A major challenge of any search for gravitational waves is to distinguish true astrophysical signals from those of terrestrial origin. Gravitational-wave experiments therefore make use of multiple ...detectors, considering only those signals which appear in coincidence in two or more instruments. It is unclear, however, how to interpret loud gravitational-wave candidates observed when only one detector is operational. In this paper, we demonstrate that the observed rate of binary black hole mergers can be leveraged in order to make confident detections of gravitational-wave signals with one detector alone. We quantify detection confidences in terms of the probability P(S) that a signal candidate is of astrophysical origin. We find that, at current levels of instrumental sensitivity, loud binary black hole candidates observed with a single Advanced LIGO detector can be assigned P(S)≳0.4. In the future, Advanced LIGO may be able to observe binary black hole mergers with single-detector confidences exceeding P(S)∼90%.
We investigate the effect of an important class of glitches occurring in the detector data on matched filter searches of gravitational waves from coalescing compact binaries in the advanced detector ...era. The glitches, which can be modeled as sine-Gaussians, can produce triggers with significant time delays and thus have important bearing on veto procedures as will be described in the paper. We provide approximated analytical estimates of the trigger signal to noise ratio (SNR) and time as a function of the parameters describing the sine-Gaussian (center time, center frequency and Q-factor) and the inspiral filter (chirp mass). We validate our analytical predictions through simple numerical simulations, performed by filtering noiseless sine-Gaussians with the inspiral matched filter and recovering the time and value of the maximum of the resulting SNR time series. Although we identify regions of the parameter space in which each approximation no longer reproduces the numerical results, the approximations complement each other and together effectively cover the whole parameter space.
In light of the recent discoveries of binary black hole events and one neutron star event by the advanced LIGO (aLIGO) and advanced Virgo (aVirgo) detectors, we propose a new astrophysical source, ...namely, the mini creation event (MCE) as a possible source of gravitational waves (GW) to be detected by advanced detectors. The MCE is at the heart of the quasi steady state cosmology (QSSC) and is not expected to occur in standard cosmology. Generically, the MCE is anisotropic and we assume a Bianchi Tpye I model for its description. We compute its signature waveform and assume masses, distances analogous to the events detected. The striking feature of the waveform associated with this model of the MCE is that it depends only on one amplitude parameter and thus allows for simpler data analysis. By matched filtering the signal we find that, for a broad range of model parameters, the signal to noise ratio of the randomly oriented MCE is sufficiently high for a confident detection by aLIGO and aVirgo. We therefore propose the MCE as a viable astrophysical source of GW. The detection or non-detection of such a source also hold implications for QSSC, namely, whether it is a viable cosmology or not.
This paper calculates the expected gravitational wave background (GWB) in the quasi-steady state cosmology (QSSC). The principal sources of gravitational waves in the QSSC are the mini-creation ...events (MCE). With suitable assumptions the GWB can be computed both numerically and with analytical methods. It is argued that the GWB in QSSC differs from that predicted for the standard cosmology and a future technology of detectors will be able to decide between the two predictions. We also derive a formula for the flux density of a typical extragalactic source of gravitational waves.
In order to attain the requisite sensitivity for LISA (Laser Interferometric Space Antenna)--a joint space mission of the ESA and NASA--the laser frequency noise must be suppressed below the ...secondary noises such as the optical path noise, acceleration noise etc. By combining six appropriately time-delayed data streams containing fractional Doppler shifts--a technique called time-delay interferometry (TDI)--the laser frequency noise may be adequately suppressed. We consider the general model of LISA where the armlengths vary with time, so that second-generation TDI are relevant. However, we must envisage the possibility that not all the optical links of LISA will be operating at all times, and therefore, we here consider the case of LISA operating with two arms only. As shown earlier in the literature, obtaining even approximate solutions of TDI to the general problem is very difficult. Since here only four optical links are relevant, the algebraic problem simplifies considerably. We are then able to exhibit a large number of solutions (from a mathematical point of view an infinite number) and further present an algorithm to generate these solutions.
Spacer is a vital component in assembly of nuclear fuel rod bundles. It is used to support and maintain suitable distance between the rods in assembly of nuclear fuel bundle. Spacer promotes the ...local heat transfer in downstream to the spacer in rod bundle. The objective of present work is to analyse the spacer effects on thermal and hydraulic performance of R-134a at supercritical condition of pressure 4.5 MPa in an annular flow. A Computational Fluid Dynamics (CFD) code ANSYS Fluent has been used for present numerical analysis and SST (Shear Stress Transport) k-ω turbulence model was considered for turbulence flow analysis. Numerical analysis was carried out in an annular channel of 6 mm hydraulic diameter with spacer, located at middle of channel. Hydraulic and thermal performance due to the spacer have been investigated for three different mass flow rates (0.33175, 0.41469 and 0.53909 kg/s) and three different heat fluxes (60, 100 and 160 kW/m2 ). Two blockage ratios of 0.3 and 0.38 have been used in present analysis. Due to the presence of spacer as flow obstruction, it is observed that at spacer location, velocity increased significantly and subsequent decrease in pressure. Also; it is noticed that the wall temperature is decreased and corresponding coefficient of heat transfer enhanced significantly at the location of spacer in annular channel. The observed value of ratio of Nusselt number for the case of spacer and without spacer (Nu/Nu*) shows better agreement with correlations data for flow obstacle at Re=97000.
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, S.V., Nayak, K.R., Vinet, J.-Y. Time delay interferometry for LISA with one arm dysfunctional. 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 we 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 the generation number n⩽3. We have worked out a set of 3-year optimized mission orbits of LISA spacecraft starting at January 1, 2021 using the 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 1cm (or 30ps). The maximum path length difference, for all configuration calculated, is below 1m (3ns). This is well below the limit under which the laser frequency noise is required to be suppressed. The numerical simulation in this paper can be applied to other space-borne interferometers for gravitational wave detection with the simplification of having only one interferometer.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
In order to attain the requisite sensitivity for LISA – a joint space mission of the ESA and NASA- the laser frequency noise must be suppressed below the secondary noises such as the optical path ...noise, acceleration noise etc. By combining six appropriately time-delayed data streams containing fractional Doppler shifts – a technique called time delay interferometry (TDI) – the laser frequency noise may be adequately suppressed. Here we investigate the problem of TDI in the general case of unequal up-down links and also include the effect of the Earth on the spacecraft and the optical links. We show that there are symmetries in the physics which can be successfully used to simplify the algebra of the TDI. We finally give the example of the first generation modified Sagnac observable in which the laser frequency noise is suppressed because of the symmetries.
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.
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