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The Ninth Edoardo Amaldi conference on gravitational waves (Amaldi 9) and the 2011 Numerical Relativity – Data Analysis meeting (NRDA 2011) were held on July 10–15, 2011 in Cardiff, UK.

The summer of 2011 marked the beginning of a crucial time for the field of gravitational-wave astronomy. After the successful completion of long-duration data taking, the initial LIGO and Virgo detectors were shut down and the era of first-generation laser interferometric gravitational-wave detectors came to an end. With the analysis of the last set of first-generation data approaching completion, the field now faces the challenge of preparing for the era of second-generation detectors, and, hopefully, the regular detection of gravitational waves.

The first of the advanced detectors should begin operation in 2014, but the intervening years are far from a time of sitting and waiting. This will be a hectic time for experimenters, who have to fight the limits of current technology to make their theoretical noise curves a reality. During Amaldi 9 we were led through the upgrades to advanced detectors, and the challenges that the experimenters face. We also heard about proposals for going yet further with third-generation and space-based detectors.

This is also a crucial time for theoretical work. With the increased sensitivity of advanced detectors, we hope to not only make the first detections of gravitational waves, but to learn about their sources, and interpret what this means for astrophysics. We need more complete source modelling, more sophisticated and efficient search pipelines and parameter estimation tools, as well as a greater understanding of what we can learn about the universe. Amaldi 9 included a number of talks on the status of these efforts, and the open questions that will be the focus in the coming years.

Sunday July 10th was devoted entirely to NRDA 2011. In recent years the NRDA meetings have brought together numerical relativists who model compact-binary sources, and gravitational-wave data analysts, who want to use the numerical results to aid gravitational-wave detection and parameter estimation. This work has coalesced around the Numerical INJection Analysis (NINJA) project, which is now in its second incarnation, and will be used to test and refine data-analysis procedures on black-hole binary waveforms injected into real LIGO–Virgo data. This NRDA meeting focused on preparing the set of numerical waveforms, and paving the way for data analysis projects.

The rest of the week consisted of Amaldi and NRDA-specific sessions, which contained talks on the most pressing issues facing gravitational-wave science. The participants enjoyed a successful meeting that included plenty of time scheduled for informal discussions, and popular poster sessions. Most evenings featured public lectures by prominent Cardiff academics following wine and cheese receptions. The Wednesday afternoon social excursions saw participants exploring the fairy-tale Castle Coch, the imposing Caerphilly Castle, and downtown Cardiff itself. The conference banquet on Thursday evening was hosted in the National Gallery, which included viewing of works by Renoir, Monet, and Cezanne in the Gallery's Impressionist wing.

The organization of these meetings was overseen by the Gravitational Wave International Committee (GWIC), the NRDA Scientific Organizing Committee, and the Amaldi Local Organizing Committee. The organisers wish to extend special thanks for the generous support of Cardiff University, in particular to Samantha Emmott, Cardiff & Co., and the students and staff of the Cardiff University School of Physics and Astronomy, who bore the brunt of the effort at ground level. We thank IUPAP for financial support. We also wish to thank Adam Day and Ben Sheard of IOP for their assistance in the preparation of this Special Issue. Finally, to all the participants, we say thank you for making these meetings a success.

These proceedings represent a small fraction of the science presented, discussed, and imagined at Amaldi 9 / NRDA 2011. Additional proceedings are published in the accompanying edition of Classical and Quantum Gravity. It is our hope that these articles will be a resource for the field for years to come.

The Editors

This is a co-publication with Classical and Quantum Gravity which also features papers from the Edoardo Amaldi Conference on Gravitational Waves (Amaldi 9) and Numerical Relativity and Data Analysis 2011 (NRDA2011).

All papers published in this volume of Journal of Physics: Conference Series have been peer reviewed through processes administered by the proceedings Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing.

This paper describes a new implementation of monolithic horizontal sensor, developed at the University of Salerno, based on the Folded Pendulum architecture, configurable both as seismometer and as accelerometer. The large low-frequency band (10^-6 ÷ 10Hz), the high sensitivity ( in the band 0.1 ÷ 10 Hz) and the high quality factor in air (Q > 1500) are largely better than all the previous Folded Pendulum implementations. Moreover its monolithic implementation of the whole mechanics, coupled with a full tunability of its resonance frequency (70 mHz ÷ 1.2 Hz) obtained with a specially designed calibration procedure and with an integrated laser optical readout, guarantees both compactness, robustness and immunity to environmental noises. This makes this sensor suitable for a large number of scientific applications, also in high vacuum and cryogeny. Applications of this sensor are already started in the field of geophysics, including the study of seismic and newtonian noise for characterization of suitable sites for future underground interferometric detectors of gravitational waves.

Preliminary investigations of a novel method to measure the laser power accurately using the radiation pressure are reported here. We aim to measure the laser power within one percent error to then obtain an accurate quantum efficiency (QE) of a photodiode. Since the typical error of QE is still a few percent due to the uncertainty of measured laser power, an accurate measurement of the laser power contributes a precise estimation of the QE. Our experimental setup is a suspended Michelson interferometer, where one of the pendulums is small, consisting of a 20-mg mirror and 10-um fiber. The motion of this small mirror is very sensitive to changes in radiation pressure. Due to this, the number of photons in the incident (intensity modulated) laser beam can be counted accurately by measuring displacement of the mirror. We set up the apparatus, and have found a suitable frequency band for the accurate measurement. Displacement caused by the radiation pressure was observed using the feedback signal.

Here we present a status report of the Schenberg antenna. In the past three years it has gone to a radical upgrading operation, in which we have been installing a 1K pot dilution refrigerator, cabling and amplifiers for nine transducer circuits, designing a new suspension and vibration isolation system for the microstrip antennas, and developing a full set of new transducers, microstrip antennas, and oscillators. We are also studying an innovative approach, which could transform Schenberg into a broadband gravitational wave detector.

Fluctuations of the local gravitational field as a result of seismic and atmospheric displacements will limit the sensitivity of ground based gravitational wave detectors at frequencies below 10 Hz. We discuss the implications of Newtonian noise for future third generation gravitational wave detectors. The relevant seismic wave fields are predominately of human origin and are dependent on local infrastructure and population density. Seismic studies presented here show that considerable seismic noise reduction is possible compared to current detector locations. A realistic seismic amplitude spectral density of a suitably quiet site should not exceed 0.5 nm/(Hz/f)² above 1 Hz. Newtonian noise models have been developed both analytically and by finite element analysis. These show that the contribution to Newtonian noise from surface waves due to distance sources significantly reduces with depth. Seismic displacements from local sources and body waves then become the dominant contributors to the Newtonian fluctuations.

Higher order Laguerre-Gauss (LG) beams have been proposed for use in future generation gravitational wave detectors for their potential to reduce the effects of the thermal noise of the test masses. However, it has been reported that due to the degeneracy of higher order modes using these beams will be extremely challenging. Our aim was to quantify these degeneracy effects. We present a new analytical approximation to compute the coupling between different LG modes, verified with simulation results of realistic arm cavities. This method is applied to Advanced LIGO mirror maps and used to derive requirements for mirrors for the use of the LG₃₃ beam.

Noise due to surface charge on gravitational wave detector test masses could potentially become a limiting low frequency noise source in future detectors. It is therefore very important that the behavior of charging noise is experimentally verified so that accurate predictions of charging noise can be made. A torsion balance that is sensitive to small forces has been constructed at the University of Glasgow in order to measure charging noise. In this article the torsion balance apparatus being developed will be described in detail. There will also be a description of the calibration of the instrument and preliminary measurements that have been taken. These measurements show that it is possible to distinguish between the surface charge and polarisation charge on a silica sample. From this measurement it was possible to estimate the surface charge on the silica disc. The remainder of the article will discuss the improvements in sensitivity that have been made which will allow initial measurements of charging noise to begin.

We present results of finite element analysis simulations which could lead to more accurate calibration of interferometric gravitational wave detectors. Calibration and actuation forces applied to the interferometer test masses cause elastic deformation, inducing errors in the calibration. These errors increase with actuation frequency, and can be greater than 50% at frequencies above a few kilohertz. We show that they can be reduced significantly by optimizing the position at which the forces are applied. The Advanced LIGO [1] photon calibrators use a two-beam configuration to reduce the impact of local deformations of the test mass surface. The position of the beams over the test mass can be chosen such both the local and the bulk induced elastic deformation are minimized. Our finite element modeling indicates that with two beams positioned within ±1 mm of their optimal locations, calibration errors due to test mass elastic deformation can be kept below 1% for frequencies up to 3.5 kHz. We thus show that precise control of the location of calibration forces could considerably improve calibration accuracy, especially at high frequencies.

To support the research effort for the third generation of gravitational wave interferometers, the Laboratoire des Matériaux Avancés (LMA) at Lyon, France has developed a new cryogenic facility to characterize optics at low temperature. The new cryostat is installed in a clean room and allows samples to be cooled down to 10 Kelvin in around 12 hours.

Currently, two independent experiments have been installed in the cryostat: the measure of the optical absorption of silicon and the measurement of the coating mechanical loss. After a short presentation of the cryogenic and optical setup, preliminary results from the optical absorption experiment will be presented.

A resonant-mass spherical gravitational wave detector is been built at the Physics Institute of Sao Paulo University which will be part of a detection network with a similar one that is under construction in The Netherlands. The goal of such detector is to reach a sensitivity of 10^-21 in h at frequencies close to 3200 Hz within a bandwidth of 200 Hz. Its expected sensitivity will be close to the quantum limit and for such sensitivity to be reached several parameters must be optimized. One of them is the calibration of the mechanical impedance matchers, which are mechanical oscillators assembled on the sphere with the purpose of coupling the oscillations of the sphere surface to the electromechanical transducers that are used as motion sensors. This work has the goal to optimize such mechanical coupling, consequently the detector sensitivity, using a microwave parametric transducer for which an important variable is the electrical quality factor. The study involves the simulation of the oscillation of the mechanical parts of the detector with its all 17 frequency modes while checking whether these modes behave as predicted by the theory. We found that the simulation works adequately and that most of the frequency modes investigated are in good agreement with the theory about vibration quadrupole modes in spheres. Other modes did not fit so well in the theory and we comment on this in the text.

Gravitational wave detectors of the advanced generation are expected to be limited in sensitivity by thermal noise of the optics. The reduction of this noise is therefore of high importance for future detectors which aim to surpass the sensitivity of the advanced generation. A proposed method for reducing the impact of this noise is to use higher-order Laguerre-Gauss (LG) modes for the readout beam, as opposed to the currently used fundamental mode. We present here a synopsis of the research program undertaken by the University of Birmingham into the suitability of LG mode technology for future gravitational wave detectors. This will cover our previous and current work on this topic, from initial simulations and table-top LG mode experiments up to implementation in a prototype scale suspended cavity and high-power laser bench.

The RareNoise project aims at studying how ground-based gravitational wave detector are affected by the thermodynamic non-equilibrium states which are present in their experimental apparatus. We present the RareNoise experimental work which focuses on the study of the 'thermal noise' of low loss oscillators subject to steady-state thermal gradients. We also present the first results of the experimental campaign on steady-state non-equilibrium oscillators around room temperature.

The main purpose of the AEI 10 m Prototype is to reach and eventually surpass the Standard Quantum Limit at frequencies ranging from 20 Hz to 1 kHz with a 10 m arm-length Michelson interferometer named the sub-SQL interferometer. The frequency control system uses a 20 m optical path length triangular suspended cavity named the reference cavity, with the goal of suppressing frequency noise of the input laser to a level of ~ 10^-4 Hz/ at 20 Hz rolling off to below 6 × 10^-6 Hz/ above 1 kHz. It is expected that tight angular control of the reference cavity's mirrors is necessary to reach this stringent requirement.

In the course of the high-frequency upgrade of GEO 600, its optical configuration was extended by a squeezed-light laser [1], Recently, a non-classically enhanced measurement sensitivity of GEO 600 was reported [2], In this paper, a characterization of the squeezed-light laser is presented. Thereupon, the status of the integration into GEO 600 is reviewed, focussing on the sources of optical loss limiting the shot noise reduction by squeezing at the moment. Finally, the possibilities for a future loss reduction are discussed.

Diffraction gratings have been proposed as replacements for transmissive optical elements in the next generation of gravitational wave detectors. However, they couple additional alignment noise to phase noise, and current models are based on unrealistic plane-wave expansion theories. There is a need for a description of grating-related phase noise which is compatible with standard interferometer tools. In this paper we investigate the grating-related phase shift by presenting a fully analytical Gaussian model for the phase accumulation of a displaced beam when diffracted from a grating. We consider a first-order modal decomposition as the method employed by simulation tools for off-axis beams. We show that the phase distribution of a typical displaced beam and a decomposed beam is accurate to within 3.9 × 10⁻⁸ radians. However, we find that the grating-related phase noise is not present, and this is further validated experimentally by the absence of a phase shift in beams with different modes. The phase noise must therefore be implemented manually into existing interferometer simulation tools.

In order to observe quantum radiation pressure noise and reduce it by measuring the ponderomotively squeezed light on a table-top experiment, we are developing a laser interferometer with Fabry-Perot cavities with very small suspended mirrors. As a preliminary setup, we have constructed a Fabry-Perot cavity of finesse 1300 with a suspended mirror of 20 mg. The cavity was locked stably at low laser power for which the classical radiation pressure caused little effect on the dynamics of the small mirror. For the stable operation of this cavity with higher laser power, a technique to control the motion of the small mirror, especially its yaw motion, is necessary. We describe that the motion can be stabilized through the radiation pressure of light inside the cavity, by controlling the motion of the front mirror of a Fabry-Perot cavity properly.

Thermal effects in the test masses of the gravitational waves interferometric detectors may result in a strong limitation to their operation and sensitivity. Already in initial LIGO and Virgo, these effects have been observed and required the installation of dedicated compensation systems. Based on CO₂ laser projectors, the thermal compensators heat the peripheral of the input test masses to reduce the lensing effect. In advanced detectors, the power circulating in the interferometer will increase, thus making thermal effects more relevant. In this paper, the concept of the compensation system for Advanced Virgo is described.

We performed a simultaneous observational run with prototypes of Torsion-bar Antenna (TOBA) and searched for a stochastic gravitational waves (GW) background. TOBA is a new type of GW detector which measures differential rotation of two test-mass bars caused by tidal force from GWs. It fundamentally has a good sensitivity at lower frequencies, such as 0.1–1.0 Hz. The prototype has a 20-cm test mass bar which is levitated by the pinning effect of a superconductor. The data was taken from 1:00 am to 10:00 am on March 11th 2011, at Tokyo and Kyoto in Japan. As a result, we did not detect a stochastic GW background with false alarm rate of 5 %, and set an upper limit on a stochastic GW background. Our 95 % confidence upper limit is Ω_gwh²₀ < 1.2 × 10¹⁹ at 0.06 – 0.9 Hz, where Ω_gw is the GW energy density per logarithmic frequency interval in units of the critical density and h_o is the Hubble constant per 100 km/sec/Mpc. We had established the simultaneous observation and the analysis pipeline with two TOBAs, and set an upper limit at a wider frequency band.

Three mode interactions could induce parametric instability in advanced gravitational wave detectors with high optical power circulating in the cavities. One of the conditions for parametric instability to occur is when the cavity frequency difference between fundamental mode and the high order mode matches the test mass acoustic mode frequency. The optical mode spacing is a function of cavity g-factor (radius of curvature). At the Gingin High Optical Power Facility, we have an 80 meter optical cavity particularly designed for studying high optical power effects in advanced gravitational wave detectors such as parametric instabilities. Here we present the recent results of thermal tuning the cavity g-factor by heating the test mass surface with a CO₂ laser to investigate the 3-mode interactions. Observation of test mass thermal noise peaks above 160 kHz enhanced by 3 mode interaction is presented.

Extreme-Mass-Ratio Inspirals (EMRIs) are one of the most promising sources of gravitational waves (GWs) for space-based detectors like the Laser Interferometer Space Antenna (LISA). EMRIs consist of a compact stellar object orbiting around a massive black hole (MBH). Since EMRI signals are expected to be long lasting (containing of the order of hundred thousand cycles), they will encode the structure of the MBH gravitational potential in a precise way such that features depending on the theory of gravity governing the system may be distinguished. That is, EMRI signals may be used to test gravity and the geometry of black holes. However, the development of a practical methodology for computing the generation and propagation of GWs from EMRIs in theories of gravity different than General Relativity (GR) has only recently begun. In this paper, we present a parameter estimation study of EMRIs in a particular modification of GR, which is described by a four-dimensional Chern-Simons (CS) gravitational term. We focus on determining to what extent a space-based GW observatory like LISA could distinguish between GR and CS gravity through the detection of GWs from EMRIs.

Strongly magnetised neutron stars are prime candidates for multi-messenger astronomy given their proximity and regular, energetic flaring events. We present non-linear, ideal MHD simulations of strongly magnetised neutron stars in general relativity that are models for post-flare internal dynamics of these stars. In particular, magnetic field instabilities are used to trigger global reconfigurations of the magnetic field, which in turn excites both fluid and Alfvén modes throughout the star. These simulations are discussed in the context of gravitational wave emissions and detectability for ground-based gravitational wave detectors.

We describe a new kludge scheme to model the dynamics of generic extreme-mass-ratio inspirals (EMRIs; stellar compact objects spiraling into a spinning supermassive black hole) and their gravitational-wave emission. The Chimera scheme is a hybrid method that combines tools from different approximation techniques in General Relativity: (i) A multipolar, post-Minkowskian expansion for the far-zone metric perturbation (the gravitational waveforms) and for the local prescription of the self-force; (ii) a post-Newtonian expansion for the computation of the multipole moments in terms of the trajectories; and (iii) a BH perturbation theory expansion when treating the trajectories as a sequence of self-adjusting Kerr geodesies. The EMRI trajectory is made out of Kerr geodesic fragments joined via the method of osculating elements as dictated by the multipolar post-Minkowskian radiation-reaction prescription. We implemented the proper coordinate mapping between Boyer-Lindquist coordinates, associated with the Kerr geodesies, and harmonic coordinates, associated with the multipolar post-Minkowskian decomposition. The Chimera scheme is thus a combination of approximations that can be used to model generic inspirals of systems with extreme to intermediate mass ratios, and hence, it can provide valuable information for future space-based gravitational-wave observatories, like LISA, and even for advanced ground detectors. The local character in time of our multipolar post-Minkowskian self-force makes this scheme amenable to study the possible appearance of transient resonances in generic inspirals.

Sources of gravitational waves are often expected to be observable through several messengers, such as gamma-rays, X-rays, optical, radio, and/or neutrino emission. The simultaneous observation of electromagnetic or neutrino emission with a gravitational-wave signal could be a crucial aspect for the first direct detection of gravitational waves. Furthermore, combining gravitational waves with electromagnetic and neutrino observations will enable the extraction of scientific insight that was hidden from us before. We discuss the method that enables the joint search with the LIGO-Virgo-IceCube-ANTARES global network, as well as its methodology, science reach, and outlook for the next generation of gravitational-wave detectors.

Localising the sources of gravitational waves (GWs) in the sky is crucial to observing the electromagnetic counterparts of GW sources. The localisation capability is poor by a single GW detector yet can be improved by adding more detectors to the detector network. In this paper we review recent studies on scientific benefits of global detector networks and focus on their localisation capability. We employ Wen-Chen's formula to compare this merit of current and future detector networks for localising gravitational wave bursts. We find that the addition of a new detector located in Japan, or India, or Australia will increase angular resolution 3~5 fold with respect to current LIGO-Virgo network, and that the angular resolution improvement by adding a single detector in Australia is comparable to that achieved by adding detectors in both India and Japan. A six-site network achieves a 11-fold improvement in angular resolution compared with the existing three-site network.

The understanding of noise in interferometric gravitational wave detectors is fundamental in terms of both enabling prompt reactions in the mitigation of noise disturbances and in the establishment of appropriate data-cleaning strategies. Monitoring tools to perform online and offline noise analysis in areas such as transient signal detection, line identification algorithms and coherence are used to characterise the Virgo detector noise. In this paper, we describe the framework into which these tools are integrated - the Noise Monitor Application Programming Interface (NMAPI) - and provide examples of its application.

The noise in the output of a gravitational-wave interferometer is known not to be due to stationary Gaussian processes. In fact, even after whitening, it will contain spikes of very large power (called glitches), due to environmental disturbances, instabilities in detector systems, and other factors. These glitches can sometimes mimic, and, due to their loudness, obfuscate real signals close in time. In this article we outline a new method of discriminating these glitches from gravitational-wave signals which works on the principle of the spherical harmonic decomposition of the correlation of the data streams in the detector network. It is intrinsically a coherent all-sky method (working, as it does, in the spherical harmonic domain) which can produce a time-series showing the glitchiness of the underlying data. We demonstrate this spherical-harmonic technique using real interferometer data and compare it to another glitch-rejection method in current use.

Energetic electromagnetic flares from magnetars - highly magnetized neutron stars - are associated with sudden rearrangements of the mechanical and/or magnetic configurations of the star, which can give rise to mechanical oscillations, some of which may be strong radiators of gravitational waves. General arguments have indicated that gravitational-wave bursts associated temporally with (giant) flares from galactic magnetars may be observable with ground-based gravitational wave detectors. After discussing the expectations based on the astrophysical models, we present results from several campaigns to search for such bursts using the first generation of LIGO, GEO, and Virgo detectors over the period 2005-2009, emphasizing the most recent results. No detections have been made, and we present astrophysically informed limits. Finally, we discuss prospects for progress.

Low-latency event triggers to signify the presence of gravitational waves from coalescing binaries will be required to make prompt electromagnetic follow-up observations of electromagnetic counterparts. We present the recent progress made on implementing the time-domain low-latency detection algorithm known as summed parallel infinite impulse response (SPIIR) filtering into a real gravitational wave search pipeline.

In this paper we elaborate on earlier work by the same authors in which a novel Bayesian inference framework for testing the strong-field dynamics of General Relativity using coalescing compact binaries was proposed. Unlike methods that were used previously, our technique addresses the question whether one or more 'testing coefficients' (e.g. in the phase) parameterizing deviations from GR are non-zero, rather than all of them differing from zero at the same time. The framework is well-adapted to a scenario where most sources have low signal-to-noise ratio, and information from multiple sources as seen in multiple detectors can readily be combined. In our previous work, we conjectured that this framework can detect generic deviations from GR that can in principle not be accomodated by our model waveforms, on condition that the change in phase near frequencies where the detectors are the most sensitive is comparable to that induced by simple shifts in the lower-order phase coefficients of more than a few percent (~ 5 radians at 150 Hz). To further support this claim, we perform additional numerical experiments in Gaussian and stationary noise according to the expected Advanced LIGO/Virgo noise curves, and coherently injecting signals into the network whose phasing differs structurally from the predictions of GR, but with the magnitude of the deviation still being small. We find that even then, a violation of GR can be established with good confidence.

Pulsar timing now has a rich history in placing limits on the stochastic background of gravitational waves, and we plan soon to reach the sensitivity where we can detect, not just place limits on, the stochastic background. However, the capability of pulsar timing goes beyond the detection of a background. Herein I review efforts that include single source detection, localization, waveform recovery, a clever use of a "time-machine" effect, alternate theories of gravity, and finally studies of the noise in our "detector" that will allow us to tune and optimize the experiment. Pulsar timing arrays are no longer "blunt" instruments for gravitational-wave detection limited to only detecting an amplitude of the background. Rather they are shrewd and tunable detectors, capable of a rich and dynamic variety of astrophysical measurements.

We present an algorithm for population study which optimally uses information obtained from the electromagnetic (or particle) counterpart of gravitational wave (GW) events. Existing methods do not associate suitable weight factors to the triggers besides trivial ones like a hard cutoff on flux. However, the assignment of weights needs to take into account the background astrophysical distribution to be estimated. This is done using a likelihood-based approach where electromagnetic (or particle) and gravitational wave data are incorporated into a common likelihood before the parameters of a given population distribution are estimated. We present preliminary results from this method using simulated data corresponding to simplified models of GW and electromagnetic detectors.

The gravitational wave (GW) signature of a binary black hole (BBH) coalescence is characterized by rapid frequency evolution in the late inspiral and merger phases. For a system with total mass larger than 100 M_☉, ground based GW detectors are sensitive to the merger phase, and the in-band whitened waveform is a short-duration transient lasting about 10-30 ms. For a symmetric mass system with total mass between 10 and 100 M_☉, the detector is sensitive instead to the inspiral phase and the in-band signal has a longer duration, between 30 ms -3 s. Omega is a search algorithm for GW bursts that, with the assumption of locally stationary frequency evolution, uses sine-Gaussian wavelets as a template bank to decompose interferometer strain data. The local stationarity of sine-Gaussian waveforms induces a performance loss for the detection of lower mass BBH signatures, due to the mismatch between template and signal. We present the performance of a modified version of the Omega algorithm, Chirplet Omega, which allows a linear variation of frequency, to target BBH coalescences. The use of Chirplet-like templates enhances the measured signal-to-noise ratio due to less mismatch between template and data, and increases the detectability of lower mass BBH coalescences. We present the results of a performance study of Chirplet Omega in colored Gaussian noise at initial LIGO sensitivity.

The time-frequency transforms are important tools for identification of transient events in the output of the gravitational-wave detectors. Produced by the terrestrial and possibly by astrophysical sources, the transient events can be identified as patterns on the time-frequency plane with the excess power above stationary detector noise. In this paper we consider a particular case of the Wilson-Daubechies time-frequency transform for use in the gravitational-wave burst analysis. The presented Wilson-Daubechies basis shares some properties with the Gabor frames, but circumvents the Balian-Low theorem. It also shares similarity with the Meyer wavelet, which is actively used in the gravitational-wave burst analysis. The main advantages of the Wilson-Daubechies transform are the low computational cost, spectral leakage control, flexible structure of the frequency sub-bands, and the existence of the analytic time-delay filters, which are important for localization of the gravitational-wave sources in the sky. These properties of the Wilson-Daubechies transform may prove useful not only in the transient analysis, but also in other areas of the gravitational wave data analysis and detector characterization.

During the most recent LIGO-GEO-Virgo science run a number of partner telescopes performed follow-up observations of gravitational wave (GW) candidates. One of these collaborators was the ROTSE project. Consisting of four optical telescopes, ROTSE responded to GW triggers and took over 700 follow-up images. Analysis of these images is currently under way using ROTSE's own image processing pipeline. We describe the analysis used to search for transients of astrophysical significance, and steps being taken to automate and optimise the analysis for rapid identification of electromagnetic (EM) counterparts to GW candidates.

We outline the scientific motivation behind a search for gravitational waves associated with short gamma ray bursts detected by the InterPlanetary Network (IPN) during LIGO's fifth science run and Virgo's first science run. The InterPlanetary Network localisation of short gamma ray bursts is limited to extended error boxes of different shapes and sizes and a search on these error boxes poses a series of challenges for data analysis. We will discuss these challenges and outline the methods to optimise the search over these error boxes.

We outline the eccentricity evolution of sub-parsec massive black hole binaries (MBHBs) forming in galaxy mergers. In both stellar and gaseous environments, MBHBs are expected to grow large orbital eccentricities before they enter the gravitational wave (GW) observational domain. We re-visit the predicted eccentricities detectable by space based laser interferometers (as the proposed ELISA/NGO) for both environments. Close to coalescence, many MBHBs will still maintain detectable eccentricities, spanning a broad range from < 10⁻⁵ up to 0.5. Stellar and gas driven dynamics lead to distinct distributions, with the latter favoring larger eccentricities. At larger binary separations, when emitted GWs will be observed by pulsar timing arrays (PTAs), the expected eccentricities are usually quite large, in the range 0.01 – 0.7, which poses an important issue for signal modelling and detection algorithms. In this window, large eccentricities also have implications on proposed electromagnetic counterparts to the GW signal, which we briefly review.

During the most recent LIGO-Virgo science run (Dec 17 2009 to Jan 8 2010 and Sep 2 to Oct 20 2010) multi-messenger searches were performed using several partner telescopes. This resulted in large data sets with images covering several square degrees of the sky. Analysis of these images is currently underway using a variety of different tools. We present an overview of these efforts, in particular the development of new tools which enable us to establish the efficiency for transient images in the fields. This is critical in establishing the sensitivity of gravitational wave and electromagnetic multi-messenger searches to the astrophysical signals we expect to be associated with gravitational waves.

The data collected by a gravitational wave interferometer are inevitably affected by instrumental artefacts and environmental disturbances. In particular, for continuous gravitational wave (CW) studies it is important to detect narrow-band disturbances (the so-called "noise lines") during science runs, and to help scientists to identify and possibly remove or mitigate their sources. The NoEMi (Noise Frequency Event Miner) framework exploits some of the algorithms implemented for the CW search to identify, on a daily basis, the frequency lines observed in the Virgo science data and in a subset of the environmental sensors, looking for lines that match in frequency. A line tracker algorithm reconstructs the lines over time, and stores them in a database, which is made accesible via a web interface. We describe the workflow of NoEMi, providing examples of its use for the investigation of noise lines in past Virgo runs (VSR2, VSR3) and in the most recent run (VSR4).

We describe the extension to multiple datasets of a coherent method for the search of continuous gravitational wave signals, based on the computation of 5-vectors. In particular, we show how to coherently combine different datasets belonging to the same detector or to different detectors. In the latter case the coherent combination is the way to have the maximum increase in signal-to-noise ratio. If the datasets belong to the same detector the advantage comes mainly from the properties of a quantity called coherence which is helpful (in both cases, in fact) in rejecting false candidates. The method has been tested searching for simulated signals injected in Gaussian noise and the results of the simulations are discussed.

The Virgo detector undertook its second science run (VSR2) from July 2009 to January 2010, providing unprecedented sensitivity to gravitational waves at frequencies below 40 Hz. The VSR2 dataset presented an ideal opportunity [1] to search for gravitational waves from the Vela pulsar (B0833-45, J0835-4510), for which gravitational wave emission is expected at ~ 22 Hz assuming it is a non axi-symmetric rotator. We give a summary of the results obtained in [1], describing the Bayesian method more fully and presenting further details of the data used.

The cross-correlation search for gravitational waves, also known as 'radiometry', has been previously applied to map the gravitational wave stochastic background in the sky and also to target gravitational waves from rotating neutron stars/pulsars. We consider the Virgo cluster which may appear as a 'hot spot' spanning few pixels in the sky in a radiometry analysis. Our results show that sufficient signal to noise ratio can be accumulated with integration times of the order of a year. We also present a numerical simulation of radiometric analysis, assuming ground-based detectors which are currently under construction or being upgraded. The point spread function of the injected sources is confirmed by numerical tests. The typical resolution of radiometry analysis is a few square degrees, as compared to the several thousand pixels for the full sky in an all-sky map.

We describe the consistency testing of a new code for gravitational wave signal parameter estimation in known pulsar searches. The code uses an implementation of nested sampling to explore the likelihood volume. Using fake signals and simulated noise we compare this to a previous code that calculated the signal parameter posterior distributions on both a grid and using a crude Markov chain Monte Carlo (MCMC) method. We define a new parameterisation of two orientation angles of neutron stars used in the signal model (the initial phase and polarisation angle), which breaks a degeneracy between them and allows more efficient exploration of those parameters. Finally, we briefly describe potential areas for further study and the uses of this code in the future.

t Glitches in pulsars are likely to trigger oscillation modes in the fluid interior of neutron stars. We examined these oscillations specifically at r-mode frequencies. The excited r-modes will emit gravitational waves and can have long damping time scales (minutes - days). We use simple estimates of how much energy the glitch might put into the r-mode and assess the detectability of the emitted gravitational waves with future interferometers.

We derive two different methods to compute the minimal required integration time of a fully coherent follow-up of candidates produced in wide parameter space semi-coherent searches, such as global correlation StackSlide searches using Einstein@Home. We numerically compare these methods in terms of integration duration and computing cost. In a Monte Carlo study we confirm that we can achieve the required detection probability.

The OSE (Offline Simulations Environment) simulator of the LPF (LISA Pathfinder) mission is intended to simulate the different experiments to be carried out in flight. Amongst these, the thermal diagnostics experiments are intended to relate thermal disturbances and interferometer readouts, thereby allowing the subtraction of thermally induced interferences from the interferometer channels. In this paper we report on the modelling of these simulated experiments, including the parametrisation of different thermal effects (radiation pressure effect, radiometer effect) that will appear in the Inertial Sensor environment of the LTP (LISA Technology Package). We report as well how these experiments are going to be implemented in the LTPDA toolbox, which is a dedicated tool for LPF data analysis that will allow full traceability and reproducibility of the analysis thanks to complete recording of the processes.

Cosmic rays and energetic solar particles constitute one of the most important sources of noise for future gravitational wave detectors in space. Radiation monitors were designed for the LISA Pathfinder (LISA-PF) mission. Similar devices were proposed to be placed on board LISA and ASTROD. These detectors are needed to monitor the flux of energetic particles penetrating mission spacecraft and inertial sensors. However, in addition to this primary use, radiation monitors on board space interferometers will carry out the first multipoint observation of solar energetic particles (SEPs) at small and large heliolongitude intervals and at very different distances from Earth with minor normalization errors. We illustrate the scientific goals that can be achieved in solar physics and space weather studies with these detectors. A comparison with present and future missions devoted to solar physics is presented.

The coalescence history of massive black holes is derived from cosmological simulations, in which their evolution and that of the host galaxies are followed in a consistent way. With the coalescence rate per comoving volume and per mass interval derived from the simulations we estimate the expected detection rate distribution of "ring-down" gravitational wave signals along frequencies accessible by LISA and Einstein Telescope (ET). For LISA, a total detection rate of about 15 yr⁻¹ is predicted for events having a signal-to-noise ratio equal to 10. For ET, one event each 14 months down to one event each 4 years is expected with a signal-to-noise ratio of 5. The detection of these gravitational signals and their distribution in frequency would be in the future an important tool able to discriminate among different scenarios for the origin of supermassive black holes.

A perturbed black hole emits gravitational radiation, usually termed the ringdown signal, whose frequency and time-constant depends on the mass and spin of the black hole. I investigate the case of a binary black hole merger resulting from two initially non-spinning black holes of various mass ratios, in quasi-circular orbits. The observed ringdown signal will be determined, among other things, by the black hole's spin-axis orientation with respect to Earth, its sky position and polarization angle - parameters which can take any values in a particular observation. I have carried out a statistical analysis of the effect of these variables, focusing on detection and measurement of the multimode ringdown signals using the reformulated European LISA mission, Next Gravitational-Wave Observatory, NGO, the third generation ground-based observatory, Einstein Telescope and the advanced era detector, aLIGO. To the extent possible I have discussed the effect of these results on plausible event rates, as well as astrophysical implications concerning the formation and growth of supermassive and intermediate mass black holes.

The LISA Pathfinder mission (LPF) aims to test key technologies for the future LISA mission. The LISA Technology Package (LTP) on-board LPF will consist of an exhaustive suite of experiments and its outcome will be crucial for the future detection of gravitational waves. In order to achieve maximum sensitivity, we need to have an understanding of every instrument on-board and parametrize the properties of the underlying noise models. The Data Analysis team has developed algorithms for parameter estimation of the system. A very promising one implemented for LISA Pathfinder data analysis is the Markov Chain Monte Carlo. A series of experiments are going to take place during flight operations and each experiment is going to provide us with essential information for the next in the sequence. Therefore, it is a priority to optimize and improve our tools available for data analysis during the mission. Using a Bayesian framework analysis allows us to apply prior knowledge for each experiment, which means that we can efficiently use our prior estimates for the parameters, making the method more accurate and significantly faster. This, together with other algorithm improvements, will lead us to our main goal, which is no other than creating a robust and reliable tool for parameter estimation during the LPF mission.

We report on a double torsion pendulum, where motion along two degrees of freedom (DoFs) is almost free. The Test Mass (TM) is enclosed in a replica of the LISA-Pathfinder electrostatic readout and actuation system. This apparatus is designed to perform extensive ground testing of undesired effects such as leakage of the readout noise from one DoF to another, or actuation cross talks with closed feedback loop. Such investigation is relevant to the noise budget of LISA and LISA-Pathfinder missions, as the TM will be sensitive to weak forces along all 6 degrees of freedom (DoFs). The instrument being developed in Firenze is capable of measuring the forces and stiffnesses acting simultaneously along the 2 soft DoFs. We have completed an upgrade of the apparatus to a definitive configuration and we report on both advances in the commissioning tests and on measurements of residual charge, with the first DoF released.

The design of the Radiation Monitor in the LISA Technology Package on board LISA Pathnder is based on two silicon PIN diodes, placed parallel to each other in a telescopic configuration. One of them is able to record spectral information of the particle hitting the diode. A test campaign for the flight model Radiation Monitor was done in the Paul Scherrer Institute Proton Irradiation Facility in September 2010. Its purpose was to check correct functionality of the Radiation Monitor under real high energy proton fluxes. Here we present the results of the experiments done and their assessment by means of a simulated flight model geometry using GEANT4 toolkit. No deviation from nominal RM performance was detected, which means the instrument is fully ready for flight.

Previous research with Anisotropic Magnetoresistive sensors (AMR) have shown significant improvements for weak magnetic field applications using dedicated noise reduction techniques in the signal conditioning circuit. However, an important source of error that must be addressed is the thermal dependence of the sensor system, more significant in the AMR sensitivity. The external temperature fluctuations affect the output of the sensors due to the temperature coefficient of the magnetoresistors, which may cause an increase of the estimation of the noise spectral density at low frequencies. Ongoing research using a low noise/low temperature coefficient current source to supply the sensor's bridge enhances the thermal performance of the sensors at the lower end of the LISA bandwidth. Preliminary results are shown in this paper.

Proposed space-based gravitational-wave (GW) detectors such as DECIGO and BBO will detect ~ 10⁶ neutron-star (NS) binaries and determine the luminosity distances to the binaries with high precision. Combining the luminosity distances with cosmologically-induced phase corrections on the GWs, cosmological expansion out to high redshift can be measured without the redshift determinations of host galaxies by electromagnetic observation and can be a unique probe for dark energy. This article is based on the results obtained in [1] where we investigated constraining power of the GW standard siren without redshift information on the equation of state of dark energy with future space-based GW detectors. We also compare the results with those obtained with other instruments and methods.

The LISA Pathfinder data analysis team has been developing in the last years the infrastructure and methods required to run the mission during flight operations. These are gathered in the LTPDA toolbox, an object oriented MATLAB toolbox that allows all the data analysis functionalities for the mission, while storing the history of all operations performed to the data, thus easing traceability and reproducibility of the analysis. The parameter estimation methods in the toolbox have been applied recently to data sets generated with the OSE (Off-line Simulations Environment), a detailed LISA Pathfinder non-linear simulator that will serve as a reference simulator during mission operations. These simulations, so called operational exercises, are the last verification step before translating these experiments into tele-command sequences for the spacecraft, producing therefore very relevant datasets to test our data analysis methods. In this contribution we report the results obtained with three different parameter estimation methods during one of these operational exercises.

Optical fiber and semiconductor laser technologies have evolved dramatically over the last decade due to the increased demands from optical communications. We are developing a laser (master oscillator) and optical amplifier based on those technologies for interferometric space missions, including the gravitational-wave missions NGO/SGO (formerly LISA) and the climate monitoring mission GRACE Follow-On, by fully utilizing the matured wave-guided optics technologies. In space, where simpler and more reliable system is preferred, the wave-guided components are advantageous over bulk, crystal-based, free-space laser, such as NPRO (Non-planar Ring Oscillator) and bulk-crystal amplifier.

The Mock LISA Data Challenge 4.0 simulated the joint two-year recording of gravitational wave signals from mergers of spinning black holes, extreme mass ratio inspirals, Galactic white dwarf binaries, bursts from cosmic strings, and a stochastic background—all over LISA instrument noise. We analysed this data using a global multi-start box and bound optimization scheme, incorporating multi-dimensional Nelder Mead simplex 2 optimization. Our scheme identified 2658 binaries. Of these, 2246 were found to systematically decompose the power in a strong spinning black hole merger into a "white dwarf binary transform". The remaining 416 binaries were identified with a false alarm rate of ~ 23%.

If we assume that we live in the center of a spherical inhomogeneous universe, we can explain the apparent accelerating expansion of the universe without introducing the unknown dark energy or modifying gravitational theory. Direct measurement of the cosmic acceleration can be a powerful tool in distinguishing ΛCDM and the inhomogeneous models. If ΛCDM is the correct model, we have shown that DECIGO/BBO has sufficient ability to detect the positive redshift drift of the source by observing gravitational waves from neutron star binaries for 5-10 years. This enables us to rule out any Lemaître-Tolman-Bondi (LTB) void model with monotonically increasing density profile. Furthermore, by detecting the positive redshift drift at z ~ 0, we can even rule out generic LTB models unless we allow unrealistically steep density gradient at z ~ 0. We also show that the measurement accuracy is slightly improved when we consider the joint search of DECIGO/BBO and the third generation Einstein Telescope. This test can be performed with GW observations alone without any reference to electromagnetic observations.

We have established a program aimed at developing computer applications and web applets to be used for educational purposes as well as gravitational wave outreach activities. These applications and applets teach gravitational wave physics and technology. The computer programs are generated in collaboration with undergraduates and summer students as part of our teaching activities, and are freely distributed on a dedicated website. As part of this program, we have developed two computer-games related to gravitational wave science: 'Black Hole Pong' and 'Space Time Quest'. In this article we present an overview of our computer related outreach activities and discuss the games and their educational aspects, and report on some positive feedback received.