66 research outputs found
Feedback cooling of the normal modes of a massive electromechanical system to submillikelvin temperature
We apply a feedback cooling technique to simultaneously cool the three
electromechanical normal modes of the ton-scale resonant-bar gravitational wave
detector AURIGA. The measuring system is based on a dc Superconducting Quantum
Interference Device (SQUID) amplifier, and the feedback cooling is applied
electronically to the input circuit of the SQUID. Starting from a bath
temperature of 4.2 K, we achieve a minimum temperature of 0.17 mK for the
coolest normal mode. The same technique, implemented in a dedicated experiment
at subkelvin bath temperature and with a quantum limited SQUID, could allow to
approach the quantum ground state of a kilogram-scale mechanical resonator.Comment: 4 pages, 4 figure
Dual detectors of gravitational waves
In a "Dual" gravitational wave (GW) detector a wide band sensitivity is obtained by measuring the differential displacement, driven by the GW, of the facing surfaces of two nested massive bodies mechanically resonating at different frequencies. A "selective readout" scheme, capable of specifically selecting the signal contributed by the vibrational modes sensitive to the gravitational waves, could then reduce the thermal noise contribution from the not sensitive modes. In a dual detector the sensitivity improvement in the displacement transduction could be pursued by means of mechanical amplification systems. This solution is innovative for the resonant GW detectors and we report about preliminary theoretical and experimental study
Nonequilibrium steady state fluctuations in actively cooled resonators
We analyze heat and work fluctuations in the gravitational wave detector
AURIGA, modeled as a macroscopic electromechanical oscillator in contact with a
thermostat and cooled by an active feedback system. The oscillator is driven to
a steady state by the feedback cooling, equivalent to a viscous force. The
experimentally measured fluctuations are in agreement with our theoretical
analysis based on a stochastically driven Langevin system. The asymmetry of the
fluctuations of the absorbed heat characterizes the oscillator's nonequilibrium
steady state and reveals the extent to which a feedback cooled system departs
from equilibrium in a statistical mechanics perspective.Comment: to be published in Phys. Rev. Let
IGEC2: A 17-month search for gravitational wave bursts in 2005-2007
We present here the results of a 515 days long run of the IGEC2 observatory,
consisting of the four resonant mass detectors ALLEGRO, AURIGA, EXPLORER and
NAUTILUS. The reported results are related to the fourfold observation time
from Nov. 6 2005 until Apr. 14 2007, when Allegro ceased its operation. This
period overlapped with the first long term observations performed by the LIGO
interferometric detectors. The IGEC observations aim at the identification of
gravitational wave candidates with high confidence, keeping the false alarm
rate at the level of 1 per century, and high duty cycle, namely 57% with all
four sites and 94% with at least three sites in simultaneous observation. The
network data analysis is based on time coincidence searches over at least three
detectors: the four 3-fold searches and the 4-fold one are combined in a
logical OR. We exchanged data with the usual blind procedure, by applying a
unique confidential time offset to the events in each set of data. The
accidental background was investigated by performing sets of 10^8 coincidence
analyses per each detector configuration on off-source data, obtained by
shifting the time series of each detector. The thresholds of the five searches
were tuned so as to control the overall false alarm rate to 1/century. When the
confidential time shifts was disclosed, no gravitational wave candidate was
found in the on-source data. As an additional output of this search, we make
available to other observatories the list of triple coincidence found below
search thresholds, corresponding to a false alarm rate of 1/month.Comment: 10 pages, 8 figures Accepted for publication on Phys. Rev.
Results of the IGEC-2 search for gravitational wave bursts during 2005
The network of resonant bar detectors of gravitational waves resumed
coordinated observations within the International Gravitational Event
Collaboration (IGEC-2). Four detectors are taking part in this collaboration:
ALLEGRO, AURIGA, EXPLORER and NAUTILUS. We present here the results of the
search for gravitational wave bursts over 6 months during 2005, when IGEC-2 was
the only gravitational wave observatory in operation. The network data analysis
implemented is based on a time coincidence search among AURIGA, EXPLORER and
NAUTILUS, keeping the data from ALLEGRO for follow-up studies. With respect to
the previous IGEC 1997-2000 observations, the amplitude sensitivity of the
detectors to bursts improved by a factor about 3 and the sensitivity bandwidths
are wider, so that the data analysis was tuned considering a larger class of
detectable waveforms. Thanks to the higher duty cycles of the single detectors,
we decided to focus the analysis on three-fold observation, so to ensure the
identification of any single candidate of gravitational waves (gw) with high
statistical confidence. The achieved false detection rate is as low as 1 per
century. No candidates were found.Comment: 10 pages, to be submitted to Phys. Rev.
3-mode detection for widening the bandwidth of resonant gravitational wave detectors
We have implemented a novel scheme of signal readout for resonant
gravitational wave detectors. For the first time, a capacitive resonant
transducer has been matched to the signal amplifier by means of a tuned high Q
electrical resonator. The resulting 3-mode detection scheme widens
significantly the bandwidth of the detector. We present here the results
achieved by this signal readout equipped with a two-stage SQUID amplifier. Once
installed on the AURIGA detector, the one-sided spectral sensitivity obtained
with the detector operated at 4.5 K is better than 10^-20 Hz^-1/2 over 110 Hz
and in good agreement with the expectations.Comment: 17 pages, 4 figure
Upper limits on gravitational waves emission in association with the Dec 27 2004 giant flare of SGR1806-20
At the time when the giant flare of SGR1806-20 occurred, the AURIGA "bar" gw
detector was on the air with a noise performance close to stationary gaussian.
This allows to set relevant upper limits, at a number of frequencies in the
vicinities of 900 Hz, on the amplitude of the damped gw wave trains, which,
according to current models, could have been emitted, due to the excitation of
normal modes of the star associated with the peak in X-rays luminosity.Comment: 4 pages, 3 figure
A Cross-correlation method to search for gravitational wave bursts with AURIGA and Virgo
We present a method to search for transient GWs using a network of detectors
with different spectral and directional sensitivities: the interferometer Virgo
and the bar detector AURIGA. The data analysis method is based on the
measurements of the correlated energy in the network by means of a weighted
cross-correlation. To limit the computational load, this coherent analysis step
is performed around time-frequency coincident triggers selected by an excess
power event trigger generator tuned at low thresholds. The final selection of
GW candidates is performed by a combined cut on the correlated energy and on
the significance as measured by the event trigger generator. The method has
been tested on one day of data of AURIGA and Virgo during September 2005. The
outcomes are compared to the results of a stand-alone time-frequency
coincidence search. We discuss the advantages and the limits of this approach,
in view of a possible future joint search between AURIGA and one
interferometric detector.Comment: 11 pages, 6 figures, submitted to CQG special issue for Amaldi 7
Proceeding
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