1,025 research outputs found
Gravitational wave astronomy - astronomy of the 21st century
An enigmatic prediction of Einstein's general theory of relativity is
gravitational waves. With the observed decay in the orbit of the Hulse-Taylor
binary pulsar agreeing within a fraction of a percent with the theoretically
computed decay from Einstein's theory, the existence of gravitational waves was
firmly established. Currently there is a worldwide effort to detect
gravitational waves with interferometric gravitational wave observatories or
detectors and several such detectors have been built or being built. The
initial detectors have reached their design sensitivities and now the effort is
on to construct advanced detectors which are expected to detect gravitational
waves from astrophysical sources. The era of gravitational wave astronomy has
arrived. This article describes the worldwide effort which includes the effort
on the Indian front - the IndIGO project -, the principle underlying
interferometric detectors both on ground and in space, the principal noise
sources that plague such detectors, the astrophysical sources of gravitational
waves that one expects to detect by these detectors and some glimpse of the
data analysis methods involved in extracting the very weak gravitational wave
signals from detector noise.Comment: The contents of this article were finalised few months ago. The
discussion in the article pertains to the situation prevailing at that tim
Time Delay Interferometry for LISA with one arm dysfunctional
In order to attain the requisite sensitivity for LISA - a joint space mission
of the ESA and NASA- the laser frequency noise must be suppressed below the
secondary noises such as the optical path noise, acceleration noise etc. By
combining six appropriately time-delayed data streams containing fractional
Doppler shifts - a technique called time delay interferometry (TDI) - the laser
frequency noise may be adequately suppressed. We consider the general model of
LISA where the armlengths vary with time, so that second generation TDI are
relevant. However, we must envisage the possibility, that not all the optical
links of LISA will be operating at all times, and therefore, we here consider
the case of LISA operating with two arms only. As shown earlier in the
literature, obtaining even approximate solutions of TDI to the general problem
is very difficult. Since here only four optical links are relevant, the
algebraic problem simplifies considerably. We are then able to exhibit a large
number of solutions (from mathematical point of view an infinite number) and
further present an algorithm to generate these solutions
Adaptive filtering techniques for interferometric data preparation: removal of long-term sinusoidal signals and oscillatory transients
We propose an adaptive denoising scheme for poorly modeled non-Gaussian
features in the gravitational wave interferometric data. Preliminary tests on
real data show encouraging results.Comment: 4 pages, 2 figures. Proceedings of GWDAW99 (Roma, Dec. 1999), to
appear in Int. J. Mod. Phys.
The mathematical theory of resonant transducers in a spherical gravity wave antenna
The rigoruos mathematical theory of the coupling and response of a spherical
gravitational wave detector endowed with a set of resonant transducers is
presented and developed. A perturbative series in ascending powers of the
square root of the ratio of the resonator to the sphere mass is seen to be the
key to the solution of the problem. General layouts of arbitrary numbers of
transducers can be assessed, and a specific proposal (PHC), alternative to the
highly symmetric TIGA of Merkowitz and Johnson, is described in detail.
Frequency spectra of the coupled system are seen to be theoretically recovered
in full agreement with experimental determinations.Comment: 31 pages, 7 figures, LaTeX2e, \usepackage{graphicx,deleq
Coherent versus coincidence detection of gravitational wave signals from compact inspiraling binaries
We compare two multi-detector detection strategies, namely, the coincidence
and the coherent, for the detection of spinless inspiraling compact binary
gravitational wave signals. The coincident strategy treats the detectors as if
they are isolated - compares individual detector statistics with their
respective thresholds while the coherent strategy combines the detector network
data {\it phase coherently} to obtain a single detection statistic which is
then compared with a single threshold. In the case of geographically separated
detectors, we also consider an {\it enhanced} coincidence strategy because the
usual (naive) coincidence strategy yields poor results for misaligned
detectors. For simplicity, we consider detector pairs having the same power
spectral density of noise, as that of initial LIGO and also assume the noise to
be stationary and Gaussian. We compare the performances of the methods by
plotting the \emph{receiver operating characteristic} (ROC) for the two
strategies. A single astrophysical source as well as a distribution of sources
is considered. We find that the coherent strategy performs better than the two
coincident strategies under the assumptions of stationary Gaussian detector
noise.Comment: Based on the presentation at the 1st Galileo Xu Guangqi conference,
Shanghai
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