Search Talks

I will report on some recent results obtained using the fully general relativistic magnetohydrodynamic code Whisky in simulating equal and unequal-mass binary neutron star (BNS) systems during the last phases of inspiral, merger and collapse to black hole surrounded by a torus. BNSs are among the most important sources of gravitational waves which are expected to be detected by the current or next generation of gravitational wave detectors, such as LIGO and Virgo, and they are also thought to be at the origin of very important astrophysical phenomena, such as short gamma-ray bursts. I will in particular describe both the gravitational wave signals generated by these sources and the properties of the tori that can be formed. I will also describe how the Effective One Body (EOB) model can be used to accurately compute the gravitational wave signal generated during the inspiral of BNSs by comparing it with the longest general relativistic numerical simulations of BNSs performed up to now.

We describe a Markov-Chain Monte-Carlo technique to study the source parameters of gravitational-wave signals from the inspirals of stellar-mass compact binaries detected with ground-based detectors such as LIGO and Virgo. We can apply this technique to both spinning and non-spinning waveforms and we use a variety of tools like parallel tempering to improve the sampling efficiency of the algorithm in a multi-dimensional parameter space. We describe new developments in model-selection techniques for distinguishing between alternative signal models. We present preliminary results from the application of these techniques to data sets containing injections of numerical-relativity waveforms into simulated Gaussian detector noise. We study the source parameters of signals from the inspirals of stellar-mass compact binaries detected with ground-based gravitational-wave detectors such as LIGO and Virgo. We use automatic adaptation of the step size and take into account the correlations between parameters to efficiently probe the parameter space while keeping the algorithm suitable for a wide range of signals. We shall discuss the performance of the MCMC algorithm and the typical measurement accuracy of the source parameters as a function of the binary parameters and the number of detectors in the network. We will show that despite the lower positional accuracy compared to other astronomical observations an association of a gravitational-wave event with e.g. an electromagnetic detection is possible with three or even two 4-km-size interferometers.

Direct detection of gravitational wave stands at a cross roads; the first generation of interferometric detectors will soon be decommissioned and the second generation projects are underway. In this talk, I will describe the Initial LIGO and VIRGO generation of instruments, the techniques required to achieve a strain sensitivity of 3 x 10^{-23} and an NS / NS inspiral range of 15 Mpc. I'll follow with a description of the Advanced detectors and the differences that should improve the sensitivity by a factor of ten. Finally, I will describe projects from radio and microwave astronomy to measure gravitational waves using pulsar timing and the CMB B-mode polarization.

We present a new construction of phenomenological templates for non-precessing spinning black hole binaries. This approach utilizes a frequency domain matching of post-Newtonian inspiral waveforms with numerical relativity based binary black hole coalescence waveforms. We quantify the various possible sources of systematic errors that could arise in matching post-Newtonian and numerical relativity waveforms and we use a matching criteria based on minimizing these errors. An analytical formula for the dominant mode of the gravitational radiation of non-precessing black-hole binaries is presented that captures the phenomenology of the hybrid waveforms. Its implementation in the current searches for gravitational waves should allow cross-checks of other inspiral-merger-ringdown waveform families as well as an improvement of the reach of the detection algorithms.

I will review recent advances in the effective-one-body formalism aimed at describing the dynamics and gravitational-wave emission from coalescing black holes. I will discuss the implications of those advances for the search of gravitational waves from binary black holes and for the recoil velocity of black holes formed through merger.

The dynamics of black-hole binaries is a very complex problem which has been solved only very recently through time-expensive numerical-relativity calculations. In spite of this mathematical complexity many results of these calculations can be accurately reproduced with phenomenological approaches based on test particles combined with Post-Newtonian theory and black-hole perturbation theory. In this talk I will focus on effective-one-body models, which have proved a useful and fast tool to accurately reproduce numerical-relativity waveforms. In particular I will present a novel, self-consistent effective-one-body model for spinning black-hole binaries, and show that this model does not suffer from the shortcomings of the existing models which have been put forward in the literature.

The quest for gravitational waves from binary inspiral is performed via matched filtering and thus requires a detailed knowledge of the signal. For non-precessing binaries complete analytic waveforms exist from inspiral to merger and ring-down. Here we present complete waveforms for generically spinning equal mass systems.They have been constructed by bridging the gap between the analytically known inspiral phase described by spin Taylor (T4) approximants in the restricted waveform approximation and the ring-down phase. These two phases are connected by a phenomenological intermediate phase calibrated by confrontation with numerically generated waveforms.The values of the overlap integral between numerical waveforms and our semi-analitic ones range between 0.96 and 0.99.

Recently generated asymptotic expansions zanolin et al. arXiv:0912.0065 [gr-qc] showa frequentist approach to go beyond Fisher information assessments of the accuracy for maximum likelihood parameter estimations. In this talk we describe the application of these techniques to directional reconstruction fornumerical relativity waveforms.

Most searches with ground-based detectors for gravitational-wave signals from the inspirals of stellar-mass compact binaries use template based methods. Those work well for non-spinning systems but since the dimensionality of the parameter space of spinning waveforms is large a template bank search is not feasible. We describe Bayesian and Markov-chain Monte-Carlo methods for parameter estimation of spinning waveforms using hybrid spinning waveforms matching the ringdown from Numerical Relativity results. We compare those results when using post-Newtonian only waveforms. We explore the parameter space and discuss different ways to overcome its high dimensionality and multi-modality.

Black hole-neutron star binary (BHNS) mergers are likely sources for detectable gravitational radiation and candidate engines for short-hard gamma-ray bursts. However, accurate modeling of these mergers requires fully general relativistic simulations, incorporating both relativistic hydrodynamics for the matter and Einstein's field equations for the (strong) gravitational fields. I will review techniques and results from recent fully general relativistic BHNS merger simulations. These simulations examine the effects of the BH:NS mass ratio, BH spin, and NS equation of state, focusing on both the gravitational waveforms and remnant disk.