83 research outputs found

### Optimal Source Tracking and Beaming of LISA

We revisit the directionally optimal data streams of LISA first introduced in
Nayak etal. It was shown that by using appropriate choice of Time delay
interferometric (TDI) combinations, a monochromatic fixed source in the
barycentric frame can be optimally tracked in the LISA frame. In this work, we
study the beaming properties of these optimal streams. We show that all the
three streams V+, Vx and Vo with maximum, minimum and zero directional SNR
respectively are highly beamed. We study in detail the frequency dependence of
the beaming.Comment: 8 pages, 9 figures. To appear in the proceedings of Sixth
International LISA Symposiu

### A data-analysis strategy for detecting gravitational-wave signals from inspiraling compact binaries with a network of laser-interferometric detectors

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-interferometric detectors having arbitrary
orientations and arbitrary locations around the globe. The MLM is based on the
network likelihood ratio (LR), which is a function of eight signal-parameters
that determine the Newtonian inspiral waveform. In the MLM-based strategy, the
LR must be maximized over all of these parameters. Here, we show that it is
possible to maximize it analytically over four of the eight parameters.
Maximization over a fifth parameter, the time of arrival, is handled most
efficiently by using the Fast-Fourier-Transform algorithm. This allows us to
scan the parameter space continuously over these five parameters and also cuts
down substantially on the computational costs. Maximization of the LR over the
remaining three parameters is handled numerically. This includes the
construction of a bank of templates on this reduced parameter space. After
obtaining the network statistic, 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.Comment: 40 pages, 2 figures, uses RevTex and psfig, submitted to Phys. Rev.
D, A few minor changes adde

### Detection of gravitational waves using a network of detectors

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 essentially the magnitude of the network correlation
vector constructed from 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
to address the problem of detection of such waves from other sources by some
other types of detectors, e.g., bars or spheres, or even by networks of
spatially well-separated detectors.Comment: 14 pages, RevTex, 1 postscript figure. Based on talk given at
Workshop on Cosmology: Observations confront theories, IIT-Kharagpur, India
(January 1999

### Validating delta-filters for resonant bar detectors of improved bandwidth foreseeing the future coincidence with interferometers

The classical delta filters used in the current resonant bar experiments for
detecting GW bursts are viable when the bandwidth of resonant bars is few Hz.
In that case, the incoming GW burst is likely to be viewed as an impulsive
signal in a very narrow frequency window. After making improvements in the
read-out with new transducers and high sensitivity dc-SQUID, the
Explorer-Nautilus have improved the bandwidth ($\sim 20$ Hz) at the sensitivity
level of $10^{-20}/\sqrt{Hz}$. Thus, it is necessary to reassess this
assumption of delta-like signals while building filters in the resonant bars as
the filtered output crucially depends on the shape of the waveform. This is
presented with an example of GW signals -- stellar quasi-normal modes, by
estimating the loss in SNR and the error in the timing, when the GW signal is
filtered with the delta filter as compared to the optimal filter.Comment: 7 pages, presented in Amaldi6, accepted for publication in Journal of
Physics: Conference Serie

### Detection of gravitational waves from inspiraling compact binaries using a network of interferometric detectors

We formulate the data analysis problem for the detection of the Newtonian
waveform from an inspiraling compact-binary by a network of arbitrarily
oriented and arbitrarily distributed laser interferometric gravitational wave
detectors. We obtain for the first time the relation between the optimal
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.Comment: 6 pages, RevTeX. Based on talk given at GWDAW-99, Rom

### Exploring Short-GRB afterglow parameter space for observations in coincidence with gravitational waves

Short duration Gamma Ray Bursts(SGRB) and their afterglows are among the most
promising electro-magnetic (EM) counterparts of Neutron Star (NS) mergers. The
afterglow emission is broadband, visible across the entire electro-magnetic
window from $\gamma$-ray to radio frequencies. The flux evolution in these
frequencies is sensitive to the multi-dimensional afterglow physical parameter
space. Observations of gravitational wave (GW) from BNS mergers in spatial and
temporal coincidence with SGRB and associated afterglows can provide valuable
constraints on afterglow physics. We run simulations of GW-detected BNS events
and assuming all of them are associated with a GRB jet which also produces an
afterglow, investigate how detections or non-detections in X-ray, optical and
radio frequencies can be influenced by the parameter space. We narrow-down the
regions of afterglow parameter space for a uniform top-hat jet model which
would result in different detection scenarios. We list inferences which can be
drawn on the physics of GRB afterglows from multi-messenger astronomy with
coincident GW-EM observations.Comment: Published in MNRA

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