IUCAA Preprints
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Item Radiation pressure induced instabilities in laser interferometric detectors of gravitational waves(2015-03-13) Pai, A.; Dhurandhar, S.V.; Hello, P.; Vinet, J.Y.The large scale interferometric gravitational wave detectors consist of Fabry-Perot cavities operating at very high powers ranging from tens of kW to MW. The high powers may result in several nonlinear effects which would affect the performance of the detector. In this paper, we investigate the effects of radiation pressure, which tend to displace the mirrors from their resonant position resulting in the detuning of the cavity. We observe a remarkable effect, namely, that the freely hanging mirrors gain energy continuously and swing with increasing amplitude. It is found that the 'time delay', that is, the time taken for the field to adjust to its instantaneous equilibrium value, when the mirrors are in motion, is responsible for this effect. This effect is likely to be important in the optimal functioning of the full-scale interferometers such as the VIRGO and LIGO.Item Search for gravitational waves from the millisecond pulsar PSR 0437-471(2015-03-11) Mohanty, S.D.; Heng, I.S.; Blair, D.G; Dhurandhar, S.V.; Tobar, M.; Ivanov, E.A search for gravitational waves from the millisecond pulsar PSR 0437-471has been initiated using the bar detector NIOBE which is located at the University of Western Australia. This search involves a very long coherent integration of the bar output which may stretch over a few years. We present a detailed report on the data analysis algorithm, called phase plane rotation,which will be used in this search. A discussion of the actual implementation of the algorithm is presented.Item Hierarchial search strategy for inspiraling compact binaries(2015-03-11) Dhurandhar, S.V.Item Search for continuous gravitational wave signals from sources in binary system(2015-03-01) Dhurandhar, S.V.; Vecchio, AlbertWe analyze the computational costs of searches for continuous monochromatic gravitational waves emitted by rotating neutron stars orbiting a companion object. As a function of the relevant orbital parameters, we address the computational load involved in targeted searches, where the position of the source is known; the results are applied to known binary radio pulsars and Sco-Xl.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 The thermo-optical coupling in optical resonators(2015-02-07) Dhurandhar, S.V.; Hello, P.; Sathyaprakash, B.S.Interferometric detectors of gravitational waves employ long baseline FabryPerot cavities with stored power of the order of 10 kW. The mirrors have a high reflectivity with absorption coefficient of a few parts in a million. The laser beam therefore acts as a source of heat creating a thermal gradient in the substrate and the consequent deformation in the mirror which in turn modifies the intra-cavity light field. The problem is thus coupled and nonlinear. Though the effect is expected to be negligible in the case of initial interferometers future interferometers are expected to employ much higher powers and it is necessary to ascertain thermo-elastic deformations and their effect on the stability of the laser field in the cavity. In this paper, which is first in a series to study instabilities in giant high power laser cavities, we have analytically solved the coupled problem of thermo-elastic deformations and their effect on the laser field, perturbatively and we show that within the realm of our (physically reasonable) assumptions there are no instabilities in the frequency range of 1 Hz-1 kHz.Item Coincidence detection of broadband signals by networks of the planned interferometric gravitational wave detectors(2015-01-25) Bhawal, Biplab; Dhurandhar, S.V.We describe how the six planned detectors (2 LIGOs, VIRGO, GEO, AIGO, TAMA) can be used to perform coincidence experiments for the detection of broadband signals from either coalescing compact binaries or burst sources. We make comparisons of the achievable sensitivities of these detectors under different optical configurations and find that a meaningful coincidence experiment for the detection of coalescing binary signals can only be performed by a network where the LIGOs and VIRGO are operated in power recycling mode and other medium scale detectors are operated in dual recycling mode. For the model of burst waveform considered by us (i.e. uniform power upto 2000Hz), we find that the relative sensitivity of the power-recycled VIRGO is quite high as compared to others with their present design parameters and thus coincidence experiment performed by including VIRGO in the network would not be a meaningful one. We also calculate optimized values for the time-delay window sizes for different possible networks. The effect of filtering on the calculation of thresholds has also been discussed. We set the thresholds for different detectors and find out the volume of sky that can be covered by different possible networks and the corresponding rate of detection of coalescing binaries in the beginning of the next century. We note that a coincidence experiment of power-recycled LIGOs and VIRGO and dual-recycled GEO and AIGO can increase the volume of the sky covered by 3.2 times as compared with only the power-recycled LIGO detectors and by 1.7 times the sky covered by the power-recycled LIGO-VIRGO network. These values are far less than the range that can be covered by only the LIGO-VIRGO network with dual recycling operation at a later stage, but the accuracy in the determination of direction, distance and other source parameters will be much better in a coincidence experiment in which other detectors and especially AIGO take part.Item Estimation of parameters of gravitational waves from coalescing binaries(2015-01-25) Balasubramanian, R.; Sathyaprakash, B.S.; Dhurandhar, S.V.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.