Table of contents

The Seventh Edoardo Amaldi Conference on Gravitational Waves was held on 8–14 July 2007, Sydney Convention and Exhibition Centre, Darling Harbour, Sydney, Australia. The bulk of the papers, after peer review, are published in Journal of Physics: Conference Series. However a selection of papers, chosen by the conference organisers, are published separately in a special issue of Classical and Quantum Gravity.

The proposed southern hemisphere gravitational wave detector AIGO increases the projected average baseline of the global array of ground based gravitational wave detectors by a factor ∼4. This allows the world array to be substantially improved. The orientation of AIGO allows much better resolution of both wave polarisations. This enables better distance estimates for inspiral events, allowing unambiguous optical identification of host galaxies for about 25% of neutron star binary inspiral events. This can allow Hubble Law estimation without optical identification of an outburst, and can also allow deep exposure imaging with electromagnetic telescopes to search for weak afterglows. This allows independent estimates of cosmological acceleration and dark energy as well as improved understanding of the physics of neutron star and black hole coalescences. This paper reviews and summarises the science benefits of AIGO and presents a preliminary conceptual design.

CLIO (Cryogenic Laser Interferometer Observatory) is a Japanese gravitational wave detector project. One of the main purposes of CLIO is to demonstrate thermal-noise suppression by cooling mirrors for a future Japanese project, LCGT (Large-scale Cryogenic Gravitational Telescope). The CLIO site is in Kamioka mine, as is LCGT. The progress of CLIO between 2005 and 2007 (room- and cryogenic-temperature experiments) is introduced in this article. In a room-temperature experiment, we made efforts to improve the sensitivity. The current best sensitivity at 300 K is about 6 × 10^-21/√Hz around 400 Hz. Below 20 Hz, the strain (not displacement) sensitivity is comparable to that of LIGO, although the baselines of CLIO are 40-times shorter (CLIO: 100m, LIGO: 4km). This is because seismic noise is extremely small in Kamioka mine. We operated the interferometer at room temperature for gravitational wave observations. We obtained 86 hours of data. In the cryogenic experiment, it was confirmed that the mirrors were sufficiently cooled (14 K). However, we found that the radiation shield ducts transferred 300K radiation into the cryostat more effectively than we had expected. We observed that noise caused by pure aluminum wires to suspend a mirror was suppressed by cooling the mirror.

Pulsar timing experiments are reaching sufficient sensitivity to detect a postulated stochastic gravitational wave background generated by merging supermassive black hole systems in the cores of galaxies. We describe the techniques behind the pulsar timing detection method, provide current upper bounds on the amplitude of any gravitational wave background, describe theoretical models predicting the existence of such a background and highlight new techniques for providing a statistically rigorous detection of the background.

We open the discussion into how the Laser Interferometer Space Antenna (LISA) observations of supermassive black-hole (SMBH) mergers (in the mass range ∼ 10⁶–10⁸ M_⊙) may be complementary to pulsar timing-based gravitational wave searches. We consider the toy model of determining pulsar distances by exploiting the fact that LISA SMBH inspiral observations can place tight parameter constraints on the signal present in pulsar timing observations. We also suggest, as a future path of research, the use of LISA ring-down observations from the most massive (≳ a few 10⁷ M_⊙) black-hole mergers, for which the inspiral stage will lie outside the LISA band, as both a trigger and constraint on searches within pulsar timing data for the inspiral stage of the merger.

The European Space Agency is currently pursuing a comprehensive industrial study of the complete LISA mission within a contract awarded to Astrium Satellites GmbH in 2005. The study is in its final phase and has developed a consolidated mission and payload concept. The feasibility and robustness of the mission concept has been confirmed. The mission performance and the resulting technical requirements have been investigated in detail and converted into an optimised technical design for instrument, spacecraft and constellation. Designed mainly in order to cope with the dynamics of the LISA constellation, three suitable instrument architectures have been defined: (1) two independently rotating optomechanical/reference sensor assemblies serving the adjacent interferometer arms with stationary laser beam path inside, (2) one fixed opto-mechanical and two reference sensors assembly with telescope in-field pointing of laser beams, (3) one fixed opto-mechanical assembly with telescope in-field pointing of laser beams and one active reference sensor. The final baseline selection will be guided by mission robustness and reliability, technical complexity, cost and engineering budgets.

DECi-hertz Interferometer Gravitational wave Observatory (DECIGO) is the future Japanese space gravitational wave antenna. The goal of DECIGO is to detect gravitational waves from various kinds of sources mainly between 0.1 Hz and 10 Hz and thus to open a new window of observation for gravitational wave astronomy. DECIGO will consist of three drag-free spacecraft, 1000 km apart from each other, whose relative displacements are measured by a Fabry—Perot Michelson interferometer. We plan to launch DECIGO pathfinder first to demonstrate the technologies required to realize DECIGO and, if possible, to detect gravitational waves from our galaxy or nearby galaxies.

We are developing a detector with two laser interferometers for gravitational waves at 100 MHz. Each interferometer is a Sagnac interferometer with a 75-cm baseline synchronous recycling (or resonant recycling) cavity. Two such interferometers are constructed to perform cross-correlation analysis. The original signals at around 100 MHz are converted into electrical signals at lower frequencies before we collect the data. The output noise of each interferometer is measured to correspond to less than 1×10^-16 Hz^-1/2 in strain amplitude at around 100 MHz.

Future gravitational wave detectors will be limited by different kinds of noise. Thermal noise from the coatings and the substrate material will be a serious noise contribution within the detection band of these detectors. Cooling and the use of a high mechanical Q-factor material as a substrate material will reduce the thermal noise contribution from the substrates. Silicon is one of the most interesting materials for a third generation cryogenic detector. Due to the fact that the coefficient of thermal expansion vanishes at 18 and 125 K the thermoelastic contribution to the thermal noise will disappear. We present a systematic analysis of the mechanical Q-factor at low temperatures between 5 and 300 K on bulk silicon (100) samples which are boron doped. The thickness of the cylindrical samples is varied between 6, 12, 24, and 75mm with a constant diameter of 3 inches. For the 75mm substrate a comparison between the (100) and the (111) orientation is presented. In order to obtain the mechanical Q-factor a ring-down measurement is performed. Thus, the substrate is excited to resonant vibrations by means of an electrostatic driving plate and the subsequent ring-down is recorded using a Michelson-like interferometer. The substrate itself is suspended as a pendulum by means of a tungsten wire loop. All measurements are carried out in a special cryostat which provides a temperature stability of better than 0.1K between 5 and 300K during the experiment. The influence of the suspension on the measurements is experimentally investigated and discussed. At 5.8K a highest Q-factor of 4.5 × 10⁸ was achieved for the 14.9 kHz mode of a silicon (100) substrate with a diameter of 3 inches and a thickness of 12 mm.

An unexpected large heat load was observed in a cooling test of the cryostat for a prototype cryogenic interferometric gravitational wave detector. By conducting additional studies involving an experiment and a simulation, we found that the large heat load was caused by conduction of thermal radiation in a thermal radiation shield pipe, which was inserted in the beam duct to reduce solid angle from 300K to 4K. To achieve the design of LCGT cryogenic system, the heat load had to be reduced below a few percent. By introducing metal baffles in the shield pipe, this requirement was fulfilled.

The Horizontal Access Module Seismic Attenuation System (HAM-SAS) is a mechanical device expressly designed to isolate a multipurpose optical table and fit in the tight space of the LIGO HAM Ultra-High-Vacuum chamber. Seismic attenuation in the detectors' sensitivity frequency band is achieved with state of the art passive mechanical attenuators. These devices should provide an attenuation factor of about 70dB above 10Hz at the suspension point of the Advanced LIGO triple pendulum suspension. Automatic control techniques are used to position the optical table and damp rigid body modes. Here, we report the main results obtained from the full scale prototype installed at the MIT LIGO Advanced System Test Interferometer (LASTI) facility. Seismic attenuation performance, control strategies, improvements and limitations are also discussed.

In this paper we describe the architecture and the performances of a hybrid modular acquisition and control system prototype developed for the implementation of distributed monitoring and control systems. The system, an alternative to the VME-UDP/IP based system, is based on a dual-channel 18-bit low noise ADC and 16-bit DAC module at 800 kHz, managed by an ALTERA FPGA. Experimental tests have demonstrated that this architecture allows the implementation of distributed control systems with delay time t < 30μs, on single channel, using a standard laptop PC for the real-time computation. The system was used for the longitudinal control of the end mirror of a suspended Michelson Interferometer, performed through an electrostatic actuators, giving effective performances. The preliminary results are also reported.

This paper describes a mechanical monolithic tunable sensor prototype with elliptical hinges, shaped with electric-discharge-machining, that can be used both as seismometer and, in a force-feedback configuration, as accelerometer in the control of mechanical suspensions of interferometric gravitational waves detectors. The monolithic mechanical design and a laser optical readout make it a very compact instrument, very sensitive in the low-frequency seismic noise band and with a very good immunity to environmental noises. The theoretical sensitivity curves and the simulations show a very good agreement with the measurements. Very interesting scientific result its measured natural resonance frequency of ≈ 70mHz with a Q ≈ 140 in air.

A new seismic isolation system, TAMA Seismic Attenuation System (TAMA-SAS), was installed to TAMA300 in order to improve the sensitivity at low frequencies. Inertial damping is one of the hierarchical control systems of the TAMA-SAS which are employed to give full play to its ability. We have established two servo loops to control the Inverted Pendulum (IP) which composes the SAS. One is the servo loop using LVDT position sensors to keep the position of the IP. The other is the inertial damping which uses accelerometers to control the inertial motion of the IP for the horizontal direction. The fluctuation of the IP was reduced using our servo system. In addition, reduction of angular and longitudinal fluctuation of the mirror was also confirmed. These results indicate that the control for the IP properly works and the isolation performance of the TAMA-SAS was improved.

In next-generation interferometric gravitational wave detectors that are being designed, the power of their light sources will be larger than 100 W. As a consequence, the light power at the detection port of the interferometers must be increased by a factor of more than 10, compared with that of the current detectors; thus, a high-power photo-detection system is indispensable. Here, we present the photo-detection system which can detect the laser power of 500 mW at 1064 nm with a single photodiode of 3-mm diameter. Its response to DC and AC input signals are reported.

We evaluated the parametric instabilities of LCGT (Japanese interferometric gravitational wave detector project) arm cavity. The number of unstable modes of LCGT is 10-times smaller than that of Advanced LIGO (USA). Since the strength of the instabilities of LCGT depends on the mirror curvature more weakly than that of Advanced LIGO, the requirement of the mirror curvature accuracy is easier to be achieved. The difference in the parametric instabilities between LCGT and Advanced LIGO is because of the thermal noise reduction methods (LCGT, cooling sapphire mirrors; Advanced LIGO, fused silica mirrors with larger laser beams), which are the main strategies of the projects. Elastic Q reduction by the barrel surface (0.2 mm thickness Ta₂O₅) coating is effective to suppress instabilities in the LCGT arm cavity. Therefore, the cryogenic interferometer is a smart solution for the parametric instabilities in addition to thermal noise and thermal lensing.

We developed a laser stabilization system composed of optical fibers. In this system all optical devices used for stabilization are connected with optical fibers. This system has advantages for space use and for low-frequency (< 10 Hz) stabilization. We suppressed the intensity noise to 6 × 10^-7/√Hz at 1 Hz, and to 4 × 10^-8/√Hz at 1 kHz. We also suppressed the frequency noise to 20 Hz/√Hz at 1 Hz, and to 2 Hz/√Hz at 80 Hz. This system is one of the candidates for the laser stabilization system of DECIGO.

LCGT plans to use tuned RSE as the optical configuration for its interferometer. A tuned RSE interferometer has five degrees of freedom that need to be controlled in order to operate a gravitational-wave detector, although it is expected to be very challenging because of the complexity of its optical configuration. A new control scheme for a tuned RSE interferometer has been developed and tested with a prototype interferometer to demonstrate successful control of the tuned RSE interferometer. The whole RSE interferometer was successfully locked with the control scheme. Here the control scheme and the current status of the experiment are presented.

We designed and fabricated an all-reflective 50/50 beam splitter based on a dielectric grating. This beam splitter was used to set up a power-recycled Michelson interferometer with a finesse of about F_PR ≈ 880. Aspects of the diffractive beam splitter as well as of the interferometer design are discussed.

In the sensitivity of laser interferometer gravitational-wave detectors, there exists the standard quantum limit (SQL), derived from Heisenberg's uncertainty relation. The SQL can be overcome using the quantum correlation between shot noise and radiation-pressure noise. One of the methods to overcome SQL, signal recycling, is considered so far only in a recombined-type interferometer such as Advanced-LIGO, LCGT, and GEO600. In this paper, we investigated quantum noise and signal recycling in a differential-type interferometer. We also applied it to a real detector and compared the sensivity with a recombined type.

We describe an experimental conceptual design for observation and reduction of radiation pressure noise. The radiation pressure noise is increased in a high finesse cavity with a small mass mirror. In our experiment a Fabry-Perot Michelson interferometer with a homodyne detection scheme will be built with Fabry-Perot cavities of finesse of 10000 containing suspended mirrors of 23 mg. To observe the radiation pressure noise, the goal sensitivity is set to 1×10^-17 [m/ √Hz] at 1 kHz. Then the radiation pressure noise is reduced by adjusting the homodyne phase. To achieve the sensitivity, the other noise sources such as thermal noises, seismic noise and laser frequency noise should be suppressed below 1×10^-18 [m/√ Hz] at 1kHz. The whole interferometer is suspended as a double pendulum on double-layer stacks. As a preliminary setup, a Fabry-Perot cavity of finesse of 800 with a suspended mirror of 100 mg was locked. The current best sensitivity is 1×10^-15 [m/ √Hz] at 1 kHz.

The Low Frequency Facility (LFF) experimental set-up consists of one 1 cm long cavity hanging from a mechanical insulation system, that damps seismic noise transmission to the optical components of the VIRGO interferometer. Radiation pressure generates an opto-mechanical coupling between the two mirrors of the cavity, that we call an optical spring. The measured relative displacement power spectrum is compatible with a system at thermal equilibrium within its environment; the optical spring has a stiffness k_opt of the order of 10⁴N/m.

An upper limits of 10^-15 m/√Hz at 10 Hz for seismic and thermal noise contamination of the Virgo test masses suspended by a SuperAttenuator is derived from measured data.

We present the partial demonstration of displacement- and laser-noise free interferometer (DFI) and the next experimental plan to examine the complete configuration. A part of the full implementation of DFI has been demonstrated to confirm the cancellation of beamsplitter displacements. The displacements were suppressed by about two orders of magnitude. The aim of the next experiment is to operate the system and to confirm the cancellation of all displacement noises, while the gravitational wave (GW) signals survive. The optical displacements will be simulated by electro-optic modulators (EOM). To simulate the GW contribution to laser lights, we will use multiple EOMs.

We present an experimental investigation into non-stationary events that occur in a homodyne detection system. The importance of non-stationary events is that it is a possible mechanism preventing shot-noise-limited homodyne detection at low frequencies, a necessary condition that needs to be routinely fulfilled in order to detect squeezed states at these frequencies. These non-stationary events are thought to arise due to airborne dust passing through the laser beam paths. We show that these non-stationary events which occur in our laboratory environment can be minimised by placing the experiment in an airtight enclosure. Isolation against non-stationary events achieved improvement of the colour of the noise spectrum by 3dB at 10Hz towards a flat shot noise spectrum and improvement in the noise distribution of the signal towards a Gaussian distribution.

This document describes some results of time domain simulation for a Fabry-Perot cavity with Advanced LIGO parameters. Future interferometer will employ a high power laser and high finesse cavities. Lock acquisition of arm cavity will be more difficult due to the optical instabilities which are caused by very high power inside the cavity. According to this simulation, the arm cavity should be locked with very low power, and additional hard/software techniques will be needed to establish the first fringe lock. In this paper, possibility of using a new algorithm called 'Guidelock' and a suspension point interferometer are discussed. After lock is acquired, alignment controls must be engaged before increasing the power. This simulation predicts that alignment optical instabilities show up due to a shift of high power beam axis, and they can be stabilized by proper alignment controls.

The alignment sensing and control scheme of the resonant sideband extraction interferometer is still an unsettled issue for the next-generation gravitational wave antennas. The issue is that it is difficult to extract separate error signals for all 12 angular degrees of freedom, which is mainly arising from the complexity of the optical system and cavity 'degeneracy'. We have suggested a new sensing scheme giving reasonably separated signals which is fully compatible with the length sensing scheme. The key of this idea is to resolve the 'degeneracy' of the optical cavities. By choosing an appropriate Gouy phase for the degenerate cavities, alignment error signals with much less admixtures can be extracted.

The most sensitive gravitational-wave detectors today are based on large-scale laser interferometers whose optics are suspended from pendulums to decouple the instrument from seismic motion. Complex control systems are required to set and maintain the microscopic position of each mirror at a precisely defined value. Such control systems use the interferometer signals as input signals, and ideally it is designed such that the degrees of freedom (mirror positions) are well decoupled in the interferometer signals. However, this is not always feasible, in particular the mirror alignment control signals in interferometric gravitational wave detectors often show strong couplings between the different degrees of freedom. In this paper we will describe a simple and powerful method to quantify in advance the performances of an alignment control system by analyzing the optical matrix of the proposed read-out system. We will motivate the method using a Fabry-Perot cavity as an example, and we will further present results for the Virgo alignment system where this method was used to characterize and improve the alignment sensing scheme.

The seismic attenuation system (SAS) in TAMA300 consists of a three-legged inverted pendulum and mirror isolation filters in order to provide a high level of seismic isolation. However, the mirror isolation filters have torsion modes with long decay time which disturb the interferometer operation for about half an hour if they get excited. In order to damp the torsion modes of the filters, we constructed a digital damping system using reflective photosensors with a large linear range. This system was installed to all of four SASs. By damping of the target torsion modes, the effective quality factors of the torsion modes are reduced to less than 10 or to unmeasurable level. This system is expected to reduce the inoperative period by the torsion mode excitation, and thus will contribute to improve the duty time of the gravitational wave detector.

Since the Stanford pioneering work of Paik in the 1970s, cryogenic resonant-mass gravitational wave detectors have used resonant transducers, which have the effect of increasing both the detector sensitivity and bandwidth. Now nanotechnology is opening new possibilities towards the construction of ultra-high sensitivity klystron cavity transducers. It might be feasible to construct TeraHz/micron parametric transducers in a near future. They would be so sensitive that there would be no need for multimode resonant transducers. The resonant-antenna would act as a broadband detector for gravitational waves. A spherical antenna, such as Schenberg or Mini-Grail, could add to this quality the advantage of wave position and polarity determination. Here we propose an extreme geometry for a re-entrant klystron cavity (df/dg ∼ 10¹⁸ Hz/m, where f stands for the microwave pump frequency and g for variations in the cavity gap), obtaining a frequency response for the strain sensitivity of the Schenberg gravitational wave detector such that its bandwidth increases from 50 Hz (using the so-called resonant mode coupling) to ∼4000 Hz when operating @ 20 mK, and, when compared to LIGO experimental curve, shows a competitive band of about 2000 Hz. We also study some of the technological complications that can be foreseen to design such a resonant cavity.

A spherical gravitational wave (GW) detector has a heavy ball-shaped mass which vibrates when a GW passes through it. Such motion is monitored by transducers and the respective electronic signal is digitally analyzed. One of such detectors, SCHENBERG, will have resonant frequencies around 3.2 kHz with a bandwidth near 200 Hz. The frequencies of other resonant-mass detectors typically lay below 1 kHz, making the transducer development for this higher frequency detector somewhat more complex. In this work we present a series of finite element studies of a sphere coupled to resonant mushroom shaped resonators that will work as mechanical impedance matchers between the sphere and the transducer. We describe the search for a shape of the impedance matcher that might improve the performance of the detector. We find that the normal modes of the coupled system are not exactly degenerate, while theoretical calculations predict that they should be.

We present the results of measurements of mechanical dissipations in silicon and silicon carbide samples within the 2-300 K range of temperature. These materials are possible candidates for the sensitive mass of DUAL detector. We have investigated sintered and infiltrated Silicon Carbide (SiC) and P-doped Silicon (Si) in flat plates and cantilevers. Moreover the dissipation of bonded P-doped silicon wafers is scheduled for measurement in the 2-300 K range for the next cryogenic run. We tested a nodal suspension with sapphire and inox steel spheres for flat plates within the same temperature range. We developed two different kinds of capacitive readout: electrostatic comb one for semiconductor silicon and plane capacitor-like for conductor silicon carbide. Moreover an optical lever readout was employed to measure loss angle on SiC cantilevers and silicon disks.

We are developing a prototype of cryogenic parametric converter transducer operating at 5 GHz, for the upgrade of the ROG Collaboration resonant G. W. antennas. This device is built on the experience of the Niobe detector (D. G. Blair et al.), with substantial modifications that should let us achieve better stability and sensitivity. The prototype uses as parametric converter a superconducting coaxial cavity with a 50 micron gap (Q₀ = 5 × 10 ⁸ at 1.5K and 100μW RF power dissipation), and a contacless RF coupling for thermal insulation between the 2K stage and the ultra cryogenic (100mK) antenna. The coupler features a constant transmission loss of 0.2dB over a range of displacements of ± 5mm in x, y and z around the nominal operating position with a separation of 8mm between the two halves of the coupler. In this way the large, low frequency swings (0.5 and 17 Hz), of the 2 Tons antenna around its suspension point have no influence on the transducer performance. To test all the components of the transducer and the system performance, a room temperature prototype is installed on the TART (Test Antenna at Room Temperature) facility at the INFN labs. Using critical coupling for the RF cavity input coupler we manage to keep to a minimum the leakage of the drive signal to the first RF amplifier. In this way we avoid degradation of the RF amplifier noise figure (0.6 dB at room temperature) produced by the RF amplifier saturation Experimental results agree with the full analysis of the room temperature detector performances.

This paper presents techniques developed by the LIGO Scientic Collaboration to search for the stochastic gravitational-wave background using the co-located pair of LIGO interferometers at Hanford, WA. We use correlations between interferometers and environment monitoring instruments, as well as time-shifts between two interferometers (described here for the first time) to identify correlated noise from non-gravitational sources. We veto particularly noisy frequency bands and assess the level of residual non-gravitational coupling that exists in the surviving data.

We report on an all-sky search with the LIGO detectors for periodic gravitational waves in the frequency range 50-1000 Hz and having a negative frequency time derivative with magnitude between zero and 10^-8 Hz/s. Data from the fourth LIGO science run have been used in this search. Three different semi-coherent methods of summing strain power were applied. Observing no evidence for periodic gravitational radiation, we report upper limits on strain amplitude and interpret these limits to constrain radiation from rotating neutron stars.

Many LIGO data analysis pipelines use either the DARM ERR or AS Q channels as the data source and use a response function R(f) generated from time-dependent calibration measurements to convert to strain in the frequency domain. As calibration varies on a timescale of tens of seconds, the response function must be updated frequently. An alternative is to use time-domain calibrated strain h(t). During the recent year-long LIGO science run (S5), preliminary strain data was published alongside raw interferometer output, typically within half an hour of the raw data being produced. As strain data is now available in highly-reduced form within the LIGO data archive, it represents a convenient alternative for LIGO search pipelines. This paper examines a measure of quality for calibrated strain data by calculating the band-limited RMS (BLRMS) difference between h(t) and strain h^e(t) as calculated directly from DARM ERR in the frequency domain.

We review and expand on a Bayesian model selection technique for the detection of gravitational waves from neutron star ring-downs associated with pulsar glitches. The algorithm works with power spectral densities constructed from overlapping time segments of gravitational wave data. Consequently, the original approach was at risk of falsely identifying multiple signals where only one signal was present in the data. We introduce an extension to the algorithm which uses posterior information on the frequency content of detected signals to cluster events together. The requirement that we have just one detection per signal is now met with the additional bonus that the belief in the presence of a signal is boosted by incorporating information from adjacent time segments.

We present a new wavelet packet decomposition method meant to gravitational wave detection. An issue in wavelet analysis is the choice of time-frequency resolution in order to best represent and reduce data, while in quest of a signal of unknown shape like a burst. In other wavelet methods currently employed, like the LIGO WaveBurst for instance, the analysis is performed at some trial resolutions. We propose a decomposition which automatically selects the best resolution at any frequency. The core of this best resolution selection criterion is the minimization of a function on the wavelet packet coefficients domain, named entropy, like the entropy function used in information theory. As a qualitative application we show how a multiresolution time-frequency scalogram looks like for a sample signal injected over Gaussian noise. As a quantitative application of the method, we use the wavelet packet decomposition to perform a non-linear filter of the data by rejecting the wavelet coefficients under a given threshold, analogously to what is done by the WaveBurst algorithm. Taking coincidences between the events obtained by WaveBurst on the original data and on the data filtered after the wavelet packet decomposition, the false alarm rate has been lowered with negligible effects on the efficiency.

Extreme-mass-ratio inspirals (EMRIs) of compact objects with mass m ∼ 1–10 M_⊙ into massive black holes with mass M ∼ 10⁶M_⊙ can serve as excellent probes of strong-field general relativity. The Laser Interferometer Space Antenna (LISA) is expected to detect gravitational wave signals from ∼ 100 EMRIs per year, but the data analysis of EMRI signals poses a unique set of challenges due to their long duration and the extensive parameter space of possible signals. One possible approach is to carry out a search for EMRI tracks in the time-frequency domain. We have applied a time-frequency search to the data from the Mock LISA Data Challenge (MLDC) with promising results. Our analysis used the Hierarchical Algorithm for Clusters and Ridges to identify tracks in the time-frequency spectrogram corresponding to EMRI sources. We then estimated the EMRI source parameters from these tracks. In these proceedings, we discuss the results of this analysis of the MLDC round 1.3 data.

We report for the first time a method-independent geometrical expression for the angular resolution of an arbitrary network of interferometric gravitational wave (GW) detectors when the arrival-time of a GW is unknown. We discuss the implications of our results on how to improve angular resolutions of a GW network and on improvements of localization methods. An example of an improvement to the null-stream localization method for GWs of unknown waveforms is demonstrated.

We present studies of the collapse of neutron stars that undergo a hadron-quark phase transition. A spherical Lagrangian hydrodynamic code has been written. As initial condition we take different neutron star configurations taking into account its density, energy density and pressure distribution. The phase transition is imposed at different evolution times. We have found that a significant amount of matter on the surface can be ejected while the remaining star rings in the fundamental and first pressure modes.

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

We study the generation of a stochastic gravitational wave (GW) background produced by a population of neutron stars (NSs) which go over a hadron-quark phase transition in its inner shells. We obtain, for example, that the NS phase transition, in cold dark matter scenarios, could generate a stochastic GW background with a maximum amplitude of hBG ∼ 10^-24, in the frequency band ≃ 20-2000 Hz for stars forming at redshifts of up to z ≃ 20. We study the possibility of detection of this isotropic GW background by correlating signals of a pair of 'advanced' LIGO observatories.

At GR17 in Dublin in 2004, it was decided to hold GR18 in Sydney in 2007. Every six years, the GR conference (held every three years) and Amaldi meeting (held every two years) occur in the same year around July. This was to be the case in 2007. By mutual agreement of the International Society on General Relativity and Gravitation (ISGRG), which oversees the GR conferences and The Gravitational Wave International Committee (GWIC), which oversees the Amaldi meetings, it was decided to hold these two important conferences concurrently, for the first time, at the same venue, namely Sydney. At a time when the gravitational wave community was beginning to explore the possibility of searches to probe various aspects of the theory, the vision was to bring that community together with the community of gravitational theorists in order to better appreciate the work being done by both parties and to explore possibilities for future research using the mutual expertise.

The logistics of running two such large meetings concurrently were considerable. The format agreed upon by the ISGRG and GWIC was the following: common plenary sessions in the mornings from Monday to Friday; six parallel GR workshop sessions and an Amaldi session each afternoon from Monday to Friday (except Wednesday); a combined poster session on Wednesday; a full day of Amaldi sessions on the final day (Saturday). The scientific programme for GR18 was overseen by a Scientific Organising Committee established by the ISGRG and chaired by Professor Sathyaprakash. The scientific programme for Amaldi7 was overseen by GWIC chaired by Professor Cerdonio.

One of the highlights of the conferences was the breadth and quality of the plenary programme put together by the scientific committees. Not only did these talks give an excellent snapshot of the entire field at this time, but they also explored the interfaces with other related fields, which proved of special interest to participants. We were given superb overviews of the state of the art of: observational handles on dark energy; collider physics experiments designed to probe cosmology; gravitational dynamics of large stellar systems; and the use of analogue condensed-matter systems in the laboratory to investigate black hole event horizons. In the more mainstream areas we were given timely reviews of: the Gravity Probe B and STEP missions; quasi-local black hole horizons and their applications; cosmic censorship; the spin foam model approach to quantum gravity; the causal dynamical triangulations approach to quantum gravity; superstring theory applied to questions in particle physics; the current status and prospects for gravitational wave astronomy; ground-based gravitational wave detection; and technology developments for the future LISA mission.

A special issue of Classical and Quantum Gravity (Volume 25, Number 11, 7 June 2008) is published as the proceedings of GR18 and Amaldi7. It contains the overview articles by the plenary speakers, the summaries of each GR18 workshop parallel session as provided by the workshop chairs, and the highlights of the Amaldi7 meeting as selected by the Amaldi7 chairs. Other Amaldi7 talks and posters appear in this refereed issue of the electronic Journal of Physics: Conference Series. This issue of JPCS and the CQG Special Issue are electronically linked.

The conference organisers would like to acknowledge the financial support of: The Australian National University; IUPAP; The Australian Institute of Physics; BHP Billiton; The University of Western Australia; The University of New South Wales; The Institute of Physics; The Gravity Research Foundation; SGI; CosNet; The Australian Mathematical Sciences Institute; Springer; Duraduct; the New South Wales Government; The Australasian Society for General Relativity and Gravitation; the Mexican GR bid; the Centre for Precision Optics; The Anglo-Australian Observatory; Newspec; CSIRO; and The University of Melbourne.

We would like to thank the GR18 Scientific Organising Committee, GWIC and the Local Organising Committee for all their hard work in putting together these very successful combined conferences, which attracted 520 participants. Many of the practical aspects of the organisation were handled by the event management company Conexion, and their professionalism, expertise and dedication were greatly appreciated. Finally, we would like to thank all the participants for their lively and colourful contributions to making these conferences a success.

Susan M Scott Chair, Local Organising Committee David E McClelland Deputy Chair, Local Organising Committee Centre for Gravitational Physics, The Australian National University, Australia Guest Editors

Participants gather prior to opening ceremony

Participants entering auditorium for opening ceremony

Chair of Local Organising Committee – Susan M Scott – opening ceremony

President of the International Society on General Relativity and Gravitation – Clifford M Will – opening ceremony

Amusing moment at opening ceremony

Chair of the Gravitational Wave International Committee – James Hough – opening ceremony

Welcome to the land by traditional land owner

Welcome to the land by traditional land owner

First plenary speaker – Stan E Whitcomb

Exhibition booth – Australian National University College of Science – Kimberley Heenan (left), Lachlan McCalman (right)

Exhibition booth – Springer

Exhibition booth – GR19 Mexico City

Amaldi7 posters

Participants gather before Kip Thorne's public lecture

Participants gather before Kip Thorne's public lecture

Entering auditorium for Kip Thorne's public lecture

Public lecture by Kip Thorne

Public lecture by Kip Thorne

Kip Thorne – public lecture

Kip Thorne – public lecture

Roger Penrose (left), Adam Spencer (right)

From left to right: John Steele, Susan Scott, Roger Penrose, David McClelland, John Webb, Adam Spencer

Opening of Roger Penrose's public lecture – from left to right: John Webb, Adam Spencer, Roger Penrose

Roger Penrose at opening of his public lecture

Public lecture by Roger Penrose

Public lecture by Roger Penrose