2011 (IPP)

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Author: search.filters.author.Dhurandhar, Sanjeev

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    Numerical simulation of time delay interferometry for LISA with one arm dysfunctional
    (2011-02-25) Dhurandhar, Sanjeev; Ni, W.-T.; Wang, G.
    In order to attain the requisite sensitivity for LISA, laser frequency noise must be suppressed below the secondary noises such as the optical path noise, acceleration noise etc. In a previous paper (Dhurandhar et al., Class. Quantum Grav., 27, 135013, 2010), we have found a large family of second generation analytic solutions of time delay interferometry with one arm dysfunctional and also estimated the laser noise due to residual time-delay semi-analytically from orbit perturbations due to Earth. Since other planets and solar-system bodies also perturb the orbits of LISA spacecraft and affect the time delay interferometry (TDI), we simulate the time delay numerically in this paper for all solutions with n ≤ 3. To conform to the actual LISA planning, we have worked out a set of 3-year optimized mission orbits of LISA spacecraft starting at June 21, 2021 using CGC2.7 ephemeris framework. We then use this numerical solution to calculate the residual optical path differences in the second generation solutions of our previous paper, and compare with the semi-analytic error estimate. The accuracy of this calculation is better than 1 cm (or 30 ps). The maximum path length difference, for all configuration calculated, is below 1 m (3 ns). This is well below the limit under which the laser frequency noise is required to be suppressed.
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    Gravitational wave astronomy- astronomy of the 21st century
    (2011-02-07) Dhurandhar, Sanjeev
    An 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.
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    Cross-correlation search for a hot spot of gravitational waves
    (2011-05-31) Dhurandhar, Sanjeev; Tagoshi, H.; Okada, Yuta; et al.
    The cross-correlation search has been previously applied to map the gravitational wave (GW) stochastic background in the sky and also to target GW from rotating neutron stars/pulsars. Here we investigate how the cross-correlation method can be used to target a small region in the sky spanning at most a few pixels, where a pixel in the sky is determined by the diffraction limit which depends on the (i) baseline joining a pair of detectors and (ii) detector bandwidth. Here as one of the promising targets, we consider the Virgo cluster - a ”hot spot” spanning few pixels - which could contain, as estimates suggest ~ 10¹¹ neutron stars, of which a small fraction would continuously emit GW in the bandwidth of the detectors. For the detector baselines, we consider advanced detector pairs among LCGT, LIGO, Virgo, ET etc. Our results show that sufficient signal to noise can be accumulated with integration times of the order of a year. The results improve for the multibaseline search. This analysis could as well be applied to other likely hot spots in the sky and other possible pairs of detectors.