[0707.4327] Stochastic background from extra-galactic double neutron stars

Authors: T. Regimbau, B. Chauvineau

Date: 30 Jul 2007

Abstract: We present Monte Carlo simulations of the extra galactic population of inspiralling double neutron stars, and estimate its contribution to the astrophysical gravitational wave background, in the frequency range of ground based interferometers, corresponding to the last thousand seconds before the last stable orbit when more than 96 percent of the signal is released. We show that sources at redshift z>0.5 contribute to a truly continuous background which may be detected by correlating third generation interferometers.

abs pdf

Jul 31, 2007

0707.4327 (/preprints)
2007-07-31, 08:56 [edit]


[0707.4434] LISA observations of supermassive black holes: parameter estimation using full post-Newtonian inspiral waveforms

Authors: Miquel Trias, Alicia M. Sintes

Date: 30 Jul 2007

Abstract: We study parameter estimation of supermassive black hole binary systems in the final stage of inspiral using the full post-Newtonian gravitational waveforms. We restrict our analysis to systems in circular orbit with negligible spins, in the mass range $10ˆ8\Ms-10ˆ5\Ms$, and compare the results with those arising from the commonly used restricted post-Newtonian approximation. The conclusions of this work are particularly important with regard to the astrophysical reach of future LISA measurements. Our analysis clearly shows that modeling the inspiral with the full post-Newtonian waveform, not only extends the reach to higher mass systems, but also improves in general the parameter estimation. In particular, there are remarkable improvements in angular resolution and distance measurement for systems with a total mass higher than $5\times10ˆ6\Ms$, as well as a large improvement in the mass determination.

abs pdf

Jul 31, 2007

0707.4434 (/preprints)
2007-07-31, 08:56 [edit]


[0707.3920] Higher signal harmonics, LISA's angular resolution and dark energy

Authors: K. G. Arun, Bala R. Iyer, B.S. Sathyaprakash, Siddhartha Sinha, Chris Van Den Broeck

Date: 26 Jul 2007

Abstract: It is generally believed that the angular resolution of the Laser Interferometer Space Antenna (LISA) for binary supermassive black holes (SMBH) will not be good enough to identify the host galaxy or galaxy cluster. This conclusion, based on using only the dominant harmonic of the binary SMBH signal, changes dramatically when higher signal harmonics are included in assessing the parameter estimation problem. We show that in a subset of the source parameter space the angular resolution increases by more than a factor of 10, thereby making it possible for LISA to identify the host galaxy/galaxy cluster. Thus, LISA's observation of certain binary SMBH coalescence events could constrain the dark energy equation of state to within a few percent, comparable to the level expected from other dark energy missions.

abs pdf

Jul 30, 2007

0707.3920 (/preprints)
2007-07-30, 09:11 [edit]


[0707.3969] Inference on inspiral signals using LISA MLDC data

Authors: Christian Röver, Alexander Stroeer, Ed Bloomer, Nelson Christensen, James Clark, Martin Hendry, Chris Messenger, Renate Meyer, Matt Pitkin, Jennifer Toher, Richard Umstätter, Alberto Vecchio, John Veitch, Graham Woan

Date: 26 Jul 2007

Abstract: In this paper we describe a Bayesian inference framework for analysis of data obtained by LISA. We set up a model for binary inspiral signals as defined for the Mock LISA Data Challenge 1.2 (MLDC), and implemented a Markov chain Monte Carlo (MCMC) algorithm to facilitate exploration and integration of the posterior distribution over the 9-dimensional parameter space. Here we present intermediate results showing how, using this method, information about the 9 parameters can be extracted from the data.

abs pdf

Jul 27, 2007

0707.3969 (/preprints)
2007-07-27, 08:50 [edit]


[0707.3843] Modulator noise suppression in the LISA Time-Delay Interferometric combinations

Authors: Massimo Tinto, John W. Armstrong, Frank B. Estabrook

Date: 25 Jul 2007

Abstract: We previously showed how the measurements of some eighteen time series of relative frequency or phase shifts could be combined (1) to cancel the phase noise of the lasers, (2) to cancel the Doppler fluctuations due to non-inertial motions of the six optical benches, and (3) to remove the phase noise of the onboard reference oscillators required to track the photodetector fringes, all the while preserving signals from passinggravitational waves. Here we analyze the effect of the additional noise due to the optical modulators used for removing the phase fluctuations of the onboard reference oscillators. We use a recently measured noise spectrum of an individual modulator to quantify the contribution of modulator noise to the first and second-generation Time-Delay Interferometric (TDI) combinations as a function of the modulation frequency. We show that modulator noise can be made smaller than the expected proof-mass acceleration and optical-path noises if the modulation frequencies are larger than $\approx 682$ MHz in the case of the unequal-arm Michelson TDI combination $X_1$, $\approx 1.08$ GHz for the Sagnac TDI combination $\alpha_1$, and $\approx 706$ MHz for the symmetrical Sagnac TDI combination $\zeta_1$. These modulation frequencies are substantially smaller than previously estimated and may lead to less stringent requirements on the LISA's oscillator noise calibration subsystem.

abs pdf

Jul 27, 2007

0707.3843 (/preprints)
2007-07-27, 08:49 [edit]


[0707.3962] Coherent Bayesian analysis of inspiral signals

Authors: Christian Röver, Renate Meyer, Gianluca M. Guidi, Andrea Viceré, Nelson Christensen

Date: 26 Jul 2007

Abstract: We present in this paper a Bayesian parameter estimation method for the analysis of interferometric gravitational wave observations of an inspiral of binary compact objects using data recorded simultaneously by a network of several interferometers at different sites. We consider neutron star or black hole inspirals that are modeled to 3.5 post-Newtonian (PN) order in phase and 2.5 PN in amplitude. Inference is facilitated using Markov chain Monte Carlo methods that are adapted in order to efficiently explore the particular parameter space. Examples are shown to illustrate how and what information about the different parameters can be derived from the data. This study uses simulated signals and data with noise characteristics that are assumed to be defined by the LIGO and Virgo detectors operating at their design sensitivities. Nine parameters are estimated, including those associated with the binary system, plus its location on the sky. We explain how this technique will be part of a detection pipeline for binary systems of compact objects with masses up to $20 \sunmass$, including cases where the ratio of the individual masses can be extreme.

abs pdf

Jul 27, 2007

0707.3962 (/preprints)
2007-07-27, 08:49 [edit]


[0707.0535] Measuring a Parity Violation Signature in the Early Universe via Ground-based Laser Interferometers

Authors: Naoki Seto, Atsushi Taruya

Date: 4 Jul 2007

Abstract: We show that pairs of widely separated interferometers are advantageous for measuring the Stokes parameter V of a stochastic background of gravitational waves. This parameter characterizes asymmetry of amplitudes of right- and left-handed waves and generation of the asymmetry is closely related to parity violation in the early universe. The advantageous pairs include LIGO(Livingston)-LCGT and AIGO-Virgo that are relatively insensitive to Omega_GW (the simple intensity of the background). Using at least three detectors, information of the intensity Omega_GW and the degree of asymmetry V can be separately measured.

abs pdf

Jul 25, 2007

0707.0535 (/preprints)
2007-07-25, 18:36 [edit]


[0707.3319] Discovering Relic Gravitational Waves in Cosmic Microwave Background Radiation

Authors: L. P. Grishchuk

Date: 23 Jul 2007

Abstract: The authority of J. A. Wheeler in many areas of gravitational physics is immense, and there is a connection with the study of relic gravitational waves as well. I begin with a brief description of Wheeler's influence on this study. One part of the paper is essentially a detailed justification of the very existence of relic gravitational waves, account of their properties related to the quantum-mechanical origin, derivation of the expected magnitude of their effects, and reasoning why they should be detectable in the relatively near future. This line of argument includes comparison of relic gravitational waves with density perturbations of quantum-mechanical origin, and severe criticism of methods and predictions of inflationary theory. Another part of the paper is devoted to active searches for relic gravitational waves in cosmic microwave background radiation (CMB). Here, the emphasis is on the temperature-polarization TE cross-correlation function of CMB. The expected numerical level of the correlation, its sign, statistics, and the most appropriate interval of angular scales are identified. The overall conclusion is such that the observational discovery of relic gravitational waves looks like the matter of a few coming years, rather than a few decades.

abs pdf

Jul 24, 2007

0707.3319 (/preprints)
2007-07-24, 08:46 [edit]


[0707.2748] Theory of gravitation theories: a no-progress report

Authors: Thomas P Sotiriou, Valerio Faraoni, Stefano Liberati

Date: 18 Jul 2007

Abstract: Already in the 1970s there where attempts to present a set of ground rules, sometimes referred to as a theory of gravitation theories, which theories of gravity should satisfy in order to be considered viable in principle and, therefore, interesting enough to deserve further investigation. From this perspective, an alternative title of the present paper could be ‘why are we still unable to write a guide on how to propose viable alternatives to general relativity?’. Attempting to answer this question, it is argued here that earlier efforts to turn qualitative statements, such as the Einstein Equivalence Principle, into quantitative ones, such as the metric postulates, stand on rather shaky grounds -- probably contrary to popular belief -- as they appear to depend strongly on particular representations of the theory. This includes ambiguities in the identification of matter and gravitational fields, dependence of frequently used definitions, such as those of the stress-energy tensor or classical vacuum, on the choice of variables, etc. Various examples are discussed and possible approaches to this problem are pointed out. In the course of this study, several common misconceptions related to the various forms of the Equivalence Principle, the use of conformal frames and equivalence between theories are clarified.

abs pdf

Jul 18, 2007

0707.2748 (/preprints)
2007-07-18, 20:07 [edit]


[0707.2410] Interpreting the results of searches for gravitational waves from coalescing binaries

Authors: Stephen Fairhurst, Patrick Brady

Date: 16 Jul 2007

Abstract: We introduce a method based on the loudest event statistic to calculate an upper limit or interval on the astrophysical rate of binary coalescence. The calculation depends upon the sensitivity and noise background of the detectors, and a model for the astrophysical distribution of coalescing binaries. There are significant uncertainties in the calculation of the rate due to both astrophysical and instrumental uncertainties as well as errors introduced by using the post--Newtonian waveform to approximate the full signal. We catalog these uncertainties in detail and describe a method for marginalizing over them. Throughout, we provide an example based on the initial LIGO detectors.

abs pdf

Jul 17, 2007

0707.2410 (/preprints)
2007-07-17, 17:38 [edit]


[0707.2559] Recoil velocities from equal-mass binary black-hole mergers: a systematic investigation of spin-orbit aligned configurations

Authors: Denis Pollney, Christian Reisswig, Luciano Rezzolla, Bela Szilagyi, Marcus Ansorg, Barrett Deris, Peter Diener, Ernst Nils Dorband, Michael Koppitz, Alessandro Nagar, Erik Schnetter

Date: 17 Jul 2007

Abstract: Binary black-hole systems with spins aligned with the orbital angular momentum are of special interest, as studies indicate that this configuration is preferred in nature. If the spins of the two bodies differ, there can be a prominent beaming of the gravitational radiation during the late plunge, causing a recoil of the final merged black hole. We perform an accurate and systematic study of recoil velocities from a sequence of equal-mass black holes whose spins are aligned with the orbital angular momentum, and whose individual spins range from a = +0.584 to -0.584. In this way we extend and refine the results of a previous study and arrive at a consistent maximum recoil of 448 +- 5 km/s for anti-aligned models as well as to a phenomenological expression for the recoil velocity as a function of spin ratio. This relation highlights a nonlinear behavior, not predicted by the PN estimates, and can be readily employed in astrophysical studies on the evolution of binary black holes in massive galaxies. An essential result of our analysis is the identification of different stages in the waveform, including a transient due to lack of an initial linear momentum in the initial data. Furthermore we are able to identify a pair of terms which are largely responsible for the kick, indicating that an accurate computation can be obtained from modes up to l=3. Finally, we provide accurate measures of the radiated energy and angular momentum, finding these to increase linearly with the spin ratio, and derive simple expressions for the final spin and the radiated angular momentum which can be easily implemented in N-body simulations of compact stellar systems. Our code is calibrated with strict convergence tests and we verify the correctness of our measurements by using multiple independent methods whenever possible.

abs pdf

Jul 17, 2007

0707.2559 (/preprints)
2007-07-17, 17:38 [edit]


[astro-ph/0703495] Intermediate and Extreme Mass-Ratio Inspirals -- Astrophysics, Science Applications and Detection using LISA

Authors: Pau Amaro-Seoane, Jonathan R. Gair, Marc Freitag, M. Coleman Miller, Ilya Mandel, Curt J. Cutler, Stanislav Babak

Date: 19 Mar 2007

Abstract: Black hole binaries with extreme ($\gtrsim 10ˆ4:1$) or intermediate ($\sim 10ˆ2-10ˆ4:1$) mass ratios are among the most interesting gravitational wave sources that are expected to be detected by the proposed Laser Interferometer Space Antenna. These sources have the potential to tell us much about astrophysics, but are also of unique importance for testing aspects of the general theory of relativity in the strong field regime. Here we discuss these sources from the perspectives of astrophysics, data analysis, and applications to testing general relativity, providing both a description of the current state of knowledge and an outline of some of the outstanding questions that still need to be addressed. This review grew out of discussions at a workshop in September 2006 hosted by the Albert Einstein Institute in Golm, Germany.

abs pdf

Jul 17, 2007

0703495 (/preprints/astro-ph)
2007-07-17, 12:36 [edit]


[0707.1202] Matched-filtering and parameter estimation of ringdown waveforms

Authors: Emanuele Berti, Jaime Cardoso, Vitor Cardoso, Marco Cavaglia

Date: 9 Jul 2007

Abstract: Using recent results from numerical relativity simulations of non-spinning binary black hole mergers we revisit the problem of detecting ringdown waveforms and of estimating the source parameters, considering both LISA and Earth-based interferometers. We find that Advanced LIGO and EGO could detect intermediate-mass black holes of mass up to about 1000 solar masses out to a luminosity distance of a few Gpc. For typical multipolar energy distributions, we show that the single-mode ringdown templates presently used for ringdown searches in the LIGO data stream can produce a significant event loss (> 10% for all detectors in a large interval of black hole masses) and very large parameter estimation errors on the black hole's mass and spin. We estimate that more than 10ˆ6 templates would be needed for a single-stage multi-mode search. Therefore, we recommend a "two stage" search to save on computational costs: single-mode templates can be used for detection, but multi-mode templates or Prony methods should be used to estimate parameters once a detection has been made. We update estimates of the critical signal-to-noise ratio required to test the hypothesis that two or more modes are present in the signal and to resolve their frequencies, showing that second-generation Earth-based detectors and LISA have the potential to perform no-hair tests.

abs pdf

Jul 16, 2007

0707.1202 (/preprints)
2007-07-16, 09:52 [edit]


[0707.0711] Spin distribution following minor mergers and the effect of spin on the detection range for low-mass-ratio inspirals

Authors: Ilya Mandel

Date: 5 Jul 2007

Abstract: We compute the probability distribution for the spin of a black hole following a series of minor mergers with isotropically distributed, non-spinning, inspiraling compact objects. By solving the Fokker-Planck equation governing this stochastic process, we obtain accurate analytical fits for the evolution of the mean and standard deviation of the spin distribution in several parameter regimes. We complement these analytical fits with numerical Monte-Carlo simulations in situations when the Fokker-Planck analysis is not applicable. We find that a ~150 solar-mass intermediate-mass black hole that gained half of its mass through minor mergers with neutron stars will have dimensionless spin parameter chi=a/M~0.2 \pm 0.08. We estimate the effect of the spin of the central black hole on the detection range for intermediate-mass-ratio inspiral (IMRI) detections by Advanced LIGO and extreme-mass-ratio inspiral(EMRI) detections by LISA. We find that for realistic black hole spins, the inclination-averaged Advanced-LIGO IMRI detection range may be increased by up to 10% relative to the range for IMRIs into non-spinning intermediate-mass black holes. For LISA, we find that the detection range for EMRIs into 10ˆ5 solar-mass massive black holes (MBHs) is not significantly affected by MBH spin, the range for EMRIs into 10ˆ6 solar-mass MBHs is affected at the ~ 10% level, and EMRIs into maximally spinning 10ˆ7 solar-mass MBHs are detectable to a distance ~25 times greater than EMRIs into non-spinning black holes. The resulting bias in favor of detecting EMRIs into rapidly spinning MBHs will play a role when extracting the MBH spin distribution from EMRI statistics.

abs pdf

Jul 09, 2007

0707.0711 (/preprints)
2007-07-09, 01:10 [edit]


[0707.0301] Anatomy of the binary black hole recoil: A multipolar analysis

Authors: Jeremy D. Schnittman, Alessandra Buonanno (U Maryland), James R. van Meter, John G. Baker (NASA Goddard), William D. Boggs (U Maryland), Joan Centrella, Bernard J. Kelly (NASA Goddard), Sean T. McWilliams (U Maryland)

Date: 2 Jul 2007

Abstract: We present a multipolar analysis of the gravitational recoil computed in recent numerical simulations of binary black hole (BH) coalescence, for both unequal masses and non-zero, non-precessing spins. We show that multipole moments up to and including l=4 are sufficient to accurately reproduce the final recoil velocity (within ~2%) and that only a few dominant modes contribute significantly to it (within ~5%). We describe how the relative amplitudes, and more importantly, the relative phases, of these few modes control the way in which the recoil builds up throughout the inspiral, merger, and ringdown phases. We also find that the numerical results can be reproduced by an ‘effective Newtonian’ formula for the multipole moments obtained by replacing the radial separation in the Newtonian formulae with an effective radius computed from the numerical data. Beyond the merger, the numerical results are reproduced by a superposition of three Kerr quasi-normal modes (QNMs). Analytic formulae, obtained by expressing the multipole moments in terms of the fundamental QNMs of a Kerr BH, are able to explain the onset and amount of ‘anti-kick’ for each of the simulations. Lastly, we apply this multipolar analysis to help explain the remarkable difference between the amplitudes of planar and non-planar kicks for equal-mass spinning black holes.

abs pdf

Jul 03, 2007

0707.0301 (/preprints)
2007-07-03, 17:42 [edit]


[0707.0428] Template-based searches for gravitational waves: efficient lattice covering of flat parameter spaces

Authors: Reinhard Prix

Date: 3 Jul 2007

Abstract: The construction of optimal template banks for matched-filtering searches is an example of the sphere covering problem. For parameter spaces with constant-coefficient metrics a (near-) optimal template bank is achieved by the A_n* lattice, which is the best lattice-covering in dimensions n <= 5, and is close to the best covering known for dimensions n <= 16. Generally this provides a substantially more efficient covering than the simpler hyper-cubic lattice. We present an algorithm for generating lattice template banks for constant-coefficient metrics and we illustrate its implementation by generating A_n* template banks in n=2,3,4 dimensions.

abs pdf

Jul 03, 2007

0707.0428 (/preprints)
2007-07-03, 17:42 [edit]


[0707.0128] F-statistic search for white-dwarf binaries in the first Mock LISA Data Challenge

Authors: Reinhard Prix, John T. Whelan

Date: 1 Jul 2007

Abstract: The F-statistic is an optimal detection statistic for continuous gravitational waves, i.e., long-duration (quasi-)monochromatic signals with slowly-varying intrinsic frequency. This method was originally developed in the context of ground-based detectors, but it is equally applicable to LISA where many signals fall into this class of signals. We report on the application of a LIGO/GEO F-statistic code to LISA data-analysis using the long-wavelength limit (LWL), and we present results of our search for white-dwarf binary signals in the first Mock LISA Data Challenge. Somewhat surprisingly, the LWL is found to be sufficient -- even at high frequencies -- for detection of signals and their accurate localization on the sky and in frequency, while a more accurate modelling of the TDI response only seems necessary to correctly estimate the four amplitude parameters.

abs pdf

Jul 02, 2007

0707.0128 (/preprints)
2007-07-02, 20:04 [edit]


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