40 research outputs found
False discovery rate: setting the probability of false claim of detection
When testing multiple hypothesis in a survey --e.g. many different source
locations, template waveforms, and so on-- the final result consists in a set
of confidence intervals, each one at a desired confidence level. But the
probability that at least one of these intervals does not cover the true value
increases with the number of trials. With a sufficiently large array of
confidence intervals, one can be sure that at least one is missing the true
value. In particular, the probability of false claim of detection becomes not
negligible. In order to compensate for this, one should increase the confidence
level, at the price of a reduced detection power. False discovery rate control
is a relatively new statistical procedure that bounds the number of mistakes
made when performing multiple hypothesis tests. We shall review this method,
discussing exercise applications to the field of gravitational wave surveys.Comment: 7 pages, 3 table, 3 figures. Prepared for the Proceedings of GWDAW 9
(http://lappc-in39.in2p3.fr/GWDAW9) A new section was added with a numerical
example, along with two tables and a figure related to the new section. Many
smaller revisions to improve readibilit
Correlation between Gamma-Ray bursts and Gravitational Waves
The cosmological origin of -ray bursts (GRBs) is now commonly
accepted and, according to several models for the central engine, GRB sources
should also emit at the same time gravitational waves bursts (GWBs). We have
performed two correlation searches between the data of the resonant
gravitational wave detector AURIGA and GRB arrival times collected in the BATSE
4B catalog. No correlation was found and an upper limit \bbox{} on the averaged amplitude of gravitational waves
associated with -ray bursts has been set for the first time.Comment: 7 pages, 3 figures, submitted to Phys. Rev.
ON-LINE CONSISTENCY TESTS FOR BAR DETECTORS
In order to detect gravitational wave signals with resonant bar detectors using Wiener–Kolmogorov (WK) filters, both a model for the power spectrum density (PSD) of the noise and a signal template should be provided. As the analysis is not meant to handle non-gaussian data, we have to discriminate (and constrain to) time periods where the noise follows a quasi-stationary gaussian model. Within these periods, candidate events are selected in the WK filter output, and their fundamental parameters (time of arrival and amplitude) are computed. A necessary and sufficient condition for the reliability of such estimates is the consistency of the signal shape with the template. This is done performing a goodness-of-the-fit test
Testing of optimal filters for gravitational wave signals: An experimental implementation
We have implemented likelihood testing of the performance of an optimal filter within the online analysis of AURIGA, a sub-Kelvin resonant-bar gravitational wave detector. We demonstrate the effectiveness of this technique in discriminating between impulsive mechanical excitations of the resonant-bar and other spurious excitations. This technique also ensures the accuracy of the estimated parameters such as the signal-to-noise ratio. The efficiency of the technique to deal with non-stationary noise and its application to data from a network of detectors are also discussed
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
First room temperature operation of the AURIGA optical readout
In the frame of the AURIGA collaboration, a readout scheme based on an optical resonant cavity has been implemented on a room temperature resonant bar detector of gravitational waves. The bar equipped with the optical readout has been operating for a few weeks and we report here the first results
Initial operation of the International Gravitational Event Collaboration
The International Gravitational Event Collaboration, IGEC, is a coordinated
effort by research groups operating gravitational wave detectors working
towards the detection of millisecond bursts of gravitational waves. Here we
report on the current IGEC resonant bar observatory, its data analysis
procedures, the main properties of the first exchanged data set. Even though
the available data set is not complete, in the years 1997 and 1998 up to four
detectors were operating simultaneously. Preliminary results are mentioned.Comment: 8 pages, 2 figures, 3 tables; Proceeding of the GWDAW'99. Submitted
to the International Journal of Modern Physic
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
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.
Coherent detection method of gravitational wave bursts for spherical antennas
We provide a comprehensive theoretical framework and a quantitative test of
the method we recently proposed for processing data from a spherical detector
with five or six transducers. Our algorithm is a trigger event generator
performing a coherent analysis of the sphere channels. In order to test our
pipeline we first built a detailed numerical model of the detector, including
deviations from the ideal case such as quadrupole modes splitting, and
non-identical transducer readout chains. This model, coupled with a Gaussian
noise generator, has then been used to produce six time series, corresponding
to the outputs of the six transducers attached to the sphere. We finally
injected gravitational wave burst signals into the data stream, as well as
bursts of non-gravitational origin in order to mimic the presence of
non-Gaussian noise, and then processed the mock data. We report quantitative
results for the detection efficiency versus false alarm rate and for the
affordability of the reconstruction of the direction of arrival. In particular,
the combination of the two direction reconstruction methods can reduce by a
factor of 10 the number false alarms due to the non-Gaussian noise.Comment: 31 pages, 15 figure