SNR = 1 is now (corresponding to a total energy of less than 0.001 solar masses for a source in the Galactic Center). The sensitivity for monochromatic waves is for one year of integration and about for stochastic background detection. Large resonant detectors operating at 1 kHz might reach, in the near future, a spectral amplitude sensitivity of the order of and, for pulse and monochromatic wave sensitivity, respectively, and . Cross-correlating two such large antennas for one year can give a sensitivity for stochastic background detection of the order of , corresponding to a ratio between the gravitational wave energy density to that needed for a closed Universe of .

Correlation between the Maryland and Rome gravitational-wave detectors and the Mont Blanc, Kamioka and IMB particle detectors during SN 1987 A

SummaryFollowing a previously found correlation between the gravitational-wave detectors and the Mont Blanc particle detector, we have searched for a similar correlation between the data of the experiments mentioned in the title. We have found that both the Kamioka and the IMB data have a correlation with the gravitational-wave data that occurs with the same characteristics and at the same time of that already found with Mont Blanc. This correlation extends for a period of one or two hours centred at the hour 2∶45 UT of 23 February 1987. It shows that the particle detector signals are delayed with respect to the gravitational-wave detector signals by (1.2±0.5) s. The probability that the additional correlation due to Kamioka and IMB is only accidental is estimated of the order of 10−3 or 10−4.

Time dispersion and efficiency of coincident detection of signals in resonant bar gravitational wave detectors

Using simulated signals and measured noise with the EXPLORER and NAUTILUS detectors we find the efficiency of signal detection and the signal arrival time dispersion versus the signal-to-noise ratio. 1 Introduction There are today five detectors of gravitational waves (GW) in operation [1, 2, 3, 4, 5], all of them of the resonant type. It is thus important to study in detail the problem of the coincidence search. In the past, after the initial works of Weber, three papers on coincidence search have been published [6, 7, 8]. These coincidence search was made under two hidden assumptions: a)the signal-to-noise ratio (SNR) was considered to be very large, b)the event time was considered to be equal to the signal time. Since we expect very tiny signals, the study of the problem when dealing with small SNRs is fundamental. This is our object here using simulated signals but with real noise measured with the EXPLORER and NAUTILUS detectors.

An adaptive filter for gravitational-wave antennas

SummaryWe 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.

Data analysis for a gravitational wave antenna with resonant capacitive transducer

SummaryWe 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:h0≏3·10−23.RiassuntoSi 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:h0≏3.·10−23.РезюмеПредлагается 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:h0≏3·10−23.

The EXPLORER gravitational wave antenna: recent improvements and performances

Since the beginning of 2000 the EXPLORER gravity wave (GW) detector has been operated continuously after a stop devoted to improve the apparatus. The antenna has been equipped with a new read-out. The use of a new transducer, characterized by a very small gap, and a dc-SQUID with a high coupling, led to a better sensitivity and a larger bandwidth. The EXPLORER sensitivity in terms of spectral noise amplitude, at present (June 2001), is 10−20 Hz−1/2 over a bandwidth of 35 Hz and 3 × 10−21 Hz−1/2 with a bandwidth of about 6 Hz, corresponding to a sensitivity to short conventional GW bursts of h = 4 × 10−19. The performance is stable and the apparatus is taking data with a duty cycle in excess of 80%.