S. Dhurandhar

AIGO: a southern hemisphere detector for the worldwide array of ground-based interferometric gravitational wave detectors

This paper describes the proposed AIGO detector for the worldwide array of interferometric gravitational wave detectors. The first part of the paper summarizes the benefits that AIGO provides to the worldwide array of detectors. The second part gives a technical description of the detector, which will follow closely the Advanced LIGO design. Possible technical variations in the design are discussed.

Revival of the Penrose process for astrophysical applications

By utilizing the curious existence of negative energy orbits outside the event horizon of the Kerr black hole, Penrose proposed that rotational energy of the black hole can be extracted. It was independently shown by Bardeen et al. (1972) and Wald (1974) that this process cannot offer an astrophysically viable mechanism for high-energy jets, because for significant gain in energy the breakup of the incident particle must itself be relativistic. In this paper, it is shown that the inconvenient requirement of relativistic splitting could be easily overcome for a black hole immersed in an electromagnetic field.

High efficiency of the Penrose process of energy extraction from rotating black holes immersed in electromagnetic fields

The conditions are analyzed under which maximum efficiency is obtained for the Penrose process (PP) of energy extraction from rotating black holes immersed in electromagnetic fields. The components of the dipole magnetic field are displayed superposed on the background Kerr metric as a representative case. Mathematical methods for analyzing the disintegrational PP are developed, obtaining an equation to a mass-hyperbola defined by mass parameters of fragments resulting from the disintegration of a particle incident on the black hole. The efficiency of the PP is considered, analyzing all the factors contributing toward high efficiency along with the plausible astrophysical limits. In particular, it is shown that the incident particle splitting near the static limit of the Kerr geometry gives an efficiency from which 100 percent energy extraction efficiency can be assumed in constructing the PP-based model of the central engine in AGNs. Finally, the use of these techniques in modeling AGNs is discussed.

LIGO-Virgo searches for gravitational waves from coalescing binaries: A status update

Coalescing compact binaries of neutron stars and/or black holes are considered as one of the most promising sources for Earth based gravitational wave detectors. The LIGO-Virgo joint collaborations Compact Binary Coalescence (CBC) group is searching for gravitational waves emitted by these astrophysical systems by matched filtering the data against theoretically modeled template waveforms. A variety of waveform template families are employed depending on the mass range probed by the search and the stage of the inspiral phase targeted: restricted post-Newtonian for systems having total mass less than 35M?, numerical relativity inspired complete inspiral-merger-ringdown waveforms for more massive systems up to 100M? and ringdown templates for modeling perturbed black holes up to 500M?. We give a status update on CBC groups current efforts and upcoming plans in detecting signatures of astrophysical gravitational waves.

Stability of giant Fabry–Perot cavities of interferometric gravitational-wave detectors

We consider the coupling of the thermoelastic mirror deformations to the resonance of giant cavities involved in interferometric detectors of gravitational waves. As this problem is coupled and nonlinear, instabilities could occur a priori. We analytically solve the coupled problem of thermoelastic 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 that can simulate a false event in the observational frequency range of 1 Hz to 1 kHz.

Time-delay interferometry for LISA with one arm dysfunctional

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 \leq 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.

Detecting gravitational waves from inspiraling binaries with a network of detectors: Coherent strategies for correlated detectors

We discuss the coherent search strategy to detect gravitational waves from inspiraling compact binaries by a network of correlated laser interferometric detectors. From the maximum likelihood ratio statistic, we obtain a coherent statistic which is slightly different from and generally better than what we obtained in our previous work. In the special case when the cross spectrum of two detectors normalized by the power spectrum density is constant, the new statistic agrees with the old one. The quantitative difference of the detection probability for a given false alarm rate is also evaluated in a simple case.

General relativistic treatment of LISA optical links

LISA is a joint space mission of the NASA and the ESA for detecting low-frequency gravitational waves in the band 10−5 to 1 Hz. In order to attain the requisite sensitivity for LISA, the laser frequency noise must be suppressed below the other secondary noises such as the optical path noise, acceleration noise, etc. This is achieved by the technique called time delay interferometry (TDI) in which the data are combined with appropriate time delays. In this paper we approximately compute the spacecraft orbits in the gravitational field of the Sun and Earth. We have written a numerical code which computes the optical links (time delays) in the general relativistic framework within an accuracy of ~10 m, which is sufficient for TDI. Our computation of the optical links automatically takes into account the effects such as the Sagnac, Shapiro delay, etc. We show that by optimizing LISA orbits, and using the symmetries inherent in the configuration of LISA and in the physics, the residual laser noise in the modified first-generation TDI can be adequately suppressed. We demonstrate our results for some important TDI observables.

A study of the gravitational wave form from pulsars

We present analytical and numerical studies of the Fourier transform (FT) of the gravitational wave (GW) signal from a pulsar, taking into account the rotation and orbital motion of the Earth. We also briefly discuss the Zak– Gelfand integral transform and a special class of the generalized hypergeometric function of potential relevance. The Zak–Gelfand integral transform that arises in our analytic approach has also been useful for Schr¨ odinger operators in periodic potentials in condensed matter physics (Bloch wavefunctions) and holds promise for the study of periodic GW signals for long integration times.

Computational cost for detecting inspiralling binaries using a network of laser interferometric detectors

We extend a coherent network data-analysis strategy developed earlier for detecting Newtonian waveforms to the case of post-Newtonian (PN) waveforms. Since the PN waveform depends on the individual masses of the inspiralling binary, the parameter-space dimension increases by one from that of the Newtonian case. We obtain the number of templates and estimate the computational costs for PN waveforms: for a lower mass limit of 1M� ,f or LIGO-I noise and with 3% maximum mismatch,the online computational speed requirement for single detector is a few Gflops; for a two-detector network it is hundreds of Gflops and for a three-detector network it is tens of Tflops. Apart from idealistic networks, we obtain results for realistic networks comprising of LIGO and VIRGO. Finally, we compare costs incurred in a coincidence detection strategy with those incurred in the coherent strategy detailed above.