IUCAA Preprints
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Item Detection of gravitational waves using a network of detectors(2015-03-01) Bose, Sukanta; Dhurandhar, S.V.; Pai, ArchanaWe formulate the data analysis problem for the detection of the Newtonian coalescing-binary signal by a network of laser interferometric gravitational wave detectors that have arbitrary orientations, but are located at the same site. We use the maximum likelihood method for optimizing the detection problem. We show that for networks comprising of up to three detectors, the optimal statistic is just the matched network-filter. Alternatively, it is simply a linear combination of the signal-to-noise ratios of the individual detectors. This statistic, therefore, can be interpreted as the signal-to-noise ratio of the network. The overall sensitivity of the network is shown to increase roughly as the square-root of the number of detectors in the network. We further show that these results continue to hold even for the restricted post Newtonian filters. Finally, our formalism is general enough to be extended, in a straightforward way, to address the problem of detection of such waves from other sources by some other types of detectors, eg., bars or spheres, or even by networks of spatially well-separated detectors.Item Signal analysis of the gravitational waveform of pulsars(2015-01-17) Jotania, Kanti; Dhurandhar, S.V.; Valluri, S.R.Item Performance of Newtonian filters in the detection of gravitational radiation from coalescing binaries(2015-01-13) Balasubramanian, R.; Dhurandhar, S.V.Post – Newtonian corrections to the gravitational waveform emitted by coalescing binaries have been found to lead to a secular phase accumulation error as compared with the signals calculated in the Newtonian approximation. The matched filtering process which relies on the correlation between the correlation between the signal and the filter is extremely sensitive to errors in phase. We explore the possibility of compensating for the phase difference caused by the post-Newtonian terms by allowing for a shift in the Newtonian filter parameters. We find that, on the average, we lose by about 30% in the correlation.Item Response of the interferometric antenna to gravitational radiation from pulsars(2015-01-13) Jotania, Kanti; Dhurandhar, S.V.We present here a full calculation of the response of a laser interferometric gravitational wave detector on which gravitational radiation from a continuous source is incident. The observation time is taken to be of the order of few months. The long observation time implies that the motion of the detector is important and must be included in the response as a modulation effect. For simplicity we consider only two motions of the Earth , namely the rotation of the Earth about axis and the orbital motions about the sun. The orbit is assumed to be circular. We consider the detector to be situated and oriented arbitrarily on the Earth, except that we assume the arms of the detector must lie in the tangent plane to the Earth at the point where the detector is situated. The gravitational wave incident on the detector is assumed to be a plane wave having arbitrary direction and polarization. We also present here the computation of the quadrupole wave form of a typical continuous source – a pulsar-which is modelled as an almost spherical object of uniform density, spinning about an arbitrary axis with uniform angular velocity. We use techniques of spherical tensors and Gel’fandfunction developed in the literature to compute the waveformItem The search for gravitational waves(2014-11-26) Dhurandhar, S.V.The direct detection of gravitational waves is one of the most challenging problems in experimental physics today. Sustained efforts have led to impressive advances on both theoretical and experimental fronts. This article first deals with the theoretical aspects of gravitational waves and then continues on to describe the detectors in vogue, the present status and various gravitational waves sources.Item Choice of filters for the detection of gravitational waves from coalescing binaries II: detection in coloured noise(2014-11-25) Dhurandhar, S.V.; Sathyaprakash, B.S.We discuss the problem of detecting gravitational waves signals embedded in coloured noise from coalescing binary systems. The signal is assumed to be Newtonian and matched filtering techniques are employed to filter out the signal. The problem is discussed at first for a general power spectral density of the noise and then specific numerical results are obtained for the standard recycling case. Since the signal parameters are unknown, a bank of filters is needed to carry out the signal detection. The number of filters in a bank , the spacing between filter etc. is obainted for different values of minimum strength of the signal relative to the threshold. We also present an approximate analytical formula which relates the spacing between filter to the minimum strength. Finally we discuss the problem of detection probabilities given a data train.Item A parallel algorithm for filtering gravitational waves from coalescing binaries(2014-11-23) Sathyaprakash, B.S.; Dhurandhar, S.V.Coalescing binary stars are perhaps the most promising sources for the observation of gravitational waves with laser interferometric gravity wave detectors. The waveform from these sources can be predicted with sufficient accuracy for matched filtering techniques to be applied. In this paper we present a parallel algorithm for detecting signals from coalescing compact binaries by the method of matched filtering. We also report the details of its implementation on a 256-node connection machine consisting of a network of transputers. The results of our analysis indicate that parallel processing is a promising approach to on-line analysis of data from gravitational wave detectors to filter out coalescing binary signals. The algorithm described is quite general in that the kernel of the algorithm is applicable to any set of matched filters.