Browsing by Author "Bose, Sukanta"

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Computational cost for detecting inspiraling binaries using a network of laser interferometric detectors
(2001-08-15) Pai, A.; Bose, Sukanta; Dhurandhar, Sanjeev
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 inspiraling binary, the parameter-space dimension increases by 1 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⊙, for 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
Data-analysis strategy for detecting gravitational-wave signals from inspiraling compact binaries with a network of laser-interferometric detectors
(2000-04-24) Pai, A.; Dhurandhar, Sanjeev; Bose, Sukanta
A data-analysis strategy based on the maximum-likelihood method (MLM) is presented for the detection of gravitational waves from inspiraling compact binaries with a network of laser- nterferometric detectors having arbitrary orientations and arbitrary locations around the globe. For simplicity, we restrict ourselves to the Newtonian inspiral waveform. However, the formalism we develop here is also applicable to a waveform with post-Newtonian (PN) corrections. The Newtonian waveform depends on eight parameters: the distance r to the binary, the phase δc of the waveform at the time of ﬁnal coalescence, the polarization-ellipse angle ψ, the angle of inclination ǫ of the binary orbit to the line of sight, the source-direction angles {θ, φ}, the time of ﬁnal coalescence tc at the ﬁducial detector, and the chirp time ξ. All these parameters are relevant for a chirp search with multiple detectors, unlike the case of a single detector. The primary construct on which the MLM s based is the network likelihood ratio (LR). We obtain this ratio here. For the Newtonian inspiral waveform, the LR is a function of the eight signal-parameters. In the MLM-based detection strategy, the LR must be maximized over all of these parameters. Here, we show that it is possible to maxi- mize it analytically with respect to four of the eight parameters, namely, {r, δc, ψ, ǫ}. Maximization over the time of arrival is handled most eﬃciently by using the Fast-Fourier-Transform algorithm, as in the case of a single detector. This not only allows us to scan the parameter space continu- ously over these ﬁve parameters but also cuts down substantially on the computational costs. The analytical maximization over the four parameters yields the optimal statistic on which the decision must be based. The value of the statistic also depends on the nature of the noises in the detectors. Here, we model these noises to be mainly Gaussian, stationary, and uncorrelated for every pair of detectors. Instances of non-Gaussianity, as are present in detector outputs, can be accommodated n our formalism by implementing vetoing techniques similar to those applied for single detectors. Our formalism not only allows us to express the likelihood ratio for the network in a very simple and compact form, but also is at the basis of giving an elegant geometric interpretation to the de- tection problem. Maximization of the LR over the remaining three parameters is handled as follows. Owing to the arbitrary locations of the detectors in a network, the time of arrival of a signal at any detector will, in general, be diﬀerent from those at the others and, consequently, will result in signal time-delays. For a given network, these time delays are determined by the source-direction angles {θ, φ}. Therefore, to maximize the LR over the parameters {θ, φ} one needs to scan over the possible time-delays allowed by a network. We opt for obtaining a bank of templates for the chirp time and the time-delays. This means that we construct a bank of templates over ξ, θ, and φ. We ﬁrst discuss “idealized” networks with all the detectors having a common noise curve for simplicity. Such an exercise nevertheless yields useful estimates about computational costs, and also tests the formalism developed here. We then consider realistic cases of networks comprising of the LIGO and VIRGO detectors: These include two-detector networks, which pair up the two LIGOs or VIRGO with one of the LIGOs, and the three-detector network that includes VIRGO and both the LIGOs. For these networks we present the computational speed requirements, network sensitivities, and source-direction resolutions.
Detection of gravitational waves from inspiraling compact binaries using a network of interferometric detectors
(2000-06-28) Bose, Sukanta; Pai, A.; Dhurandhar, Sanjeev
We formulate the data analysis problem for the detection of the New- tonian waveform from an inspiraling compact-binary by a network of arbi- trarily oriented and arbitrarily distributed laser interferometric gravitational wave detectors. We obtain for the ﬁrst time the relation between the opti- mal statistic and the magnitude of the network correlation vector, which is constructed from the matched network-ﬁlter. This generalizes the calculation reported in an earlier work (gr-qc/9906064), where the detectors are taken to be coincident.
Detection of gravitational waves using a network of detectors
(2015-03-01) Bose, Sukanta; Dhurandhar, S.V.; Pai, Archana
We 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.
New classes of black hole spacetime in 2+1 gravity
(2015-03-01) Bose, Sukanta; Dadhich, Naresh; Kar, Syan
New multi-parameter families of black holes in three-dimensional (3D) gravity are obtained. We apply the electrogravity transformation (which implies an exchange of the Ricci and Einstein tensors) to the 3D field equations to obtain these solutions. Several properties of these geometries, including the nature of the matter that threads them, are discussed. Some of these properties are found to be strikingly different from known black holes in (2+1) dimensions.
Observational constraints on spinning, relativistic Bose-Einstein condensate stars
(IUCAA, 2015-02) Mukherjee, Arunava; Shah, Shreya; Bose, Sukanta
On the brown-york quasilocal energy, gravitational charge, and black hole event horizons
(2015-03-13) Bose, Sukanta; Dadhich, Naresh
We prove the recently proposed identity for certain black hole spacetimes that relates the difference of the Brown-York quasilocal energy and the Komar charge at the event horizon of the hole to the total energy of the spacetime. We prove this identity for the Kerr-Newman family of black hole spacetimes and for non-static (cosmological) spherically symmetric shear-free perfect fluid solutions of general relativity that contain black hole event horizons. We explicitly demonstrate its validity by applying it to several asymptotically fiat as well as non-fiat black hole solutions, including the case of a black hole with a global monopole charge.
On the electrogravity-dual solution to stringy charged black holes
(2015-03-01) Bose, Sukanta; Dadhich, Naresh
By resolving the Riemann curvature tensor relative to a timelike unit vector into electric and magnetic parts, electrogravity-duality transformation is defined. Such a transformation interchanges the "active" and "passive" electric parts of this tensor and can be used to obtain spacetime metrics dual to known solutions of any geometric theory of gravity, such as Einstein gravity. The vacuum field equations of general relativity are invariant under such a transformation. It is possible to break this symmetry by introducing matter terms in such a way that the characteristic vacuum solution is still obtained as a special case of that matter distribution. Such a possibility exists for all stationary black hole solutions. Interestingly, solutions exist even for the dual equations with the matter terms. Here, we extend this formalism to study the static, charged black hole solutions of a four-dimensional low-energy effective action of heterotic string theory. We show that analogous to general relativity, the dual solution is itself a similar black hole spacetime, endowed with a global monopole charge.
Quasilocal energy for rotating charged black hole solutions in general relativity and string theory
(2015-03-01) Bose, Sukanta; Naing, Thant Zin