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From the 14th through to the 17th of December, last year (2005), the Tenth Gravitational Wave Data Analysis Workshop took place in Brownsville, Texas. This annual event has become the established venue for presenting and discussing new results and techniques in this crucial subfield of gravitational wave astronomy.

A major attraction of the event is that scientists working with all possible instruments (be it ground based or space based, of the resonant kind or interferometric) gather to discuss their projects and report on the status of their observations. The Center for Gravitational Wave Astronomy at the University of Texas at Brownsville, USA, (a research centre funded by the NASA University Research Centers program) was the proud host of the gathering this time. As in previous years, GWDAW-10 was well attended with about 90 participants from over nine countries worldwide.

The meeting has taken place at a time that is setting the tone for the future of the field. As it was reported in the detector status session, one of the major observational facilities in the world, the LIGO (Laser Interferometer Gravitational Wave Observatory) interferometers have achieved design sensitivity. The strain sensitivity of 10^-21 RMS integrated over a 100 Hz bandwidth was not long ago considered an almost impossible task. The significance of this issue does not reside only in the engineering merit of the achievement but in the possibility of establishing meaningful observational constraints on the strength of gravitational radiation incident on Earth, and consequently on the nature of astrophysical sources and events.

Besides its traditional focus on data analysis issues, GWDAW has also become a forum of interaction between relativistic astrophysics and gravitational wave data analysis. As the new generation of high sensitivity detectors head towards the possibility of a first detection, the importance of this interaction cannot be overstated. The number of astrophysics talks was large enough that they had to be divided into two separate sessions, dedicated to the different frequency bands corresponding to ground and space based detectors respectively. Among other non-traditional presentations were the results on efforts to use pulsar timing for monitoring the ultra-low frequency band and talks on the recent breakthroughs in Black Hole merger calculations.

Another feature of the conference was the growth in the number of talks dedicated to the data analysis challenges facing the LISA mission. In fact, the conference was followed by a half-day workshop dedicated entirely to LISA. This heightened level of activity comes at a time when budget cuts at NASA have put a cloud on the future of the mission. In a tribute to the LISA project leadership, it was heartening to see the scientific community rising to the challenge by increasing the pace of work towards building a solid case for LISA rather than backing down.

The relevance of GWDAW to this effort will be strengthened in Dec 2006 with the planned presentation of results from the ongoing mock LISA data challenge that was opened in July 2006 at the 6th LISA symposium.

The mainstay of the conference continued to be the exciting flow of results from ever improving ground based detectors, both the large interferometric and the cryogenic resonant mass ones. At the start of the conference, LIGO had just embarked on its most ambitious data taking run yet with all three of its detectors operating at design sensitivity. Virgo was moving steadily on the commissioning road and GEO600 and TAMA300 were already operating with remarkable stability. Indeed the overall feeling was that the field might finally be crossing the threshold where we will see the very first astrophysical signals.

This excitement was reflected in the large number of papers concerned with joint analysis of data from a network of interferometers. We learnt also about the plans and status for the continued monitoring of the Kilo-Hertz band by the worldwide network of resonant mass detectors. Not surprisingly, besides the many excellent oral and poster presentations, we are sure that people had a lot to talk about during the breaks at this conference! The facilities where the conference was held, the newly completed Education and Business Complex with a state of the art conference room, played a not insignificant role in promoting this interaction.

Another highly successful event associated with GWDAW-10 was the public lecture given by Prof. Bruce Allen to an audience of mostly high school students. Following the lecture, one local high school (Porter High School) actually topped the many national and international teams in this category that are contributing computer cycles to the Einstein@Home project. Einstein@Home is the ambitious project to search for continuous signals using distributed computing power from volunteers through the World Wide Web. The Einstein@Home screensaver image formed the background of the GWDAW-10 conference poster.

In conclusion we would like to thank the many sources of help we received in organizing this conference. We had a dedicated and serious scientific organizing committee, which set high standards for the various sessions. The UTB administrators gave the organization of GWDAW-10 the highest priority and many roadblocks were smoothed as a result! The local organizing committee worked extremely hard and exceptionally well as a team to host a very successful conference. Finally, we thank all the participants for coming to Brownsville, Texas. If the conference was a success it was thanks to their enthusiasm and warm-hearted support.

The following institutions and companies have sponsored the 10th GWDAW: The USA National Science Foundation, the USA National Aeronautics and Space Administration, LIGO, Physics Today, Vernier, Continental Airlines, Cynmar Corporation, Imaginova.

We report on the status of the Virgo detector, under commissioning. We will focus on the last year's activity. The two commissioning runs performed during 2005 allowed us to reach a sensitivity of h ∼ 6 × 10⁻²². The data obtained during the runs were used to test a few data analysis algorithms, namely coalescing binaries and burst searches. The main improvements made on the detector during this year will be described, as well as the plans and activities foreseen in the coming years.

The GEO 600 gravitational wave detector located near Hannover in Germany is part of an international network of gravitational wave observatories. As more and more of these detectors approach their final configuration, the focus is shifted from commissioning to detector characterization. At the moment, GEO 600, the first detector using advanced technologies such as dual recycling, is preparing for a long data-taking period starting at the beginning of summer 2006. In this paper, we give an overview of detector commissioning and the detector characterization work of GEO 600 for the period between March 2005 and February 2006.

In November 2005, the LIGO interferometer network began data taking for its latest data run (S5). All three interferometers are working at design sensitivities with duty cycles expected to reach 80%. The Hanford 4 km detector regularly achieves a neutron star inspiral range of 12 Mpc. The S5 data run will record one year of coincident science data at unprecedented sensitivity ending in mid 2007.

Multidimensional classification analysis is performed on burst triggers generated by event trigger generating algorithms such as the kleineWelle algorithm in LIGO's fifth science run data. The analysis is meant to extract more information from the structures present in the data in higher dimensions and also aid in vetoing non-gravitational wave signals by grouping triggers with similar characteristics. The parameters used in the analysis include time–frequency information as well as shape attributes of the triggers. The method is demonstrated on data from one of the LIGO environmental channels.

Coherent techniques for searches of gravitational-wave bursts effectively combine data from several detectors, taking into account differences in their responses. The efforts are now focused on the maximum likelihood principle as the most natural way to combine data, which can also be used without prior knowledge of the signal. Recent studies however have shown that straightforward application of the maximum likelihood method to gravitational waves with unknown waveforms can lead to inconsistencies and unphysical results such as discontinuity in the residual functional, or divergence of the variance of the estimated waveforms for some locations in the sky. So far the solutions to these problems have been based on rather different physical arguments. Following these investigations, we now find that all these inconsistencies stem from the rank deficiency of the underlying network response matrix. In this paper we show that the detection of gravitational-wave bursts with a network of interferometers belongs to the category of ill-posed problems. We then apply the method of Tikhonov regularization to resolve the rank deficiency and introduce a minimal regulator which yields a well-conditioned solution to the inverse problem for all locations on the sky.

We present the result of a search for coincidences among the triggers found in the analysis of three 2-day-long stretches of data from the EXPLORER bar detector. The data were searched for nearly periodic gravitational waves from rapidly rotating neutron stars in our Galaxy. In this paper we propose a numerical procedure to search for coincidences and we present a theoretical formula for the expected number of coincidences. Our numerical analysis revealed no double and consequently no triple coincidences among the triggers from the three data sets. The results are in agreement with the expected number of coincidences that we estimate by our theoretical formula.

Despite their intrinsic advantages due to co-location, the two LIGO Hanford interferometers have not been used in the search for the stochastic gravitational wave background due to their coupling to a shared environment, which may be comparable to or exceed any gravitational signal. In this paper, using S4 data, we demonstrate a technique to relate the H1–H2 coherence to coupling with physical environmental channels. We show that the correspondence is tight enough to correctly identify regions of high and low coupling and the nature of the coupling in the data set. A simple thresholding provides frequency vetoes, which we can use to derive a significantly cleaner coherence spectrum. The output of this preliminary investigation suggests that H1–H2 may soon be ready to contribute to the stochastic search.

We describe the effort of inspiral searches with LIGO data from the third and fourth science runs, which took place in 2003/2004 and 2005, respectively. Although the analysis pipeline is the same for all searches, there are significant differences between the three major ongoing searches: for primordial black hole binaries, binary neutron stars and binary black holes. The horizon distance for all searches significantly increased with respect to earlier LIGO science searches.

If a coalescing binary system results in a black hole we expect it to be a perturbed Kerr black hole and to radiate gravitational waves in the form of ringdowns. A search for such signals in data from the fourth LIGO science run is currently being developed. In this paper we outline the theory on which this search is based and use it to predict the range for this data set.

We analysed the TAMA300 data in time domain using the ALF filter. Two kinds of vetoes were implemented in order to reduce fake events. One is the method based on the time scale of burst gravitational wave (GW) signals. The other is the veto using one of the auxiliary monitor channels of the interferometer operation. The analysed data were DataTaking9 data of the TAMA300 taken from 28th November 2003 to 10th January 2004. Finally, we did not find any evidence of the detection of gravitational wave events, and obtained an upper limit rate of 0.55 (events/day) with a confidence level 90% at the level of 10⁻¹⁷h_rss GW amplitude for a 1304 Hz sine-Gaussian signal.

Gravitational wave (GW) detector data taken around the time of occurrence of astronomical triggers, such as gamma ray bursts (GRBs), can be combined to search for a GW signature associated with a sample of multiple triggers. This approach accumulates a signal-to-noise ratio from weak signals that may not be individually detectable with high confidence. We study the issue of the sensitivity of such an approach in the context of a concrete model for the distribution of signal strengths from GRBs and a specific implementation that is currently being applied to LIGO data from science runs S2, S3 and S4. It is demonstrated that the population signature can be detected with a much larger probability than signals from individual GRBs. This can be used to draw useful astrophysical inferences when interesting triggers occur too far away to allow high confidence, direct detections of GW signals from individual triggers.

A number of different methods have been proposed to identify unanticipated burst sources of gravitational waves in data arising from LIGO and other gravitational wave detectors. When confronted with such a wide variety of methods one is moved to ask if they are all necessary, i.e. given detector data that is assumed to have no gravitational wave signals present, do they generally identify the same events with the same efficiency, or do they each 'see' different things in the detector? Here we consider three different methods, which have been used within the LIGO Scientific Collaboration as part of its search for unanticipated gravitational wave bursts. We find that each of these three different methods developed for identifying candidate gravitational wave burst sources are, in fact, attuned to significantly different features in detector data, suggesting that they may provide largely independent lists of candidate gravitational wave burst events.

Time-series data from multiple gravitational wave (GW) detectors can be linearly combined to form a null-stream, in which all GW information will be cancelled out. This null-stream can be used to distinguish between actual GW triggers and spurious noise transients in a search for GW bursts using a network of detectors. The biggest source of error in the null-stream analysis comes from the fact that the detector data are not perfectly calibrated. In this paper, we present an implementation of the null-stream veto in the simplest network of two co-located detectors. The detectors are assumed to have calibration uncertainties and correlated noise components. We estimate the effect of calibration uncertainties in the null-stream veto analysis and propose a new formulation to overcome this. This new formulation is demonstrated by doing software injections in Gaussian noise.

At the University of Florida, we are developing an experimental Laser Interferometer Space Antenna (LISA) simulator. The foundation for the simulator is a pair of cavity-stabilized lasers that provide realistic, LISA-like phase noise. The light travel time over the five million kilometres between spacecraft is recreated in the lab by use of an electronic phase delay technique. Initial tests will focus on phasemeter implementation, time delay interferometry (TDI) and arm-locking. In this paper we present the frequency stabilization results, results from an electronic arm-locking experiment, software phasemeter performance and results from a first optical experiment to test the TDI concept. In the future, the benchtop simulator will be extended to test several other aspects of LISA interferometry such as clock noise and Doppler shifts of the signals. The eventual long-term use of the LISA simulator will be to provide realistic data streams, including all the noise components, into which model gravitational wave signals can be injected. This will make the simulator a useful testbed for data analysis research groups.

The Laser Interferometer Space Antenna will be able to detect the inspiral and merger of super massive black hole binaries (SMBHBs) anywhere in the universe. Standard matched filtering techniques can be used to detect and characterize these systems. Markov Chain Monte Carlo (MCMC) methods are ideally suited to this and other LISA data analysis problems as they are able to efficiently handle models with large dimensions. Here we compare the posterior parameter distributions derived by an MCMC algorithm with the distributions predicted by the Fisher information matrix. We find excellent agreement for the extrinsic parameters, while the Fisher matrix slightly overestimates errors in the intrinsic parameters.

I review the status of research, conducted by a variety of independent groups, aimed at the eventual observation of extreme mass ratio inspirals (EMRIs) with gravitational wave detectors. EMRIs are binary systems in which one of the objects is much more massive than the other, and which are in a state of dynamical evolution that is dominated by the effects of gravitational radiation. Although these systems are highly relativistic, with the smaller object moving relative to the larger at nearly light-speed, they are well described by perturbative calculations which exploit the mass ratio as a natural small parameter. I review the use of such approximations to generate waveforms needed by data analysis algorithms for observation. I also briefly review the status of developing the data analysis algorithms themselves. Although this paper is almost entirely a review of previous work, it includes (as an appendix) a new analytical estimate for the time over which the influence of radiation on the binary itself is observationally negligible.

The observability of gravitational waves from supermassive and intermediate-mass black holes by the forthcoming Laser Interferometer Space Antenna (LISA), and the physics we can learn from the observations, will depend on two basic factors: the event rates for massive black hole mergers occurring in the LISA best sensitivity window and our theoretical knowledge of the gravitational waveforms. We first provide a concise review of the literature on LISA event rates for massive black hole mergers, as predicted by different formation scenarios. Then we discuss what (in our view) are the most urgent issues to address in terms of waveform modelling. For massive black hole binary inspiral, these include spin precession, eccentricity, the effect of high-order post-Newtonian terms in the amplitude and phase and an accurate prediction of the transition from inspiral to plunge. For black hole ringdown, numerical relativity will ultimately be required to determine the relative quasinormal mode excitation and to reduce the dimensionality of the template space in matched filtering.

Physically motivated gravitational wave signals are needed in order to study the behaviour and efficacy of different data analysis methods seeking their detection. GravEn, short for Gravitational-wave Engine, is a MATLAB® software package that simulates the sampled response of a gravitational wave detector to incident gravitational waves. Incident waves can be specified in a data file or chosen from among a group of pre-programmed types commonly used for establishing the detection efficiency of analysis methods used for LIGO data analysis. Every aspect of a desired signal can be specified, such as start time of the simulation (including inter-sample start times), wave amplitude, source orientation to line of sight, location of the source in the sky, etc. Supported interferometric detectors include LIGO, GEO, Virgo and TAMA.

The Laser Interferometer Space Antenna (LISA) guarantees the detection of gravitational waves by monitoring a handful of known nearby galactic binary systems, the so-called verification binaries. We consider the most updated information on the source parameters for the 30 more promising verification binaries. We investigate which of them are indeed guaranteed sources for LISA and estimate the accuracy of the additional information that can be extracted during the mission. Our analysis considers the two independent Michelson outputs that can be synthesized from the LISA constellation, and we model the LISA transfer function using the rigid adiabatic approximation. We carry out extensive Monte Carlo simulations to explore the dependency of our results on unknown or poorly constrained source parameters. We find that four sources—RXJ0806.3+1527, V407 Vul, ES Cet and AM CVn—are clearly detectable in one year of observation; RXJ0806.3+1527 should actually be observable in less than a week. For these sources LISA will also provide information on yet unknown parameters with an error between ≈1% and ≈10%. Four additional binary systems—HP Lib, 4U 1820-30, WZ Sge and KPD 1930+2752—might also be marginally detectable.

The laser interferometer space antenna (LISA) will produce a data stream containing a vast number of overlapping sources: from strong signals generated by the coalescence of massive black hole binary systems to much weaker radiation from sub-stellar mass compact binaries and extreme-mass ratio inspirals. It has been argued that the observation of weak signals could be hampered by the presence of loud ones and that they first need to be removed to allow such observations. Here we consider a different approach in which sources are studied simultaneously within the framework of Bayesian inference. We investigate the simplified case in which the LISA data stream contains radiation from a massive black hole binary system superimposed over a (weaker) quasi-monochromatic waveform generated by a white dwarf binary. We derive the posterior probability density function of the model parameters using an automatic reversible jump Markov chain Monte Carlo algorithm (RJMCMC) restricted to a single search model. We show that the information about the sources and noise are retrieved at the expected level of accuracy without the need to remove the stronger signal. Our analysis suggests that this approach is worth pursuing further and could be considered for actual analysis of the LISA data.

The analysis of data taken during the C7 VIRGO commissioning run showed strong deviations from Gaussian noise. In this work, we explore a family of distributions, derived from the hypothesis that heavy tails are an effect of a particular kind of nonstationarity, heterocedasticity (i.e. nonuniform variance), that appear to fit VIRGO noise better than a model based on the assumption of Gaussian noise. To estimate the parameters of the noise process (including the heterogeneous variance) we derived an expectation-maximization algorithm. We show the consequences of non-Gaussianity on the fitting of autoregressive filters and on the derivation of test statistics for matched filter operation. Finally, we apply the new noise model to the fitting of an autoregressive filter for whitening of data.

We introduce a new method for modelling the gravitational wave flux function of a test-mass particle inspiralling into an intermediate mass Schwarzschild black hole which is based on Chebyshev polynomials of the first kind. It is believed that these intermediate mass ratio inspiral events (IMRI) are expected to be seen in both the ground- and space-based detectors. Starting with the post-Newtonian expansion from black hole perturbation theory, we introduce a new Chebyshev approximation to the flux function, which due to a process called Chebyshev economization gives a model with faster convergence than either post-Newtonian- or Padé-based methods. As well as having excellent convergence properties, these polynomials are also very closely related to the elusive minimax polynomial. We find that at the last stable orbit, the error between the Chebyshev approximation and a numerically calculated flux is reduced, <1.8%, at all orders of approximation. We also find that the templates constructed using the Chebyshev approximation give better fitting factors, in general >0.99, and smaller errors, <1/10%, in the estimation of the chirp mass when compared to a fiducial exact waveform, constructed using the numerical flux and the exact expression for the orbital energy function, again at all orders of approximation. We also show that in the intermediate test-mass case, the new Chebyshev template is superior to both PN and Padé approximant templates, especially at lower orders of approximation.