[0806.4574] Modeling the Impulsive Noise Component and its Effect on the Operation of a Simple Coherent Network Algorithm for Unmodeled Gravitational Wave Bursts Detection

Authors: Maria Principe, Innocenzo M Pinto

Date: 27 Jun 2008

Abstract: An analytic model a la Middleton of the impulsive noise component in the data of interferometric gravitational wave detectors is proposed, based on an atomic representation of glitches. A fully analytic characterization of the coherent network data analysis algorithm proposed by Rakhmanov and Klimenko is obtained, for the simplest relevant case of triggered detection of unmodeled gravitational wave bursts, using the above noise model. The detector's performance is evaluated under a suitable central-limit hypothesis, and the effects of both the noisiness of the pseudo-templates, and the presence of the impulsive noise component are highlighted.

abs pdf

Jun 30, 2008

0806.4574 (/preprints)
2008-06-30, 02:38 [edit]


[0806.4417] Gravitational wave detection using multiscale chirplets

Authors: Emmanuel J. Candès, Philip R. Charlton, Hannes Helgason

Date: 27 Jun 2008

Abstract: A generic ‘chirp’ of the form h(t) = A(t) cos(phi(t)) can be closely approximated by a connected set of multiscale chirplets with quadratically-evolving phase. The problem of finding the best approximation to a given signal using chirplets can be reduced to that of finding the path of minimum cost in a weighted, directed graph, and can be solved in polynomial time via dynamic programming. For a signal embedded in noise we apply constraints on the path length to obtain a statistic for detection of chirping signals in coloured noise. In this paper we present some results from using this test to detect binary black hole coalescences in simulated LIGO noise.

abs pdf

Jun 30, 2008

0806.4417 (/preprints)
2008-06-30, 02:38 [edit]


[0806.4007] Simulating coalescing compact binaries by a new code SACRA

Authors: Tetsuro Yamamoto, Masaru Shibata, Keisuke Taniguchi

Date: 25 Jun 2008

Abstract: We report our new code (named SACRA) for numerical relativity simulations in which an adaptive mesh refinement algorithm is implemented. In this code, the Einstein equations are solved in the BSSN formalism with a fourth-order finite differencing, and the hydrodynamic equations are solved by a third-order high-resolution central scheme. The fourth-order Runge-Kutta scheme is adopted for integration in time. To test the code, simulations for coalescence of black hole-black hole (BH-BH), neutron star-neutron star (NS-NS), and black hole-neutron star (BH-NS) binaries are performed, and also, properties of BHs formed after the merger and gravitational waveforms are compared among those three cases. For the simulations of BH-BH binaries, we adopt the same initial conditions as those by Buonanno et al. and compare numerical results. We find reasonable agreement except for a slight disagreement possibly associated with the difference in choice of gauge conditions and numerical schemes. For an NS-NS binary, we performed simulations employing both SACRA and Shibata's previous code, and find reasonable agreement. For a BH-NS binary, we compare numerical results with our previous ones, and find that gravitational waveforms and properties of the BH formed after the merger agree well with those of our previous ones, although the disk mass formed after the merger is less than 0.1% of the total rest mass, which disagrees with the previous result. We also report numerical results of a longterm simulation (with $\sim 4$ orbits) for a BH-NS binary for the first time. All these numerical results show behavior of convergence, and extrapolated numerical results for time spent in the inspiral phase agree with post-Newtonian predictions in a reasonable accuracy.

abs pdf

Jun 26, 2008

0806.4007 (/preprints)
2008-06-26, 03:08 [edit]


[0806.3381] Astrophysical implications of hypothetical stable TeV-scale black holes

Authors: Steven B. Giddings, Michelangelo M. Mangano

Date: 20 Jun 2008

Abstract: We analyze macroscopic effects of TeV-scale black holes, such as could possibly be produced at the LHC, in what is regarded as an extremely hypothetical scenario in which they are stable and, if trapped inside Earth, begin to accrete matter. We examine a wide variety of TeV-scale gravity scenarios, basing the resulting accretion models on first-principles, basic, and well-tested physical laws. These scenarios fall into two classes, depending on whether accretion could have any macroscopic effect on the Earth at times shorter than the Sun's natural lifetime. We argue that cases with such effect at shorter times than the solar lifetime are ruled out, since in these scenarios black holes produced by cosmic rays impinging on much denser white dwarfs and neutron stars would then catalyze their decay on timescales incompatible with their known lifetimes. We also comment on relevant lifetimes for astronomical objects that capture primordial black holes. In short, this study finds no basis for concerns that TeV-scale black holes from the LHC could pose a risk to Earth on time scales shorter than the Earth's natural lifetime. Indeed, conservative arguments based on detailed calculations and the best-available scientific knowledge, including solid astronomical data, conclude, from multiple perspectives, that there is no risk of any significance whatsoever from such black holes.

abs pdf

Jun 23, 2008

0806.3381 (/preprints)
2008-06-23, 09:53 [edit]


[0806.3293] A Rigorous Derivation of Gravitational Self-force

Authors: Samuel E. Gralla, Robert M. Wald

Date: 19 Jun 2008

Abstract: There is general agreement that the MiSaTaQuWa equations should describe the motion of a "small body" body in general relativity, taking into account the leading order self-force effects. However, previous derivations of these equations have made a number of ad hoc assumptions and/or contain a number of unsatisfactory features. For example, all previous derivations have invoked, without proper justification, the step of ‘Lorenz gauge relaxation’, wherein the linearized Einstein equation is written down in the form appropriate to the Lorenz gauge, but the Lorenz gauge condition is then not imposed--thereby making the resulting equations for the metric perturbation inequivalent to the linearized Einstein equations. In this paper, we analyze the issue of ‘particle motion’ in general relativity in a systematic and rigorous way by considering a one-parameter family of metrics, $g_{ab} (\lambda)$, corresponding to having a body (or black hole) that is ‘scaled down’ to zero size and mass in an appropriate manner. We prove that the limiting worldline of such a one-parameter family must be a geodesic of the background metric, $g_{ab} (\lambda=0)$. Gravitational self-force--as well as the force due to coupling of the spin of the body to curvature--then arises as a first-order perturbative correction in $\lambda$ to this worldline. No assumptions are made in our analysis apart from the smoothness and limit properties of the one-parameter family of metrics. Our approach should provide a framework for systematically calculating higher order corrections to gravitational self-force, including higher multipole effects, although we do not attempt to go beyond first order calculations here. The status of the MiSaTaQuWa equations is explained.

abs pdf

Jun 23, 2008

0806.3293 (/preprints)
2008-06-23, 09:52 [edit]


[0805.1972] Mock LISA Data Challenge 1B: improved search for galactic white dwarf binaries using an F-statistic template bank

Authors: John T. Whelan, Reinhard Prix, Deepak Khurana

Date: 14 May 2008

Abstract: We report on our F-statistic search for white-dwarf binary signals in the Mock LISA Data Challenge 1B (MLDC1B). We focus in particular on the improvements in our search pipeline since MLDC1, namely refinements in the search pipeline and the use of a more accurate detector response (rigid adiabatic approximation). The search method employs a hierarchical template-grid based exploration of the parameter space, using a coincidence step to distinguish between primary (‘true’) and secondary maxima, followed by a final (multi-TDI) ‘zoom’ stage to provide an accurate parameter estimation of the final candidates.

abs pdf

Jun 20, 2008

0805.1972 (/preprints/mldc)
2008-06-20, 03:41 [edit]


[0804.4144] Search for a stochastic gravitational-wave signal in the second round of the Mock LISA Data Challenges

Authors: E. L. Robinson, J. D. Romano, A. Vecchio

Date: 25 Apr 2008

Abstract: The analysis method currently proposed to search for isotropic stochastic radiation of primordial or astrophysical origin with the Laser Interferometer Space Antenna (LISA) relies on the combined use of two LISA channels, one of which is insensitive to gravitational waves, such as the symmetrised Sagnac. For this method to work, it is essential to know how the instrumental noise power in the two channels are related to one another; however, no quantitative estimates of this key information are available to date. The purpose of our study is to assess the performance of the symmetrised Sagnac method for different levels of prior information regarding the instrumental noise. We develop a general approach in the framework of Bayesian inference and an end-to-end analysis algorithm based on Markov Chain Monte Carlo methods to compute the posterior probability density functions of the relevant model parameters. We apply this method to data released as part of the second round of the Mock LISA Data Challenges. For the selected (and somewhat idealised) cases considered here, we find that a prior uncertainty of a factor ~2 in the ratio between the power of the instrumental noise contributions in the two channels allows for the detection of isotropic stochastic radiation. More importantly, we provide a framework for more realistic studies of LISA's performance and development of analysis techniques in the context of searches for stochastic signals.

abs pdf

Jun 20, 2008

0804.4144 (/preprints/mldc)
2008-06-20, 03:39 [edit]


[0804.3323] Detection Strategies for Extreme Mass Ratio Inspirals

Authors: N. J. Cornish

Date: 21 Apr 2008

Abstract: The capture of compact stellar remnants by galactic black holes provides a unique laboratory for exploring the near horizon geometry of the Kerr spacetime. The gravitational radiation produced by these Extreme Mass Ratio Inspirals (EMRIs) encodes a detailed map of the black hole geometry, and the detection and characterization of these signals is a major science driver for the LISA observatory. The waveforms produced are very complex, and the signals need to be coherently tracked for hundreds to thousands of cycles to produce a detection, making EMRI signals one of the most challenging data analysis problems in all of gravitational wave astronomy. Estimates for the number of templates required to perform an optimal matched-filter search for these signals are astronomically large, and far out of reach of current computational resources. Here a sub-optimal, hierarchical approach to the EMRI detection problem is developed that employs a directed-stochastic search technique. The algorithm, dubbed Metropolis Hastings Monte Carlo (MHMC), is a close cousin of Markov Chain Monte Carlo and genetic algorithms. The utility of the MHMC approach is demonstrated using simulated data sets from the Mock LISA Data Challenge.

abs pdf

Jun 20, 2008

0804.3323 (/preprints/mldc)
2008-06-20, 03:38 [edit]


[0804.4029] Markov chain Monte Carlo searches for Galactic binaries in Mock LISA Data Challenge 1B data sets

Authors: Miquel Trias, Alberto Vecchio, John Veitch

Date: 24 Apr 2008

Abstract: We are developing a Bayesian approach based on Markov chain Monte Carlo techniques to search for and extract information about white dwarf binary systems with the Laser Interferometer Space Antenna (LISA). Here we present results obtained by applying an initial implementation of this method to some of the data sets released in Round 1B of the Mock LISA Data Challenges. For Challenges 1B.1.1a and 1b the signals were recovered with parameters lying within the 95.5% posterior probability interval and the correlation between the true and recovered waveform is in excess of 99%. Results were not submitted for Challenge 1B.1.1c due to some convergence problems of the algorithms, despite the signal was detected in a search over a 2 mHz band.

abs pdf

Jun 20, 2008

0804.4029 (/preprints/mldc)
2008-06-20, 03:38 [edit]


[0804.3322] A Constrained Metropolis-Hastings Search for EMRIs in the Mock LISA Data Challenge 1B

Authors: Jonathan R. Gair, Stanislav Babak, Edward K. Porter, Leor Barack

Date: 21 Apr 2008

Abstract: We describe a search for the EMRI sources in the Round 1B Mock LISA Data Challenge data sets. The search algorithm is a Monte-Carlo search based on the Metropolis-Hastings algorithm, but also incorporates simulated, thermostated and time annealing, plus a harmonic identification stage designed to reduce the chance of the chain locking onto secondary maxima. In this paper, we focus on describing the algorithm that we have been developing. We give the results of the search of the Round 1B data, although parameter recovery has improved since that deadline. Finally, we describe several modifications to the search pipeline that we are currently investigating for incorporation in future searches.

abs pdf

Jun 20, 2008

0804.3322 (/preprints/mldc)
2008-06-20, 03:38 [edit]


[0804.3274] A hierarchical search for gravitational waves from supermassive black hole binary mergers

Authors: I.W. Harry, S. Fairhurst, B.S. Sathyaprakash

Date: 21 Apr 2008

Abstract: We present a method to search for gravitational waves from coalescing supermassive binary black holes in LISA data. The search utilizes the $\mathcal{F}$-statistic to maximize over, and determine the values of, the extrinsic parameters of the binary system. The intrinsic parameters are searched over hierarchically using stochastically generated multi-dimensional template banks to recover the masses and sky locations of the binary. We present the results of this method applied to the mock LISA data Challenge 1B data set.

abs pdf

Jun 20, 2008

0804.3274 (/preprints/mldc)
2008-06-20, 03:38 [edit]


[0804.1084] Improved time-frequency analysis of extreme-mass-ratio inspiral signals in mock LISA data

Authors: Jonathan R Gair, Ilya Mandel, Linqing Wen

Date: 7 Apr 2008

Abstract: The planned Laser Interferometer Space Antenna (LISA) is expected to detect gravitational wave signals from ~100 extreme-mass-ratio inspirals (EMRIs) of stellar-mass compact objects into massive black holes. The long duration and large parameter space of EMRI signals makes data analysis for these signals a challenging problem. One approach to EMRI data analysis is to use time-frequency methods. This consists of two steps: (i) searching for tracks from EMRI sources in a time-frequency spectrogram, and (ii) extracting parameter estimates from the tracks. In this paper we discuss the results of applying these techniques to the latest round of the Mock LISA Data Challenge, Round 1B. This analysis included three new techniques not used in previous analyses: (i) a new Chirp-based Algorithm for Track Search for track detection; (ii) estimation of the inclination of the source to the line of sight; (iii) a Metropolis-Hastings Monte Carlo over the parameter space in order to find the best fit to the tracks.

abs pdf

Jun 20, 2008

0804.1084 (/preprints/mldc)
2008-06-20, 03:37 [edit]


[0710.5250] Time-frequency analysis of extreme-mass-ratio inspiral signals in mock LISA data

Authors: Jonathan R Gair, Ilya Mandel, Linqing Wen

Date: 27 Oct 2007

Abstract: Extreme-mass-ratio inspirals (EMRIs) of ~ 1-10 solar-mass compact objects into ~ million solar-mass massive black holes can serve as excellent probes of strong-field general relativity. The Laser Interferometer Space Antenna (LISA) is expected to detect gravitational wave signals from apprxomiately one hundred EMRIs per year, but the data analysis of EMRI signals poses a unique set of challenges due to their long duration and the extensive parameter space of possible signals. One possible approach is to carry out a search for EMRI tracks in the time-frequency domain. We have applied a time-frequency search to the data from the Mock LISA Data Challenge (MLDC) with promising results. Our analysis used the Hierarchical Algorithm for Clusters and Ridges to identify tracks in the time-frequency spectrogram corresponding to EMRI sources. We then estimated the EMRI source parameters from these tracks. In these proceedings, we discuss the results of this analysis of the MLDC round 1.3 data.

abs pdf

Jun 20, 2008

0710.5250 (/preprints/mldc)
2008-06-20, 03:37 [edit]


[0801.4070] Building a stochastic template bank for detecting massive black hole binaries

Authors: Stanislav Babak

Date: 26 Jan 2008

Abstract: Coalescence of two massive black holes is the strongest and most promising source for LISA. In fact, gravitational signal from the end of inspiral and merger will be detectable throughout the Universe. In this article we describe the first step in the two-step hierarchical search for gravitational wave signal from the inspiraling massive BH binaries. It is based on the routinely used in the ground base gravitational wave astronomy method of filtering the data through the bank of templates. However we use a novel Monte-Carlo based (stochastic) method to lay a grid in the parameter space, and we use the likelihood maximized analytically over some parameters, known as F-statistic, as a detection statistic. We build a coarse template bank to detect gravitational wave signals and to make preliminary parameter estimation. The best candidates will be followed up using Metropolis-Hasting stochastic search to refine the parameter estimation. We demonstrate the performance of the method by applying it to the Mock LISA data challenge 1B (training data set).

abs pdf

Jun 20, 2008

0801.4070 (/preprints/mldc)
2008-06-20, 03:37 [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

Jun 20, 2008

0707.3969 (/preprints/mldc)
2008-06-20, 03:36 [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

Jun 20, 2008

0707.0128 (/preprints/mldc)
2008-06-20, 03:36 [edit]


[0704.2447] A Three-Stage Search for Supermassive Black Hole Binaries in LISA Data

Authors: Duncan A. Brown, Jeff Crowder, Curt Cutler, Ilya Mandel, Michele Vallisneri

Date: 19 Apr 2007

Abstract: Gravitational waves from the inspiral and coalescence of supermassive black-hole (SMBH) binaries with masses ~10ˆ6 Msun are likely to be among the strongest sources for the Laser Interferometer Space Antenna (LISA). We describe a three-stage data-analysis pipeline designed to search for and measure the parameters of SMBH binaries in LISA data. The first stage uses a time-frequency track-search method to search for inspiral signals and provide a coarse estimate of the black-hole masses m_1, m_2 and of the coalescence time of the binary t_c. The second stage uses a sequence of matched-filter template banks, seeded by the first stage, to improve the measurement accuracy of the masses and coalescence time. Finally, a Markov Chain Monte Carlo search is used to estimate all nine physical parameters of the binary. Using results from the second stage substantially shortens the Markov Chain burn-in time and allows us to determine the number of SMBH-binary signals in the data before starting parameter estimation. We demonstrate our analysis pipeline using simulated data from the first LISA Mock Data Challenge. We discuss our plan for improving this pipeline and the challenges that will be faced in real LISA data analysis.

abs pdf

Jun 20, 2008

0704.2447 (/preprints/mldc)
2008-06-20, 03:35 [edit]


[0704.0048] Inference on white dwarf binary systems using the first round Mock LISA Data Challenges data sets

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

Date: 31 Mar 2007

Abstract: We report on the analysis of selected single source data sets from the first round of the Mock LISA Data Challenges (MLDC) for white dwarf binaries. We implemented an end-to-end pipeline consisting of a grid-based coherent pre-processing unit for signal detection, and an automatic Markov Chain Monte Carlo post-processing unit for signal evaluation. We demonstrate that signal detection with our coherent approach is secure and accurate, and is increased in accuracy and supplemented with additional information on the signal parameters by our Markov Chain Monte Carlo approach. We also demonstrate that the Markov Chain Monte Carlo routine is additionally able to determine accurately the noise level in the frequency window of interest.

abs pdf

Jun 20, 2008

0704.0048 (/preprints/mldc)
2008-06-20, 03:35 [edit]


[0704.2917] Extracting galactic binary signals from the first round of Mock LISA Data Challenges

Authors: Jeff Crowder, Neil J. Cornish

Date: 23 Apr 2007

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.

abs pdf

Jun 20, 2008

0704.2917 (/preprints/mldc)
2008-06-20, 03:35 [edit]


[gr-qc/0701167] Searching for Massive Black Hole Binaries in the first Mock LISA Data Challenge

Authors: Neil J. Cornish, Edward K. Porter

Date: 30 Jan 2007

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.

abs pdf

Jun 20, 2008

0701167 (/preprints/mldc)
2008-06-20, 03:34 [edit]


[astro-ph/0611546] A Solution to the Galactic Foreground Problem for LISA

Authors: Jeff Crowder, Neil Cornish

Date: 17 Nov 2006

Abstract: Low frequency gravitational wave detectors, such as the Laser Interferometer Space Antenna (LISA), will have to contend with large foregrounds produced by millions of compact galactic binaries in our galaxy. While these galactic signals are interesting in their own right, the unresolved component can obscure other sources. The science yield for the LISA mission can be improved if the brighter and more isolated foreground sources can be identified and regressed from the data. Since the signals overlap with one another we are faced with a ‘cocktail party’ problem of picking out individual conversations in a crowded room. Here we present and implement an end-to-end solution to the galactic foreground problem that is able to resolve tens of thousands of sources from across the LISA band. Our algorithm employs a variant of the Markov Chain Monte Carlo (MCMC) method, which we call the Blocked Annealed Metropolis-Hastings (BAM) algorithm. Following a description of the algorithm and its implementation, we give several examples ranging from searches for a single source to searches for hundreds of overlapping sources. Our examples include data sets from the first round of Mock LISA Data Challenges.

abs pdf

Jun 20, 2008

0611546 (/preprints/mldc)
2008-06-20, 03:34 [edit]


[0806.2110] The Mock LISA Data Challenges: from Challenge 1B to Challenge 3

Authors: 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 (the Mock LISA Data Challenge Task Force), Keith Arnaud, Leor Barack, Arkadiusz Błaut, Curt Cutler, Stephen Fairhurst, Jonathan Gair, Xuefei Gong, Ian Harry, Deepak Khurana, Andrzej Królak, Ilya Mandel, Reinhard Prix, B. S. Sathyaprakash, Pavlin Savov, Yu Shang, Miquel Trias, John Veitch, Yan Wang, Linqing Wen, John T. Whelan (the Challenge 1B participants)

Date: 12 Jun 2008

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.

abs pdf

Jun 19, 2008

0806.2110 (/preprints)
2008-06-19, 09:31 [edit]


[0803.4097] Detecting gravitational wave emission from the known accreting neutron stars

Authors: Anna Watts (MPA/Amsterdam), Badri Krishnan (AEI/MPG), Lars Bildsten (KITP/UCSB), Bernard Schutz (AEI/MPG)

Date: 28 Mar 2008

Abstract: Detection of gravitational waves from accreting neutron stars (NSs) in our galaxy, due to ellipticity or internal oscillation, would be a breakthrough in our understanding of compact objects and explain the absence of NSs rotating near the break-up limit. Direct detection, however, poses a formidable challenge. Using the current data available on the properties of the accreting NSs in Low Mass X-Ray Binaries (LMXBs), we quantify the detectability for the known accreting NSs, considering various emission scenarios and taking into account the negative impact of parameter uncertainty on the data analysis process. Only a few of the persistently bright NSs accreting at rates near the Eddington limit are detectable by Advanced LIGO if they are emitting gravitational waves at a rate matching the torque from accretion. A larger fraction of the known population is detectable if the spin and orbital parameters are known in advance, especially with the narrow-band Advanced LIGO. We identify the most promising targets, and list specific actions that would lead to significant improvements in detection probability. These include astronomical observations (especially for unknown orbital periods), improvements in data analysis algorithms and capabilities, and further detector development.

abs pdf

Jun 19, 2008

0803.4097 (/preprints)
2008-06-19, 09:29 [edit]


[0806.2419] Observation time to first detection of double neutron star mergers by gravitational wave observatories

Authors: D.M. Coward

Date: 15 Jun 2008

Abstract: We constrain the uncertainty in waiting times for detecting the first double-neutron-star (DNS) mergers by gravitational wave observatories. By accounting for the Poisson fluctuations in the rate density of DNS mergers and galaxy space density inhomogeneity in the local Universe, we define a detection ‘zone’ as a region in a parameter space constrained by the double neutron star merger rate and two LIGO operations parameters: an observation horizon distance and science run duration. Assuming a mean rate of about 80 DNS mergers per Milky Way galaxy Myrˆ{-1}, we find a 1/20 chance of observing a merger by Enhanced LIGO in only 1 yr of observation. The minimum waiting time and temporal zone width for an Advanced LIGO sensitivity are much shorter and imply that there is a 95% probability of detecting a DNS merger in less than 60 days and a 1/20 chance of a first detection in about 1 day. At the 5% probability threshold for a first detection, we find that the effect of galaxy clusters on detection is smoothed out and may only influence detection rates after 5-10 years observation time.

abs pdf

Jun 19, 2008

0806.2419 (/preprints)
2008-06-19, 09:28 [edit]


[0806.1531] Probes and Tests of Strong-Field Gravity with Observations in the Electromagnetic Spectrum

Authors: Dimitrios Psaltis (Arizona)

Date: 9 Jun 2008

Abstract: Neutron stars and black holes are the astrophysical systems with the strongest gravitational fields in the universe. In this article, I review the prospect of probing with observations of such compact objects some of the most intriguing General Relativistic predictions in the strong-field regime: the absence of stable circular orbits near a compact object and the presence of event horizons around black-hole singularities. I discuss the need for a theoretical framework within which future experiments will provide detailed, quantitative tests of gravity theories. Finally, I summarize the constraints imposed by current observations of neutron stars on potential deviations from General Relativity.

abs pdf

Jun 19, 2008

0806.1531 (/preprints)
2008-06-19, 09:28 [edit]


[0805.0806] Modelling a Particle Detector in Field Theory

Authors: Fabio Costa, Federico Piazza

Date: 7 May 2008

Abstract: The Hamiltonian of traditionally adopted ("Unruh-DeWitt") detector models features off diagonal elements between the vacuum and the one particle states of the field to be detected. We argue that in realistic detector models the configuration "detector in its ground state + vacuum of the field" should be an eigenstate of the Hamiltonian, because it generally corresponds to a stable bound state of the underlying fundamental theory (e.g. the ground state-hydrogen atom in a suitable QED with electrons and protons). As a concrete example, we study a local relativistic field theory where a stable particle can capture a light quantum and form a quasi-stable state. As expected, to such a stable particle correspond eigenstates of the full theory, as is shown explicitly by using a dressed particle formalism at first order in perturbation theory. We derive a model of detector (at rest) where the stable particle and the quasi-stable configurations correspond to the two internal levels, "ground" and "excited", of the detector. Our analysis suggests that realistic detectors have no direct access to the local field degrees of freedom. As opposed to the Unruh-DeWitt detector, our model seems to show no response when forced along an accelerated trajectory.

abs pdf

Jun 19, 2008

0805.0806 (/preprints)
2008-06-19, 09:27 [edit]


[0805.3337] Two timescale analysis of extreme mass ratio inspirals in Kerr. I. Orbital Motion

Authors: Tanja Hinderer, Eanna E. Flanagan

Date: 21 May 2008

Abstract: Inspirals of stellar mass compact objects into massive black holes are an important source for future gravitational wave detectors such as Advanced LIGO and LISA. Detection of these sources and extracting information from the signal relies on accurate theoretical models of the binary dynamics. We cast the equations describing binary inspiral in the extreme mass ratio limit in terms of action angle variables, and derive properties of general solutions using a two-timescale expansion. This provides a rigorous derivation of the prescription for computing the leading order orbital motion. As shown by Mino, this leading order or adiabatic motion requires only knowledge of the orbit-averaged, dissipative piece of the self force. The two timescale method also gives a framework for calculating the post-adiabatic corrections. For circular and for equatorial orbits, the leading order corrections are suppressed by one power of the mass ratio, and give rise to phase errors of order unity over a complete inspiral through the relativistic regime. These post-1-adiabatic corrections are generated by the fluctuating piece of the dissipative, first order self force, by the conservative piece of the first order self force, and by the orbit-averaged, dissipative piece of the second order self force. We also sketch a two-timescale expansion of the Einstein equation, and deduce an analytic formula for the leading order, adiabatic gravitational waveforms generated by an inspiral.

abs pdf

Jun 19, 2008

0805.3337 (/preprints)
2008-06-19, 09:27 [edit]


[0806.2794] Astrophysical Sources of Stochastic Gravitational-Wave Background

Authors: T. Regimbau, V. Mandic

Date: 17 Jun 2008

Abstract: We review the spectral properties of stochastic backgrounds of astrophysical origin and discuss how they may differ from the primordial contribution by their statistical properties. We show that stochastic searches with the next generation of terrestrial interferometers could put interesting constrains on the physical properties of astrophysical populations, such as the ellipticity and magnetic field of magnetars, or the coalescence rate of compact binaries.

abs pdf

Jun 19, 2008

0806.2794 (/preprints)
2008-06-19, 09:26 [edit]


[0806.3052] Nonrotating black hole in a post-Newtonian tidal environment

Authors: Stephanne Taylor, Eric Poisson

Date: 18 Jun 2008

Abstract: We examine the motion and tidal dynamics of a nonrotating black hole placed within a post-Newtonian external spacetime. The tidal perturbation created by the external environment is treated as a small perturbation. At a large distance from the black hole, the gravitational field of the external distribution of matter is assumed to be sufficiently weak to be adequately described by the (first) post-Newtonian approximation to general relativity. There, the black hole is treated as a monopole contribution to the total gravitational field. There exists an overlap in the domains of validity of each description, and the black-hole and post-Newtonian metrics are matched in the overlap. The matching procedure produces the equations of motion for the black hole and the gravito-electric and gravito-magnetic tidal fields acting on the black hole. We first calculate the equations of motion and tidal fields by making no assumptions regarding the nature of the post-Newtonian environment; this could contain a continuous distribution of matter or any number of condensed bodies. We next specialize our discussion to a situation in which the black hole is a member of a post-Newtonian two-body system. As an application of our results, we examine the geometry of the deformed event horizon and calculate the tidal heating of the black hole, the rate at which it acquires mass as a result of its tidal interaction with the companion body.

abs pdf

Jun 19, 2008

0806.3052 (/preprints)
2008-06-19, 09:25 [edit]


[0806.2999] Imprints of cosmic strings on the cosmological gravitational wave background

Authors: Kostas Kleidis, Demetros B Papadopoulos, Enric Verdaguer, Loukas Vlahos

Date: 18 Jun 2008

Abstract: The equation which governs the temporal evolution of a gravitational wave (GW) in curved space-time can be treated as the Schrodinger equation for a particle moving in the presence of an effective potential. When GWs propagate in an expanding Universe with constant effective potential, there is a critical value (k_c) of the comoving wave-number which discriminates the metric perturbations into oscillating (k > k_c) and non-oscillating (k < k_c) modes. As a consequence, if the non-oscillatory modes are outside the horizon they do not freeze out. The effective potential is reduced to a non-vanishing constant in a cosmological model which is driven by a two-component fluid, consisting of radiation (dominant) and cosmic strings (sub-dominant). It is known that the cosmological evolution gradually results in the scaling of a cosmic-string network and, therefore, after some time (\Dl \ta) the Universe becomes radiation-dominated. The evolution of the non-oscillatory GW modes during \Dl \ta (while they were outside the horizon), results in the distortion of the GW power spectrum from what it is anticipated in a pure radiation-model, at present-time frequencies in the range 10ˆ{-16} Hz < f < 10ˆ5 Hz.

abs pdf

Jun 19, 2008

0806.2999 (/preprints)
2008-06-19, 09:25 [edit]


[0806.1738] The high-energy collision of two black holes

Authors: U. Sperhake, V. Cardoso, F. Pretorius, E. Berti, J. A. Gonzalez

Date: 10 Jun 2008

Abstract: We study the head-on collision of two highly boosted equal mass, nonrotating black holes. We determine the waveforms, radiated energies, and mode excitation in the center of mass frame for a variety of boosts. For the first time we are able to compare analytic calculations, black hole perturbation theory, and strong field, nonlinear numerical calculations for this problem. Extrapolation of our results, which include velocities of up to 0.94c, indicate that in the ultra-relativistic regime about (14\pm 3)% of the energy is converted into gravitational waves. This gives rise to a luminosity of order 10ˆ-2 cˆ5/G, the largest known so far in a black hole merger.

abs pdf

Jun 12, 2008

0806.1738 (/preprints)
2008-06-12, 08:57 [edit]


[0806.1731] Experimental Tests of General Relativity

Authors: Slava G. Turyshev

Date: 10 Jun 2008

Abstract: Einstein's general theory of relativity is the standard theory of gravity, especially where the needs of astronomy, astrophysics, cosmology and fundamental physics are concerned. As such, this theory is used for many practical purposes involving spacecraft navigation, geodesy, and time transfer. Here I review the foundations of general relativity, discuss recent progress in the tests of relativistic gravity in the solar system, and present motivations for the new generation of high-accuracy gravitational experiments. I discuss the advances in our understanding of fundamental physics that are anticipated in the near future and evaluate the discovery potential of the recently proposed gravitational experiments.

abs pdf

Jun 11, 2008

0806.1731 (/preprints)
2008-06-11, 08:25 [edit]


[0801.4387] Magnetized Neutron Star Mergers and Gravitational Wave Signals

Authors: Matthew Anderson, Eric W. Hirschmann, Luis Lehner, Steven L. Liebling, Patrick M. Motl, David Neilsen, Carlos Palenzuela, Joel E. Tohline

Date: 28 Jan 2008

Abstract: We investigate the influence of magnetic fields upon the dynamics of and resulting gravitational waves from a binary neutron star merger in full general relativity coupled to ideal magnetohydrodynamics (MHD). We consider two merger scenarios, one where the stars begin with initially aligned poloidal magnetic fields and one with no magnetic field. Both mergers result in a strongly differentially rotating object. In comparison to the non-magnetized scenario, the aligned magnetic fields delay the final merger of the two stars. During and after merger we observe phenomena driven by the magnetic field, including Kelvin-Helmholtz instabilities in shear layers, winding of the field lines, and transition from poloidal to toroidal fields. These effects not only produce electromagnetic radiation, but also can have a strong influence on the gravitational waves. Thus, there are promising prospects for studying such systems with both types of waves.

abs pdf

Jun 11, 2008

0801.4387 (/preprints)
2008-06-11, 08:25 [edit]


[0806.1591] Resolving Super Massive Black Holes with LISA

Authors: Stanislav Babak, Mark Hannam, Sascha Husa, Bernard Schutz

Date: 10 Jun 2008

Abstract: We study the angular resolution of the gravitational wave detector LISA and show that numerical relativity can drastically improve the accuracy of position location for coalescing Super Massive Black Hole (SMBH) binaries. For systems with total redshifted mass above $10ˆ7 M_{\odot}$, LISA will mainly see the merger and ring-down of the gravitational wave (GW) signal, which can now be computed numerically using the full Einstein equations. Using numerical waveforms that also include about ten GW cycles of inspiral, we improve inspiral-only position estimates by an order of magnitude. We show that LISA localizes half of all such systems at $z=1$ to better than 3 arcminutes and the best 20% to within one arcminute. This will give excellent prospects for identifying the host galaxy.

abs pdf

Jun 11, 2008

0806.1591 (/preprints)
2008-06-11, 08:21 [edit]


[0806.1037] Comparisons of eccentric binary black hole simulations with post-Newtonian models

Authors: Ian Hinder, Frank Herrmann, Pablo Laguna, Deirdre Shoemaker

Date: 5 Jun 2008

Abstract: We present the first comparison between numerical relativity (NR) simulations of an eccentric binary black hole system with corresponding post-Newtonian (PN) results. We evolve an equal-mass, non-spinning configuration with an initial eccentricity e = 0.1 for 21 gravitational wave cycles before merger, and find agreement in the gravitational wave phase with an adiabatic eccentric PN model with 2 PN radiation reaction within 0.1 radians for 8 cycles. The NR and PN phase difference grows to 0.8 radians by 5 cycles before merger. We find that these results can be obtained by expanding the eccentric PN expressions in terms of the frequency-related variable x = (omega M)ˆ{2/3} with M the total mass of the binary. When using instead the mean motion n = 2 pi/P, where P is the orbital period, the comparison leads to significant disagreements with NR. We also introduce a new method for matching NR and PN waveforms, based on extrapolating parameters determined from least squares fitting as t -> -infinity.

abs pdf

Jun 09, 2008

0806.1037 (/preprints)
2008-06-09, 17:45 [edit]


[0806.0665] Indeterminacy of Quantum Geometry

Authors: Craig J. Hogan

Date: 4 Jun 2008

Abstract: An effective theory of quantum spacetime geometry based on wave optics is used to describe fundamental limits on propagation and measurement of information in holographic spacetimes. Wavefunctions describing spacetime event positions are modeled as complex disturbances of quasi-monochromatic Planck wavelength radiation. The transverse position on a two-dimensional geometrical wavefront, represented by the optical complex degree of coherence, is related to a prepared state represented by a transverse distribution of intensity on an initial wavefront. The transverse position distributions describing two macroscopically null-separated events are shown to approximate Fourier transforms of each other. This relationship is interpreted as an uncertainty inherent to spacetime: the product of standard deviations of transverse position of two events is equal to the product of their separation and the Planck length. For macroscopically separated events the uncertainty is much larger than the Planck length, and is predicted to be observable in devices, such as Michelson interferometers, that measure transverse displacements at macroscopic separations. This geometrical indeterminacy causes irreducible holographic noise in relative position with a distinctive shear spatial character, and an absolutely normalized frequency spectrum with no parameters once the fundamental wavelength is fixed from the theory of gravitational thermodynamics. This noise spectrum is shown to approximately account for currently unexplained noise in the GEO600 interferometric gravitational-wave detector between about 300 and 1400Hz, and is predicted to dominate midband noise in the next generation of LIGO detectors.

abs pdf

Jun 05, 2008

0806.0665 (/preprints)
2008-06-05, 08:30 [edit]


[0805.4582] Supermassive binary black hole mergers

Authors: L&#xe1;szl&#xf3; &#xc1;. Gergely, Peter L. Biermann

Date: 29 May 2008

Abstract: When galaxies collide, dynamical friction drives their central supermassive black holes close enought to each other such that gravitational radiation becomes the leading dissipative effect. Gravitational radiation takes away energy, momentum and angular momentum from the compact binary, such that the black holes finally merge. In the process, the spin of the dominant black hole is reoriented. On observational level, the spins are directly related to the jets, which can be seen at radio frequencies. Images of the X-shaped radio galaxies together with evidence on the age of the jets illustrate that the jets are reoriented, a phenomenon known as spin-flip. Based on the galaxy luminosity statistics we argue here that the typical galaxy encounters involve mass ratios between 1:3 to 1:30 for the central black holes. Based on the spin-orbit precession and gravitational radiation we also argue that for this typical mass ratio in the inspiral phase of the merger the initially dominant orbital angular momentum will become smaller than the spin, which will be reoriented. We prove here that the spin-flip phenomenon typically occurs already in the inspiral phase, and as such is describable by post-Newtonian techniques.

abs pdf

Jun 04, 2008

0805.4582 (/preprints)
2008-06-04, 09:59 [edit]


[0805.4758] Beating the spin-down limit on gravitational wave emission from the Crab pulsar

Authors: The LIGO Scientific Collaboration: B. Abbott, et al

Date: 30 May 2008

Abstract: We present direct upper limits on gravitational wave emission from the Crab pulsar using data from the first nine months of the fifth science run of the Laser Interferometer Gravitational-wave Observatory (LIGO). These limits are based on two searches. In the first we assume that the gravitational wave emission follows the observed radio timing, giving an upper limit on gravitational wave emission that beats indirect limits inferred from the spin-down and braking index of the pulsar and the energetics of the nebula. In the second we allow for a small mismatch between the gravitational and radio signal frequencies and interpret our results in the context of two possible gravitational wave emission mechanisms.

abs pdf

Jun 04, 2008

0805.4758 (/preprints)
2008-06-04, 09:58 [edit]


[0806.0293] Detectability of Gravitational Waves from Phase Transitions

Authors: Tina Kahniashvili, Arthur Kosowsky, Grigol Gogoberidze, Yurii Maravin

Date: 2 Jun 2008

Abstract: Gravitational waves potentially represent our only direct probe of the universe when it was less than one second old. In particular, first-order phase transitions in the early universe can generate a stochastic background of gravitational waves which may be detectable today. We briefly summarize the physical sources of gravitational radiation from phase transitions and present semi-analytic expressions for the resulting gravitational wave spectra from three distinct realistic sources: bubble collisions, turbulent plasma motions, and inverse-cascade helical magnetohydrodynamic turbulence. Using phenomenological parameters to describe phase transition properties, we determine the region of parameter space for which gravitational waves can be detected by the proposed Laser Interferometer Space Antenna. The electroweak phase transition is detectable for a wide range of parameters.

abs pdf

Jun 04, 2008

0806.0293 (/preprints)
2008-06-04, 09:58 [edit]


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