Gravitational Wave Physics & Astronomy Workshop

= **Keynote Selected**

= **Contributed Talk**

Institution: Seoul National University

Gravitational waves from the pulsar glitch can be detected by next generation gravitational wave observatories. We investigate characteristics of the modes that can emit the gravitational waves excited by three different types of perturbations satisfying conservation of total rest mass and angular momentum. These perturbations mimic the pulsar glitch theories i.e., change of moment of inertia due to the star quakes or angular momentum transfer by vortex unpinning at crust-core interface. We carry out numerical hydrodynamic simulations using the pseudo-Newtonian method which makes weak field approximation for the dynamics, but taking all forms of energies into account to compute the Newtonian potential. Unlike other works, we found that the first and second strongest modes that give gravitational waves are ${}^{2}p_1$ and $H_1$ rather than ${}^{2}f$ and their strains are between $h_c\sim 2\times10^{-24}$ and $10^{-25}$. We also found that vortex unpinning model excites the inertial mode in quadrupole moment quite effectively. The inertial mode may evolve into the non-axisymmetric r- mode.

Institution: UW-Milwaukee

I will discuss what is known and unknown about the local neutron star population, and how this impacts the detectability of neutron stars within the GW horizon. In particular, I will focus on neutron stars that escape traditional detection methods (i.e., radio searches), but how constraints from other wavelengths inform our knowledge of the population.

Institution: Astrophysikalisches-Institut und Universitäts-Sternwarte Jena

We created a catalogue of all OB stars and massive red giants within a distance of 3 kpc. We restricted our first catalogue to those objects observed by both HIPPARCOS and 2MASS, because they are observed best and have best precision. Hence, with BVJHK photometry we estimated interstellar absorption and with V band magnitude and known parallax we derived the luminosity. Using the spectral classification we were able to derive mass and age with evolutionary models (Schaller, 1992; Bertelli, 1994; Claret et al., 2004) and calculated the remaining lifetime (models from Tinsley, 1980; Maeder & Meynet, 1989; Kodama, 1997). Hence, we were able to derive the spatially and temporally resolved supernova-rate (SN) for the near future (which should be the same for the recent past). In the Solar vicinity (<600 pc) we derived a rate of about one event per 50 000 years (Hohle, Neuhaeuser, Schutz, 2010). We then added to our catalogue all other massive OB stars, red giants and Wolf-Rayet stars known in the galaxy to complete the sample for apparent fainter stars and raising the lower limits of the work before. Within 600 pc all SN events take place in 8% area of the sky, whereas 90% of the events take place in 5% area of the sky. For a distance of 5 kpc 90% of all SN events take place in only 9% area of the sky (Schmidt et al. in prep.). If the SN rate in the near future is the same to the recent past, there should be unknown neutron stars (NSs) concentrated in those areas. 100...150 NSs are expected within 1 kpc and younger than 5 Myr (Popov et al., 2003-2010; Palomba 2005), also considering large space velocities. Only ca. 10% of those numbers are known today (ATNF database). Thus it seems very promising to search for young nearby neutron stars in the areas predicted by us. Although those stars may not be detectable in the X-rays they are potential source of gravitational waves, if those NSs are not rotating perfectly spherical and/or precessing. The restricted search to our spatial distribution allows to restrict searches like Einstein@home to certain small areas on the sky, i.e. to perform them with higher sensitivity (Wette et al., 2008).

Institution: Monash Centre for Astrophysics

Rapidly-rotating neutron stars are the only candidates for persistent gravitational wave emission, for which a targeted search can be performed based on the spin period measured from electromagnetic (e.g. radio and X-ray) observations. Apart from the expected weakness of the emission, the principal difficulty for such searches is the lack of precision in measurements of the spin as well as the other physical parameters of the system. I present preliminary results from a pilot program of optical observations of the stellar counterparts to X-ray bright accreting neutron stars, in order to improve the precision of the binary parameters. We observed the optical counterpart of Sco X-1 in 2011 June with the William Herschel Telescope at La Palma, to provide an additional epoch of radial velocity measurements. I will present the revised orbital parameters based on the (now) 12-year baseline, as well as estimates of the likely precision that can be achieved throughout Advanced LIGO observation. These measurements will allow sensitivity improvements for future gravitational wave searches, and will also facilitate pulsation searches with the extensive X-ray timing data from NASA's Rossi X-ray Timing Explorer, to measure the spin frequency.

Institution: California Institute of Technology

Non-axisymmetric neutron stars are expected to emit continuous gravitational radiation. If the star rotates with a millisecond-scale rotation period and possesses sufficiently large asymmetry, this radiation could be detected with Earth based interferometric detectors. Based on the current results for such radiation from the initial LIGO and Virgo detectors, we discuss prospects for future searches using data from advanced gravitational wave interferometers.

Institution: Rochester Institute of Technology

The low-mass X-ray binary (LMXB) Scorpius X-1 (Sco X-1) is a promising source of gravitational waves in the advanced detector era. A variety of methods have been used or proposed to perform the directed search for gravitational waves from a binary source in a known sky location with unknown frequency and residual uncertainty in binary orbital parameters. These include a fully coherent search over a small amount of data, an unmodelled search for a narrowband stochastic signal, and a search for a pattern of sidebands arising from the Doppler modulation of the signal by the binary orbit. A modification of the cross-correlation method used in the stochastic search has been proposed, which takes into account the signal model of a rotating neutron star to allow cross-correlation of data from different times. By varying the maximum allowed time lag between cross-correlated segments, one can tune this semicoherent search and strike a balance between sensitivity and computing cost. I describe the details of and prospects for application of this method to searches for Sco X-1 and other LMXBs.

Institution: University of Masschusetts Amherst

Energetic events in neutron stars, such as pulsar glitches and magnetar flares, excite fundamental mode oscillations leading to gravitational-wave emission which may be observed by advanced gravitational-wave detectors. Searches for GW signals associated with neutron star f-modes in initial generation detectors made few assumptions on waveform morphology and the time-frequency content of the signal. We describe how neutron star spin can lead to a more richly structured gravitational-wave signal than previously assumed by breaking degeneracies in mode frequencies. We also demonstrate how observations of stellar parameters, such as mass and radius, may be used to inform the f-mode signal parameter space for use in future searches and parameter estimation.

Institution: AEI Hannover

For decades, observation of radio pulsars has been the primary driver for our understanding of neutron stars. For the first time, the Fermi Large Area Telescope (LAT) has enabled us to probe the theorized, large population of "radio-quiet" gamma-ray pulsars. These objects can only be found through blind searches for pulsations directly in the LAT data. This is a computationally bound problem. Exploiting novel, efficient data-analysis methods, originally developed for detecting continuous gravitational waves from fast spinning neutron stars, has enabled the discovery of many new pulsars in the LAT data. This presentation will elucidate the new survey and the discoveries made to date. In addition, I will describe how the volunteer computing project Einstein@Home is now being used to increase the computational power for the survey and thus the prospects for further discoveries.

Institution: University Of Warsaw

The development of gravitational wave observatories (Advanced LIGO/Virgo, Einstein Telescope) is proceeding apace, and the direct detection of gravitational waves should be imminent. The last decade of observational and theoretical developments in stellar and binary evolution provides an opportunity to incorporate major improvements to the predictions from populations synthesis models. Among the most important revisions in the formation and evolution of double compact objects are: updated wind mass loss rates, a realistic treatment of the common envelope phase, and a qualitatively new neutron star/black hole mass distribution (consistent with the observed “mass gap”). I will present the effects that this improved physics has on the merger rates of double compact object.

Institution: AEI Hannover

Intermediate mass black holes cover the mass spectrum from tens to thousands solar masses. Their discovery could help shed the light on the plausible evolutionary process from stellar to super-massive black holes and on the dynamical aspects of the stellar clusters that they reside in. Up to few hundreds solar masses, gravitational radiation from collapsing binary systems consisting of two intermediate mass black holes (IMBBHs) is expected to be observable in the LIGO and Virgo interferometers bandwidths. We present results for unmodeled IMBBHs all-sky search performed on data collected by the LIGO-Virgo first generation detectors between November 2005 and October 2007. No significant gravitational wave candidate was found and upper limits on the rate of IMBBHs mergers were calculated. Search performances are then compared to those expected for analogous studies performed in the era of the LIGO-Virgo advanced detectors. Results are stated in terms of effective range, whose dependence on IMBBH physical parameters as components masses and spins is calculated. In particular, larger total mass and spin systems will be visible with second generation interferometers. We investigate the enlargement of the parameters space which will be accessible to unmodeled gravitational waves searches in the next years.

Institution: AEI-Golm

In recent years, several approaches were developed to calculate the final spin of the remnant of binary black hole mergers. I present a new model, based on one of these approaches, which allows us to predict the spin of the black hole remnant of black hole-neutron star binary mergers. I validate the model and assess its accuracy by testing it against the results of numerical-relativity simulations. I then show how the final spin may be used, in turn, to also estimate the mass of the black hole remnant. Further, I discuss the predictions obtained by applying the model to the space of parameters formed by the binary total mass, the binary mass ratio, the initial black hole spin, and the neutron star equation of state. In the second part of the talk, I report on new fully general-relativistic numerical simulations of magnetized binary neutron star mergers leading to the formation of a rapidly and differentially rotating hyper-massive neutron star. Finally, I examine the resulting electromagnetic radiation and compare it to other recent simulations.

Institution: Cardiff University

In a typical gravitational wave search a threshold is applied to the output of a filtering algorithm to separate the background from candidate signals and reduce computational costs. This procedure introduces a selection bias unless it is carefully accounted for. We present a general treatment of thresholded data and apply it to a model gravitational wave search, showing how to derive optimal, unbiased estimates from the results. We also examine how the choice of threshold level affects the precision of such estimates. This will allow us to extract the most information from searches in the post-detection era.

Institution: Albert Einstein Institute

Searches for gravitational waves from coalescing black holes crucially rely on accurate models of the expected signals, and current efforts to describe complete inspiral, merger and ringdown signatures employ a combination of analytical post-Newtonian information with data from numerical-relativity simulations. These hybridization techniques have advanced over the last years, and I will explicitly show how multiple harmonic modes of precessing binaries can now be combined successfully. However, neither hybrid waveforms nor the resulting models are free of errors, and an estimate of systematic errors in the parameter estimation problem is discussed in comparison with statistical errors to address the fundamental question how physical conclusions based on gravitational-wave searches for binary black holes are restricted by current models.

Institution: Cardiff University

During 2009 and 2010, both LIGO and Virgo undertook extended science runs. A simulated GW signal was input directly to the LIGO and Virgo interferometers (a "hardware injection") during the during the data collection without the knowledge of the data analysis teams as part of a "blind injection challenge". This challenge was intended to test the data analysis procedures and processes for evaluating candidate events. Prior to its unveiling as an injection, the event was determined to be a candidate gravitational wave: it was found to have a false alarm rate of less than 1 in 7000 yr and no evidence for an instrumental or environmental origin could be found. In this talk, we discuss the steps that led to the blind injection being identified as a gravitational wave candidate event.

Institution: Perimeter Institute for Theoretical Physics and University of Birmingham

Intermediate mass ratio inspirals (IMRIs) of stellar-mass compact objects into intermediate-mass black holes are tentative astrophysical sources potentially detectable by Advanced LIGO/Virgo. Their unambiguous detection, which would shed light on open astrophysical problems, requires waveforms applicable to highly asymmetric mass ratio systems. Here we consider a class of hybrid inspiral waveforms based on the so-called ''Numerical Kluge'' scheme and compare them to PN and EOBNR waveforms in the IMRI regime. We address the issue of the effectiveness of PN and EOBNR waveforms to detect and extract information about IMRI sources in the advanced detector era.

Institution: Northwestern University and CIERA

The search for gravitational waves emitted by spinning compact-object binaries with ground based detectors poses a great data analysis challenge due to the high number of parameters necessary to describe these signals, which need to be searched over. Computational constraints currently limit the size of waveform template banks that can be used to filter year-long stretches of data; the large dimensionality of the parameter space associated with generic double-spin signals makes them unusable for an actual search, however single-spin templates can be deployed with reasonably small banks. We present a prototype data analysis strategy which deploys physical templates to search for gravitational waves emitted by precessing binaries with only one significantly spinning component, we show its efficiency and we assess the feasibility of a search on LIGO/Virgo data.

Institution: University of Toronto

The dual-frame approach to solving Einstein's equations was introduced by Scheel et al 2006. The initial work used Euler's angles to parametrize the rotation part of the dual-frame map. While this allows for successful simulation of non/mildly precessing compact binaries, the approach fails when there is a significant precession of the orbital plane. We present a new, quaternion-based map, which allows for simulation of highly-precessing binaries

Institution: University of Toronto

At the start of numerical simulations of binary black hole inspirals, there is always a brief burst of high amplitude, high frequency radiation, known as "junk radiation". Here, we investigate how the amount of junk radiation depends on the initial separations of the black holes and on their spins. The junk radiation is measured in three ways: The energy it carries away from the system, how it affects the masses of the black holes, and how it changes the spins of the black holes. We also compare the cases of conformally flat initial data and non-conformally flat initial data (Superposed Kerr-Schild initial data).

Institution: MPG Hannover

Mass and spin are the key parameters to be measured in binary black hole inspirals. We show how previously ignored self-spin interaction terms in the Post-Newtonian waveform can have a large effect on our ability to accurately measure and constrain black hole spin, in some cases by up to a factor of ten. In light of this, we discuss what techniques can be employed to provide astrophysical constraints on black hole spins.

Institution: CITA, U. of Toronto

Numerical simulations of compact object binaries and other strongly gravitating systems fulfill several interrelated roles. In combination with analytical relativity and theoretical astrophysics, simulations explore the range of behaviors of strongly gravitating systems (from black hole kicks to gamma ray bursts) and elucidate the physical processes behind these phenomena. Combined with analytical approximation methods, it provides gravitational waveforms for compact object binaries. These waveforms play an integral role in utilizing current and future gravitational wave detectors, both for event detection and parameter estimation. This talk will give an overview of the current numerical capabilities, and describe the impact of numerical simulations on the modeling of gravitational wave signals. I will also summarize some of the open questions, and venture to predict the expected progress in this area over the coming years.

Institution: Georgia Tech

With advanced, ground-based gravitational-wave detectors expected to be operational within a few years, the numerical relativity and data analysis communities are at an important juncture -- We need to not only simulate ever increasingly generic binary black hole systems but also to synthesize what we learn and to get this information into data analysis pipelines. Here I present work on understanding the role of non-dominate harmonics on event loss using an advanced LIGO noise curve to provide a look into where complexities in the BBH merger signal arise and how they might impact detection.

Institution: Caltech

The core collapse of a massive star is among the most energetic events in the Universe, liberating energies on the order of 10^53 ergs. About 99% of the energy is emitted in neutrinos, and a tiny fraction is emitted in gravitational waves. Both, neutrino and gravitational wave signals are generated inside the core region where the deciding dynamics occur. Thus, observing these signals will yield important information on the core collapse dynamics and explosion mechanism. I report on results from recent 3D general relativistic simulations of stellar core collapse with an approximate treatment of neutrino transport. I focus on the gravitational wave and neutrino signals from core collapse, bounce, protoneutron star oscillations, and subsequent collapse to a black hole. We find a new correlation between gravitational wave signal and neutrino luminosities induced by excited global protoneutron star oscillation modes after core bounce. In the context of black hole formation, we identify a unique gravitational wave signature associated with the early phase of collapsar formation.

Institution: Caltech

Electromagnetically triggered searches for gravitational waves (GWs), such as the ones associated with Gamma-Ray Bursts (GRBs), have been systematically carried out by the LIGO and Virgo GW detectors during the past decade. On the other hand, the electromagnetic counterparts of GRBs and other transient GW sources may potentially be discovered with a low latency response to GW triggers. Finding electromagnetic (radio, optical, X-ray) counterparts to GW triggers is technically challenging due to imperfect localization of the GW signal and uncertainty regarding the relative timing of the GW and electromagnetic emissions. However, GW-triggered searches may yield fundamental discoveries, such as the first direct confirmation of the "jet model" for GRBs. In 2009-2010, the LIGO and Virgo collaborations performed the first prompt search for electromagnetic counterparts of GW triggers from the LIGO/Virgo detector network. In this talk, I give an overview of these electromagnetic follow-ups, and discuss their importance in view of the advanced GW detectors era.

Institution: UW-Milwaukee

We will discuss ongoing and future efforts to find radio transients across a range of timescales with two new radio telescopes: the Murchison Widefield Array and the Australian Square Kilometer Array Pathfinder, both of which are being built in Western Australia. These efforts directly complement gravitational-wave searches. [Note that this would be my preferred talk]

Institution: University of Birmingham

Accurate localization of gravitational-wave events generated by neutron star binary mergers is necessary to enable electromagnetic follow-ups. The large GW error box means that the use of astrophysical priors, particularly known galaxy catalogs, can be very important for successful EM searches. These priors depend on our assumptions about the completeness of the galaxy catalog, the scaling of BNS merger rates with observables such as the blue-light luminosity, and the possibility of BNS mergers occurring outside host galaxies due to natal kicks. We present an analysis of the effects on EM follow-up success rates of the choice of astrophysical priors, tested against simulated distributions of candidate events under a range of corresponding astrophysical models.

Institution: university of birmingham

When the next generation of gravitational-wave interferometers come online we expect to follow up detections of coalescing compact binaries with electromagnetic observations. Accurate sky locations will be needed to help point these follow-up searches. We have developed a number of codes based on Bayesian analysis that search for the parameters of a source, including its sky position. Here we present the first systematic comparison of the performance of the different algorithms. In particular we investigate the trade-off between a potentially greater positional accuracy in these fully coherent codes and the faster algorithms that rely on timing triangulation alone.

Institution: University of Wisconsin - Madison

IceCube, a cubic kilometer neutrino detector located in glacial ice at the South Pole, has recently become the first neutrino telescope with a sensitivity below the TeV-PeV neutrino flux predicted from gamma-ray bursts if GRBs are responsible for the observed extragalactic cosmic-ray flux. These neutrinos are produced in interactions between the accelerated cosmic ray protons and the photons present in the burst fireball, allowing neutrino observations to directly constrain or confirm proton acceleration in these sources. Recent results from searches for this flux using the IceCube detector will be presented, as well as implications of this result for cosmic-ray acceleration in GRBs and prospects for future searches.

Institution: Max Planck Institute, AEI Hannover

Multi-messenger astronomy is entering an exciting period with the recent development of experimental techniques that have opened new windows of observation of the cosmic radiation in all its components. Cataclysmic cosmic events can be plausible sources of both Gravitational Waves (GWs) and High Energy Neutrinos (HENs). Such messengers could reveal new, hidden sources that are not observed by conventional photon astronomy. Requiring consistency between GW and HEN detection channels shall enable new searches and a detection will yield significant additional information about the common source. A neutrino telescope such as ANTARES can determine accurately the time and direction of high energy neutrino events. A network of gravitational wave detectors such as LIGO and Virgo can also provide timing/directional information for gravitational wave bursts. By combining the information from these totally independent detectors, one can search for cosmic events that may arrive from common astrophysical sources. I will talk about the first joint analysis between GW and HENs using LIGO, Virgo and ANTARES data.

Institution: University of Florida

The advanced LIGO and Virgo gravitational-wave (GW) detectors target first detection starting in 2015. To maximize the scientific output of the GW observations and multi-messenger measurements, two more detector sites are developed in Japan and India. This presentation considers the effect of the detector topology (shape and orientation of the detector arms) on detection and reconstruction of transient GW signals, particularly the source localization. The network performance can be considerably improved if instead of the classical L-shape topology, interferometers with the "invariant" topologies are used. Such detector topologies enable a significantly better reconstruction of GW signals with a fewer number of detector sites. In our study we identify the optimal detector topologies and network configurations, and compare them with the existing and planned detector networks.

Institution: MIT

A first multi-wavelength follow-up observation of candidate gravitational-wave (GW) transient events recorded by LIGO and Virgo took place during their 2009-2010 science run. During this run a low-latency search allowed the prompt identification and sky localization of such GW transient event candidates. This was then used for pointing the X-ray and Ultra-Violet/Optical telescopes aboard Swift in order to search for possible afterglows associated with the transient event candidates. Image transient analysis was used to analyze the electromagnetic data. Monte Carlo techniques were used to quantify the sensitivity improvement which joint electromagnetic and GW observations can bring. We present the methods and results from this first combined analysis and discuss its implications in terms of sensitivity for the present and future instruments.

Institution: MIT

The follow-up observations of the candidate gravitational-wave (GW) transient events with the optical/X-ray/radio telescopes in search of associated electromagnetic (EM) counterparts can potentially provide very rich, complementary information about the GW sources and their environment. If detected the EM counterparts may also increase the overall significance of the GW candidates and thus improve sensitivity of the joint search. We present methodology for a generic joint analysis of GW and EM data that combines information from both observations into a single detection statistic - the composite likelihood-ratio. We identify the key factors determining sensitivity of the joint search (e.g. sky-coverage and latency of observations, background of accidental EM transients and GW probability sky-map) and discuss some of the open issues that should be addressed in the future multi-messenger searches.

Institution: Università di Urbino/INFN Sezione di Firenze

A pioneering electromagnetic observation follow-up program of candidate gravitational wave events has been performed during the last LIGO/Virgo run (Dec 17 2009 to Jan 8 2010 and Sep 4 to Oct 20 2010) and involved wide-field optical telescopes. The joint gravitational wave and optical study requires the development of specific image analysis procedures able to discriminate the possible optical counterpart of gravitational wave triggers from background/contaminant events. We will present the image analysis procedure developed for the identification of the electromagnetic counterparts in the images taken with TAROT, Zadko and QUEST.

Institution: Università di Urbino/INFN Sezione di Firenze

Multi-wavelength astronomy from radio waves to gamma rays has provided the most complete picture of the Universe so far. In the coming years the ground-based interferometers Virgo and LIGO will reach sensitivities good enough to observe for the first time the gravitational-wave signals. This poster discusses the joint analysis of gravitational waves and high-energy photons, aiming at a multi messenger investigation of compact objects like neutron stars and black holes. These objects are the most promising sources of gravitational signals: mergers of compact objects are believed to power the short Gamma Ray Bursts, and rotating neutron stars are the engine of pulsar emission. We plan to investigate: i) the use of all-sky survey of gamma-ray satellites (e.g. Fermi) during the electromagnetic follow-up of gravitational wave triggers; ii) exploiting gamma-ray observations of pulsar glitches to search for gravitational wave signals and iii) producing accurate predictions for the Advanced interferometer detection rate from new dynamical models and simulations.

Institution: University of Southampton

In this talk I will summarize the current state of the field of radio transients, and how it has been reinvigorated by the (ongoing) construction of a new generation of wide-field arrays. I will breifly discuss the chances of a GW event having a radio counterpart. Finally I will discuss how with LOFAR we are already planning to coordinate with Advanced LIGO to search for coherent radio bursts from GW events in a number of novel ways.

Institution: CNRS AstroParticule et Cosmologie

We present a data analysis procedure which aims at searching for gravitational-wave transients in coincidence with high-energy neutrinos. In this procedure, the time and direction of the high-energy neutrinos are used to define the time interval and sky region where the available gravitational-wave data will be searched. The pipeline essentially relies on coherent WaveBurst (cWB), an all-sky all-time search pipeline for gravitational-wave bursts. Changes have been made in order to restrict the production of cWB events consistent in time and space with the neutrino candidates. The pipeline allows the analysis of thousandths of neutrino candidates in a bandwidth ranging up to several kHz with standard computing ressources. A comparison with earlier analyses is presented using a set of simulated neutrino candidates and time-shifted gravitational-wave data. Abstract presented in collaboration with B Bouhou, B Baret, A Kouchner, F Salemi and G Vedovato

Institution: AEI - Hannover

Gamma-ray bursts are among the most violent events observed in the universe; their progenitors are most likely the coalescence of a neutron star with another neutron star or black hole, and extreme cases of stellar core-collapse. Both progenitors should also emit copious amounts of gravitational waves. We discuss the astrophysics of these progenitors and describe two gravitational wave searches tailored towards each progenitor. We present the results of these searches in the 2009-2010 data from the LIGO and Virgo network of gravitational wave detectors, and discuss prospects of future observations in the advanced gravitational wave detectors era.

Institution: Stockholm University

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 could be a crucial aspect for the first direct detection of gravitational waves. Information on the progenitor, such as trigger time, direction and expected frequency range, can enhance our ability to identify gravitational wave signatures with amplitudes close to the noise floor of the detector. Furthermore, combining gravitational waves with electromagnetic and neutrino observations will enable the extraction of scientific insight that was hidden from us before. We discuss methods that enable searches for common sources with the IceCube-ANTARES-LIGO-GEO-Virgo global network as well as their methodology, science reach, and outlook for next generation gravitational-wave detectors.

Institution: National Center for Nuclear Research

The poster is presents the idea that lies behind Optical Transient ExtTrig Search project. The main aim of the project is to make externaly triggered search connected with optical transients registered by Pi of the Sky telescopes. Most of them of unknown origin and very short duration (less than 10 s). The optical transients, that were taken for the analysis, were observed from September 2004 up to May 2009 and during summer 2011.

Institution: NASA GSFC

In recent years, the time to identify triggers for transient gravitational wave (GW) signals from the LIGO/Virgo network has been reduced from weeks to minutes. The ability to find and characterize a GW transient with low-latency creates the possibility of pointing x-ray, optical, and radio telescopes towards the GW source to find an electromagnetic (EM) counterpart. The precision with which a GW signal can be localized depends on a number of factors, including the GW detectors, the signal strength, and knowledge of source models. In the near-term, GW localization is likely to be limited, so directing instruments to the right location will require a carefully planned strategy. This talk will present an overview of the status and prospects of joint GW/EM low-latency searches.

Institution: Tokyo Institute of Technology

The plan for multi-messenger observation of GW events is described. In the X-ray band, an all-sky X-ray monitor operating on the ISS since August 2009, scans nearly the whole sky every 92 minutes to search for transients. In addition, a soft X-ray large solid angle monitor experiment is proposed. In the optical band, wide-field telescopes are being prepared for follow-up observations. The neutrino experiment optimized for detecting supernova neutrino is also planned. For a GW trigger of a binary merger, we first search for temporary coincident event in the X-ray band, which should give a sub-degree localization if detected. In fact, theories predict more unbeamed or off-axis emission in the soft X-ray band than in the traditional gamma-ray band. The X-ray position will be followed up with robotic optical telescope to obtain arcsec positions that enables deep observations with big facilities either on the ground or in the space. For a less frequent supernova in the local Universe, the neutrino detection should give a temporal trigger and a degree-size localization. In addition to the EM follow-up to characterize the supernova, the GW data should be examined for temporal coincident signal to lower levels than is usually possible.

Institution: Max-Planck-Institut für Radioastronomie

Radio timing of an array of several tens of millisecond pulsars (MSPs) has the potential to detect gravitational waves generated through the inspiral of binary supermassive black holes in the nearby (z<2) Universe. In this talk, I will give an overview of the current state of these detection efforts, the challenges ahead and ongoing efforts to overcome said challenges. Furthermore, I will comment on the potential information that could be gained about the supermassive binary black holes and about gravity in general.

Institution: Max-Planck institute for radio astronomy

I will report recent progress about the IPTA data challenge and explain the algorithm of simulating the data. The expected results feedback report will be also explained.

Institution: California Institute of Technology

We revisit the suggestion that dual jets can be produced during the inspiral and merger of supermassive black holes when these are immersed in a force-free plasma threaded by a uniform magnetic field. By performing independent calculations and by computing the electromagnetic emission in a way which is consistent with estimates using the Poynting flux, we show that a dual-jet structure is present in our simulations, but energetically subdominant with respect to a non-collimated and predominantly quadrupolar emission, which is similar to the one computed when the binary is in electrovacuum. While our findings set restrictions on the detectability of dual jets from coalescing binaries, they also increase the chances of detecting an EM counterpart from these systems.

Institution: AEI Potsdam

In the next decade the detection of gravitational waves (GW) will be a reality, opening a completely new window on the Universe. Massive black holes (MBH) binaries (MBHBs) are expected to be among the primary actors on this upcoming stage. In this framework, I will describe prospects of detecting and disentangling multiple MBHBs with forthcoming pulsar timing arrays (PTAs). Triangulation of the source position with a large number of pulsars in the array, will allow to resolve several individual sources at each frequency, and to locate them in the sky with good precision.

Institution: Osaka City University

The upper limit which we estimate with network of future ground-based detectors(KAGRA, aLIGO, aVIRGO, AIGO) for isotropic stochastic gravitational wave background(SGWB) is $Omega_{gw} h^2 > 10^-9$. When we think about this upper limit and theoretical prediction of SGWB, we may detect gravitational wave(GW) from cosmic string. Although there are cusp and kink of structure which emit GW on cosmic strings, in this study we focus especially on GW from cusp. The behavior of GW from cusp depends on the size of its amplitude. GW of bigger amplitude much than detector noise is seen as burst gravitational wave, and GW of smaller amplitude appear as continuum of stochastic background. We are also interested in the behavior of small GW components - "grains of small bursts" -, which amplitudes are similar to the detector instrumental noise level and its rate is order of 1Hz. Less enough analysis has performed for such GW before. The waveform of GW from cosmic string in time domain is known. Then we generate simulation data by method that one GW superpositions many times. And we will have to find new analysis method for "grains of small burst".

Institution: IUCAA

Abstract: CMB polarization measurements have improved immensely in recent years. In particular, the upper-limits on the curl component (B-mode) have considerably tightened. A stochastic GW background of cosmological, or, astrophysical origin would gravitationally lens the well measured gradient (E-mode) component of polarization into B-mode polarization. We show that the lensing due to GW is far more efficient in E to B power transfer than the corresponding effect due to the, more commonly studied, lensing due to density perturbation. We explore the possibility of constraining the power in GW background at different length scales and at different cosmological epochs using the current and near future B-mode upper limits.

Institution: Observatoire de la Cote d'Azur

Compact binary coalescences, such as binary neutron stars or black holes, are among the most promising candidate sources for the current and future terrestrial gravitational-wave detectors. While such sources are best searched using matched template techniques and chirp template banks, integrating chirp signals from binaries over the entire Universe also leads to a gravitational-wave background (GWB). In this paper we systematically scan the parameter space for the binary coalescence GWB models, taking into account uncertainties in the star formation rate and in the delay time between the formation and coalescence of the binary, and we compare the computed GWB to the sensitivities of the second and third generation gravitational-wave detector networks. We find that second generation detectors are likely to detect the binary coalescence GWB, while the third generation detectors will probe most of the available parameter space. The binary coalescence GWB will, in fact, be a foreground for the third-generation detectors, potentially masking the GWB background due to cosmological sources. Accessing the cosmological GWB with third generation detectors will therefore require identification and subtraction of all inspiral signals from all binaries in the detectors' frequency band.

Institution: Albert Einstein Institut Hannover

The most promising gravitational wave backgrounds are investigated; the sources that produce them are binary systems (composed of white dwarfs, neutron stars, stellar-mass black holes and supermassive black holes) and rotating neutron stars (pulsars, magnetars and gravitars). The spectrum of the background is presented over the frequencies of all existing and planned detectors. Different regimes of the background are distinguished, depending on its resolvability. In some frequency intervals, the background is unresolvable, since it is made of signals whose waveforms cannot be distinguished from each other or subtracted out of the data. Besides a realistic expectation of the level of binaries background, upper and lower limits are given, to account for the uncertainties in some astrophysical parameters such as binary coalescence rates. A robust upper limit for the background of rotating neutron stars is obtained; it does not exceed the detection threshold of two cross-correlated Advanced LIGO interferometers. Different initial spin frequency distributions lead to very different estimations of the background of rotating neutron stars. For one of the models, with slow initial spins, the detection of this background by present or planned detectors can be rejected. However, other models do predict the detection of this background, that would be unresolvable, by the future detector ET. If gravitars exist and constitute more than a few percent of the neutron star population, they produce an unresolvable background that can be observed by ET. With the most optimistic model, the background produced by magnetars can also be detected by ET, but not by BBO or DECIGO.

Institution: University of Warsaw

The current star formation models imply that the binary fraction of population III stars is non zero. The evolution of such binaries must have led to formation of compact object binaries. In this work we estimate the gravitational wave background originating in such binaries and discuss its observability. The properties of the population III binaries are investigated using a binary population synthesis code. We numerically model the background and we take into account the evolution of eccentric binaries. The gravitational wave background from population III binaries dominates the spectrum below 100 Hz. If the binary fraction is larger than 0.01 the background will be detectable by LISA and DECIGO. Gravitational wave background from population III binaries will dominate the spectrum below 100 Hz. LISA, ET and DECIGO should either see it easily or, in case of non detection, provide very strong constraints on the properties of the population III stars.

Institution: INPE

Both detectors, Mario Schenberg (Brazil) and MiniGRAIL (Netherlands), share almost the same features. Spherical detectors present the possibility of multichannel analysis and therefore they are able to determine gravitational wave direction and polarisation. This was already shown in the offline data analysis pipeline developed for MiniGRAIL. This pipeline could be applied with minor changes to Mario Schenberg. Presently, we are developing a low latency data analysis able to determine the direction of high SNR bursts. Triggers are vetoed to reduce the false alarm rate. The method is tested on simulated data. A simulator for Mario Schenberg was already developed. We present here the low latency method and preliminary results. The Mario Schenberg’s transducers have been redesigned to improve the sensibility and a new commissioning run is planned by the end of the year. Its new status will be also briefly commented.

Institution: Caltech

This presentation gives an overview of and future plans for the AuxMVC project, which employs multivariate classifiers for the purpose of noise artifact, or "glitch", identification in LIGO detectors. The input to the multivariate classifiers is information from the hundreds of auxiliary channels that monitor potential noise sources and non-gravitational wave degrees of freedom for the detectors. We compare three different classifiers (artificial neural network, support vector machine, and random forest of bagged decision trees) and discuss the possibilities these powerful methods offer for incorporation of information from the auxiliary channels into gravitational-wave searches. We present the performance of these classifiers on the S4 and S6 data sets, and discuss how these tools could be implemented in the advanced detector era.

Institution: NIMS / PNU

In the gravitational wave channel (GW) of LIGO detectors, there is a significant number of noise artifacts of non-astrophysical origin that give rise to high signal-to-noise ratio noise transients in the searches for gravitational waves from astrophysical sources. To detect gravitational wave signals effectively, the non-gaussian noise transients should be vetoed from gravitational wave channels. These noise artifacts originate from various sources such as seismic disturbance, environmental motion, thermal property of test mirror, suspensions, quantum effect of laser, and their combinations. Since hundreds of auxiliary channels, which response to gravitational waves is negligible, monitor the noise sources, figuring out correlations between triggers in GW channel and auxiliary channels provides us with a useful tool for distinguishing real GW signals from noise artifacts. For this purpose, we employ Artificial Neural network (ANN), one of the popular machine learning algorithms, to handle large dimensional parameter space and complexity of noise patterns. In this presentation, we focus on the application results of ANN to identification of noise artifacts using auxiliary channel data of the LIGO Hanford detector from the fourth Science Run (S4) and of Livingston detector from a week of the sixth Science Run (S6). This work is a part of the ongoing activities of applying machine learning algorithm such as Random Forest of Baggered Decision Trees, and Support Vector Machine to identification of noise artifacts using auxiliary channel information.

Institution: AEI Hannover

One of the most exciting prospects for the second generation GW detectors is joint EM-GW observation of a GW source. In order to maximize the probability of such a detection, the latency of GW detection and follow-up telescope pointing must be driven down. This past winter the LSC and Virgo Collaboration ran their first advanced detector Engineering Run (ER1) with such a focus. ER1 was geared toward testing low-latency data transfer and analysis of simulated data from second generation detectors. It also included a "mock data challenge" in the form of a set of blind burst and compact binary inspiral signals. The rate of the latter was around that expected astrophysically. Here I summarize the ER1 infrastructure and report on the results of analyzing the simulated ER1 data in low latency.

Institution: Università di Urbino - INFN Firenze

A gravitational waves detector presents many kinds of non-linear physical processes, hence noise structures in auxiliary channels, including narrow spectral features, may be converted non-linearly into noise polluting the gravitational channel. Uncovering such non-linear relationships between auxiliary channels and the gravitational wave channel can be very useful to characterize the detector and possibly also to improve the confidence of the GW searches. We are developing and testing on Virgo data a procedure based on a forward-regression orthogonal estimator applied to non-linear system identification, to identify non-linear noise in gravitational waves detector output. The identification accuracy is improved by filtering the error in a specified frequency region. An outcome of the algorithm is a ranking of the auxiliary channel significance for a given analyzed region.

Institution: Niigata University

The Hilbert-Huang transform is the combination of the empirical mode decomposition and the Hilbert spectral analysis. Here we investigate a possibility of constructing an alert system with the Hilbert-Huang transform in search for gravitational wave signals.

Institution: Yamanashi Eiwa College, Japan

The Hilbert-Huang transform (HHT) is a novel, adaptive approach to time series analysis that does not make assumptions about the data form. This algorithm is adaptive and does not impose a basis set on the data, and thus the time-frequency decomposition is not limited by time-frequency uncertainty spreading. Because of its high time-frequency resolution, it will have important applications to the detection of gravitational wave signals. The HHT consists of the empirical mode decomposition (EMD), followed by the Hilbert Spectral Analysis (HSA). The EMD decomposes the data into intrinsic mode function (IMF), each representing a locally monochromatic frequency scale of the data. Summing over all IMFs will recover the original data. The HSA derives the instantaneous amplitude (IA) and frequency (IF) from the analytical complex representation of each IMF; the IMF itself and the Hilbert transform of the IMF are the real and imaginary parts, respectively. The IA and the IF are given by taking the absolute value and by differentiating the phase. However, since the EMD is empirical method, there are some parameters to be fixed in the EMD. Therefore, we propose and demonstrate a method to fix these parameters.

Institution: Kotel'nikov Institute of Radioengineering and Electronics, Russian Academy of Sciences

Every laser gravitational wave detector is the complex electrodynamics system which besides the main laser cavities (master and slave laser resonators) consists of additional optical elements and auxiliaries. Any of these details are sure to reflect and scatter some part of laser radiation and thus the multi-mirror optical cavities or resonators with intricate phase equations are formed. Periodic and stochastic variations of the laser intensity and its frequency due to temporal phase instability of such external resonators are frequently observed in high precision laser interferometer configurations. Gravitational wave detectors, which are based on more complicated dual-recycled interferometer scheme, would suffer from these annoyances particularly. The backscattering from signal-recycling mirror, which is used for changing the resonance frequency of the signal recycling cavity as well as reflections and scattering from high power photodiode receivers would be obligatory components to be taken into account when the phase sensitivity of 10(-9) radians for the optical response of the instrument is appointed. The methods of calculation of phase distortions in large-scale multi-mirror cavities, feedback effect testing and control by phase monitoring and frequency shifting of scattered light are described in this report. Residual backscattering effects are considered to be additional left out of account sources of seismic noise in the advanced laser gravitational wave detectors. These effects can be appreciable even in fully suspended dual-recycled interferometer if some of scattering elements are not involved into the length-control servo. Extensive experience and practical results of seismic observations by long-path laser interferometers in frequency band from 1 Hz up to 10 kHz are presented and new means of their application in geophysics and modern seismology are discussed.

Institution: AEI Hannover

Continuous gravitational-wave emission from unknown isolated objects can be searched for via fully coherent matched-filtering grid-based methods, which in the case of weak signals, implies short observation time (~days) or prohibitive computing costs. In recent years, semi-coherent techniques, applied in all-sky surveys using the distributed computing environment Einstein@Home, have enabled more sensitive long-observation (~year) searches, reducing the total parameter space to some smaller interesting regions around a parameter space point or candidate. However, the important step of transition from semi-coherent to fully-coherent search, in order to confirm or discard the candidate, using all of the available data has been lacking. We address this problem by applying a mesh adaptive direct search algorithm. Such algorithms do not depend on a predefined search grid, but adapt to the likelihood surface, resulting in acceptable computing cost even for very long fully-coherent observations (~year). We show, based on Monte Carlo studies with simulated data, that such algorithms are suitable for systematic follow-up of interesting Einstein@Home candidates.

Institution: Jet Propulsion Laboratory

I present a novel, computationally efficient method to map the distribution of the maximum-likelihood parameters for signals detected in Gaussian noise. This method can be applied to problems of experimental design (answering the question, what is the expected accuracy of low-SNR observations?) and to the tuning of Markov-Chain Monte Carlo searches (providing proposal distributions), in the context of gravitational-wave astronomy, but not only.

Institution: AEI Hannover

All-sky, broadband searches for gravitational-wave pulsars are computationally limited. It is therefore important to make efficient use of available computational resources, for example by minimising the number of templates needed to cover the parameter space of sky position and frequency evolution. A difficulty is that, for searches over the sky, the required template resolution is different for each sky position, and this makes it difficult to achieve an efficient covering. Previous work on this problem have found choices of sky and frequency coordinates, with respect to which the parameter space metric (which determines the template resolution) is constant. These approaches, however, are limited to coherent integration times of a few days, which in turn limits the sensitivity achievable by e.g. a hierarchical search pipeline. We present recent work on new sky and frequency coordinates, with a flat parameter-space metric, that do not suffer from this limitation. By allowing integration times of, e.g., longer than a week, improvements in search sensitivity may be possible using the new coordinates.

Institution: NIMS & Hanyang University

We report the performance test of a supervised machine learning algorithm to identification of gravitational-wave (GW) signals from noise transients. The LIGO Scientific Collaboration (LSC) developed a sophisticated search pipeline for gravitational waves emitted by central engine of short duration Gamm-Ray Bursts (GRBs). However, noise transients originating from non-astrophysical sources hinder identification of gravitational wave signals in data analysis. We apply the Random Forest of Bagged Decision Trees method, one of supervised learning algorithms, to the post-process of the Compact Binary Coalescence (CBC) - GRB search pipeline. In this presentation, we demonstrate the preliminary performance of the method in identifying GW signals from background noise.

Institution: Albert Einstein Institute

We present an all-sky search for periodic gravitational waves in the frequency range [50, 1190] Hz and with frequency derivative range of ~ [-20, 1.1] x 10^{-10} Hz/s for the fifth LIGO science run (S5). The search uses a non-coherent Hough-transform to combine the information from ~1-day coherent searches over a year. Because these searches are very computationally intensive, they have been carried out with the Einstein@Home volunteer distributed computing project. We compare the search treated here with the previous Einstein@Home search of early S5 LIGO data, and present the post-processing pipeline that allowed us to discard various thousands of false candidate events.

Institution: AEI Hannover

In this work, I present a novel likelihood transform which can make the structure of the likelihood surface much simpler, hence reducing the intrinsic difficulty of data analysis. Simple examples are followed to demonstrate the methods.

Institution: INFN Roma

In targeted searches for continuous gravitational wave signals, an upper limit on signal amplitude is computed when there is no statistically significant detection. Often upper limits are computed within a frequentist framework, based on the value of the detection statistic obtained in the actual analysis and having chosen a given confidence level $\alpha_0$. If the value of the detection statistic falls within the first $1-\alpha_0$ quantile of its noise-only distribution, the resulting upper limit is zero. Although legitimate, this result is not very satisfying, especially when results obtained in the analysis of different datasets are compared: the upper limit obtained with a "worse" dataset (in terms of expected sensitivity) could be much lower than that obtained with a better dataset. Here we discuss an alternative and very intuitive way of setting upper limits, based on a mixed frequentist-Bayesian approach, which allows solving the "problems" of the pure frequentist method, while keeping its advantages and also permits easy incorporation of any prior information on signal parameters. A comparison with the frequentist and with the Feldman-Cousins unified approaches is presented, using both analytical computations and numerical simulations.

Institution: Albert-Einstein-Institut Hannover

The traditional approach to searching for continuous gravitational-wave (CW) signals in wide parameter spaces of "phase parameters" (such as sky-position, frequency, spin-down ..) is based on the orthodox "maximum-likelihood method": a likelihood statistic is computed over the parameter space, and "loud" points of the statistic are selected for further scrutiny. However, the Neyman-Pearson lemma shows that the optimal detection method consists of marginalizing the likelihood-ratio (resulting in the "Bayes factor"). Here we discuss the potential benefits of phase-parameter marginalization compared to maximization in identifying candidate signals.

Institution: INFN Roma

The search for unknown isolated neutron stars using the Virgo data of the VSR2 and VSR4 run is now under way. We will describe here the whole analysis procedure which consists of several different steps. In particular we will describe the following: veto of noise artifacts, candidate selection with a coarse grid, immediately followed by a parameter refinement, coincidence of candidates found in different datasets, and follow-up of candidates surviving coincidences. The final sensitivity of the method and the computing needs, as a function of the analyzed parameter space, are studied and characterized both analytically and through simulations.

Institution: Trento University and INFN Padova

One of the most difficult issues faced in gravitational wave (GW) searches comes from non gaussian excess noise. To mitigate this problem, a partial noise cancellation has been recently developed by a regression analysis of auxiliary environmental and instrumental channels. These methods measure the coupling of the auxiliary channels to the GW channel, inlcuding non-linear cases, and estimate the contribution of auxiliary channels into the excess noise of the GW channel. The subtraction of this prediction provides the noise suppression. The impact on continuous GW searches can be relevant, both in widening the frequency bands useful for the search and in improving the GW sensitivity. We present preliminary results of the noise cancellation methods under development for continuous GW searches, using real data of the first joint LIGO-Virgo run. The performance will be tested by analyzing software and hardware GW signal injections for a sample of frequency bands.

Institution: University of Urbino/INFN

A coherent follow-up of gravitational wave events originated by coalescing binaries is expected to run on triggers obtained by standard search pipelines in order to obtain a better parameter estimation, including sky localization. Using spinning or non-spinning waveforms for the follow-up has drastic consequences on the time-duration of the analysis but also on the accuracy of the sky position recovery.

Institution: Osaka City University

We often generate time series signal which consists of noise and gravitational wave for the interferometer using FFT/IFFT. However, since FFT/IFFT method treat the data with finite time chunks, it is not good to use for the study of continuous processing of signals across long duration over the chunks. Moreover these generated noises will not joint smoothly to neighbor chunks. To mimic the realistic raw data taking and calibration process, we would like to generate seamless time series data. We try to generate seamless gaussian noise to interface transfer function with white gaussian noise in time region. Where, transfer function is interferometer sensitivity written in complex frequencies. In this calculation we use laplace transform and matrix operation. About another noises (line noise, thermal noise, etc) we can generate time series directly considering Q-value, repetition of excitation. We will display these methods in detail and show result of simulation.

Institution: Osaka City University

The calculation for Gravitational Wave analysis will take much cost, e.g. for huge number of templates in matched filter for compact star binary, sweeping many pixels and frequency band for the radiometry and so on.Then, to make those calculation rapidly, we try to employ GPGPU(General-Purpose computing on Graphics Processing Units ) to the gravitational wave analysis. As the first instance, we are trying to apply GPGPU to Gravitational Wave Radiometry. Gravitational Wave Radiometry is an analysis method, using two or more detectors and take that cross-correlation for a long time to see, for example stochastic gravitational wave background, continuous gravitational wave which comes regularly from particular direction. Here, we show why GPGPU is useful for Gravitational Wave Radiometry, and what we can say is GPGPU has more advantageous if the frequency resolution become higher.

Institution: The Australian National University

The most promising sources of gravitational waves expected to be detected in the near future may be considered sparse in four main sensing representations. The early (stationary phase) inspiral portion of an unstable close compact binary (‘CBC’) system is expected to have a compact expression in the time-frequency (‘chirp’) plane, while transient (‘burst’) sources are expected to appear as isolated pulses in the time domain (CBC events may also be classed as a burst event). Quasi-monochromatic (‘continuous wave’; CW) signals appear as a small number of non-stationary spectral lines in the Fourier domain. Finally the so-called ‘stochastic background’ is sparse in an inter-detector cross-correlation space in the Fourier domain. Here I present an overview of how the sparse nature of these signals might be exploited in order to improve prospects of detection. I illustrate this with two simplified case simulations. The first involves a possible reduction in the computational complexity of many CW searches by making use of a recently developed Sparse Fast Fourier Transform, with a corresponding decrease in run-time compared to the usual FFT algorithm that is proportional to the sparsity of the signal. Because many potential CW searches have a strong computational bound, such an improvement might increase the number of viable targets for a given detector sensitivity. The second is an illustration of a potential improvement in the spatial position reconstruction of gravitational wave burst events, via an application of compressive sampling. Chirp template mismatch, as a result of aliasing in the time-frequency plane, leads to corresponding signal-to-noise degradation. By potentially reducing the impact of aliasing, the event may be better localised in the time-frequency plane, leading to better position reconstruction, given a network of detectors. Such an improvement would be of especially great benefit in a multi-messenger context.

Institution: AEI Hannover

An all-sky search for continuous gravitational waves from unknown neutron stars in binary systems is notorious for its computational challenge. The TwoSpect algorithm exploits the periodic orbital modulation of the source waves by searching for patterns in doubly-Fourier transformed data. We discuss the astrophysical parameter space searchable using TwoSpect, and we present results from simulated data showing the estimated upper-limit sensitivity attainable and the potential for successful detections of simulated signals by the TwoSpect search method.

Institution: AEI Hannover

We investigate the effect of neglecting precession on the sensitivity of searches for compact binary coalescences using non-spinning waveform models. We introduce the "constant precession cone" approximation and show that it leads to a simple model of the waveform phasing. This leads to closed-form expressions that predict the overall amplitude of the signal and its mismatch with non-spinning search templates.

Institution: AEI Hannover

The first detection of GW signals in ground-based detectors will require high statistical confidence that the claimed signal is not due to unpredictable, non-Gaussian noise, which dominates the population of false alarms in current transient searches. Powerful, reliable and reproducible methods of background estimation are thus needed. I describe limitations of the existing time-shift method used in LSC-Virgo analyses, and compare with proposed new methods, using a period of LIGO S5 data with simulated signals as a test case.

Institution: Università di Roma Sapienza

The monitoring and identification of noise lines in the science data of a gravitational wave interferometer is an important task for continuous wave (CW) searches as well as for detector characterisation studies. The NoEMi (Noise Event Miner) framework was developed to monitor the noise lines during the science runs and record them in a database for off-line analysis purposes. We will show the results of the analysis of the lines detected by NoEMi in the Virgo runs VSR2-VSR4, which has led to the identification of the source of more than 90% of the lines and provided relevant information about the data quality of the runs. We will also discuss how the line database is used to identify and reject the fake signal candidates in the all-sky CW search.

Institution: Laboratoire de l'Accélérateur Linéaire

STAMP, for Stochastic Transient Analysis Multi-Detector Pipeline, is an analysis pipeline dedicated to the search of long-duration gravitational waves transients (O(1s) to O(1 week)). Such events can be produced by sources such as eccentric black holes binaries, accretion disk instabilities, core-collapse supernovae post-bounce or neutron star instabilities. In the case where the production of gravitational waves would not be accompanied by a detectable counterpart (light or neutrino emission), it is necessary to run the analysis on every possible location in space and time. This is the purpose of the all-sky extension of the STAMP pipeline. Here we present the current status of the STAMP all-sky development, as well as preliminary results regarding the efficiency of the study, using LIGO data from 2005-2007.

Institution: Osaka University, Graduate School of Science

In this talk, I will present the effects of the higher harmonics of the post-Newtonian wave form of the inspiraling compact binary on the parameter estimation accuracy including the source localization accuracy by the network of advanced ground-based interferometers and the Einsten Telescope.

Institution: Observatoire de la Cote d'Azur

Third generation GW detectors, such as the projected Einstein Telescope (ET), should take GW astronomy to a new level, due to the large numbers and high SNRs of detectable sources. The ET Mock Data & Science Challenges (ETMDSC) consist of simulated ET detector noise plus signals from a range of sources including a large population of compact binaries. The data sets may be used to develop advanced data analysis methods to separate overlapping sources and measure the properties of both individual sources and of the catalog as a whole. ET Science Challenges will also encompass the application of such results to outstanding problems in fundamental physics, astrophysics and cosmology. Encouraged by the success of the first ETMDC containing BNS coalescence signals, we are preparing a new, longer data set with a greater variety of sources. The goals of this round include further understanding the issues in analyzing data with long-duration compact binary signals and occasional transients; and assessing the accuracy with which ``input'' parameters - the ET PSD, signal waveforms, source parameters and rates, cosmology, possible deviations from GR, etc. -- can be reconstructed. We present the choices made for the second round of ETMDSC and the status of data generation.

Institution: Albert Einstein Institute Hannover

Continuous gravitational waves (CW) are expected from spinning neutron stars with non-axisymmetric deformations. Detection of these very weak signals requires very sensitive instruments and data analysis techniques. The standard multi-detector F-statistic often used for CW data analysis is optimal in Gaussian noise, but susceptible to false alarms from noise artifacts in the form of strong monochromatic lines in a single detector. In the past, ad-hoc post-processing vetoes have been used to remove these artifacts. Here we provide a systematic framework to develop and benchmark this class of vetoes. With an extended noise model including a line hypothesis, we can use a Bayesian odds ratio to derive a generalized detection statistic, the line veto (LV-) statistic. We test this LV-statistic on both simulated and real detector data, showing that it retains most of the detection power of the F-statistic in Gaussian noise while being much more robust in the presence of line artifacts. Furthermore, we briefly describe current efforts to implement line vetoing for the Einstein@Home distributed-computing analysis of LIGO S6 data.

Institution: Northwestern University

For several years, the "first-order" approximation of gravitational-wave parameter estimation accuracy has been the Fisher Information Matrix (FIM) due to its ease-of-use and rapid computation time. While the theoretical failings of this method (such as the signal-to-noise ratio (SNR) limit and Gaussian-only posteriors) are well understood, the practical effectiveness compared to a real parameter estimation technique (e.g. Markov Chain Monte Carlo) remains an open question. Here, I present a direct comparison between the FIM error estimates and the Bayesian posterior PDFs produced by the parameter estimation code, LALInference. I will discuss the merits of both methods as an initial step in understanding observational capabilities, and how the results from previous FIM studies will compare to the realities of low-SNR parameter estimation in the advanced-detector era.

Institution: University of Texas at Brownsville

Advanced gravitational wave(GW) detectors are expected to eventually make regular GW observations. Methods that quickly and confidently distinguish between instrumental artifacts and potential GW signals will help increase the confidence of low latency GW search candidates sent to the rest of the astronomical community. The Critical Coupling Likelihood(CCL) is one proposed method designed to quantify the operational state of GW detector. We plan to present a case study showing CCL noise rejection results run with multiple analysis configurations, alongside LIGO's current veto methods technique. In addition to this we will show the method's operating characteristics, which are critical in setting an appropriate threshold. This yet to be determined threshold should be aggressive but not discard an unnecessary amount of detector data. We will also show that even though we may be forced to discard data this discarded data, while not desirable for GW searches, can lead to useful instrument information like an approximate transfer function. This approximate can be used to help understand a detector's output signal properties like signal amplitude and frequency in response to identified input noise properties.

Institution: Cardiff University

A new method is presented for performing searches for GW bursts associated with GRBs in the presence of non-Gaussian excess noise events ("glitches"). Glitch suppression is typically done by applying cuts or weighting factors based on a small number of measured properties of an event in the GW data channel, such as time coincidence between detectors. Multivariate analysis (MVA) techniques test a large number of variables simultaneously to discriminate signal from noise. We illustrate this method by applying MVA classifiers to the X-pipeline "burst" analysis using LIGO-Virgo S5-VSR1 data, and see an improvement in detection range of up to 40%.

Institution: University of Birmingham

The measurement of astrophysical parameters of coalescing binaries, encoded in their gravitational-wave signature, is a crucial step for enabling gravitational-wave astronomy. However, our ability to make such measurements may be jeopardized by unknown systematic uncertainties in the waveform templates used for parameter estimation. I present a study of whether one particular source -- neutron-star binaries -- may be largely immune to systematic waveform uncertainties. I also express my personal views on what waveform features are most crucial to maximize the astrophysical potential of advanced ground-based gravitational-wave detectors.

Institution: Wigner RCP, RMKI

A general purpose computational tool called CBwaves is introduced. CBwaves provides a fast and accurate computational tool to determine the gravitational waveforms yielded by generic spinning binaries of neutron stars and/or black holes on closed possibly eccentric orbits or on open ones. Configurations with relevance for the new generation ground based detectors and the use of CBwaves in generating burst type events and in parameter estimation processes are also considered.

Institution: Indian Institute of Science Education and Research Thiruvananthapuram

Phasing formula of non-spinning compact binaries is fully characterized by the two component masses. If two of the post-Newtonian (PN) phasing coefficients are independently measured, the masses can be estimated. Future gravitational wave observations could measure many of the 8 independent PN coefficients calculated to date. These additional measurements can be used to test the PN predictions of the underlying theory of gravity. Since all of these parameters are functions of the two component masses, there is strong correlation between the parameters when treated independently. We use Singular Value Decomposition to obtain a new set of parameters which are shown to be very accurate. This sets the stage for testing the PN theory.

Institution: NAOJ

We consider tests of relativistic gravity theory from observations of gravitational wave bursts. Tests of gravity theory are a fundamental physics issue, and one of the plausible alternative gravity theories is scalar-tensor theory. A significant difference between the scalar-tensor theory and general relativity is the existence of a scalar field which is connected with the gravity field with coupling parameters, and a resulting scalar gravitational wave. We present a fully implemented pipeline to detect a scalar gravitational wave and discuss constraints on the coupling parameters using simulated noise of advanced LIGO, advanced Virgo, KAGRA, and LIGO-india.

Institution: Nikhef

The gravitational waveforms associated with coalescing binary neutron stars and black holes are increasingly well-understood, and will be a powerful tool to test the genuinely strong-field dynamics of General Relativity (GR). We present TIGER, a Bayesian inference framework which tests the consistency of coefficients appearing in the waveforms with the predictions made by GR, without relying on any specific alternative theory of gravity. TIGER is suitable for low signal-to-noise ratio events through the construction of multiple subtests, most of which involve only a limited number of coefficients. It also naturally allows for the combination of information from multiple sources to increase one’s confidence in GR or a violation thereof. In the case of inspiraling binary neutron stars, TIGER has been fully implemented as a data analysis pipeline in the LIGO Algorithms Library. We show results for a range of numerical experiments in simulated stationary and Gaussian noise that follows the expected Advanced LIGO and Virgo noise curves. Potential concerns are addressed, such as differences between waveform approximants, the effects of instrumental calibration errors, tidal deformability of the neutron stars, and the influence of spins. Finally, we discuss possible ways of extending TIGER to the coalescence of binary black holes.

Institution: University of Glasgow

General Relativity predicts that there are only two independent polarisations of gravitational waves. Any general metric theory of gravity allows up to four more polarisation modes: two vectors modes and two scalar modes. We present a preliminary study of how the presence of non-GR modes (in this case for Brans-Dicke theory containing the two additional scalar modes) affects our ability to recover the source parameters for a known pulsar when incorrectly assuming that the signal is consistent with GR.

Institution: University of Southampton

Pulsars are celebrated tools to test theories of gravity and so far general relativity has passed every test with flying colors. Since the discovery of the first binary pulsar by Hulse and Taylor in 1974, relativistic corrections were needed to account for the departure of the orbit from Newtonian dynamics. Later, the same pulsar provided the first indirect observation of gravitational wave emission when its orbit was found to decay in the way predicted by general relativity. In 2003, the discovery of the first - and so far unique - "double pulsar" system rejuvenated this area of research with five independent tests of gravity, including the first high-precision measurement of relativistic spin-precession in a system consisting of two strong self-gravitating bodies. Binary pulsars having white dwarf companions are also very well suited for testing the equivalence principle, and were more recently used to put strong constraints on modified newtonian gravity and the more general class of scalar-tensor theories. In this talk, I will review the science behind testing gravity with (binary) pulsars and I will presents some of the recent advances in that field.

Institution: Cardiff University

We have used numerical simulations to understand the spectrum of quasi-normal modes of black holes that result from the merger of spinning black hole binaries. The amplitudes of the various excited quasi-normal modes, for non-precessing and a few precessing cases, show a very interesting pattern, which could be useful in extracting the masses and spins of the progenitor black holes. In the case of progenitors with aligned spins, we are able to cleanly extract the mass ratio and a combination of the progenitor black hole spins. Future observations of black hole quasi-normal modes in ground- and space-based detectors should provide an excellent opportunity to test the precise nature of quasi-normal mode excitations, both complex frequencies and their amplitudes, in general relativity.

Institution: University of Wisconsin - Milwaukee

In anticipation of the new era of gravitational wave detectors, it is especially important to develop methods for gaining information about astrophysical systems from gravitational wave signals. We have been working on developing a method for testing the cosmic censorship conjecture using the inspiral portion of the compact binary coalescence gravitational waveform. The cosmic censorship conjecture states that any massive body undergoing complete gravitational collapse must result in a singularity concealed by an event horizon, meaning this singularity will not be visible to a distant observer. The method we are developing will allow us to say whether detected systems are consistent with the cosmic censorship conjecture, within the context of the Kerr geometry, or are more exotic horizon-less systems. The Kerr geometry places an upper limit on the allowed spin of a compact object with a horizon. We look at ways to improve parameter estimation errors on the spin and mass parameters appearing in the gravitational waveform. The Kerr limit on spin along with a physical limit on the mass parameter allows us to say whether a system is consistent with a Kerr black hole within our calculated measurement error.

Institution: Kyoto University

A gravitational-wave signal from a compact binary object, called the standard siren, provides a unique way to measure the luminosity distance to the source and can be an accurate tracer of the cosmic expansion. However, to distinguish various models for dark energy and modified gravity theories, it is crucial to constrain not only the background expansion but also the inhomogeneities in the Universe. In this presentation, we show that how future space-based gravitational-wave detectors (LISA/DECIGO/BBO) would be able to measure cosmological structures using the weak-lensing magnifications of the standard-siren signals.

Institution: University of Chicago

I will discuss some of the interesting cosmological measurements that may be possible with gravitational wave sources, focusing on measurements of the Hubble constant and why they are important for cosmology.

Institution: Vladimir state university

There has been developed a program – analytical system to investigate signal structures in spectral and time ranges caused by geophysical processes. The main aim in developing such a system is to investigate signal structures in spectral and time ranges caused by geophysical and astrophysical processes in the electrical and magnetic field of the atmosphere surface boundary layer, and to investigate under noise periodical processes of geophysical and astrophysical structure. The novelty of the developed method is that initial time series itself is not subjected to spectral analysis but its eigen vectors are subjected to its and that allows to use spectral analysis to save separate non – correlated time series components connected with the definite physical processes. Using the method of eigen vectors can considerably raise the selectivity of any known analyzing method (including a spectral one) because the latter ones will be used not to the whole time series but to its independent components including those which do not posses energic dominating and they are not “thin” structure of the time series. Signal – to – noise ratio (the ratio of the maximum value of the amplitude spectrum at the chosen eigen vectors to its mean value) at the frequencies of GW radiation of the binary star systems for component E2 for the stations with long time monitoring (Voyeikovo, Verchnyays Dubrova, Dushety, Vsu, Baikal and Obninsk) was average 150 to 300. Signal – to – noise ratio (the ratio of the maximum value of the amplitude spectrum at the chosen eigen vectors to its mean value) at the frequencies of GW radiation of the binary star system for the geomagnetic field components for the stations with long – time monitoring (VSU, IZMIRAS), Kakioka, Memambetsu) was average100 to 300. The work are supported by grants RFFI 11-05-97518, FCP № 14.740.11.0407, FCP № 16.740.11.0185 and GZ № 5.2971.2011.

Institution: Theoretisch-Physikalisches Institut, Friedrich-Schiller-Universitaet Jena

We provide full-analytic gravitational wave forms for inspiralling eccentric compact binaries of arbitrary mass ratio in the time Fourier domain for the case of vanishing spins. Tail terms are not considered. In our prescription, the semi-analytical property of recent descriptions, i.e. the demand of inverting the higher-order Kepler equation numerically but keeping all other computations analytic, is avoided.

Institution: Albert Einstein Institute Hannover

Pulsar Timing Arrays (PTAs) are very similar to ground-based detectors. Propagation of electromagnetic signals are perturbed by gravitational-waves, and multiple detector arms are required to extract these signals. Especially since we are entering an era where PTA sensitivity is starting to get high enough to allow for an actual detection, the data analysis methods for PTAs should receive extra attention, also from other gravitational-wave communities. The recently released first International PTA (IPTA) mock data challenge has been designed as a competition for all PTA data analysis algorithms. Simple enough for newcomers to not get lost in details, but still realistic enough to capture the important data analysis challenges. Everyone is invited to participate. As an example, the data challenge pipeline of the European PTA data analysis team is presented.

Institution: AEI - Hannover

During their last joint run in 2009-2010, the LIGO-Virgo gravitational-wave (GW) detectors collected data with improved sensitivity. Combining this data with the previous joint run (2005-2007), resulted in 594 days of total observation time and produced the most sensitive un-triggered burst search to date. GW bursts are short-duration signals with unknown or poorly modeled waveforms. Such signals may accompany astrophysical events like core-collapse supernovae, mergers of compact binary stars, the excitations of neutron stars modes and other violent astrophysical phenomena. No candidate events were observed. In this talk, we discuss the astrophysical interpretation of the search results and present typical sensitivity ranges for different morphologies of GW signals. Moreover, a case study of so-called "Big Dog event", a blind hardware signal injection, is presented from the perspective of an un-modeled burst search.

Institution: AEI Hannover

LISA Pathfinder (LPF) is the technology demonstration mission for eLISA/NGO. Containing two free float- ing test masses, whose relative position should be measured with picometre precision, LPF is supposed to be sent to Lagrange point one to test the drag-free control and interferometry for the future laser gravitational wave observatory. The high differential acceleration sensitivity of LPF led to the proposal of using LPF as a gradiometer to test for the anomalous gradients predicated by Modified Gravity Theories which may be detectable near the Earth – Sun saddle point. The high sensitivity in a bandwidth around 1 mHz together with the expected velocity allow the use of the spacecraft for this test without any modifications. Here we explore a rigorous data analysis approach for the experiment. Firstly, the characterisation of the signal parameter space and the influence of the parameter errors on the signal templates are assessed. Then the criterion for the model selection that will allow us to make the conclusions based on the observed data is derived. We perform time-domain simulations to allow for the investigation of the non-gaussianity and non-stationarity of the data and estimation the false alarm rate. The outcome is the development of the data analysis pipeline tested with the LPF simulator and prepared for the experiment.

Institution: Kepler Intitute of Astronomy, University of Zielona Góra

Binary neutron star merger lead to the formation of a massive differentially rotating neutron star (or a strange star) or to the prompt collapse to a black hole. The maximum mass of a differentially rotating remnant is crucial for distinguishing between these two final objects. The observations of them allow us to make constraints on the neutron star equation of state. We study the effect of a degree of differential rotation and stiffnest of the equation of state on the maximum mass of neutron stars. We numerically construct stellar models using a highly accurate relativistic code based on a multi-domain spectral method (Ansorg, Gondek-Rosinska, Villain, 2009). We find various types of configurations, which were not considered in previous work, mainly due to numerical limitations.

Institution: Kepler Institute of Astronomy, University of Zielona Góra

Strange quark stars are considered as a possible alternative to neutron stars as compact objects (e.g. Weber 1999). We present the first relativistic calculations of differentially rotating strange stars. A newly born, hot compact star, formed in a supernova explosion is supposed to rotate differentially. Using a highly accurate, relativistic code we calculate main properties (e.g. allowed masses, spins) of rigidly and differentially rotating strange stars. We show that rotation may cause a significant increase of maximum allowed mass of strange star, much larger than in the case of neutron star. A compact star stabilized by differential rotation is considered to be an important source of gravitational waves.

Institution: University of Glasgow

Searches for gravitational wave signals in pulsar timing residuals from multiple pulsars often rely on the fact that the "Earth term" of a signal will be correlated between all pulsars. In general the "pulsar term" will be uncorrelated between pulsars. For a short duration burst signal (months to years) the "pulsar term" in residuals from many pulsars will generally be separated by time-spans far longer than the pulsar observations. However, we show that there are fortuitous alignments of pulsar pairs and source locations that have "pulsar terms" separated by time delays within a realistic observational time-span. We compare the detectability of a GW burst through the correlation of "Earth terms" from an entire Pulsar Timing Array, with that using using "pulsar terms".

Institution: Nikhef

Advanced interferometric gravitational-wave (GW) detectors are expected to deliver the first detections before the end of this decade. A conceptual design study was recently completed for a next generation observatory called Einstein Telescope (ET), which will see hundreds of thousands of sources per year up to redshifts of several. I will discuss how ET can contribute to the study of dark energy, testing of the genuinely strong-field dynamics of General Relativity, and the determination of the mass distribution of neutron stars and black holes as well as the equation of state of neutron stars.