Publications (43)7.37 Total impact
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ABSTRACT: Space-based gravitational wave interferometers are sensitive to the galactic
population of ultra-compact binaries. An important subset of the ultra-compact
binary population are those stars that can be individually resolved by both
gravitational wave interferometers and electromagnetic telescopes. The aim of
this paper is to quantify the multi-messenger potential of space-based
interferometers with arm-lengths between 1 and 5 Gm. The Fisher Information
Matrix is used to estimate the number of binaries from a model of the Milky Way
which are localized on the sky by the gravitational wave detector to within 1
and 10 square degrees and bright enough to be detected by a magnitude limited
survey. We find, depending on the choice of GW detector characteristics,
limiting magnitude, and observing strategy, that up to several hundred
gravitational wave sources could be detected in electromagnetic follow-up
observations.
07/2012;
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ABSTRACT: We present an update to the search for a non-trivial topology of the universe
by searching for matching circle pairs in the cosmic microwave background using
the WMAP 7 year data release. We extend the exisiting bounds to encompass a
wider range of possible topologies by searching for matching circle pairs with
opening angles 10 degree < \alpha < 90 degree and separation angles 11 degree <
\theta < 180 degree. The extended search reveal two small anomalous regions in
the CMB sky. Numerous pairs of well-matched circles are found where both
circles pass through one or the other of those regions. As this is not the
signature of any known manifold, but is a likely consequence of contamination
in those sky regions, we repeat the search excluding circle pairs where both
pass through either of the two regions. We then find no statistically
significant pairs of matched circles, and so no hints of a non-trivial
topology. The absence of matched circles increases the lower limit on the
length of the shortest closed null geodesic that self-intersects at our
location in the universe (equivalently the injectivity radius at our location)
to 98.5% of the diameter of the last scattering surface or approximately 26
Gpc. It extends the limit to any manifolds in which the intersecting arcs of
said geodesic form an angle greater than 10^o.
06/2012;
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Pau Amaro-Seoane,
Sofiane Aoudia,
Stanislav Babak,
Pierre Binétruy,
Emanuele Berti,
Alejandro Bohé,
Chiara Caprini,
Monica Colpi, Neil J. Cornish,
Karsten Danzmann, [......],
Antoine Petiteau,
Edward K. Porter,
Bernard F. Schutz,
Alberto Sesana,
Robin Stebbins,
Tim Sumner,
Michele Vallisneri,
Stefano Vitale,
Marta Volonteri,
Henry Ward
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ABSTRACT: We review the expected science performance of the New Gravitational-Wave
Observatory (NGO, a.k.a. eLISA), a mission under study by the European Space
Agency for launch in the early 2020s. eLISA will survey the low-frequency
gravitational-wave sky (from 0.1 mHz to 1 Hz), detecting and characterizing a
broad variety of systems and events throughout the Universe, including the
coalescences of massive black holes brought together by galaxy mergers; the
inspirals of stellar-mass black holes and compact stars into central galactic
black holes; several millions of ultracompact binaries, both detached and mass
transferring, in the Galaxy; and possibly unforeseen sources such as the relic
gravitational-wave radiation from the early Universe. eLISA's high
signal-to-noise measurements will provide new insight into the structure and
history of the Universe, and they will test general relativity in its
strong-field dynamical regime.
02/2012;
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Pau Amaro-Seoane,
Sofiane Aoudia,
Stanislav Babak,
Pierre Binétruy,
Emanuele Berti,
Alejandro Bohé,
Chiara Caprini,
Monica Colpi, Neil J. Cornish,
Karsten Danzmann, [......],
Antoine Petiteau,
Edward K. Porter,
Bernard F. Schutz,
Alberto Sesana,
Robin Stebbins,
Tim Sumner,
Michele Vallisneri,
Stefano Vitale,
Marta Volonteri,
Henry Ward
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ABSTRACT: This document introduces the exciting and fundamentally new science and
astronomy that the European New Gravitational Wave Observatory (NGO) mission
(derived from the previous LISA proposal) will deliver. The mission (which we
will refer to by its informal name "eLISA") will survey for the first time the
low-frequency gravitational wave band (about 0.1 mHz to 1 Hz), with sufficient
sensitivity to detect interesting individual astrophysical sources out to z =
15. The eLISA mission will discover and study a variety of cosmic events and
systems with high sensitivity: coalescences of massive black holes binaries,
brought together by galaxy mergers; mergers of earlier, less-massive black
holes during the epoch of hierarchical galaxy and black-hole growth;
stellar-mass black holes and compact stars in orbits just skimming the horizons
of massive black holes in galactic nuclei of the present era; extremely compact
white dwarf binaries in our Galaxy, a rich source of information about binary
evolution and about future Type Ia supernovae; and possibly most interesting of
all, the uncertain and unpredicted sources, for example relics of inflation and
of the symmetry-breaking epoch directly after the Big Bang. eLISA's
measurements will allow detailed studies of these signals with high
signal-to-noise ratio, addressing most of the key scientific questions raised
by ESA's Cosmic Vision programme in the areas of astrophysics and cosmology.
They will also provide stringent tests of general relativity in the
strong-field dynamical regime, which cannot be probed in any other way. This
document not only describes the science but also gives an overview on the
mission design and orbits.
01/2012;
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ABSTRACT: The future space-based gravitational wave detector LISA will be able to
measure parameters of coalescing massive black hole binaries, often to
extremely high accuracy. Previous work has demonstrated that the black hole
spins can have a strong impact on the accuracy of parameter measurement.
Relativistic spin-induced precession modulates the waveform in a manner which
can break degeneracies between parameters, in principle significantly improving
how well they are measured. Recent studies have indicated, however, that spin
precession may be weak for an important subset of astrophysical binary black
holes: those in which the spins are aligned due to interactions with gas. In
this paper, we examine how well a binary's parameters can be measured when its
spins are partially aligned and compare results using waveforms that include
higher post-Newtonian harmonics to those that are truncated at leading
quadrupole order. We find that the weakened precession can substantially
degrade parameter estimation. This degradation is particularly devastating for
the extrinsic parameters sky position and distance. Absent higher harmonics,
LISA typically localizes the sky position of a nearly aligned binary a factor
of $\sim 6$ less accurately than for one in which the spin orientations are
random. Our knowledge of a source's sky position will thus be worst for the
gas-rich systems which are most likely to produce electromagnetic counterparts.
Fortunately, higher harmonics of the waveform can make up for this degradation.
By including harmonics beyond the quadrupole in our waveform model, we find
that the accuracy with which most of the binary's parameters are measured can
be substantially improved. In some cases, parameters can be measured as well in
partially aligned binaries as they can be when the binary spins are random.
01/2011;
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ABSTRACT: Central to the gravitational wave detection problem is the challenge of separating features in the data produced by astrophysical sources from features produced by the detector. Matched filtering provides an optimal solution for Gaussian noise, but in practice, transient noise excursions or ``glitches'' complicate the analysis. Detector diagnostics and coincidence tests can be used to veto many glitches which may otherwise be misinterpreted as gravitational wave signals. The glitches that remain can lead to long tails in the matched filter search statistics and drive up the detection threshold. Here we describe a Bayesian approach that incorporates a more realistic model for the instrument noise allowing for fluctuating noise levels that vary independently across frequency bands, and deterministic ``glitch fitting'' using wavelets as ``glitch templates'', the number of which is determined by a trans-dimensional Markov chain Monte Carlo algorithm. We demonstrate the method's effectiveness on simulated data containing low amplitude gravitational wave signals from inspiraling binary black hole systems, and simulated non-stationary and non-Gaussian noise comprised of a Gaussian component with the standard LIGO/Virgo spectrum, and injected glitches of various amplitude, prevalence, and variety. Glitch fitting allows us to detect significantly weaker signals than standard techniques. Comment: 21 pages, 18 figures
08/2010;
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ABSTRACT: The Laser Interferometer Space Antenna (LISA) is designed to detect
gravitational wave signals from astrophysical sources, including those from
coalescing binary systems of compact objects such as black holes. Colliding
galaxies have central black holes that sink to the center of the merged galaxy
and begin to orbit one another and emit gravitational waves. Some galaxy
evolution models predict that the binary black hole system will enter the LISA
band with significant orbital eccentricity, while other models suggest that the
orbits will already have circularized. Using a full seventeen parameter
waveform model that includes the effects of orbital eccentricity, spin
precession and higher harmonics, we investigate how well the source parameters
can be inferred from simulated LISA data. Defining the reference eccentricity
as the value one year before merger, we find that for typical LISA sources, it
will be possible to measure the eccentricity to an accuracy of parts in a
thousand. The accuracy with which the eccentricity can be measured depends only
very weakly on the eccentricity, making it possible to distinguish circular
orbits from those with very small eccentricities. LISA measurements of the
orbital eccentricity can help constraints theories of galaxy mergers in the
early universe. Failing to account for the eccentricity in the waveform
modeling can lead to a loss of signal power and bias the estimation of
parameters such as the black hole masses and spins.
06/2010;
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ABSTRACT: Several scenarios have been proposed in which the orbits of binary black
holes enter the band of a gravitational wave detector with significant
eccentricity. To avoid missing these signals or biasing parameter estimation it
is important that we consider waveform models that account for eccentricity.
The ingredients needed to compute post-Newtonian (PN) waveforms produced by
spinning black holes inspiralling on quasi-eccentric orbits have been available
for almost two decades at 2 PN order, and this work has recently been extended
to 2.5 PN order. However, the computational cost of directly implementing these
waveforms is high, requiring many steps per orbit to evolve the system of
coupled differential equations. Here we employ the standard techniques of a
separation of timescales and a generalized Keplerian parameterization of the
orbits to produce efficient waveforms describing spinning black hole binaries
with arbitrary masses and spins on quasi-eccentric orbits to 1.5 PN order. We
separate the fast orbital timescale from the slow spin-orbit precession
timescale by solving for the orbital motion in a non-interial frame of
reference that follows the orbital precession. We outline a scheme for
extending our approach to higher post-Newtonian order.
04/2010;
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ABSTRACT: The detection of a stochastic background of gravitational waves could significantly impact our understanding of the physical processes that shaped the early Universe. The challenge lies in separating the cosmological signal from other stochastic processes such as instrument noise and astrophysical foregrounds. One approach is to build two or more detectors and cross correlate their output, thereby enhancing the common gravitational wave signal relative to the uncorrelated instrument noise. When only one detector is available, as will likely be the case with the Laser Interferometer Space Antenna (LISA), alternative analysis techniques must be developed. Here we show that models of the noise and signal transfer functions can be used to tease apart the gravitational and instrument noise contributions. We discuss the role of gravitational wave insensitive "null channels" formed from particular combinations of the time delay interferometry, and derive a new combination that maintains this insensitivity for unequal arm length detectors. We show that, in the absence of astrophysical foregrounds, LISA could detect signals with energy densities as low as $\Omega_{\rm gw} = 6 \times 10^{-13}$ with just one month of data. We describe an end-to-end Bayesian analysis pipeline that is able to search for, characterize and assign confidence levels for the detection of a stochastic gravitational wave background, and demonstrate the effectiveness of this approach using simulated data from the third round of Mock LISA Data Challenges. Comment: 10 Pages, 10 Figures
02/2010;
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Stanislav Babak,
John G. Baker,
Matthew J. Benacquista, Neil J. Cornish,
Shane L. Larson,
Ilya Mandel,
Sean T. McWilliams,
Antoine Petiteau,
Edward K. Porter,
Emma L. Robinson, [......],
Philip Graff,
Mike Hobson,
Joey Shapiro Key,
Andrzej Królak,
Anthony Lasenby,
Reinhard Prix,
Yu Shang,
Miquel Trias,
John Veitch,
John T. Whelan
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ABSTRACT: The Mock LISA Data Challenges are a program to demonstrate LISA data-analysis capabilities and to encourage their development. Each round of challenges consists of one or more datasets containing simulated instrument noise and gravitational waves from sources of undisclosed parameters. Participants analyze the datasets and report best-fit solutions for the source parameters. Here we present the results of the third challenge, issued in Apr 2008, which demonstrated the positive recovery of signals from chirping Galactic binaries, from spinning supermassive--black-hole binaries (with optimal SNRs between ~ 10 and 2000), from simultaneous extreme-mass-ratio inspirals (SNRs of 10-50), from cosmic-string-cusp bursts (SNRs of 10-100), and from a relatively loud isotropic background with Omega_gw(f) ~ 10^-11, slightly below the LISA instrument noise. Comment: 12 pages, 2 figures, proceedings of the 8th Edoardo Amaldi Conference on Gravitational Waves, New York, June 21-26, 2009
12/2009;
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ABSTRACT: The analysis of data from gravitational wave detectors can be divided into three phases: search, characterization, and evaluation. The evaluation of the detection - determining whether a candidate event is astrophysical in origin or some artifact created by instrument noise - is a crucial step in the analysis. The on-going analyses of data from ground based detectors employ a frequentist approach to the detection problem. A detection statistic is chosen, for which background levels and detection efficiencies are estimated from Monte Carlo studies. This approach frames the detection problem in terms of an infinite collection of trials, with the actual measurement corresponding to some realization of this hypothetical set. Here we explore an alternative, Bayesian approach to the detection problem, that considers prior information and the actual data in hand. Our particular focus is on the computational techniques used to implement the Bayesian analysis. We find that the Parallel Tempered Markov Chain Monte Carlo (PTMCMC) algorithm is able to address all three phases of the anaylsis in a coherent framework. The signals are found by locating the posterior modes, the model parameters are characterized by mapping out the joint posterior distribution, and finally, the model evidence is computed by thermodynamic integration. As a demonstration, we consider the detection problem of selecting between models describing the data as instrument noise, or instrument noise plus the signal from a single compact galactic binary. The evidence ratios, or Bayes factors, computed by the PTMCMC algorithm are found to be in close agreement with those computed using a Reversible Jump Markov Chain Monte Carlo algorithm. Comment: 19 pages, 12 figures, revised to address referee's comments
02/2009;
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ABSTRACT: Cosmic strings are predicted to form kinks and cusps that travel along the string at close to the speed of light. These disturbances are radiated away as highly beamed gravitational waves that produce a burst like pulse as the cone of emission sweeps past an observer. Gravitational wave detectors such as the Laser Interferometer Space Antenna (LISA) and the Laser Interferometer Gravitational wave Observatory (LIGO) will be capable of detecting these bursts for a wide class of string models. Such a detection would illuminate the fields of string theory, cosmology, and relativity. Here we develop template based Markov Chain Monte Carlo (MCMC) techniques that can efficiently detect and characterize the signals from cosmic string cusps. We estimate how well the signal parameters can be recovered by the advanced LIGO-Virgo network and the LISA detector using a combination of MCMC and Fisher matrix techniques. We also consider joint detections by the ground and space based instruments. We show that a parallel tempered MCMC approach can detect and characterize the signals from cosmic string cusps, and we demonstrate the utility of this approach on simulated data from the third round of Mock LISA Data Challenges (MLDCs). Comment: 10 pages, 10 figures
12/2008;
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Stanislav Babak,
John G. Baker,
Matthew J. Benacquista, Neil J. Cornish,
Jeff Crowder,
Shane L. Larson,
Eric Plagnol,
Edward K. Porter,
Michele Vallisneri,
Alberto Vecchio, [......],
Ilya Mandel,
Reinhard Prix,
B. S. Sathyaprakash,
Pavlin Savov,
Yu Shang,
Miquel Trias,
John Veitch,
Yan Wang,
Linqing Wen,
John T. Whelan
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ABSTRACT: The Mock LISA Data Challenges are a programme to demonstrate and encourage the development of LISA data-analysis capabilities, tools and techniques. At the time of this workshop, three rounds of challenges had been completed, and the next was about to start. In this article we provide a critical analysis of entries to the latest completed round, Challenge 1B. The entries confirm the consolidation of a range of data-analysis techniques for Galactic and massive--black-hole binaries, and they include the first convincing examples of detection and parameter estimation of extreme--mass-ratio inspiral sources. In this article we also introduce the next round, Challenge 3. Its data sets feature more realistic waveform models (e.g., Galactic binaries may now chirp, and massive--black-hole binaries may precess due to spin interactions), as well as new source classes (bursts from cosmic strings, isotropic stochastic backgrounds) and more complicated nonsymmetric instrument noise.
07/2008;
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ABSTRACT: Massive black hole binaries are key targets for the space based gravitational wave interferometer LISA. Several studies have investigated how LISA observations could be used to constrain the parameters of these systems. Until recently, most of these studies have ignored the higher harmonic corrections to the waveforms. Here we analyze the effects of the higher harmonics in more detail by performing extensive Monte Carlo simulations. We pay particular attention to how the higher harmonics impact parameter correlations, and show that the additional harmonics help mitigate the impact of having two laser links fail, by allowing for an instantaneous measurement of the gravitational wave polarization with a single interferometer channel. By looking at parameter correlations we are able to explain why certain mass ratios provide dramatic improvements in certain parameter estimations, and illustrate how the improved polarization measurement improves the prospects for single interferometer operation.
05/2008;
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Stanislav Babak,
John G. Baker,
Matthew J. Benacquista, Neil J. Cornish,
Jeff Crowder,
Curt Cutler,
Shane L. Larson,
Tyson B. Littenberg,
Edward K. Porter,
Michele Vallisneri, [......],
Emma L. Robinson,
Christian Roever,
Pavlin Savov,
Alexander Stroeer,
Jennifer Toher,
John Veitch,
Jean-Yves Vinet,
Linqing Wen,
John T. Whelan,
Graham Woan
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ABSTRACT: The Mock LISA Data Challenges are a program to demonstrate LISA data-analysis capabilities and to encourage their development. Each round of challenges consists of several data sets containing simulated instrument noise and gravitational-wave sources of undisclosed parameters. Participants are asked to analyze the data sets and report the maximum information about source parameters. The challenges are being released in rounds of increasing complexity and realism: in this proceeding we present the results of Challenge 2, issued in January 2007, which successfully demonstrated the recovery of signals from supermassive black-hole binaries, from ~20,000 overlapping Galactic white-dwarf binaries, and from the extreme-mass-ratio inspirals of compact objects into central galactic black holes.
12/2007;
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ABSTRACT: We report on the performance of an end-to-end Bayesian analysis pipeline for detecting and characterizing galactic binary signals in simulated LISA data. Our principal analysis tool is the Blocked-Annealed Metropolis Hasting (BAM) algorithm, which has been optimized to search for tens of thousands of overlapping signals across the LISA band. The BAM algorithm employs Bayesian model selection to determine the number of resolvable sources, and provides posterior distribution functions for all the model parameters. The BAM algorithm performed almost flawlessly on all the Round 1 Mock LISA Data Challenge data sets, including those with many highly overlapping sources. The only misses were later traced to a coding error that affected high frequency sources. In addition to the BAM algorithm we also successfully tested a Genetic Algorithm (GA), but only on data sets with isolated signals as the GA has yet to be optimized to handle large numbers of overlapping signals.
05/2007;
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ABSTRACT: The analysis of gravitational wave data involves many model selection problems. The most important example is the detection problem of selecting between the data being consistent with instrument noise alone, or instrument noise and a gravitational wave signal. The analysis of data from ground based gravitational wave detectors is mostly conducted using classical statistics, and methods such as the Neyman-Pearson criteria are used for model selection. Future space based detectors, such as the \emph{Laser Interferometer Space Antenna} (LISA), are expected to produced rich data streams containing the signals from many millions of sources. Determining the number of sources that are resolvable, and the most appropriate description of each source poses a challenging model selection problem that may best be addressed in a Bayesian framework. An important class of LISA sources are the millions of low-mass binary systems within our own galaxy, tens of thousands of which will be detectable. Not only are the number of sources unknown, but so are the number of parameters required to model the waveforms. For example, a significant subset of the resolvable galactic binaries will exhibit orbital frequency evolution, while a smaller number will have measurable eccentricity. In the Bayesian approach to model selection one needs to compute the Bayes factor between competing models. Here we explore various methods for computing Bayes factors in the context of determining which galactic binaries have measurable frequency evolution. The methods explored include a Reverse Jump Markov Chain Monte Carlo (RJMCMC) algorithm, Savage-Dickie density ratios, the Schwarz-Bayes Information Criterion (BIC), and the Laplace approximation to the model evidence. We find good agreement between all of the approaches.
05/2007;
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ABSTRACT: The Mock LISA Data Challenge is a worldwide effort to solve the LISA data analysis problem. We present here our results for the Massive Black Hole Binary (BBH) section of Round 1. Our results cover Challenge 1.2.1, where the coalescence of the binary is seen, and Challenge 1.2.2, where the coalescence occurs after the simulated observational period. The data stream is composed of Gaussian instrumental noise plus an unknown BBH waveform. Our search algorithm is based on a variant of the Markov Chain Monte Carlo method that uses Metropolis-Hastings sampling and thermostated frequency annealing. We present results from the training data sets and the blind data sets. We demonstrate that our algorithm is able to rapidly locate the sources, accurately recover the source parameters, and provide error estimates for the recovered parameters.
03/2007;
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ABSTRACT: In this work we focus on the search and detection of Massive black hole binary (MBHB) systems, including systems at high redshift. As well as expanding on previous works where we used a variant of Markov Chain Monte Carlo (MCMC), called Metropolis-Hastings Monte Carlo, with simulated annealing, we introduce a new search method based on frequency annealing which leads to a more rapid and robust detection. We compare the two search methods on systems where we do and do not see the merger of the black holes. In the non-merger case, we also examine the posterior distribution exploration using a 7-D MCMC algorithm. We demonstrate that this method is effective in dealing with the high correlations between parameters, has a higher acceptance rate than previously proposed methods and produces posterior distribution functions that are close to the prediction from the Fisher Information matrix. Finally, after carrying out searches where there is only one binary in the data stream, we examine the case where two black hole binaries are present in the same data stream. We demonstrate that our search algorithm can accurately recover both binaries, and more importantly showing that we can safely extract the MBHB sources without contaminating the rest of the data stream. Comment: Final published version. Accepted by Classical and Quantum Gravity
12/2006;
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ABSTRACT: Here we describe a hierarchal and iterative data analysis algorithm used for searching, characterizing, and removing bright, monochromatic binaries from the Laser Interferometer Space Antenna (LISA) data streams. The algorithm uses the F-statistic to provide an initial solution for individual bright sources, followed by an iterative least squares fitting for all the bright sources. Using the above algorithm, referred to as Slice & Dice, we demonstrate the removal of multiple, correlated galactic binaries from simulated LISA data. Initial results indicate that Slice & Dice may be a useful tool for analyzing the forthcoming LISA data. Comment: 5 pages, 4 figures, proceedings paper for the Sixth International LISA Symposium
08/2006;
Institutions
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1970–2011
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Montana State University
Bozeman,
MT,
USA
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1996
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Case Western Reserve University
Cleveland,
OH,
USA
