1,261 research outputs found
Validating delta-filters for resonant bar detectors of improved bandwidth foreseeing the future coincidence with interferometers
The classical delta filters used in the current resonant bar experiments for
detecting GW bursts are viable when the bandwidth of resonant bars is few Hz.
In that case, the incoming GW burst is likely to be viewed as an impulsive
signal in a very narrow frequency window. After making improvements in the
read-out with new transducers and high sensitivity dc-SQUID, the
Explorer-Nautilus have improved the bandwidth ( Hz) at the sensitivity
level of . Thus, it is necessary to reassess this
assumption of delta-like signals while building filters in the resonant bars as
the filtered output crucially depends on the shape of the waveform. This is
presented with an example of GW signals -- stellar quasi-normal modes, by
estimating the loss in SNR and the error in the timing, when the GW signal is
filtered with the delta filter as compared to the optimal filter.Comment: 7 pages, presented in Amaldi6, accepted for publication in Journal of
Physics: Conference Serie
On the crosscorrelation between Gravitational Wave Detectors for detecting association with Gamma Ray Bursts
Crosscorrelation of the outputs of two Gravitational Wave (GW) detectors has
recently been proposed [1] as a method for detecting statistical association
between GWs and Gamma Ray Bursts (GRBs). Unfortunately, the method can be
effectively used only in the case of stationary noise. In this work a different
crosscorrelation algorithm is presented, which may effectively be applied also
in non-stationary conditions for the cumulative analysis of a large number of
GRBs. The value of the crosscorrelation at zero delay, which is the only one
expected to be correlated to any astrophysical signal, is compared with the
distribution of crosscorrelation of the same data for all non-zero delays
within the integration time interval. This background distribution is gaussian,
so the statistical significance of an experimentally observed excess would be
well-defined.
Computer simulations using real noise data of the cryogenic GW detectors
Explorer and Nautilus with superimposed delta-like signals were performed, to
test the effectiveness of the method, and theoretical estimates of its
sensitivity compared to the results of the simulation. The effectiveness of the
proposed algorithm is compared to that of other cumulative techniques, finding
that the algorithm is particularly effective in the case of non-gaussian noise
and of a large (100-1000s) and unpredictable delay between GWs and GRBs.Comment: 7 pages, 4 figures, 1 table. Submitted by Phys. Rev.
Search for Periodic Gravitational Wave Sources with the Explorer Detector
We have developped a procedure for the search of periodic signals in the data
of gravitational wave detectors. We report here the analysis of one year of
data from the resonant detector Explorer, searching for pulsars located in the
Galactic Center (GC). No signals with amplitude greater than , in the range 921.32-921.38 Hz, were observed using data
collected over a time period of 95.7 days, for a source located at
hours and degrees. Our
procedure can be extended for any assumed position in the sky and for a more
general all-sky search, even with a frequency correction at the source due to
the spin-down and Doppler effects.Comment: One zipped file (Latex+eps figures). 33 pages, 14 figures. This and
related material also at http://grwav3.roma1.infn.it
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 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 >=1.2 * 10^{-18}, with 95 % probability, if we allow a time delay
between GW bursts and GRB within +-400 s, and h >= 6.5 * 10^{-19}, if the time
delay is within +- 5 s. The result is also provided in form of scaled
likelihood for unbiased interpretation and easier use for further analysis.Comment: 14 pages, 7 figures. Latex file, compiled with cernik.cls (provided
in the package
All-sky upper limit for gravitational radiation from spinning neutron stars
We present results of the all-sky search for gravitational-wave signals from
spinning neutron stars in the data of the EXPLORER resonant bar detector. Our
data analysis technique was based on the maximum likelihood detection method.
We briefly describe the theoretical methods that we used in our search. The
main result of our analysis is an upper limit of for
the dimensionless amplitude of the continuous gravitational-wave signals coming
from any direction in the sky and in the narrow frequency band from 921.00 Hz
to 921.76 Hz.Comment: 12 pages, 4 figures, submitted to Proceedings of 7th Gravitational
Wave Data Analysis Workshop, December 17-19, 2002, Kyoto, Japa
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
the year 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 favorably oriented with
respect to the Galactic Disk
Gravitational wave bursts induced by r-mode spin-down of hybrid stars
We show that sudden variations in the composition and structure of an hybrid
star can be triggered by its rapid spin-down, induced by r-mode instabilities.
The discontinuity of this process is due to the surface tension between
hadronic and quark matter and in particular to the overpressure needed to
nucleate new structures of quark matter in the mixed phase. The consequent
mini-collapses in the star can produce highly energetic gravitational wave
bursts. The possible connection between the predictions of this model and the
burst signal found by EXPLORER and NAUTILUS detectors during the year 2001 is
also investigated.Comment: 9 pages, 8 figures, revised version, to be published in Astronomy &
Astrophysic
Data analysis of gravitational-wave signals from spinning neutron stars. IV. An all-sky search
We develop a set of data analysis tools for a realistic all-sky search for
continuous gravitational-wave signals. The methods that we present apply to
data from both the resonant bar detectors that are currently in operation and
the laser interferometric detectors that are in the final stages of
construction and commissioning. We show that with our techniques we shall be
able to perform an all-sky 2-day long coherent search of the narrow-band data
from the resonant bar EXPLORER with no loss of signals with the dimensionless
amplitude greater than .Comment: REVTeX, 26 pages, 1 figure, submitted to Phys. Rev.
Vibrational excitation induced by electron beam and cosmic rays in normal and superconductive aluminum bars
We report new measurements of the acoustic excitation of an Al5056
superconductive bar when hit by an electron beam, in a previously unexplored
temperature range, down to 0.35 K. These data, analyzed together with previous
results of the RAP experiment obtained for T > 0.54 K, show a vibrational
response enhanced by a factor 4.9 with respect to that measured in the normal
state. This enhancement explains the anomalous large signals due to cosmic rays
previously detected in the NAUTILUS gravitational wave detector.Comment: 28 pages, 13 figure
A new data analysis framework for the search of continuous gravitational wave signals
Continuous gravitational wave signals, like those expected by asymmetric
spinning neutron stars, are among the most promising targets for LIGO and Virgo
detectors. The development of fast and robust data analysis methods is crucial
to increase the chances of a detection. We have developed a new and flexible
general data analysis framework for the search of this kind of signals, which
allows to reduce the computational cost of the analysis by about two orders of
magnitude with respect to current procedures. This can correspond, at fixed
computing cost, to a sensitivity gain of up to 10%-20%, depending on the search
parameter space. Some possible applications are discussed, with a particular
focus on a directed search for sources in the Galactic center. Validation
through the injection of artificial signals in the data of Advanced LIGO first
observational science run is also shown.Comment: 21 pages, 8 figure
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