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3rd Annual Report on GWA-WG2 Joint operation of antennas and network data analysis L. Baggio1, M.A. Bizouard2, L. Bosi3, L. Brocco4, G. Cella5, E. Cuoco20, S. D`Antonio4, S. Frasca4, G. Frossati 6, G. Guidi7, I.S. Heng8, A. Krolak9, F. Marion1, B. Mours1, A. Sintes10, A. Ortolan11, A. Pai12, M.A. Papa12, A. Parameswaran12, I. Pinto13, G.A. Prodi14, T. Regimbau15, E. Robinson18, J. Romano16, F. Salemi17, B.S. Sathyaprakash16, C. van den Broeck16, A. Vecchio18, A.Vicerè7, M. Visco19, A.deWaard6, G.Woan8 1 CNRS/IN2P3/LAPP, Annecy, France and EGO, Cascina, Italy 2 LAL/IN2P3, Orsay, France 3 INFN and Università di Perugia, Italy 4 INFN Sezione di Roma1, Roma, Italy 5 INFN Sezione di Pisa, Italy 6 University of Leiden, The Netherlands 7 INFN and Universita di Firenze/Urbino, Firenze, Italy 8 University of Glasgow, Great Britain 9 Polish Academy of Sciences, Warsaw, Poland 10 Universitat de les Illes Balears, Palma de Mallorca, Spain 11 INFN Laboratori Nazionali di Legnaro, Italy 12 Max-Planck-Institut für Gravitationsphysik Albert-Einstein-Institut, Golm, Germany 13 INFN and Università del Sannio, Benevento, Italy 14 INFN and University of Trento, Italy 15 CNRS/Observatoire de la Côte d'Azur, Nice, France 16 Cardiff University, Great Britain 17 INFN and University of Ferrara, Italy 18 University of Birmingham, Great Britain 19 CNR/IFSI and INFN Roma, Roma, Italy 20 EGO, Cascina, Italy Coordinators: G.M. Guidi (INFN, Urbino University), I.S. Heng (Glasgow University) 1. Introduction GWA-WG2 aims to promote discussion between European gravitational wave data analysts and study network data analysis methodologies for gravitational wave searches, especially those involving European detectors. In March 2006, a new Implementation Plan was drawn up. The coordinators of WG2 drew up an Implementation Plan based on a strategy that would provide support existing collaborations encourage the investigation and development of analyses not currently performed help build a scientific case for future generation detectors In the next few paragraphs, an overview of these topics, their importance to the search for gravitational waves and WG2 involvement in each area is provided. Many members of WG2 are already involved in the joint analysis of data between different detectors. The main joint analyses that involve WG2 members are LSC-Virgo, Virgo-bars and IGEC2. LSC-Virgo is a trans-Atlantic involving data analysts from the LIGO Scientific Collaboration (LSC), of which GEO is a member, and Virgo. Virgo-bars is a collaboration between the European resonant-bar detectors, AURIGA, EXPLORER and NAUTILUS, and Virgo. IGEC2 is a collaboration that brings together the resonant-bar detectors group from across the world (ALLEGRO, AURIGA, EXPLORER and NAUTILUS). In parallel with the support of existing joint analyses, WG2 also encourages the development of new data analysis methods. Specifically, the use of coherent network analyses and joint analyses using astronomical observations in electromagnetic spectrum are targeted as emerging analyses that have the potential to make a big impact in the gravitational wave community in the near future. Coherent network analyses for inspiral and burst searches take into account the directional sensitivity of all gravitational wave detectors in the network. This is vital for the LIGO-Virgo-GEO600 network since GEO600 and Virgo are not aligned to each other and neither detector is aligned to the LIGO detectors. Another type of analysis targeted in the Implementation Plan are searches for gravitational waves associated with astronomical observations in the electromagnetic spectrum. Studies of gamma-ray bursts have shown that sources of these bursts include merging neutron stars and supernova core collapses. Therefore, gamma-ray burst observations can be used to trigger a search for gravitational waves around the time of the burst. Similar searches can be performed using Xray and radio frequency observations. Glitches in the period of radio frequency pulses from a rapidly rotating neutron star (pulsar) could be associated with a rearrangement of the crust in the neutron star. This would cause the neutron star to oscillate and emit gravitational waves. Attention has been also devoted to the current research for the developement of pipelines for the search of GW from spinning compact objects and a workshop dedicated to this subject. The status of these searches has been reported during the 11th Gravitational Wave Data Analysis Workshop (GWDAW11), Potsdam, December 2006 (htpp://gwdaw11.aei.mpg.de). Several subjects that will be described below have been illustrated by members or collaborators of WG2 in talks and posters. There have been five phone-conferences and three meetings organised by WG2. N5 – Table 1.1: Workshops/Meetings. Date Title/subject of meeting /workshop Location Number of attendees 20/02/06 Phono-conference 9 13/04/06 Phono-conference 6 20/04/06 Phono-conference 6 27/04/06 Working group 2 meeting 20/07/06 Phono-conference 24/09/06 Working group 2 workshop on spinning compact objects 27/09/06 Phono-conference Florence, Italy 19 14 Cardiff, UK 14 16 Website address http://www.ego-gw.it/ILIASGW/N5-WP2_meetings.html http://www.ego-gw.it/ILIASGW/N5-WP2_meetings.html http://www.ego-gw.it/ILIASGW/N5-WP2_meetings.html http://www.ego-gw.it/ILIASGW/N5-WP2_meetings.html 25/10/06 Working group 2 meeting London, UK 14 http://www.ego-gw.it/ILIASGW/N5-WP2_meetings.html 2. Status of planned tasks 2.1. Study of the detector's compatibility and of the possible implementation of a coherent data analysis for transient and chirp signals As the GW detectors approach their project sensitivities, a deep study of coherent analysis methods, which make use of the informations from the different detectors have become of great importance. Based on the theoretical studies that have been developed over the last decade, the effective implementation of these pipelines and the comparison with other possible methods has been the subject of the ILIAS WG2 effort. Two main implementations of coherent pipelines for transient unmodelled signals have been examined. One can directly combine of the data streams from different detectors into a single stream for analysis by a particular method or combine the outputs of the same method applied separately to the different detector data streams. The method for the first scenario was first outlined in J. Sylvestre Phys.Rev. D68 (2003) 102005. It was applied to one day of simulated data streams from LIGO and VIRGO detectors, produced by the LIGO-VIRGO working group. The first results (see N.Leroy and GM Guidi, Coherent Analysis for Burts Detection, presentation at WG2 Florence Meeting, http://www.ego-gw.it/ILIAS-GW/N5-WP3-WP2-Florence.html) seem to indicate that, in the actual implementation, the coherent method has a comparable detection efficiency and source-sky reconstruction with two-fold coincidence detection methods already used to analyse by the LSC-VIRGO working groups. Adding GEO data to the LSC-VIRGO network will increase the sky resolution and the possibility to discriminate between real GW signals and other spurious signals. Time-series data from multiple detectors can also be linearly combined to form a null-stream, which contains no trace of an incoming GW (see P.Ajith et al, Null-stream veto for for the network analysis of GW bursts, presentation at WG2 Florence Meeting), thus allowing one to discriminate between real GWs and spurious noise triggers. With the null-stream method, the source position can be recontructed by probing the minimum of the null-stream power over the sky regions previously inferred through the analysis of the time-delays between coincident triggers. The null-stream method has also been applied to construct bursts veto using known instrumental couplings and applied to GEO S5 data (see P.Ajith et al: presentation at GWDAW11). This application permits to distinguish instrumental glitches from gravitational wave (GW) bursts. The strategy has been to make use of the transfer function from a detector subs-ystem to the main detector output in order to have a phenomenological understanding of their coupling and individuate a possible non-stationarity caused by an instrumental glitche. Some preliminary investigations into the use of the coherent algorithm developed by a S. Chatterji, P. Sutton, et al., called X-pipeline, to determine the source location of a burst gravitational wave has also been performed by L. Porter and I.S. Heng. These injections used the simulated data and signals generated for LSC-Virgo project 1b and studied the ability of the LSC-Virgo network to reconstruct the location from which a burst gravitational wave originated from. Core-collapse waveforms from the Dimmelmeier-Font-Mueller (DFM) catalogue, gaussian pulses and sine-gaussian waveforms were injected into the simulated data. The investigations showed that, for gravitational wave bursts with signal-to-noise ratios greater than 10, the source location was determined for at least 50% of the DFM catalogue waveforms. The source location could also be obtained for about 85% of the 1-millisecond gaussian pulses. However, the source location could only be obtained for only about 25% of the 4-millisecond gaussian pulses. This is because the signal-to-noise ratios for these signals were smaller. Work has been performed to develop an algorithm to determine the sky location of signals using the sky map outputs from X-pipeline. This work is ongoing. The implementation of a coherent pipeline for chirp signals is also of great importance because gravitational wave signals produced during the final inspiral stage of compact bodies like NS or BH are a very promising source of detectable gravitational waves and have been well modelled by theorists. Here too coherent analysis can increase the detection efficiency and source sky-location, and thus the comparison of the results obtained through its application with the ones obtained with a three- or two-fold coincident analysis is of the main importance. The first results presented by S Birindelli et al. (see Coherent and Coincidence Network analysis for coalescing binaries, WG2 Florence Meeting; Testing coherent code for coalescing binaries network analysis, WG2 London Meeting, http://www.ego-gw.it/ILIASGW/N5-WP2-London.html. See Poster presented at GWDAW11), based on the method analysed by Pai et al, Phys.Rev. D64 (2001) 042004, indicate a gain up to the 25% in the observable range of the detectors can be obtained in average with respect to a two- or three fold analysis in the case of the LSC-VIRGO network. Since main problem for the application of this coherent method is the computing resources required, a mixed-hierarchical approach was used for the source sky-position reconstruction. This approach determines the two- or three-fold time coincidence in the LSC-VIRGO network as a starting point. Through the successive maximisation and fitting of the coherent network Likelyhood Function the sky position’s coordinates determination was succesfully improved. This work points out that a full coherent pipeline characterisation seems in fact very important. A parallel work about parameter estimation is currently being undertaken using Monte Carlo Markov Chains methods (see N. Christensen, Bayesian Parameter Estimation for Inspiral Signals- Coherent Multi-Interferometer Study, WP2 Meeting, Florence). While the single interferometer code is already working, the multi-interferometer “coherent” code, which makes use of the coherent addition of signals, is under development: it searches - in addition to the coalescing binaries masses, the coalescing time, the phase and the distance - for the sky position parameters: polarization , angle of inclination of orbital plane , sky position RA and dec. The method is being applied also to burst search, with sine-gaussian templates hoping to catch the main characteristics of the unmodeled transient signals. The code can currently manage signals from neutron star or black hole inspirals, which are modeled to 3.5 post-Newtonian (PN) order in phase and to 2.5 PN order in amplitude (see C. Röver, GWDAW11) 2.2. Develop infrastructure stochastic GW background search with GEO-VIRGO data under LSC-VIRGO collaboration The LSC-Virgo collaboration brings together gravitational wave scientists from both sides of the Atlantic. At the moment, this collaboration is performing joint analyses for burst and inspiral gravitational wave signals on small data sets. These analyses are mainly methodological and aim to improve the understanding of the data analysts from the LSC and Virgo on each others analysis methods as performed within their respective collaborations. This work has now been expanded to include a joint search for stochastic gravitational waves. Stochastic gravitational waves can be thought of as a gravitational wave equivalent of the cosmic microwave background. Just like the cosmic microwave background, a stochastic microwave background would also arise from the processes that happened after the Big Bag. A stochastic gravitational wave background would also arise from a superposition of weak gravitational waves emitted by distant neutron star mergers and supernovae. Ideally, the best network of detectors for stochastic gravitational waves would be two aligned, co-located gravitational wave detectors. However, two widely-spaced detectors are still sensitive to a stochastic gravitational wave background provided the wavelength of the gravitational wave is larger than twice the distance between the two detectors. Figure 2.1 plots the stochastic sensitivity integrand for a white (flat as a function of frequency) stochastic gravitational wave background for different LSC-Virgo detector pairs. The sensitivity integrand folds in the design sensitivity of each detector as well as their respective orientations to calculate the sensitivity of each detector to stochastic gravitational waves. The GEO600-Virgo pair of detectors has similar sensitivities with the other pairs between about 250 Hz and 400 Hz. In fact, the GEO600-Virgo pair is about twice as sensitive as the other pairs in some narrow frequency bands within this range. Figure 2.1 Stochastic sensitivity integrand as a function of frequency. This means the analysis of data acquired by GEO600 and Virgo for a stochastic gravitational wave background will, at the minimum, be an independent check. It also provides us with the possibility of performing a directed, band-limited stochastic background search using these two detectors. In preparation for such an analysis, a team consisting of LSC and Virgo data analysts, which included WG2 members G. Cella, E. Cuoco, T. Regimbau and E. Robinson, have been testing their analysis code on common data sets to verify that they give consistent results (see G.Cella, talk at the WG2-WG3 Florence workshop, and G.Cella et al., talk held at GWDAW11). The first step was to verify that all three existing analysis codes (called matapps, LALapps and NAP) are able to process data stored in LIGO and Virgo formats. In addition to this, code to produce simulated stochastic background for injection into simulated noise streams has been written. This code generates a simulated common data set used to test the three analysis codes. The code has been succesfully tested and the analysis of the LSC-Virgo Project1b simulated data completed. The detection and simulation procedures have been extended to two different non-flat spectra, astrophysically motivated, originated by the cumulative effects of magnetars and double neutron star populations. WG2 supported the partecipation of G. Cella to Stochastic GW background search with GEOVIRGO data under LSC-VIRGO collaboration, Nizza November 20-21 2006. 2.3. Support to the on-going joint data analysis searches Virgo-bars and IGECII A large amount of work has been done in the Virgo-bars and IGEC2 collaborations, which has eventually produced new upper limits. Both the analyses have been conducted taking into account the Recommendation Report on the planning of joint observations, and proposals for the related data exchange and analysis elaborated by the WG2 (see the Appendix to the Report on WG2 Joint operation of antennas and network data analysis for the year 2005). Virgo-bars working group has examined one day of coincident data acquired by the acoustic bar detectors Auriga, Explorer and Nautilus and by Virgo interferometer in September 2005. (see L. Baggio, Status and roadmap of bar and interferometer joint burst analyses, WG2 Meeting, Florence; F Salemi et al, VIRGO-bars joint data analysis, ILIAS Annual Meeting, London; L Baggio et al, First joint search of GW waves by the Auriga - Explorer - Nautilus Virgo Collaboration, Virgo note VIR-NOT-FIR-1390-328, documet attached to this report; L Baggio et al, talk held at GWDAW11 ). The goal of the study is to assess interpreted confidence intervals on the flux of gravitational waves (damped sinusoids with central frequency in the bandwith [850-950]Hz and damping time from 1 to 30 ms) coming from the galactic center. The interpretation comes from software injections which are used to compute the efficiency of detection for a source population. The main methodology is a coincidence search on trigger lists provided by each detector: the coincident counts, divided by the efficiency and by the observation time, become observed rates (or upper limits on rates). However, a new approach is used in setting the magnitude thresholds for each detector. For each template and each target amplitude, the thresholds are optimized in order to get the best compromise between efficiency and false alarm rate. Thus the efficiency acts not just passively at the end of the analysis to calibrate the results, but also actively during an optimization phase. When the null hypothesis test is fulfilled, then the upper bound of the confidence interval is used to set upper limit. In order not to bias results by feedbacks on methods from looking at results, a blind analysis procedure is adopted by adding a “secret” time offset to the detector times of the exchanged data. The zero-lag analysis is eventually performed and the confidence intervals set according to the confidence belt already used by IGEC1. A test at 99% confidence level was performed: no excess of coincidences was found and the null hypothesis is still holding. Thus the upper bound of the chosen confidence belt is our quoted upper limit with a coverage of 95%. The work is now being reviewed by the Virgo-bars working group in view of a possible submission to a scientific journal. As the 2-fold coincidence searches on which we have based the work have a high level of accidental background, a claim of detection by a single observed double coincidence is not possible: the study could be possibly extended by performing 3-fold coincidence searches with the goal to be able to issue a claim at 99.5% confidence on a single observed triple. During most of 2005, the IGEC2 has been the only network of gravitational wave detectors in operation. Its first target in data analysis has been to perform a long term joint search for burst gravitational waves. Up to now the search has been completed on 6 months of data, from May 20th to Nov. 15th 2005 (see GA Prodi, talk held at ILIAS Annual meeting in London, and G. Vedovato, talk held at GWDAW11). The data analysis is based on a time coincidence search between candidate events exchanged by the two groups operating the three INFN detectors AURIGA, EXPLORER and NAUTILUS. The group operating the fourth operating detector, ALLEGRO (LA, USA), was not able to exchange the required data according to the scheduled plan of activities, so it has been agreed to use its data only for a posteriori studies. The confidence of the results is objective thanks to the blind procedures adopted for the search on the INFN detectors data, while any a posteriori investigations would contribute conditional evidence with an unavoidable degree of subjectivity. The most relevant differences with the first IGEC search on 1997-2000 data are: - in the IGEC2 analysis most of the observation time is covered by a three-fold coincidence search. Only the observation time in three fold coincidence among the INFN bar detectors has been considered here; - the current network data analysis has been tuned to allow the identification of a single gw candidate with very high statistical confidence, allowing a false alarm rate of 1.0 per century. In addition, the background of accidental coincidences has been investigated with higher accuracy, by resampling the experiment up to 20 millions times with different pipelines and choices of the time shifts; - the target signals has been extended also to templates showing some color in the Fourier transform within the AURIGA bandwidth, in addition to the usual bursts of ms duration; - to take into account easily the statistical correlations among the multiple trials here implemented, the trials has been merged together by an OR logic. In particular the overall accidental background of the entire search is estimated from the union of the accidental coincidences found in each trial. The IGEC2 network analysis is not optimized for setting upper limits, but instead to identify with a satisfactory confidence a single gravitational wave candidate. In fact the null hypothesis (i.e. no signals present in the data) would be rejected if at least one triple coincidence were found with a significance of 99.64% corresponding to a false claim rate of 1.005/ century over the 130.8 days of net three-fold observation time. Figure 2.2 Histogram of the number of accidental coincidences found per each resampling of the composite search (e.g. the union of three partially correlated trials). The histogram is in agreement with a Poisson distribution with mean 0.00364 (chi2 = 0.06 with 1 degree of freedom), which is taken as the reference distribution for the coincidences assuming that only accidental coincidences are present. The false detection probability is 0.00363, corresponding to 1.01 false alarms per century. No triple coincidences has been found and therefore IGEC2 did not identify gravitational wave candidates. The interpretation of the IGEC2 result in terms of upper limits would require a measurement of the IGEC2 detection efficiency to some specific source models. This has not been performed during the six months observations. However, thanks to the VIRGO-bars activity, the detection efficiency has been measured on one sample day; therefore, this analysis can directly benefit from the detailed information exchange and discussions within WG2. IGECII collaboration is now starting the analysis of 2006 data. 2.4. Support the activities of multilateral project between European and nonEuropean detectors LSC-Virgo Working Group is a multilateral project between LSC and Virgo collaborations aimed at performing a deep comparison between the analysis pipelines developed separately in the two collaborations and assess the capability of performing a joint search. Several people participating at the LSC-Virgo work are members of WG2, and this makes it easy for exchanges between the groups. LIGO-Virgo simulated data sets has been in fact used for the test of pipelines and new algorithms already presented in the previous sessions, i.e. the coherent pipelines for transient and chirps signals, the MCMC coherent parameters’ estimation. During the last months, after having concluded the joint analysis of one day long simulated data set (see the preprint of the two articles which has been submitted to a scientific journal: gr-qc/0701027 and gr-qc/0701026 at http://babbage.sissa.it), the efforts have been first devoted to the characterisation of the search pipelines over non-coincident calibrated real data from the GEO detector, the LIGO Hanford detector, and the Virgo detector. The scope of this first exercise with real data has been to repeat the study previously performed on 3 hours of simulated LIGO and Virgo data. The goal was to come to an understanding of how both collaborations currently handle the details of real detector data (such as lock segment, data quality, and veto information), to develop a common language for describing the information, and to begin to develop the infrastructure to exchange them. The inclusion of a number of burst and inspiral hardware injections has also permitted a simple cross-validation study of search algorithms’ performance on real data. This has provided confidence in the ability of the various search algorithms to handle non-stationarities of real detector data and enabled comparisons of how they approach this task. The results of these studies have been compared at a meeting of the LSC-Virgo working group on 23 June, 2006 in Orsay, France ( http://virgo.web.lal.in2p3.fr/MEETINGS/LSCVirgo-2006/F2F-LSC-Virgo-June2006.html). Currently a second study is being performed using real coincident data from the GEO, LIGO, and Virgo detectors. The purpose of this study is to develop and test the planned search strategies for the full network of detectors in a way that is as close as possible to a real joint astrophysical analysis. The analysis is carried out over the frequency band of [800, 2000]Hz where all five instruments display sensitivities within a factor of a few, and is adressing the research of transient burst signals in this frequency range. Data quality, event-by-event vetoes studies are performed in order to asses the background rates. An all-sky, all-times Monte Carlo is taking place throught the injections of Sine Gaussian waveforms in a coincident way in the ITFs to permit the tuning of the search pipeline and study the sensitivity of the different network configurations that are possible with five detectors. The exercise will possibly include setting an upper limit. 2.5. Develop new and/or extend joint searches indentified in study over previous 6 months Development of searches for gravitational waves associated with pulsar glitches and gamma-ray bursts A search algorithm for gravitational wave emission from perturbed compact objects using Bayesian inference has been developed by J. Clark and I.S. Heng (see J.Clark, talk held at GWDAW11). Given some disruptive event, such as a pulsar glitch or soft gamma repeater flare, the quasi-normal modes of the object in question (in these cases, a neutron star) are excited. The oscillations are rapidly damped away by gravitational wave emission, leading to a distinct 'ringdown' (i.e., a damped sinusoid) signal in gravitational wave interferometer data. Efforts are focused on using Bayesian model selection to evaluate the relative probabilities of various models describing gravitational wave interferometer data. This is achieved by calculating the "evidence", defined as the likelihood, marginalised over all model parameters and weighted by the joint prior for the parameters, for a variety of given models. The simplest example is to compare the evidence for a ringdown waveform versus the evidence for white noise. Assuming these are the only possibilities for the data, higher evidence for a ringdown than for white noise would indicate a detection. The method is currently being extended to demonstrate the potential of including a wider set of models describing typical glitches in interferometer data to improve robustness. In addition to this, the application of method to searches for gravitational waves from different sources but with similar ringdown waveforms are also being investigated. Specifically, our interest is in the black hole ringdown expected following the formation of a GRB. Here, collaboration with experts in the field, such as A. Corsi, is vital to inform our choice of prior and encompass an appropriate parameter space. Furthermore, there are efforts to perform a search for possible gravitational wave signals associated with gamma-ray bursts in Virgo data acquired during its current commissioning phase, specifically the long GRB 050915a which was detected by the Swift satellite (see A. Corsi, talk presented at ILIAS Annual meeting; A.Corsi, talk held at GWDAW11). The approach here is to search for excess power around the time of the gamma-ray burst using a wavelet-based analysis. This study is used as a prototype to define a methodology of analysis and to evaluate up to which level VIRGO is able to constrain the GW output associated with a typical long GRB, under the assumption that also the redshift lies in a range typical for long GRBs. New approach for the detection of stochastic backgrounds using Bayesian inference methods are currently studies (see E. Robinson, poster at GWDAW11). The study addresses for the moment the problem of detection of isotropic stochastic signals of arbitrary spectral shape by applying it to a simple signal model using synthetic data sets. Spinning Coalescing Binaries Workshop One of the main problems currently being addressed in the search of gravitational waves from the coalescence of compact objects like neutron starts and/or black holes, is the knowledge of the exact temporal evolution of the signals and the implementation of detection pipelines which are able to identify them. While for non-spinning stars the task can be accomplished by standard matched filtering techniques over a bank of templates which reproduce, for the expected range of stellar parameters, the signals, the situation is complicated for spinning objects due to the large number of parameters for which a huge computing power is required. This problem has been addressed at the Spinning Coalescing Binaries Workshop of the WG2 working group held on 14-15 September, 2006 in Cardiff, UK. The workshop has been concentrated on source modelling and data analysis techniquess. The dynamics of spinning compact binaries has been the subject of two presentations (G. Faye, The dynamics of spinning compact binaries at the second-and-a-half post-Newtonian approximation; L.A. Gergely, Spin and quadrupole moment effects in the post-Newtonian dynamics of compact binaries ), which described new results on the computation of the spinorbit terms and its first Post-Newtonian correction and of spin-spin terms, quadrupole moments and magnetic dipolar contributions, together with a possible explanation of the spinflip phenomenon. Detection improvement for earth-based interferometers and LISA coming from the knowledge of these corrections were also examined. Template bank construction for Buonnanno Chen Vallisneri (BCV) phenomenological templates and its use in the search over real data (H. Takahashi, Template banks for spinning black hole binaries; C. Van Den Broek, Searching for spinning binaries with BCV-spin templates using the full metric; G. Jones, Searching for Spinning Binaries BH in LIGO S3 data ), and alternative detection algorithms (D. Brown, Implementation of the Physical Templates Family for Spinning NS/BH Binaries searches; G.M. Guidi, Efficiency and Clustering for NS-BH binaries) has been discussed in the Data Analysis section of the workshop, together with the problem of the determination of coincidence triggers over a network of interferometers (C. Robinson, Coincidence analysis using error ellipsoid; A Sengupta, TrigScan, a clustering algorithm for inspiral search pipelines ). The workshop has permitted an ample exchange of ideas. In addition to this, new possible collaborations between different groups have been discussed. 2.6. Apply stochastic background search to GEO-VIRGO data exchanged under LSC-VIRGO collaboration The analysis of 24 hours of coincident real data from LSC-Virgo detectors has just begun. This data set will be used to study the performance of the stochastic analysis algorithm on real noise coming from the detectors. This work is ongoing. 2.7. Review and report results from existing joint searches, expecially Virgo-bars and IGEC II This task has been partly addressed in section 2.3 together with the description of the Virgobars and IGECII work. The results from existing joint searches have been indeed reported several time in different conferences and/or workshop (WG2-WG3 Florence meeting, ILIAS Annual meeting, GWDAW11), as indicated throughout this documents. 2.8. Preparation of the science case for future detectors. Compact binary inspiral Ground-based detectors will be able to observe the last stages of the inspiral of two compact objects (neutron stars and/or black holes), where the motion is adiabatic in the sense that the period of a single orbit is much smaller than the inspiral timescale. This regime is wellunderstood in the post-Newtonian approximation, where accurate waveforms have been derived. Using the best available waveforms, the performance of EGO was compared with that of Advanced LIGO, and a number of qualitative differences were identified: At distances of a few hundred Mpc, EGO would be able to observe inspiral events with total mass up to 1200 solar masses, or 3 times as high as Advanced LIGO. This mass range comprises not only stellar mass binaries, but also binaries involving intermediate mass black holes of the kind that may form in galactic nuclei and in globular clusters. At these distances, EGO would be able to resolve individual component masses with only a few percent uncertainty for systems with total mass up to ~500 solar masses. By contrast, in Advanced LIGO these errors will be at best in the order of 10%, and then only in a very limited mass interval. In this way, EGO would be able to accurately ``map" the mass distribution of black holes. EGO would be able to establish even minor violations of the Kerr geometry outside a rotating black hole, which could occur if the cosmic censorship conjecture fails to hold, or if one or both components of a binary system are Boson stars (or still more exotic objects). EGO would see inspiral events occurring throughout a significant part of the visible Universe. Very conservative estimates indicate a detection rate of at least three orders of magnitude higher than in Advanced LIGO. In the stellar mass regime, parameter estimation with EGO at a luminosity distance of 15 Gpc would be as good as in Advanced LIGO at a distance of only 1 Gpc. Given a network of detectors at the level of EGO, distances could be determined from the gravitational wave signal. This would allow us to study the evolution of the population of (massive) stars over cosmological timescales by looking at the kind of black holes they produce. If one has multiple detectors one can also determine the sky position of an inspiral event. This may allow the identification of the host galaxy (or of the host galaxy cluster), which will have some definite redshift. With many such observations one would be able to fit the luminosity distance as a function of redshift. The relation between the two depends on several cosmological parameters (such as the Hubble constant), which could be measured in this way. At the largest scales, galaxy clusters tend to be on the surfaces of ``bubbles" surrounding ``voids". A network of EGO detectors would have the requisite distance reach to check whether black hole binaries are similarly distributed, which may be of interest to dark matter studies. Spinning and precessing neutron stars. Spinning neutron stars (NS) with any sort of departure from sphericity are candidate sources of gravitational waves. A simple model in which a spinning NS has an equatorial ellipticity of ≈ 1-b/a, where a and b are the semi-major and semi-minor axes, respectively, emits gravitational waves of amplitude proportional to and at twice the spin frequency. EGO will be able to detect all milli-second neutron stars of ellipticity as small as 10-8 anywhere in the galaxy with a large signal-to-noise ratio. Some of the closer systems will be detectable even if their ellipticity is O(10-10). On a standard NS this is equivalent to a ``mountain'' of size smaller than the tenth of a m. It would be remarkable to survey the entire galaxy for neutron stars with such a small departure from sphericity. Low-mass X-ray binaries in which the accretion torque seems to be balanced by the radiation reaction produced by the emission of gravitational waves are potential sources for advanced detectors. While advanced LIGO will have to tune itself to a narrow-band mode to observe LMXBs, EGO could watch the entire frequency band of 100 Hz to a kHz with in broad-band mode but with the same sensitivity as advanced LIGO. Using signal-recycling techniques EGO will be able to dig deeper for LMXBs. As neutron stars lose rotational kinetic energy through electromagnetic radiation, they lose ellipticity. This can cause a breaking of the crust, leading to the formation of small ``mountains" on the surface. The associated triaxiality will induce a precessing motion, with a precession frequency that is typically much smaller than the rotation frequency. To leading order, the gravitational wave spectrum will then contain the following spectral lines: A main line at twice the rotational frequency; if the star is not precessing then only this line will be present. With precession, there will be a second line at approximately the rotation frequency, as well as a third line appearing as a sidelobe to the first one. If all three lines are visible, in principle one would be able to measure the neutron star's precession angle, its oblateness, and its deviation from axisymmetry due to ``mountains", which would yield information on the structure of the crust. Together with the precession damping timescale one could infer how the crust interacts with the superfluid interior and get a better understanding of the latter's equation of state. In an Advanced LIGO detector equipped with a signal recycling mirror at the output, in a narrow frequency interval one can have a strain sensitivity as low as 10-24 Hz-1/2, tunable between 500 Hz and 1000 Hz. A few months' integration time could then reveal all three spectral lines for sources at a distance up to ~10 kpc, but only if the precession angle is near the physical upper limit. Even considering uncertainties in the damping timescale, the number of such sources will be very low. With third generation detectors the situation would be different. If one can have a tunable narrowband sensitivity of 10-25 Hz-1/2 in the same frequency range as Advanced LIGO, the above spectrum may be visible for sources as far as the center of the galaxy, with reasonable precession angles. A further improvement to 10-26 Hz-1/2 might allow visibility of the three spectral lines for sources in neighboring galaxies. Stochastic Background A set of two or more co-located inteferometers with the same sensitivity as EGO will be able to detect a stochastic background of gravitational waves. For instance, currently we are considering a configuration of an equilateral triangle for EGO. Such a configuration can be used to construct three co-located EGOs. The sensitivity of such a configuration will be sensitive to a background of gravitational waves of density at the level of GW = 2 10-11, a factor of 15 better than advanced LIGO. Figure 2.3 The projected sensitivity of a future generation detector (labelled EGO). Also plotted are the expected signal strengths for a variety of sources. 3. Conclusions GWA-WG2 is an active organisation which has brought together European gravitational wave data analysts and theorists to discuss important issues in the gravitational wave field through the organisation of meetings, workshops and phone-conferences. WG2 has provided some support to existing collaborations for the joint data analysis projects that involve data acquired by European gravitational wave detectors. WG2 has also targeted emerging issues in gravitational wave data analysis and provided travel support to European scientists to build collaborations in these areas. All Tasks listed in the Implementation Plan have been performed. 4. List of publications and conference proceedings L Baggio et al. First joint search of GW waves by the Auriga - Explorer - Nautilus - Virgo Collaboration, Virgo note VIR-NOT-FIR-1390-328 (2006) P. Ajith, M. Hewitson and I. S. Heng Null-stream veto for two collocated detectors: implementation issues Classical and Quantum Gravity 23 19 S741-S749 (2006) F Beauville et al Detailed comparison of LIGO and Virgo Inspiral Pipelines in Preparation for a Joint Search, gr-qc/0701027 (2006) F Beauville et al A comparison of methods for gravitational wave burst searches from LIGO and Virgo gr-qc/0701026 (2006)