IUCAA Preprints
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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 Lensing by gravitational waves in scalar – tensor gravity: Einstein frame analysis(2015-03-11) Faraoni, Valerio; Gunzing , EdgardThe amplification of a light beam due to intervening gravitational waves is studied. The previous Jordan frame result according to which the amplification is many orders of magnitude larger in scalar-tensor gravity than in general relativity does not hold in the Einstein conformal frame. Lensing by gravitational waves is discussed in relation to the ongoing and proposed VLBI observations aimed at detecting the scintillation effect.Item A comparison of CMB lensing e ciency of gravitational waves and large scale structure(IUCAA, 2015-02) Padmanabhan, Hamsa; Rotti, Aditya; Tarun, SauradeepItem Hemispherical Asymmetry from Isotropy Violated Stochastic Gravitational Wave Background(IUCAA, 2015-02) Mukherjee, SuvodipItem Astrophysical motivation for directed searches for a stochastic gravitational wave background(IUCAA, 2015-02) Mazumder, Nairwita; Mitra, Sanjit; Dhurandhar, SanjeevItem Estimation of parameters of gravitational waves from coalescing binaries(2015-01-25) Balasubramanian, R.; Sathyaprakash, B.S.; Dhurandhar, S.V.Item Gravitational wave data analysis for laser interferometrie space antenna(2011-07-05) Dhurandhar, Sanjeev; Vinet, Jean-YvesItem A faster implementation of the hierarchical search algorithm for detection of gravitational waves from inspiraling compact binaries(2011-06-05) Sengupta, Anand; Dhurandhar, Sanjeev; Lazzarini, AlbertThe first scientific runs of kilometer scale laser interferometric detectors like LIGO are underway. Data from these detectors will be used to look for signatures of gravitational waves (GW) from astrophysical objects like inspiraling neutron star/blackhole binaries using matched filtering. The computational resources required for online flat-search implementation of the matched filtering are large if searches are carried out for small total mass. Flat search is implemented by constructing a single discrete grid of densely populated template waveforms spanning the dynamical parameters - masses, spins - which are correlated with the interferometer data. The correlations over the kinematical parameters can be maximized apriori without constructing a template bank over them. Mohanty and Dhurandhar (1996) showed that a significant reduction in computational resources can be accomplished by using a hierarchy of such template banks where candidate events triggered by a sparsely populated grid is followed up by the regular, dense flat search grid. The estimated speed up in this method was a factor ∼ 25 over the flat search. In this paper we report an improved implementation of the hierarchical search, wherein we extend the domain of hierarchy to an extra dimension - namely the time of arrival of the signal in the bandwidth of the interferometer. This is accomplished by lowering the Nyquist sampling rate of the signal in the trigger stage. We show that this leads to further improvement in the efficiency of data analysis and speeds up the online computation by a factor of ∼ 65 − 70 over the flat search. We also take into account and discuss issues related to template placement, trigger thresholds and other peculiar problems that do not arise in earlier implementation schemes of the hierarchical search. We present simulation results for 2PN waveforms embedded in the noise expected for initial LIGO detectors.Item Data analysis techniques for gravitational wave observations(2011-07-06) Dhurandhar, SanjeevAstrophysical sources of gravitational waves fall broadly into three categories: (i) transient and bursts, (ii) periodic or continuous wave and (iii) stochastic. Each type of source requires a di®erent type of data analysis strategy. In this talk various data analysis strategies will be reviewed. Optimal ¯ltering is used for extracting binary inspirals; Fourier transforms over Doppler shifted time intervals are computed for long duration periodic sources; optimally weighted cross-correlations for stochastic background. Some recent schemes which e±ciently search for inspirals will be described. The performance of some of these techniques on real data obtained will be discussed. Finally, some results on cancellation of systematic noises in laser interferometric space antenna (LISA) will be presented and future directions indicated.Item Gravitational wave astronomy- astronomy of the 21st century(2011-02-07) Dhurandhar, SanjeevAn enigmatic prediction of Einstein’s eneral theory of relativity are 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 inteferomet-ric 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 GravitationalWave 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.