36 research outputs found
On the background estimation by time slides in a network of gravitational wave detectors
Time shifting the outputs of Gravitational Wave detectors operating in
coincidence is a convenient way to estimate the background in a search for
short duration signals. However this procedure is limited as increasing
indefinitely the number of time shifts does not provide better estimates. We
show that the false alarm rate estimation error saturates with the number of
time shifts. In particular, for detectors with very different trigger rates
this error saturates at a large value. Explicit computations are done for 2
detectors, and for 3 detectors where the detection statistic relies on the
logical ``OR'' of the coincidences of the 3 couples in the network.Comment: accepted for publication in CQ
Coincidence and coherent data analysis methods for gravitational wave bursts in a network of interferometric detectors
Network data analysis methods are the only way to properly separate real
gravitational wave (GW) transient events from detector noise. They can be
divided into two generic classes: the coincidence method and the coherent
analysis. The former uses lists of selected events provided by each
interferometer belonging to the network and tries to correlate them in time to
identify a physical signal. Instead of this binary treatment of detector
outputs (signal present or absent), the latter method involves first the
merging of the interferometer data and looks for a common pattern, consistent
with an assumed GW waveform and a given source location in the sky. The
thresholds are only applied later, to validate or not the hypothesis made. As
coherent algorithms use a more complete information than coincidence methods,
they are expected to provide better detection performances, but at a higher
computational cost. An efficient filter must yield a good compromise between a
low false alarm rate (hence triggering on data at a manageable rate) and a high
detection efficiency. Therefore, the comparison of the two approaches is
achieved using so-called Receiving Operating Characteristics (ROC), giving the
relationship between the false alarm rate and the detection efficiency for a
given method. This paper investigates this question via Monte-Carlo
simulations, using the network model developed in a previous article.Comment: Spelling mistake corrected in one author's nam
Comparison of filters for detecting gravitational wave bursts in interferometric detectors
Filters developed in order to detect short bursts of gravitational waves in
interferometric detector outputs are compared according to three main points.
Conventional Receiver Operating Characteristics (ROC) are first built for all
the considered filters and for three typical burst signals. Optimized ROC are
shown for a simple pulse signal in order to estimate the best detection
efficiency of the filters in the ideal case, while realistic ones obtained with
filters working with several ``templates'' show how detection efficiencies can
be degraded in a practical implementation. Secondly, estimations of biases and
statistical errors on the reconstruction of the time of arrival of pulse-like
signals are then given for each filter. Such results are crucial for future
coincidence studies between Gravitational Wave detectors but also with neutrino
or optical detectors. As most of the filters require a pre-whitening of the
detector noise, the sensitivity to a non perfect noise whitening procedure is
finally analysed. For this purpose lines of various frequencies and amplitudes
are added to a Gaussian white noise and the outputs of the filters are studied
in order to monitor the excess of false alarms induced by the lines. The
comparison of the performances of the different filters finally show that they
are complementary rather than competitive.Comment: 32 pages (14 figures), accepted for publication in Phys. Rev.
Reconstruction of source location in a network of gravitational wave interferometric detectors
This paper deals with the reconstruction of the direction of a gravitational
wave source using the detection made by a network of interferometric detectors,
mainly the LIGO and Virgo detectors. We suppose that an event has been seen in
coincidence using a filter applied on the three detector data streams. Using
the arrival time (and its associated error) of the gravitational signal in each
detector, the direction of the source in the sky is computed using a chi^2
minimization technique. For reasonably large signals (SNR>4.5 in all
detectors), the mean angular error between the real location and the
reconstructed one is about 1 degree. We also investigate the effect of the
network geometry assuming the same angular response for all interferometric
detectors. It appears that the reconstruction quality is not uniform over the
sky and is degraded when the source approaches the plane defined by the three
detectors. Adding at least one other detector to the LIGO-Virgo network reduces
the blind regions and in the case of 6 detectors, a precision less than 1
degree on the source direction can be reached for 99% of the sky.Comment: Accepted in Phys. Rev.
An elliptical tiling method to generate a 2-dimensional set of templates for gravitational wave search
Searching for a signal depending on unknown parameters in a noisy background
with matched filtering techniques always requires an analysis of the data with
several templates in parallel in order to ensure a proper match between the
filter and the real waveform. The key feature of such an implementation is the
design of the filter bank which must be small to limit the computational cost
while keeping the detection efficiency as high as possible. This paper presents
a geometrical method which allows one to cover the corresponding physical
parameter space by a set of ellipses, each of them being associated to a given
template. After the description of the main characteristics of the algorithm,
the method is applied in the field of gravitational wave (GW) data analysis,
for the search of damped sine signals. Such waveforms are expected to be
produced during the de-excitation phase of black holes -- the so-called
'ringdown' signals -- and are also encountered in some numerically computed
supernova signals.Comment: Accepted in PR
Detection of a close supernova gravitational wave burst in a network of interferometers, neutrino and optical detectors
Trying to detect the gravitational wave (GW) signal emitted by a type II
supernova is a main challenge for the GW community. Indeed, the corresponding
waveform is not accurately modeled as the supernova physics is very complex; in
addition, all the existing numerical simulations agree on the weakness of the
GW emission, thus restraining the number of sources potentially detectable.
Consequently, triggering the GW signal with a confidence level high enough to
conclude directly to a detection is very difficult, even with the use of a
network of interferometric detectors. On the other hand, one can hope to take
benefit from the neutrino and optical emissions associated to the supernova
explosion, in order to discover and study GW radiation in an event already
detected independently. This article aims at presenting some realistic
scenarios for the search of the supernova GW bursts, based on the present
knowledge of the emitted signals and on the results of network data analysis
simulations. Both the direct search and the confirmation of the supernova event
are considered. In addition, some physical studies following the discovery of a
supernova GW emission are also mentioned: from the absolute neutrino mass to
the supernova physics or the black hole signature, the potential spectrum of
discoveries is wide.Comment: Revised version, accepted for publication in Astroparticle Physic
Proton structure function F_2 (X, Q"2) at HERA H1 collaboration
Communication to the International Conference on High Energy Physics (ICHEP.94) Glasgow, July 20-27 1994SIGLEAvailable at INIST (FR), Document Supply Service, under shelf-number : RP 12906 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc