G. V. Pallottino

The gravitational wave detector NAUTILUS operating at T = 0.1 K

Abstract We report on the ultralow-temperature resonant-mass gravitational-wave detector NAUTILUS, operating at the Frascati INFN Laboratories. The present aim of this detector is to achieve a sensitivity sufficient to detect bursts of gravitational radiation from sources located in our Galaxy and in the local group. Progress in transducer technology is likely to lead to sensitivities that will enable us to observe events from sources as far away as the Virgo cluster of galaxies. We describe the cryogenic apparatus, readout system, cosmic-ray veto system, and give first results obtained during one year of continuous operation at T = 0.1 K. In particular the Brownian noise of the detector at T = 0.1 K was measured. The measured strain sensitivity was h ≈ 6 · 10 −22 Hz − 1 2 at the frequencies of the two modes, 908 Hz and 924 Hz, with bandwidths of about 1 Hz.

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.

Study of the coincidences between the gravitational wave detectors EXPLORER and NAUTILUS in 2001

We report the result from a search for bursts of gravitational waves using data collected by the cryogenic resonant detectors EXPLORER and NAUTILUS during 2001 for a total measuring time of 90 days. With these data we repeated the coincidence search performed on the 1998 data (which showed a small coincidence excess) applying data analysis algorithms based on known physical characteristics of the detectors. With the 2001 data, a new interesting coincidence excess is found when the detectors are favourably oriented with respect to the galactic disc.

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.

Increasing the Bandwidth of Resonant Gravitational Antennas: The Case of Explorer

Resonant gravitational wave detectors with an observation bandwidth of tens of hertz are a reality: the antenna Explorer, operated at CERN by the ROG Collaboration, has been upgraded with a new readout. In this new configuration, it exhibits an unprecedented useful bandwidth: in over 55 Hz about its center operating frequency of 919 Hz the spectral sensitivity is better than 10(-20) Hz(-1/2). We describe the detector and its sensitivity and discuss the foreseeable upgrades to even larger bandwidths.

Upper limit for a gravitational-wave stochastic background with the EXPLORER and NAUTILUS resonant detectors

We discuss the sensitivity of resonant-mass gravitational-wave detectors to a cosmic stochastic background of gravitational waves. We report the experimental upper limits given by the gravitational wave detectors EXPLORER and NAUTILUS.

Search for correlation between GRB's detected by BeppoSAX and gravitational wave detectors EXPLORER and NAUTILUS

Data obtained during five months of 2001 with the gravitational wave ~GW! detectors EXPLORER and NAUTILUS, operating with a bandwidth of a few Hz at frequencies near 900 Hz, were studied in correlation with the gamma ray burst data ~GRB! obtained with the BeppoSAX satellite. During this period BeppoSAX was the only GRB satellite in operation, while EXPLORER and NAUTILUS were the only GW detectors in operation. No correlation between the GW data and the GRB bursts was found. The analysis, performed over 47 GRB’s, excludes the presence of signals of amplitude h>6.5310 219 , with 95% probability, if we allow a time delay between GW bursts and GRB within 65 s, and h>1.2310 218 , if the time delay is within 6400 s. The result is also provided in the form of scaled likelihood for unbiased interpretation and easier use for further analysis.

Energetic cosmic rays observed by the resonant gravitational wave detector NAUTILUS

The passage of cosmic rays has been observed to excite mechanical vibrations in the resonant gravitational wave detector NAUTILUS operating at temperature of 100 mK. A very significant correlation (more than 10 standard deviations) is found.

Search for coincident excitation of the widely spaced resonant gravitational wave detectors EXPLORER, NAUTILUS and NIOBE

We report the search for coincidences among three resonant mass detectors: EXPLORER at CERN and NAUTILUS in Frascati of the Rome group and NIOBE in Perth of the UWA group. The three detectors have a sensitivity for short bursts of GW in the h ≈ 10−18 range, about one thousand times better in energy than Webers original detectors. The analysis is based on the comparison of candidate event lists recorded by the detectors in the period December 1994 through October 1996. The events have been obtained by applying a pulse detection filter to the raw data and using a predetermined threshold. Due to the different periods of data taking it was not possible to search for triple coincidences. We searched for coincidences between EXPLORER and NAUTILUS during the years 1995 and 1996 for a total time coverage of 1372 hours and between EXPLORER and NIOBE in 1995 for a coverage of 1362 hours. The results have been: a weak indication of a coincidence excess with respect to the accidental ones between EXPLORER and NAUTILUS and no coincidence excess between EXPLORER and NIOBE.