GWPAW 2017
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Europe/Paris
Impérial Palace
Impérial Palace
Allée de l'Impérial, Annecy
Description
GWPAW 2017
From May 30th afternoon to June 2nd 2017
GWPAW is the annual open workshop (formerly called GWDAW) on the physics and astronomy of gravitational waves, techniques for their detection, and interpretation of data and results. It is the continuation of a series of workshops started in the 90', with its last edition hosted by MIT in Cape Cod. GWPAW is sponsored by the Gravitational Waves International Committee (GWIC).
With the gravitational wave (GW) events observed during the first run of the advanced LIGO detectors, the field has entered a new era. The second observing run of the LIGO detectors, soon to be joined by Advanced Virgo, and the prospect of an expanding detector network will bring new information, shape and possibly answer some of the key questions of this booming field. What will come up from this new grasp on black holes? Are we going to observe electromagnetic counterparts to GW events anytime soon? What will be the impact on science? What could we learn on nuclear matter or nuclear synthesis from GW events? How can we probe General Relativity? What is needed to better model the sources? How to make the best of multi-wavelength GW observations? What will be the science of third generation ground-based detectors?
The meeting will be hosted in France by LAPP-Annecy, and held at the Imperial Palace Hotel, which is easily reachable from the Geneva International Airport.
The workshop will take place from May 30 to June 2, 2017 (Tuesday afternoon through Friday).
May we suggest that you consider extending your stay in Annecy for the 1st ASTERICS-OBELICS International School on Advanced Software Programming for Astrophysics and Astroparticle Physics? The summer school will be held at LAPP the week after GWPAW (June 6-9 2017).
Photos credits : © DgC Photography - © Rick Peterson - © LIGO T. Pyle - © DgC Photography - © NASA/ESA
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Registration
No lunch provided
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News from the detectors: Session chair: Nobuyuki Kanda
Session chair: Nobuyuki Kanda
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Matter wave interferometry for GW detectionAtom interferometry has been proposed for the realization of GW detectors in the infrasound band (10 mHz - 10 Hz) [1]. Such frequency band is forbidden to current ground based GW detectors due to low frequency gravity gradient noise that causes a tidal effect on the suspended mirrors used as test masses for the detection of gravitational radiation. Adopting as probes arrays of atom clouds in free fall and interrogated simultaneously in a gravity-gradiometer configuration allows the suppression of Newtonian Noise [2], enables low frequency sensitivity, and opens the way toward the realization of infrasound GW detectors on Earth. In this framework, I will report on the MIGA project [3], whose target is to build a demonstrator for GW detection using atom interferometry in the underground environment of LSBB (Rustrel, France). [1] S. Dimopoulos,et al, Phys. Lett. B 678, 37 (2009) [2] W. Chaibi,et al, Phys. Rev. D. 93 (2), 021101 (2009) [3] B. Canuel, et al, arXiv:1703.02490v2 [physics.atom-ph]Orateur: Andrea Bertoldi (LP2N)
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Coffee break
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Un-modeled signals, Bursts: Session chair: Kipp Cannon
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Gravitational wave signatures from multi-dimensional core-collapse supernova modelsBased on our 3D(-GR) simulations with spectral (or gray) neutrino transport using non-rotating and rapidly rotating progenitors, we report the gravitational-wave (GW) signatures and discuss the detectability in both 2nd and 3rd generation interferometers. We also discuss how we can extract information of the central engine based on detailed correlation analysis of the GW and neutrino signals.Orateur: Dr Kei Kotake (Fukuoka University)
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Search for intermediate mass black hole binaries in the first observing run of Advanced LIGODuring their first observational run (O1), the two Advanced LIGO detectors attained an unprecedented sensitivity, resulting in the first direct detections of gravitational-wave signals produced by stellar-mass binary black hole systems. We present here the results of the O1 all-sky search for gravitational waves (GWs) from merging intermediate mass black hole binaries (IMBHBs). Two independent search techniques were used in this study: the first employs a matched-filter algorithm that uses a bank of filters covering the GW signal parameter space, while the second is a generic search for GW transients (bursts). No GWs from IMBHBs were detected, thus we constrain the rate of several classes of IMBHB mergers. The most stringent limit is obtained for black holes of individual mass $100\,M_\odot$, with spins aligned with the binary orbital angular momentum. For such systems, the merger rate is constrained to be less than $0.93~\mathrm{Gpc^{-3}\,yr}^{-1}$ in comoving units at the $90\%$ confidence level, an improvement of nearly two orders of magnitude over previous upper limits.Orateur: Dr Francesco Salemi (AEI - Hannover)
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Circular Polarizations of Gravitational Waves from Core-Collapse Supernovae: A Clear Indication of Rapid RotationWe propose to employ the circular polarization of gravitational waves emitted by core-collapse supernovae as an unequivocal indication of rapid rotation deep in their cores just prior to collapse. It has been demonstrated by three dimensional simulations that nonaxisymmetric accretion flows may develop spontaneously via hydrodynamical instabilities in the postbounce cores. It is not surprising, then, that the gravitational waves emitted by such fluid motions are circularly polarized. We show that a network of the second generation detectors of gravitational waves worldwide can be able to detect such polarizations up to the opposite side of the Galaxy as long as the rotation period of the core is shorter than a few seconds prior to collapse.Orateur: Prof. Kazuhiro Hayam (KAGRA Observatory, ICRR, U tokyo)
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Enhancing un-modeled gravitational wave searches sensitivity with WavegraphThe first direct detection of gravitational waves (GW) showed that un-modeled search pipelines can reliably detect "heavy" binary black holes (BBH). Un-modeled searches such as Coherent WaveBurst (cWB) make minimal assumptions on the target signal. Operationally this implies that those search algorithms do not impose constraints on the clusters of significant time-frequency coefficients extracted from the observation data. We propose an alternative clustering scheme named Wavegraph dedicated to cWB that instead restrict the search to a priori astrophysically motivated clusters. We present the basic principles of Wavegraph and we show using colored simulated Gaussian noise and playground detector data whether this method extends the search capabilities in the BBH case.Orateur: Philippe Bacon (Laboratoire Astroparticule et Cosmologie)
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Binary Black Hole Science: I; Session chair: Frederique Marion
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Quasinormal modes of black holes: review and recent updatesSlightly perturbed dissipative systems display characteristic solutions that are not quite normal modes. Nevertheless, these quasi-normal modes encode valuable information about the underlying physics, as well as the nature of the preceding perturbation. In the case of black holes, this means that quasinormal modes may tell us not only about the source spacetime, but also about that spacetime's recent history. In this talk I will review the relationships between quasinormal modes and their source black hole, and I will discuss efforts to decode this information from current and future gravitational wave observations.Orateur: Dr Lionel London (Cardiff University)
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Constructive summation of Quasi Normal Modes from a population of Binary Black Hole Mergers.In General Relativity, the Quasi Normal Modes (QNM) from a perturbed Kerr Black Hole (BH) are the superimposition of damped sinusoids. These modes are completely defined by the final black hole parameters, mass and spin. For the current generation of the ground based detectors, the gravitational waves associated with the QNM are weak and hence the extraction of single QNMs is challenging. I will present a method for extraction of constructively summed QNMs from multiple observations of BBH merger signals. We can constructively sum up the first leading mode (lm=22), and we are presently working to extend this method to the next leading modes, lm=33 and 44.Orateur: Dr Carlos Filipe Da Silva Costa (INPE)
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The effect of the choice of prior on measurements of binary black hole spinsThe distribution of the component spins of binary black holes is one of the most astrophysically interesting results that could be produced by gravitational-wave detectors in the coming years. Unfortunately, the component spins are also one of the most difficult parameters to infer from gravitational waves. Better measurements are obtained of the “effective spin” and "effective precession" parameters, which are mass-weighted combinations of the spin components parallel and perpendicular to the orbital angular momentum, respectively. Even these parameters are not well constrained at the signal-to-noise ratios of current detections, and are subject to the choice of prior. Current published results on detected events use a prior for each spin that is uniform in magnitude and isotropic in orientation. While astrophysically plausible, this prior couples the effective spin and effective precession parameters, making it difficult to produce independent estimates of each. I demonstrate the effect the choice of prior can have on spin measurements of simulated GW151226-like events by comparing posterior distributions from three different priors: uniform in magnitude and isotropic in orientation, cubic in magnitude and isotropic in orientation (“volumetric”), and a new prior that is uniform in effective spin and effective precession, which decouples these two parameters.Orateur: Dr Collin Capano (Albert Einstein Institute)
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A “No-hair” test of binary black hole natureCompact objects such as neutron stars or black holes or those of more exotic origin, by the virtue of their spin incur deformations that can be characterised in terms of the spin-induced quadrupole and other higher order moments. The magnitude of these deformations depends on the specific nature of compact objects in question. If the compact object is a Kerr black hole, its quadrupole moment can be expressed solely in terms of its mass and spin. On the other hand, for a compact object of different nature, these induced deformations will also depend on some additional parameters (such as on equation of state) of the compact object. Gravitational wave observations of compact binary sources can be used to measure these deformations and hence can allow one to test the nature of the observed compact binary source. Here we present the results of our recent investigations where we follow a novel approach to test the binary black hole nature of a compact binary source by measuring the spin-induced quadrupole moment of the binary using its gravitational wave observations in advanced LIGO detectors.Orateur: Dr Chandra Kant Mishra (IIT Madras)
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The status of phenomenological inspiral-merger-ringdown waveform modelsThe interpretation of gravitational waves from coalescing compact binaries relies on accurate source models which are used in complex data analysis techniques. State-of-the-art models used in LIGO analyses make a number of assumptions that may severely limit their accuracy for systems with, e.g., asymmetric masses or large misaligned spin magnitudes that cause precession. In this talk I discuss the the next generation of inspiral-merger-ringdown "Phenomenological" waveform models which will include higher harmonic contributions and an improved description of the precession dynamics. Achieving this level of accuracy will allow us to more accurately measure source parameters and test for evidence of precession.Orateur: Dr Sebastian Khan (AEI Hannover)
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A new method for incorporating precession and higher-order modes in searches for compact binariesAdvanced LIGO's current matched-filter searches for binary mergers model only the dominant mode of binaries whose orbital angular momentum is aligned with the total angular momentum. Some models of binary formation predict a population of systems where these simplifying assumptions will not hold, and so a search that includes them may be necessary to discriminate between these models. In this talk we describe a new technique for including the effects of higher-order modes and precession, that directly maximizes the likelihood over extrinsic parameters without a grid search.Orateur: Dr Joshua Willis (Abilene Christian University)
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Coffee break
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Binary Black Hole Science: II: Session chair: Chris Van Den Broeck
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How do black hole binaries form ? Studying stellar evolution with gravitational wave observationsThe recent detection of gravitational waves by Advanced LIGO demonstrates the existence of binary black holes that merge within the age of the Universe. Moreover, the first LIGO event originated from the merger of black holes more massive than previously observed in X-ray binaries in our Galaxy. Future observations with LIGO and VIRGO will probe the mass and spin distributions of black holes in various galactic environments. Since stellar-mass black holes form at the end of the nuclear lifetimes of massive stars, these measurements will help constrain stellar evolution models. In this talk I will review several black hole formation scenarios that were proposed to explain LIGO observations and describe a framework that can be used to calculate the mass distribution of merging black hole binaries in the context of galaxy evolution models.Orateur: Dr Irina Dvorkin (Institut d'Astrophysique de Paris)
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The formation of binary stellar black holesI will present the current theoretical models and the multiple strands of observational evidence for the formation of binary stellar black holes, the first sources of gravitational waves detected by LIGO. It is believed that stellar black holes (BHs) can be formed in two different ways: Either a massive star collapses directly into a BH without a supernova (SN) explosion, or an explosion occurs in a proto-neutron star, but the energy is too low to completely unbind the stellar envelope, and a large fraction of it falls back onto the short-lived neutron star (NS), leading to the delayed formation of a BH. Theoretical models set progenitor masses for BH formation by implosion, namely, by complete or almost complete collapse, but observational evidences have been elusive. Here are reviewed the observational insights on BHs formed by implosion without large natal kicks from: (1) the kinematics in three dimensions of space of five Galactic BH X-ray binaries (BH-XRBs), (2) the diversity of optical and infrared observations of massive stars that collapse in the dark, with no luminous SN explosions, possibly leading to the formation of BHs, and (3) the sources of gravitational waves produced by mergers of stellar BHs so far detected with LIGO. The multiple insights of BH formation without ejection of a significant amount of matter and with no natal kicks obtained from these different areas of observational astrophysics, and the recent observational confirmation of the expected dependence of BH formation on metallicity and redshift, are qualitatively consistent with the high merger rates of binary black holes (BBHs) inferred from the first detections with LIGO.Orateur: Dr Felix Mirabel (CEA-France & CONICET-Argentina)
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Distinguishing between stellar and primordial black hole merger eventsFollowing the first Advanced LIGO detection, several studies investigated the possibility that GW150914 was of primordial origin and could provide evidence that stellar-mass black holes form part of dark matter. The support for the primordial hypothesis is extremely circumstantial. However, these studies raise an interesting question: how can one confirm or refute the primordial hypothesis for black hole binaries with stellar masses? In this study, we attempt to answer the questions: what would constitute smoking-gun evidence for (stellar-mass) primordial black holes, and what detector sensitivity is required to achieve this goal? We show that a population of primordial back holes can be reliably identified using measurements of redshift. We quantify what fraction of events would need to originate from a primordial population in order to differentiate between the progenitor populations using current and planned detectors.Orateur: Dr Letizia Sammut (Monash University)
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Properties of Dynamically Formed Black Hole Binaries in Globular ClustersThe first GW source that is confirmed by the advanced LIGO is a binary black hole (BBH). In coming years, advanced LIGO and advanced Virgo will find more BBHs. In this work, we investigate dynamically formed BBHs in core-collapsed globular clusters using direct N-body simulations. We assume two types of BH mass functions: two-component mass function and a continuous mass function (adapted from population synthesis). We find that almost all BHs are ejected from the cluster eventually, and 30 per cent of the ejected BHs are in binaries. In particular, heavier BHs are more likely to form binaries and get ejected as binaries. Some of these ejected BBHs with tight orbital separation can be detected by GW detectors. Therefore, BH mass function inferred from observed samples can be biased toward heavier masses in comparison with the intrinsic BH mass function. We will show restuls of N-body simulations and discuss dynamics of BBH formation and ejection in cluster environment. Finally, we will comment on the expected BH mass function for GW detectors.Orateur: Dr Chunglee Kim (Korea Astronomy and Space Science Institute (KASI))
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Lunch
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Low frequency signals: Session chair: Ed Porter
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Probing The Nanohertz Gravitational-wave Landscape With Pulsar Timing Arrays: A Status ReportDecade-length observation campaigns of millisecond pulsars offer the potential to probe the nanohertz band of gravitational-waves, where the dominant sources are supermassive black-hole binaries formed during massive galaxy mergers. With three major collaborations timing tens of these pulsars over many years, and on the verge of forging a combined dataset, I will review the most recent advances in the pulsar-timing search for gravitational-waves. Stringent constraints have allowed us to comment on the merger-rate of massive galaxies, and the mechanisms by which the final-parsec problem of massive black-hole binary evolution is mitigated. Detection is expected within 5-10 years, which will prove that the final-parsec problem is overcome for the most massive black-hole binaries, and will subsequently allow us to study the dynamical environments of these systems.Orateur: Stephen Taylor (JPL)
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The space detectors status and science-Orateur: Rita Dolesi (University of Trento)
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Coffee break
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Posters
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A Riemann manifold Hamiltonian Monte Carlo (RMHMC) for binary neutron star parameter estimation.The Hamiltonian Monte Carlo (HMC) is a sampling algorithm that eliminates a random walk in parameter space by applying Hamilton’s equations on the position and momentum of a fiducial particle. In this way, one is able to explore the posterior in a very efficient way, since information from the posterior is directly used to compute the dynamics of the particle at each step in its trajectory. In general, the HMC converges D times faster than a standard Markov Chain, where D is the dimensionality of the parameter space. However, efficiency comes at a cost since each Hamiltonian trajectory requires multiple numerical calculations of the gradient of the log-likelihood that can make the computational cost explode, hence making this method less competitive compared to other sampling methods. By using information from the topology of the parameter space, and an analytic approximation to the gradients, we propose an application of the HMC algorithm for the parameter estimation of binary neutron star coalescence in the context of ground-based gravitational waves data analysis that now runs on an acceptable timescale.Orateur: M. Yann Bouffanais (Laboratoire APC)
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An improved semi-coherent follow-up method for FrequencyHough all-sky candidatesIn the all-sky search for continuous gravitational waves emitted by spinning neutron stars, the most significant candidates are selected and subject to a follow-up step. The follow-up allows to strongly increase the detection confidence for real gravitational wave signals and to reject candidates of non-gravitational origin. The computational cost of the follow-up is an important issue as it affects the number of candidates which can be taken into account, with an impact on the search sensitivity. We present an improved semi-coherent method to perform the follow-up of candidates selected by the FrequencyHough pipeline, based on the recently developed concept of Band Sample Data collection. This new method allows to gain at least 2 orders of magnitude in computing cost, thanks to the possibility to run the barycentric corrections in a computationally cheap way and to an optimised incoherent step. At fixed computing cost this implies the possibility to perform a number of follow-ups much larger than before and to significantly increase the coherence time of the follow-up for the most interesting candidates.Orateur: Sabrina D'Antonio (INFN Tor Vergata)
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Fast localization with a hierarchical network of gravitational wave detectorsWe present expected fast sky localisation of coalescing binaries with a hierarchical search using three gravitational wave (GW) detectors, HLV (Hanford/Livingston/Virgo). A hierarchical search can be used with different sensitivity GW detectors, and is aimed at making effective use of the least sensitive detector’s information. In the hierarchical network, the less sensitive detectors are included into the network with a lower SNR threshold than the higher sensitivity detectors, only when a coincidence trigger is detected by the sub network of higher sensitivity detectors. Here we demonstrated the sky localisation using a hierarchical search using the two higher sensitivity LIGO detectors and the less sensitive Virgo detector, using simulated signals.Orateur: M. Yoshinori Fujii (U. of Tokyo / National Astronomical Observatory of Japan)
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Hierarchical data-driven approach to fitting waveform models for non-precessing binary black holes to numerical dataIn previous work we have developed a method to systematically approach the problem of fitting a model to the 3-dimensional parameter space of non-precessing quasi-circular binary black holes, and applied it to construct accurate fits to final spin, radiated energy and peak luminosity, which avoid over-fitting. In this work we extend our approach to a phenomenological waveform model in the frequency domain for the dominant quadrupole spherical harmonic. This model extends the PhenomD model that is currently in use in data analysis to unequal spins and extreme mass ratios, and increases the number of numerical waveforms used for calibration by an order of magnitude. We discuss the accuracy of the model and implications for data analysis.Orateur: Dr Sascha Husa (University of the Balearic Islands)
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Enhancing binary neutron stars studies by combining inspiral and postmerger informationRecent discoveries of binary black holes by gravitational-wave detection hint at the opportunity of observing binaries containing neutron stars. Unlike with black holes alone, the presence of a neutron star can help us constrain the equation of state of ultradense matter. The feasibility of constraining the equation of state through gravitational-wave detections have typically been studied using the inspiral and post-merger stages separately. We quantify the benefits of combining the inspiral and the postmerger stages when analysing binary neutron star signals. Moreover, we show that one can probe whether the merged object remains in a hyper-massive neutron star phase or whether it promptly collapses into a black hole.Orateur: Prof. Tjonnie Li (The Chinese University of Hong Kong)
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X-PIPELINE: Gravitational-Wave Burst search applied to LIGO dataThe rapid analysis of gravitational-wave data is not trivial for many reasons, such as the non-stationary nature of the background noise in gravitational-wave detectors and the lack of a definite and exhaustive waveform models, especially for gravitational-wave burst signals. One active research area is based on the use of X-PIPELINE [1], a software package designed for performing autonomous searches for un-modelled gravitational-wave bursts (GWBs). Functions in X-PIPELINE such as automated running, including background estimation, efficiency studies, unbiased optimal tuning of search thresholds and prediction of upper limits, are all performed automatically without requiring human intervention. X-PIPELINE has a novel approach based on spherical radiometry [2]. The core of our spherical radiometer pipeline is a set of fast cross-correlator codes written in C. This engine, called X-SPHRAD, transforms the problem of computing correlations between time series data streams into the spherical harmonic domain and allows correlation between detectors (in a network) to be performed quickly. X-SPHRAD is focused on optimising the sensitivity of the search. Applications of X-PIPELINE include the general problem of identifying signals of duration greater than 1 second, for which sources include GRBs and some classes of supernova. [1] P.J. Sutton et al. New Journal of Physics 12 (2010) [2] K. Cannon Physical Review D 75, 123003 (2007) Keywords: Gravitational-wave; Burst; LIGO; X-PIPELINEOrateur: Mme Elena Massera (University of Sheffield-LIGO scientific collaboration)
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Mass-Radius Relation of Neutron Stars in a Scalar-Tensor TheoryMany researchers are trying to explain the dark sector in the universe by modifying general relativity. Recently, a new cosmological scenario which explains the existence of dark matter by adding an extra scalar field in GR, called asymmetron scenario, was proposed[1]. In this theory, the scalar field gets nontrivial values inside highly dense matter, such as neutron stars, and weaken gravitational force. Therefore, it may also explain the existence of the massive neutron star[2]. Because it can change the internal structure of neutron stars significantly, it can be tested by observing compact binary coalescences using gravitational waves. In this talk, I am going to explain how the internal structure and mass-radius relation of neutron stars are modified in this scenario. I am also going to mention that this theory allows the existence of the massive neutron star even though strange hadrons, such as hyperons, appear inside the core. Reference: [1]P. Demorest. et. al., Nature 467, 1081 (2010). [2]P. Chen, T.Suyama and J. Yokoyama, Phys. Rev. D 92, 124016 (2015).Orateur: Soichiro Morisaki (University of Tokyo)
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Development of a Wide-Field CMOS Camera: Tomo-e Gozen and Contributions to EM Follow-up Observations of Gravitational Wave EventsWe are developing a wide-field CMOS camera, Tomo-e Gozen, which will be mounted on the $105\,$cm Schmidt telescope at the Kiso Observatory, the University of Tokyo. The Tomo-e Gozen camera is composed of four camera modules, each of which is equipped with 21 CMOS image sensors with $1\,$arcsec/pix. The Tomo-e Gozen captures a sky of about 20-sq degree without any overhead due to readout time. Thus, the Tomo-e Gozen has a high survey efficiency which is beneficial to identify gravitational wave (GW) event sources. A prototype of the Tomo-e Gozen camera with 8 CMOS image sensors was developed and we confirmed that a limiting magnitude at the $V$-band is about $19\,$mag. for one second integration as designed. Development of one of the four camera modules is ongoing and will be completed by the end of 2017. The first light of the Tomo-e Gozen camera with the four camera modules is scheduled in 2018.Orateur: Ryou Ohsawa (Institute of Astronomy, University of Tokyo)
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New parameter estimation method being free from the bias depending on sky region for targeted GW searchThe first direct detection of a GW has been archived. In the next stage, it is important for a GW astronomy and cosmology to observe GW signal all over the sky by the use of global network of the interferometers. Even aLIGO-Virgo-KAGRA network, however, provides biased accuracy of the parameter estimation depending strongly on the sky location of a GW. In order to perform the parameter estimation with the same level of accuracy all over the sky, we propose a novel method based on a regularization method. Although conventional regularization methods couldn’t optimize its regulator completely, the new method is developed to optimize full of the regulator parameters. We show our method can improve most of the credible region of inclination vs luminosity distance and polarization vs initial phase over 3 times in the sky where the precision of a GW parameters has deteriorated. This method suppresses the systematic error of a GW depending on the celestial region and enables us more precise analysis of the cosmology.Orateur: M. Kenji Ono (ICRR)
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Setting up a direct search for continuous gravitational wave signals using the Band Sample Data collectionWe present a preliminary study for the setup of a directed search for continuous gravitational waves, based on the so-called Band Sample Data (BSD) collection of LIGO and Virgo data. In directed searches for continuous wave signals, the sky location of the source is well-known while the frequency and the spin-down parameters are unknown. Using the BSD collection it is possible to apply the barycentric corrections for a given sky direction in a computationally cheap way, thus allowing the use of longer coherence times, and increasing the search sensitivity.Orateur: Mlle Ornella Juliana Piccinni (University of Rome "La Sapienza" - INFN)
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Estimation of starting times of quasi-normal modes in ringdown gravitational waves with the Hilbert-Huang transformWe propose a method of determining the starting time of the quasi-normal mode (QNM) and calculating the QNM frequency and amplitude of gravitational waves from binary black hole merger. Our method determines the starting time and calculates the parameters by regression analysis of time evolutions of the amplitude and frequency calculated by means of the Hilbert-Huang transform. We apply it to simulated merger waveforms by numerical relativity and the observed data of GW150914. As a result, we confirmed that the obtained QNM frequencies and time evolutions of amplitudes are consistent with the theoretical values within 1% accuracy for pure waveforms free from detector noise. In addition, it is revealed that there is a correlation between the starting time of the QNM and the spin of the remnant black hole. In the analysis of GW150914, the parameters of the remnant black hole determined through our method are consistent with those given by the LIGO-Virgo collaboration, and a reasonable starting time of the QNM is determined.Orateur: M. Kazuki Sakai (Nagaoka University of Technology)
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Generalised resampling methodology for binary pulsarsRapidly rotating neutron stars with non-axisymmetric deformations are an interesting type of continuous-wave source for the LIGO-Virgo detectors. Within the sensitivity band of these detectors, more than half of the known pulsars in our galaxy are in binary systems. Signals coming from binary sources are Doppler modulated due to the source orbital motion, which spreads the signal in several frequency bins resulting in a significant drop of signal-to-noise ratio, making thus the signal much harder to be detected. In order to correct for this modulation, one would need to know the orbital parameters and source sky location with very high accuracy. For unknown parameters the correction would be very computationally expensive. Directed/Narrowband searches with time domain correction using the generalized 5-vector methodology is a relatively cheaper method, and we investigate its robustness over uncertainty in all orbital parameters.Orateur: akshat singhal (GSSI)
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Physical Metric, Gravitational Waves and Dark EnergyDark energy is not needed to explain the rate of acceleration of the universe. The improvement in the accuracy of time delay experiment data combined with the physical metric produces the correct model to prove/predict the rate of acceleration of the universe. The measurement of time delay experiment data of the solar system has been improved by the use of the Cassini satellite as a reflector, instead of using planets. The data accuracy is now 1 in 10^5. This data does not fit the Schwarzschild metric. The metric that fits the data was introduced by the Author and is called the “Physical Metric”. In the Physical Metric, the radius of compact objects, black holes and neutron stars, becomes 2.60 times the Schwarzschild radius, which is called the extended horizon. The enhancement of the size of black hole requires a change in the analysis of the observed gravitational waves by the merger of black holes. The masses in a black hole merger in the LIGO event, GW150914, should be 14 and 11 Solar Mass, instead of reported 36 and 29 Solar Mass. By coordinate transformation between the Physical Metric and the Friedmann metric, one can predict the universe expansion acceleration rate. It is a result of the repulsive nature of gravity inside the extended horizon for the Physical Metric. In other words, dark energy is not needed for the explanation of acceleration of the universe. It is a natural result of the Physical Metric, which fits the data of time delay experiment correctly.Orateur: M. Yukio Tomozawa (University of Michigan)
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Extracting the post-merger gravitational wave signal from binary neutron starsGravitational wave (GW) emission from a binary neutron star (BNS) coalescence carries the signature of its complex dynamics and of neutron star (NS) properties such as the equation of state (EoS). In particular, the extraction and characterization of the signal emitted in the post-merger phase by the massive NS remnant offers an opportunity to strongly constrain the behaviour of matter at supranuclear densities. Since the signal morphology cannot be accurately predicted, a model independent analysis is necessary. Here we present a new tool under development to perform a follow-up search for the identification within a selected purity of the post-merger GW emission from the BNS merger remnant. Moreover, it performs the characterization of the signal morphology and provides estimates of key parameters, such as the frequency of the main post-merger peak and the brightness curve of the signal. The tool is based on the coherent WaveBurst pipeline, a LIGO-Virgo algorithm to target unmodeled (burst) signals.Orateur: Mlle Maria Concetta Tringali (University of Trento and INFN-TIFPA)
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Application of a zero-latency whitening filter to compact binary coalescence gravitational-wave searchesWe examine the performance of a zero-latency whitening filter in a detection pipeline for compact binary coalescence (CBC) gravitational-wave (GW) signals. We find that the filter reproduces sufficiently consistent signal-to-noise ratio (SNR) for both noise and artificial GW signals (called injections) with the results of the original high latency and phase preserving filter. Additionally, we demonstrate that these two filters have a great agreement of squared-chi value, a discriminator for gravitational wave signals.Orateur: M. Leo Tsukada (The University of Tokyo)
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Templated search for black hole echo signals in LIGO dataWe show details of the AEI search for black hole echoes in LIGO public data. Echoes of gravitational waves of a compact binary merger provide a potential way to test alternative models of black holes. Abedi et al. claimed in 2016 to have found evidence of these echoes in LIGO public data. We have developed an extended analysis pipeline to evaluate these claims. This includes extending the parameter space of the echo signal and searching over more of the LIGO open data. The effect of a phase flip at the inner reflective boundary is investigated. We test our analysis with injected signals and pure Gaussian noise, and are able to recover signals similar to those claimed to be found by Abedi et al.. We conclude that current results do not provide sufficient observational evidence for claiming the existence of Planck-scale structures at black hole horizons, while encouraging further investigation of this interesting possibility as well as collaboration using the LIGO open data.Orateur: M. Julian Westerweck (AEI Hannover)
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Study of Hilbert-Huang transform using iKAGRA injection dataAuthors : Takaaki Yokozawa on the behalf of KAGRA collaboration KAGRA detector had test run in March and April, 2016 with room temperature and simplified configuration (called iKAGRA run). At the end stage of this run, we injected some waveforms to end test mass through arm length control system, which is called hardware injection. Hilbert-Huang Transform (HHT) is one of the time-frequency analysis method which is constructing with combination of Empirical Mode Decomposition (EMD) and Hilbert Spectral Analysis (HSA). Previous study of HHT analysis was applied to white and color gaussian simulated noise with software injection data. We analyzed 100Hz sine-gaussian signal with SNR~100. This study showed the effectiveness of HHT analysis using obtained data with hardware and software injection data. For the future prospect of HHT analysis, we plan to apply HHT analysis to Supernova waveform. We also showed the preliminary result of HHT analysis of supernova waveform.Orateur: Dr Takaaki Yokozawa (Osaka City University)
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Looking for truffles in trash: The new DMoff veto in Einstein@Home searches for continuous gravitational wavesIn the current era of the advanced LIGO and Virgo detectors, we are closer than ever to detecting the first continuous gravitational wave signal. At the same time, our searches are becoming increasingly sensitive, to both astrophysical sources and the detector artifacts that can mimic the signals that we search for. We developed a straightforward veto to quickly and effectively exclude signal candidates that arise from these artifacts: We run a simplified version of our search but with the Doppler modulation turned off (DMoff), making instrumental artifacts more prominent while suppressing astrophysical signals. Using this new veto, we were able to exclude >99.9% of the thousands of candidates from the recent Einstein@Home all-sky search as having terrestrial origins. I will discuss the current design and implementation of this veto, as well as the prospects for its use in future searches for continuous gravitational waves.Orateur: Dr Sylvia Zhu (Albert Einstein Institute)
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Cocktail
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Testing GR: Session chair: Damir Buskulic
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Testing gravity with binary black hole coalescences: results and prospectsGravitational waves from the coalescence of compact binary systems carry a wealth of information about the merging objects, the remnant object as well as their interaction with space-time. During the coalescence of extremely compact objects such as binary black holes, the typical curvature and velocity at play are such that, from the observation of the gravitational wave signal, we can access the most extreme dynamical regimes of gravity. These are ideal conditions for testing our understanding of gravity by looking for potential departures between the solutions of general relativity and the dynamics of space-time. The LIGO observations GW150914 and GW151226 provided wonderful testing grounds for general relativity in the, up to now unaccessible, strong-field dynamical regime of gravity. In this presentation I will review and discuss several of the tests that have been devised to detect violations of the predictions of general relativity from the observation of gravitational waves from coalescing binary systems. The discussion will be centred on the results of the analysis of GW150914 and GW151226. Finally, I will conclude by discussing some of the future prospects of extending the current state-of-the-art methodologies to further aspects of general relativity.Orateur: Dr Walter Del Pozzo (Universitá di Pisa)
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Echoes from the Abyss: Evidence for Planck-scale structure at black hole horizonsIn classical General Relativity (GR), an observer falling into an astrophysical black hole is not expected to experience anything dramatic as she crosses the event horizon. However, tentative resolutions to problems in quantum gravity, such as the cosmological constant problem, or the black hole information paradox, invoke significant departures from classicality in the vicinity of the horizon. It was recently pointed out that such near-horizon structures can lead to late-time echoes in the black hole merger gravitational wave signals that are otherwise indistinguishable from GR. We search for observational signatures of these echoes in the gravitational wave data released by advanced Laser Interferometer Gravitational-Wave Observatory (LIGO), following the three black hole merger events GW150914, GW151226, and LVT151012. In particular, we look for repeating damped echoes with time-delays of $8 M \log M$ (+spin corrections, in Planck units), corresponding to Planck-scale departures from GR near their respective horizons. Accounting for the ``look elsewhere'' effect due to uncertainty in the echo template, we find tentative evidence for Planck-scale structure near black hole horizons at $2.5\sigma$ significance level (corresponding to false detection probability of $1\%$). Future data releases from LIGO collaboration, along with more physical echo templates, will definitively confirm (or rule out) this finding, providing possible empirical evidence for alternatives to classical black holes, such as in firewall or fuzzball paradigms.Orateur: M. Jahed Abedi (Sharif University of Technology)
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Analysing gravitational wave data for black hole echoesWe discuss the methods of data analysis and significance estimation used to search for black hole echoes. We conclude that current results do not provide sufficient observational evidence for claiming the existence of Planck-scale structure at black hole horizons and we suggest further techniques that could be used to explore this interesting possibility.Orateur: Dr Alex Nielsen (MPI for Gravitational Phys)
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Questions for the two previous talksOrateurs: Dr Alex Nielsen (MPI for Gravitational Phys), M. Jahed Abedi (Sharif University of Technology)
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Ringdown and echoes as probes of strong-field dynamics of general relativityThe detections of the presumed binary black hole coalescences in the first observing run of Advanced LIGO have allowed us to probe the genuinely strong-field dynamics of Einstein's general theory of relativity for the first time, and put tight constraints on the inspiral-merger-ringdown dynamics of the binary coalescence process. Subsequent detections are expected to be able to more directly probe the nature of the compact objects themselves in complementary ways. Observation of the ringdown of the merger remnant will allow for a test of the black hole no-hair theorem. One can search for systematic departures in quasinormal mode frequencies and damping times from their values as predicted by general relativity. In the first part, we present a pipeline to carry out such a test of the no-hair theorem. Exotic compact objects (e.g. boson stars, dark matter stars, gravastars), and even certain quantum modifications to black holes (e.g. firewalls) are speculated to have consequences in the form of gravitational wave echoes, or bursts of radiation that appear at regular time intervals after the ringdown has ended. In the concluding part, we discuss the prospects of a search for such post-merger signals.Orateur: Dr Archisman Ghosh (Nikhef)
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Constraining Lorentz violations using gravitational wave observationsLocal Lorentz invariance is a cornerstone of general relativity (GR). The direct detection of gravitational waves (GWs) enables unique tests for possible violations of Lorentz invariance in the gravitational sector. Propagation effects of GWs in Lorentz violating theories of gravity lead to modified dispersion relations and dephasing of GWs with respect to the GR waveform. These may be measured or constrained through GW observations of compact binary mergers with second-generation detectors such as Advanced LIGO. We present a Bayesian parameter estimation pipeline to perform such studies, and using simulated data we quantify the prospects of future GW observations to constrain possible Lorentz invariance violations.Orateurs: Mlle Anuradha Samajdar (Indian Institute of Science Education and Research Kolkata), Dr Chris Van Den Broeck (National Institute for Subatomic Physics)
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Coffee break
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New Data Analysis Methods: Session chair: Benoit Mours
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Calibration, Data Quality and Vetos: now and the upcoming challengesThe quantity and quality of observations that we can make with ground-based gravitational-wave detectors depends on three critical tasks: (i) accurately calibrating the detectors; (ii) characterizing the performance of the detectors so that we can improve their astrophysical reach; and (iii) using calibration and data-quality information in both searches and parameter measurement. The evolution of detector sensitivity, the the challenges posed by low-latency searches and sky localization for electromagnetic follow-up, and the evolution of analysis techniques used by the astrophysical analyses all present different challenges for calibration, data quality and vetoes. I will review the current techniques used and discuss the challenges for the future.Orateur: Prof. Duncan Brown (Syracuse University)
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KAGRA calibration and waveform accuracyAccurate calibration of the output of the Gravitational Wave (GW) signal is crucial to determine the physics parameters of the sources. Also in the situation of global detector network, a less relative biases between these detectors are important on the science of GW astronomy. LIGO, Virgo and KAGRA employ the photon calibrator that can calibrate the absolute displacement of the test mass by pushing the mirror surface with photon pressure. One of the serious systematic errors at high-frequency region is the elastic deformation of the mirror. We can mitigate the elastic deformation effect because of the high Young’s module of the sapphire test mass. We estimated the elastic deformation and waveform accuracy of the kHz region. The misestimate of the relative waveform between LIGO, Virgo and KAGRA makes the systematic error of localization. We also calibrate the relative waveform by comparing the absolute power of photon calibrator. We will share the standard detector whose response is calibrated by laser power standard in NIST. We plan to make the scheme for crosschecking of photon calibrator. In this talk, we report the progress of the KAGRA calibration in order to achieve the absolute accuracy of several % to meet the calibration requirements of second-generation GW detectors. We would like to discuss the problems and the possible strategy on calibration with global detector network.Orateur: Dr Yuki Inoue (Academia Sinica, Institute of Physics)
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All-Sky Searches for Compact Binary Mergers: The Engines of DetectionSearches for GW from compact binary mergers using waveform templates have already successfully detected several binary black hole signals and are set to yield further discoveries as the network of Advanced detectors matures. We describe how the binary search pipelines used by LIGO-Virgo have broadened the range of systems they target, while becoming more robust against detector noise and thus increasing sensitivity for the sources considered in LIGO's first observing run. Modelling of signal populations plays an increasing role in maintaining the sensitivity of all-sky searches.Orateur: Dr Thomas Dent (AEI Hannover)
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Are we missing the most interesting binary mergers?Current matched-filter searches for binary mergers make several simplifying assumptions about the physics of the target systems. For example, the effect of orbital precession is neglected in current searches of advanced-detector data. This can reduce the ability to detect systems that could tell us about the evolution of massive stars and tests of relativity in extreme situations. In this talk we explore the ability of current search methods to observe some of the most interesting astrophysical systems, both today and with predicted future sensitivity curves, and discuss the astrophysical implications that would arise from having an observational bias against systems that the current search technique is not targeting.Orateur: Dr Ian Harry (Max Planck Institute for Gravitational Physics)
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Lunch
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Lunch
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SOC meeting Salle Berlioz B
Salle Berlioz B
Impérial Palace
Allée de l'Impérial, Annecy
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Continuous Waves and Stochastic Signals: Session chair: Cristiano Palomba
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The detection of Continuous Gravitational Waves in the Advanced Detector EraThe recent sensitivity improvements of the worldwide advanced gravitational-wave detector network has allowed us to detect the first transient gravitational-wave signal, marking thus the official beginning of the gravitational-wave astronomy. We have then started to hone the comprehension of some of the objects populating our Universe. A broader picture would be however provided by the detection of continuous-wave signals, which are emitted by rotating neutron stars with a non-axisymmetric deformation. After presenting the most stringent results obtained to date by the LIGO-Virgo collaboration, I will focus on the prospects for detecting continuous gravitational waves by mainly exploiting innovative strategies to search for such class of signals in the current long-awaited advanced detector era.Orateur: Dr Paola Leaci (Sapienza University and INFN)
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Searching for the stochastic gravitational-wave background with Advanced LIGO and Advanced VirgoObservations by Advanced LIGO and Advanced Virgo in the coming years will allow for important limits to be set on on the strength of a stochastic gravitational-wave background; a detection may happen as well. Sources for the stochastic gravitational-wave background could be cosmologically or astrophysically produced. The implications of the recent observations of GW150914 and GW151226 indicate that a stochastic background produced from the superposition of binary black hole mergers throughout the history of the universe may be detectable by LIGO and Virgo in the coming years. Presented will be a summary of the current LIGO-Virgo search for such a stochastic background using data from the first observing run, and what implications those results will have on different models.The projected sensitivities of future observation runs with Advanced LIGO and Advanced Virgo will also be given. Finally, information on how the stochastic background searches by ground-based detectors and LISA can complement one another will be presented.Orateur: Dr Nelson Christensen (Artemis)
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Einstein@Home all-sky search for continuous gravitational waves in advanced LIGO dataRapidly rotating neutron stars are promising sources of continuous gravitational waves for the LIGO and Virgo interferometers. All-sky searches for isolated neutron stars offer the potential to detect gravitational waves from neutron stars that have not been observed electromagnetically. The broad parameter space of these all-sky searches presents a significant computational challenge. The computing power amassed via the Einstein@Home project facilitates the most sensitive all-sky searches for isolated neutron stars. In this talk, I present the results of the first all-sky search for continuous gravitational waves on Einstein@Home with advanced LIGO data. This search covers the low frequency range of 20 Hz to 100 Hz, much of which was not explored by Einstein@Home in initial LIGO.Orateur: Dr Sinéad Walsh (University of Wisconsin - Milwaukee)
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Hunting the oxymoron: transient continuous waves from disturbed neutron starsDisturbed neutron stars -- soon after their birth, after a starquake or due to episodic accretion -- could emit gravitational waves in the ground-based detector band, both in the form of initial bursts and as longer-lasting weak transients. Data analysis methods derived from the established search efforts for "continuous waves" are well suited for transient quasi-periodic signals with durations from hours to weeks. We discuss the application of such "transient continuous wave" search methods, focussing on two scenarios: targeted analysis of glitching pulsars known from electromagnetic observations, and the followup of outliers from all-sky continuous-wave searches which exhibit hints of transient behaviour. Based on mock data studies, we consider the sensitivities achievable with advanced LIGO, and the potential of transient detections -- or upper limits -- to study the structure of neutron stars and the physical mechanisms behind glitches.Orateur: Dr David Keitel (University of Glasgow)
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Searches for Gravitational Waves from Scorpius X-1 with Advanced LIGOThe low-mass X-ray binary Scorpius X-1 is a promising source of continuous gravitational waves. Its high X-ray luminosity indicates a large rate of accretion, which may power GW emission. A variety of methods have been developed and applied to search for the signal, which presents challenges because of the unknown signal frequency and residual uncertainties in orbital parameters. I will present search results from the first LIGO Observing run and consider the prospects for future searches.Orateur: Dr John Whelan (Rochester Institute of Technology)
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Coffee break
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Binary Black Hole Science: III; Session chair: Bruce Allen
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Binary black hole observations with Advanced LIGOThe first direct detection of gravitational waves originated from a binary black hole coalescence during advanced LIGO's first observing run in September 2015. A subsequent confirmed detection in December of the same year established the birth of gravitational wave astronomy and the expectation that binary black hole mergers will be frequently observed with ground-based gravitational wave observatories over the coming decade. We will discuss binary black hole discoveries to date along with the ongoing searches for black holes in advanced LIGO's second observing run, which began in November 2016.Orateur: Dr Chad Hanna (Penn State)
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Binary black hole spinsGravitational-wave observations allow us to infer black hole spins. We will review spin measurements from current LIGO observations of binary black holes. The orientations of the spins are a tracer of the formation mechanism. While spin measurements from individual systems have large uncertainties, more information can be gained by combining the population of results. We show how a hierarchical analysis of spin measurements could be performed to constrain the fraction of binaries with different spin orientations, and how this could impact our understanding of binary formation.Orateur: Dr Christopher Berry (University of Birmingham)
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Testing the area theorem with gravitational wave signalsObservations of gravitational waves from binary black hole coalescences provide an opportunity for testing the black hole area increase law, also known as the area theorem. For loud enough signals, the inspiral (ringdown) part of the waveform provides a measurement of the initial (final) parameters of the black holes. We explore how to perform such measurements with Advanced LIGO in order to independently obtain the initial and final areas. These measurements will allow us to calculate the probability that the final area has indeed increased to determine if a specific gravitational-wave event is compatible with the area theorem.Orateur: Mlle Miriam Cabero Mueller (Albert Einstein Institute Hannover)
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Gravitational Lensing of Gravitational WavesGravitational lensing phenomena are widespread in electromagnetic astrophysics, and in principle may also be uncovered with gravitational waves. We examine gravitational wave events in the limit of geometric optics, where we expect to see multiple signals from the same event with different arrival times and amplitudes, and wave optics, where we expect to see effects such as interference and diffraction. We estimate the rate of lensed signals in the Advanced LIGO era, and discuss the strategies to identify them. Moreover, we investigate the physics that we can extract from lensed gravitational-wave signals such as the particulars of the lens.Orateur: Prof. Tjonnie Li (The Chinese University of Hong Kong)
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Dinner
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Binary Systems with Neutron Stars: Session chair: Tania Regimbau
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Measuring neutron star tidal deformability with Advanced LIGO: a Bayesian analysis of neutron star - black hole binary observationsThe pioneering discovery of gravitational waves (GW) by Advanced LIGO has ushered us into an era of observational GW astrophysics. Compact binaries remain the primary target sources for GW observation, of which neutron star - black hole (NSBH) binaries form an important subset. GWs from NSBH sources carry signatures of the tidal distortion of the neutron star by its companion black hole during inspiral, and its potential tidal disruption near merger. We present a Bayesian study of the measurability of neutron star tidal deformability $\Lambda_\mathrm{NS}\propto (R/M)_\mathrm{NS}^{5}$ using observation(s) of inspiral-merger GW signals from disruptive NSBH coalescences, taking into account the crucial effect of black hole spins. If non-tidal templates are used to estimate source parameters for an NSBH signal, the bias introduced in the estimation of non-tidal physical parameters is found to be only be significant for loud signals with signal-to-noise ratios greater than $\simeq30$. We focus on how a population of realistic NSBH detections will improve our measurement of neutron star tidal deformability. For an astrophysically likely population of *disruptive* NSBH coalescences, we find that $20-35$ events are sufficient to constrain $\Lambda_\mathrm{NS}$ within $\pm 25-50\%$, depending on the neutron star equation of state. This number also depends on whether black hole masses lie within the astrophysical *mass-gap*. We find that it is the loudest $5-10$ events that provide most of the tidal information, and not the combination of tens of low-SNR events, thereby facilitating targeted numerical-GR follow-ups of NSBHs. These results are encouraging, and we recommend that an effort to measure $\Lambda_\mathrm{NS}$ be planned for upcoming NSBH observations with the LIGO-Virgo instruments.Orateur: Michael Pürrer (AEI)
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Structure of binary neutron star merger remnantsI will present results from numerical simulations of binary neutron star mergers with emphasis on the structure of the merger remnants during the phase shortly after merger, when the GW signal might still be detectable before the amplitude becomes too small. The fluid flow and radial mass distribution determined numerically has implications regarding the question which physical effects are relevant for the remnant lifetime. This should be addressed in order to better constrain the equation of state from future observations of remnant lifetimes. Further, I will discuss the occurrence of phase jumps in the GW signal during and sometimes also after merger and how those further complicate the interpretation of secondary peaks in the GW power spectrum. Finally, I will discuss the impact of the initial NS spin on the late inspiral and post-merger phases.Orateur: M. Wolfgang Kastaun (AEI Hannover)
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Constraining BNS merger rates and X-ray counterpart models with existing dataCoalescences of compact binaries play a fundamental role in astronomy. They are not only considered the most promising sources of gravitational waves for ground-based detectors such as LIGO and Virgo, but also the central engine of short gamma ray bursts (SGRBs). In the last decade, multi-wavelength observations of SGRBs and their afterglow showed a variety of unexpected features, posing new theoretical challenges. A growing theoretical effort is being devoted to explain these new observations and, at the same time, to predict the possible electromagnetic (EM) counterparts to the gravitational wave signals from compact binary mergers. In order to validate the different theoretical scenarios, we recently started a project aimed at constraining models by using archived data from past and present missions. The core of the project consists in developing two parallel codes, one dedicated to predict the number of events present in a survey for a given event rate and emission model, and one dedicated to analyse the actual data and then to constrain either the event rates or the models. The talk will present our first case study focused on the X-ray emission from long-lived binary neutron star merger remnants, as predicted by the recent model proposed in Siegel & Ciolfi (2016). Currently, we refer to data collected by XMM-Newton during its several years of operations. Although the project is at a preliminary stage, our first predictions suggest that few events should already be present in XMM-Netwon archived data.Orateur: Mme Serena Vinciguerra (University of Birmingham)
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Results and Prospects of the Search for Gravitational Waves from Neutron Star Binaries and Neutron Star-Black Hole BinariesThe first observing run of the Advanced LIGO detectors took place from September 12, 2015 to January 19, 2016. In addition to binary black hole mergers, the LIGO Scientific Collaboration's searches for compact-object binaries also targets binary neutron stars and neutron star-black hole binaries. In this talk, I will give an overview of the results of the search for binary neutron star and neutron-star black hole mergers. I will discuss the sensitive volumes of the first observing run, the astrophysical implications of the non-detection of binaries containing neutron stars in this run, and the prospects for future observations.Orateur: M. Steven Reyes (Syracuse University / LIGO)
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Coffee break
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Multi-messenger: I; Session chair: Gianluca Guidi
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Probing the intrinsic properties of short gamma-ray bursts using joint gravitational wave observationsThe observation of gravitational waves (GWs) from binary neutron star mergers coincident with short gamma-ray bursts (sGRBs) is a likely scenario for the Advanced detector era. Such observations will allow us to enhance the determination of parameters governing the signals of both emission channels. When a population of such observations are accumulated it is possible to also infer parameters governing that population. We present a general hierarchical Bayesian procedure for this purpose and provide an example analysis whereby the gamma-ray luminosity distribution of sGRBs can be measured. When modelling the sGRB luminosity distribution as a power-law we are able show that after O(10) joint detections we will be able to constrain the sGRB power-law index to +/- 0.2 and after O(100) to +/- 0.05 at 95% confidence. For the latter result the required number of joint observations requires a 3rd generation GW detector network. For the former it is feasible that the Advanced network at design sensitivity will provide enough jointly observed events.Orateur: Christopher Messenger (University of Glasgow)
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Lunch
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Multi-messenger: II; Session chair: Peter Shawhan
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Gravitational-wave transient candidate alerts: prospect and challenges for the multi-messenger astronomyThe first observation of gravitational waves by the Advanced LIGO interferometers opened a new frontier of observational astrophysics. The detection of electromagnetic signals associated with gravitational-wave observations will be crucial for giving a complete picture of the astrophysical sources and their enviroment, allowing us to probe the physics of the energetic transient phenomena in the sky, and to shed light on the formation, evolution and nature of compact objects. The talk will describe the ongoing electromagnetic follow-up program; the world-wilde effort of space and ground-based gamma-ray, x-ray, optical, infrared, and radio facilities observing together with the advanced gravitational-wave detector network to hunt the elusive electromagnetic counterparts. Prospects and challenges for joint observations and data analysis will be outlined.Orateur: Marica Branchesi (Università di Urbino/INFN-Sezione di Firenze)
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The SVOM mission in the multi-messenger eraSVOM (Space-based multiband astronomical Variable Objects Monitor) is a Sino-French mission dedicated to the time-domain astronomy. SVOM is a highly versatile satellite to be launched in 2021, with built-in multi-wavelength capabilities, autonomous repointing and dedicated ground follow-up. The SVOM core program focuses on the detection, the localization and the characterization of the prompt emission of Gamma-Ray Bursts and the GRB afterglow in multi-wavelength, including those which are highly redshifted. SVOM plays a role in the multi-messenger area thanks to its potential to follow transient triggers on the ground and in space from other facilities including gravitational waves alerts. During the presentation, I will review the different instruments on-board SVOM and on the ground, and their performance. I will also present the SVOM follow-up strategy to respond to transient triggers: I will show the first observation results of SVOM/Mini-GWAC in case of GW alerts.Orateur: Dr Sarah Antier (LAL)
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Optimal follow-up observations of gravitational wave events with small optical telescopesWe discuss optimal direction for follow-up observations by 1-3 m class optical/infrared telescopes which target optical/infrared counterparts of gravitational wave events detected with two laser interferometric gravitational wave detectors. The probability maps of transient sources, such like coalescing neutron stars and/or black holes, determined with two laser interferometers generally spread widely. They include the distant region where it is difficult for small aperture telescopes to observe the optical/infrared counterparts. For small telescopes, there is a possibility that it is more advantageous to search for nearby region even if the probability inferred by two gravitational wave detectors is low. We show that in the case of first three events of advanced LIGO, the posterior probability map, derived by using a distance prior restricted to a nearby region, is different from that derived without such restriction. This suggests that the optimal direction for small telescopes to perform follow-up observation of LIGO’s three events are different from what has been searched so far. We also show that, when the inclination angle of the binary is nearly edge-on, it is possible that the true direction is not included in the 90% posterior probability region. We discuss the optimal strategy to perform optical/infrared follow-up observation with small aperture telescopes based on these facts.Orateur: Dr Tatsuya Narikawa (ICRR, University of Tokyo)
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Estimating short gamma-ray burst luminosities in conjunction with gravitational wave observationsProgenitors of short-duration gamma-ray bursts are thought to be neutron stars coalescing with their companion black hole or neutron star. These compact binary coalescing systems are one of main targets of ground-based gravitational wave observations. In this talk, we present a Bayesian framework for combining astrophysical and gravitational wave information that allows us to probe short gamma-ray burst luminosities. We show that the combined observations not only improve progenitor distance and inclination angle estimates, they also allow short gamma-ray burst luminosities to be determined without the need for host galaxy or light curve information. We characterise our approach by simulating 1000 joint detections and comparing luminosities obtained via our analysis with the ideal scenario where the distance to the short gamma-ray burst is known exactly. We show that ~90% of the simulations have uncertainties on short gamma-ray luminosity estimates that are within a factor of 2 of the ideal scenario. This implies that, in conjunction with third-generation gravitational wave detectors, this method can be used to obtain accurate luminosity estimates for the majority of the short gamma-ray burst population within a redshift of ~1.Orateur: Dr Ik Siong Heng (University of Glasgow)
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Closure: Session chair: Peter Shawhan
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