La première détection des ondes gravitationnelles en 2015 a ouvert un nouveau plan d'étude pour l'astrophysique des étoiles binaires compactes. En utilisant les données des détections faites par les détecteurs terrestres advanced LIGO et advanced Virgo, il est possible de contraindre les paramètres physiques de ces systèmes avec une analyse Bayésienne et ainsi approfondir notre connaissance physique des étoiles binaires compactes. Cependant, pour pouvoir être en mesure d'obtenir de tels résultats, il est essentiel d’avoir des algorithmes performants à la fois pour trouver les signaux de ces ondes gravitationnelles et pour l'estimation de paramètres. Le travail de cette thèse a ainsi été centré autour du développement d’algorithmes performants et adaptées au problème physique à la fois de la détection et de l'estimation des paramètres pour les ondes gravitationnelles. La plus grande partie de ce travail de thèse a ainsi été dédiée à l'implémentation d’un algorithme de type Hamiltonian Monte Carlo adapté à l'estimation de paramètres pour les signaux d’ondes gravitationnelles émises par des binaires compactes formées de deux étoiles à neutrons. L'algorithme développé a été testé sur une sélection de sources et a été capable de fournir de meilleures performances que d'autres algorithmes de type MCMC comme l'algorithme de Metropolis-Hasting et l'algorithme à évolution différentielle. L'implémentation d'un tel algorithme dans les pipelines d’analyse de données de la collaboration pourrait augmenter grandement l'efficacité de l'estimation de paramètres. De plus, il permettrait également de réduire drastiquement le temps de calcul nécessaire, ce qui est un facteur essentiel pour le futur où de nombreuses détections sont attendues. Un autre aspect de ce travail de thèse a été dédié à l'implémentation d'un algorithme de recherche de signaux gravitationnelles pour les binaires compactes monochromatiques qui seront observées par la future mission spatiale LISA. L'algorithme est une mixture de plusieurs algorithmes évolutionnistes, avec notamment l'inclusion d'un algorithme de Particle Swarm Optimisation. Cette algorithme a été testé dans plusieurs cas tests et a été capable de trouver toutes les sources gravitationnelles comprises dans un signal donné. De plus, l'algorithme a également été capable d'identifier des sources sur une bande de fréquence aussi grande que 1 mHz, ce qui n'avait pas été réalisé au moment de cette étude de thèse. / The first detection of gravitational waves in 2015 has opened a new window for the study of the astrophysics of compact binaries. Thanks to the data taken by the ground-based detectors advanced LIGO and advanced Virgo, it is now possible to constrain the physical parameters of compact binaries using a full Bayesian analysis in order to increase our physical knowledge on compact binaries. However, in order to be able to perform such analysis, it is essential to have efficient algorithms both to search for the signals and for parameter estimation. The main part of this thesis has been dedicated to the implementation of a Hamiltonian Monte Carlo algorithm suited for the parameter estimation of gravitational waves emitted by compact binaries composed of neutron stars. The algorithm has been tested on a selection of sources and has been able to produce better performances than other types of MCMC methods such as Metropolis-Hastings and Differential Evolution Monte Carlo. The implementation of the HMC algorithm in the data analysis pipelines of the Ligo/Virgo collaboration could greatly increase the efficiency of parameter estimation. In addition, it could also drastically reduce the computation time associated to the parameter estimation of such sources of gravitational waves, which will be of particular interest in the near future when there will many detections by the ground-based network of gravitational wave detectors. Another aspect of this work was dedicated to the implementation of a search algorithm for gravitational wave signals emitted by monochromatic compact binaries as observed by the space-based detector LISA. The developed algorithm is a mixture of several evolutionary algorithms, including Particle Swarm Optimisation. This algorithm has been tested on several test cases and has been able to find all the sources buried in a signal. Furthermore, the algorithm has been able to find the sources on a band of frequency as large as 1 mHz which wasn’t done at the time of this thesis study

Some of the brightest and most energetic events in the Universe are associated with the death of stars. These stellar deaths power transient electromagnetic emission which are routinely observed on Earth. This dissertation presents our research on various such transients. Its topics includes, supernova remnants, kilonovae, gamma-ray bursts (GRBs): The "long'' type produced from core-collapse supernovae and the "short'' type associated with neutron star merger events. It also focuses on the disruption of stars by the tidal forces of supermassive black holes i.e., tidal disruption events (TDEs). We model the emission from these transients and compare them to observations in order to draw a number of conclusions and make predictions for future detections. For example, we find that the non-thermal emission from supernovae and kilonovae associated with GRBs can produce long term emission which may be detected as a re-brightening in the overall emission. The sharp cut off observed in some TDE flares can be caused by a pre-existing accretion disk present around a supermassive black hole, which is expected in active galactic nuclei. Our work successfully predicted the nature of the very first electromagnetic detection from a neutron star merger, and was able to reproduce the emission that had been observed for more than one hundred days after the merger. This dissertation also provides frameworks on how the observable features of these transients can be leveraged to probe the properties of the progenitor system and their environment. <br>

In this thesis we investigate advanced techniques for the readout and control of various interferometers. In particular, we present experimental investigations of interferometer configurations and control techniques to be used in second generation interferometric gravitational wave detectors. We also present a new technique, tilt locking, for the readout and control of optical interferometers. ¶ We report the first experimental demonstration of a Sagnac interferometer with resonant sideband extraction (RSE). We measure the frequency response to modulation of the length of the arms and demonstrate an increase in signal bandwidth of by a factor of 6.5 compared to the Sagnac with arm cavities only. We compare Sagnac interferometers based on optical cavities with cavity-based Michelson interferometers and find that the Sagnac configuration has little overall advantage in a cavity-based system. ¶ A system for the control and signal extraction of a power recycled Michelson interferometer with RSE is presented. This control system employs a frontal modulation scheme requiring a phase modulated carrier field and a phase modulated subcarrier field. The system is capable of locking all 5 length degrees of freedom and allows the signal cavity to be detuned over the entire range of possibilities, in principle, whilst maintaining lock. We analytically investigate the modulation/demodulation techniques used to obtain these error signals, presenting an introductory explanation of single sideband modulation/demodulation and double demodulation. ¶ This control system is implemented on a benchtop prototype interferometer. We discuss technical problems associated with production of the input beam modulation components and present several solutions. Operation of the interferometer is demonstrated for a wide range of detunings. The frequency response of the interferometer is measured for various detuned points and we observe good agreement with theoretical predictions. The ability of the control system to maintain lock as the interferometer is detuned is experimentally demonstrated. ¶ Tilt locking, a new technique to obtain an error signal to lock a laser to an optical cavity, is presented. This technique produces an error signal by efficient measurement of the interference between the TEM00 and TEM10 modes. We perform experimental and theoretical comparisons with the widely used Pound-Drever-Hall (PDH) technique. We derive the quantum noise limit to the sensitivity of a measurement of the beam position, and using this result calculate the shot noise limited sensitivity of tilt locking. We show that tilt locking has a quantum efficiency of 80%, compared to 82% for the PDH technique. We present experimental demonstrations of tilt locking in several applications including frequency stabilisation, continuous-wave second harmonic generation, and injection locking of a Nd:YAG slab laser. In each of these cases, we demonstrate that the performance of tilt locking is not the limiting factor of the lock stability, and show that it achieves similar performance to the PDH based system. ¶ Finally, we discuss how tilt locking can be effectively applied to two beam interferometers. We show experimentally how a two beam interferometer typically gives excellent isolation against errors arising from changes in the photodetector position, and experimentally demonstrate the use of tilt locking as a signal readout system for a Sagnac interferometer.

The inspiral and merger of two black holes is among the most exciting and extreme events in our universe. Being one of the loudest sources of gravitational waves, they provide a unique dynamical probe of strong-field general relativity and a fertile ground for the observation of fundamental physics. While the detection of gravitational waves alone will allow us to observe our universe through an entirely new window, combining the information obtained from both gravitational wave and electro-magnetic observations will allow us to gain even greater insight in some of the most exciting astrophysical phenomena. In addition, binary black-hole mergers serve as an intriguing tool to study the geometry of space-time itself. In this dissertation we study the merger process of binary black-holes in a variety of conditions. Our results show that asymmetries in the curvature distribution on the common apparent horizon are correlated to the linear momentum acquired by the merger remnant. We propose useful tools for the analysis of black holes in the dynamical and isolated horizon frameworks and shed light on how the final merger of apparent horizons proceeds after a common horizon has already formed. We connect mathematical theorems with data obtained from numerical simulations and provide a first glimpse on the behavior of these surfaces in situations not accessible to analytical tools. We study electro-magnetic counterparts of super-massive binary black-hole mergers with fully 3D general relativistic simulations of binary black-holes immersed both in a uniform magnetic field in vacuum and in a tenuous plasma. We find that while a direct detection of merger signatures with current electro-magnetic telescopes is unlikely, secondary emission, either by altering the accretion rate of the circumbinary disk or by synchrotron radiation from accelerated charges, may be detectable. We propose a novel approach to measure the electro-magnetic radiation in these simulations and find a non-collimated emission that dominates over the collimated one appearing in the form of dual jets associated with each of the black holes. Finally, we provide an optimized gravitational wave detection pipeline using phenomenological waveforms for signals from compact binary coalescence and show that by including spin effects in the waveform templates, the detection efficiency is drastically improved as well as the bias on recovered source parameters reduced. On the whole, this disseration provides evidence that a multi-messenger approach to binary black-hole merger observations provides an exciting prospect to understand these sources and, ultimately, our universe. / Schwarze Löcher gehören zu den extremsten und faszinierensten Objekten in unserem Universum. Elektromagnetische Strahlung kann nicht aus ihrem Inneren entkommen, und sie bilden die kompaktesten Objekte, die wir kennen. Wir wissen heute, dass in den Zentren der meisten Galaxien sehr massereiche schwarze Löcher vorhanden sind. Im Fall unserer eigenen Galaxie, der Milchstrasse, ist dieses schwarze Loch ungefähr vier Millionen mal so schwer wie unsere Sonne. Wenn zwei Galaxien miteinander kollidieren, führt dies auch dazu, dass ihre beiden schwarzen Löcher kollidieren und zu einem einzelnen schwarzen Loch verschmelzen. Das Simulieren einer solchen Kollision von zwei schwarzen Löchern, die Vorhersage sowie Analyse der von ihnen abgestrahlten Energie in Form von Gravitations- und elektromagnetischen Wellen, bildet das Thema der vorliegenden Dissertation. Im ersten Teil dieser Arbeit untersuchen wir die Verschmelzung von zwei schwarzen Löchern unter verschiedenen Gesichtspunkten. Wir zeigen, dass Ungleichmässigkeiten in der Geometrie des aus einer Kollision entstehenden schwarzen Loches dazu führen, dass es zuerst beschleunigt und dann abgebremst wird, bis diese Ungleichmässigkeiten in Form von Gravitationswellen abgetrahlt sind. Weiterhin untersuchen wir, wie der genaue Verschmelzungsprozess aus einer geometrischen Sicht abläuft und schlagen neue Methoden zur Analyse der Raumzeitgeometrie in Systemen vor, die schwarze Löcher enthalten. Im zweiten Teil dieser Arbeit beschäftigen wir uns mit den Gravitationswellen und elektromagnetischer Strahlung, die bei einer Kollision von zwei schwarzen Löchern freigesetzt wird. Gravitationswellen sind Wellen, die Raum und Zeit dehnen und komprimieren. Durchläuft uns eine Gravitationswelle, werden wir in einer Richtung minimal gestreckt, während wir in einer anderen Richtung minimal zusammengedrückt werden. Diese Effekte sind allerdings so klein, dass wir sie weder spüren, noch auf einfache Weise messen können. Bei einer Kollision von zwei schwarzen Löchern wird eine grosse Menge Energie in Form von Gravitationswellen und elektromagnetischen Wellen abgestrahlt. Wir zeigen, dass beide Signale in ihrer Struktur sehr ähnlich sind, dass aber die abgestrahlte Energie in Gravitationswellen um ein Vielfaches grösser ist als in elektromagnetischer Strahlung. Wir führen eine neue Methode ein, um die elektromagnetische Strahlung in unseren Simulationen zu messen und zeigen, dass diese dazu führt, dass sich die räumliche Struktur der Strahlung verändert. Abschliessend folgern wir, dass in der Kombination der Signale aus Gravitationswellen und elektromagnetischer Strahlung eine grosse Chance liegt, ein System aus zwei schwarzen Löchern zu detektieren und in einem weiteren Schritt zu analysieren. Im dritten und letzen Teil dieser Dissertation entwickeln wir ein verbessertes Suchverfahren für Gravitationswellen, dass in modernen Laser-Interferometerexperimenten genutzt werden kann. Wir zeigen, wie dieses Verfahren die Chancen für die Detektion eines Gravitationswellensignals deutlich erhöht, und auch, dass im Falle einer erfolgreichen Detektion eines solchen Signals, seine Parameter besser bestimmt werden können. Wir schliessen die Arbeit mit dem Fazit, dass die Kollision von zwei schwarzen Löchern ein hochinteressantes Phenomenon darstellt, das uns neue Möglichkeiten bietet die Gravitation sowie eine Vielzahl anderer fundamentaler Vorgänge in unserem Universum besser zu verstehen.

This thesis presents the results of the STAMPAS all-sky search for long transient gravitational waves in the 2005-2007 LIGO-Virgo data. Gravitational waves are perturbations of the space-time metric. The Virgo and LIGO experiments are designed to detect such waves. They are Michelson interferometers with 3 km and 4 km long arms, whose light output is altered during the passage of a gravitational wave.Until very recently, transient gravitational wave search pipelines were focused on short transients, lasting less than 1 second, and on binary coalescence signals. STAMPAS is one of the very first pipelines entirely dedicated to the search of long transient gravitational wave signals, lasting from 1s to O(100s).These signals originate, among other sources, from instabilities in protoneutron stars as a result of their violent birth. The standing accretion shock instability in core collapse supernovae or instabilities in accretion disks are also possible mechanisms for gravitational wave long transients. Eccentric black hole binary coalescences are also expected to emit powerful gravitational waves for several seconds before the final plunge.STAMPAS is based on the correlation of data from two interferometers. Time-frequency maps of the data are extracted, and significant pixels are clustered to form triggers. No assumption on the direction, the time or the form of the signals is made.The first STAMPAS search has been performed on the data from the two LIGO detectors, between 2005 and 2007. After a rigorous trigger selection, the analysis revealed that their rate is close to Gaussian noise expectation, which is a significant achievement. No gravitational wave candidate has been detected, and upper limits on the astrophysical rates of several models of accretion disk instability sources and eccentric black holes binary coalescences have been set. The STAMPAS pipeline demonstrated its capabilities to search for any long transient gravitational wave signals during the advanced detector era.Keywords: Gravitational waves, Interferometry, Long transients, Signal Processing, Accretion Disk Instabilities, Eccentric Black Hole Binaries.

Gravitational waves have been predicted by Einstein in his General Relativity theory. Theyare perturbation of the space-time metric and we try to reveal them by laser interferometry. More precisely,gravitational wave detectors are km long Michelson interferometers combined with Fabry-Perot cavities.The network of first generation detectors (Virgo, LIGO, GEO) did not permit a direct detection afterseveral observational runs in coincidence at the nominal sensitivity. A second generation of detectors is inpreparation with in particular the European project Advanced Virgo. This detector should have a sensitivityincreased by an order of magnitude compared to Virgo. The interferometer mirrors play a crucial role inthe Advanced Virgo sensitivity as it is limited by the mirror thermal noise in the mid-frequency regionand by the amount of photons collected in the interferometer cavities at high frequencies. The high powercirculating in the Fabry-Perot cavities induces important thermal lensing effect. This thesis is interestedfirst in the thermal lensing effect in the interferometer for different optical configurations. Then we areinterested in the mirrors composing the Fabry-Perot arm cavity from the calculation of the requirements interms of flatness to the realization of the mirrors flatness and its measurement. The mirror flatness shouldbe sub-nanometric in order to limit the optical losses in the Fabry-Perot cavities to reduce the effect of theshot noise and of the diffused light. We will see the correction of the substrates flatness by the so-calledcorrective coating technique. Finally, we study the uniformity of the dielectric multilayer coating depositionnecessary to obtained high-reflective mirrors. We study in particular the planetary motion of the substratesin the coating machine.

Paper discusses the expected uncertainty of orbital parameters of binary stars as measured by the space-based gravitational wave observatory LISA (Laser Interferometer Space Antenna) and how the inclusion of spin in the model of the binary stars affects the uncertainty. The uncertainties are found by calculating the received gravitational wave from a binary pair and then performing a linear least-squares parameter estimation. The case of a 1500 solar mass black hole that is 20 years from coalescing with a 1000 solar mass black hole--both of which are 50 x 10^6 light years away--is analyzed, and the results show that the inclusion of spin has a negligible effect upon the angular resolution of LISA but can increase the accuracy in mass and distance measurements by factors of 15 and 65, respectively.

Un siècle après leur prédiction par Albert Einstein, le 14 septembre 2015 des ondes gravitationnelles provenant de la coalescence de deux trous noirs ont été observées, ouvrant ainsi le champ à une toute nouvelle astronomie et une nouvelle manière d'étudier la gravitation. La faible amplitude des ondes gravitationnelles nécessite des détecteurs spécifiques et très sensibles. Advanced Virgo est un interféromètre kilométrique de deuxième génération dédié à la détection des ondes gravitationnelles. Un des éléments nécessaires pour atteindre la sensibilité requise est le système optique de filtrage appelé l’Output Mode Cleaner ou OMC, placé en sortie de l'interféromètre, et composé de deux cavités optiques. Ce manuscrit présente l'étude et la caractérisation de ce système optique de filtrage. Ce travail a permis de sélectionner les deux cavités actuellement installées dans le détecteur Advanced Virgo. Les performances de filtrage et l’impact de l’OMC sur la sensibilité du détecteur sont également décrits. / About 100 years after their prediction by Albert Einstein gravitational waves produced by the coalescence of two black holes were observed on the 14th of September 2015, opening the field of gravitational wave astronomy and a new way to study gravitation. The small amplitude of gravitational waves requires specific and very sensitive detectors. Advanced Virgo is a second generation kilometric interferometer dedicated to the detection of gravitational waves. A necessary element to reach the required sensitivity is the filtering optical system named the Output Mode Cleaner or OMC, placed at the output of the interferometer, and composed of two optical cavities. This thesis shows the study and characterization of this optical system. This work informed the selection of the two optical cavities actually installed in the Advanced Virgo detector. The filtering performances and impact of the OMC on the detector sensitivity are also described.

In this work we study various aspects of the behaviour of free test particles in Einstein's general relativity and analyze specific physical properties of the background spacetimes. In the first part we investigate geodesic motions in the four-dimensional constant curvature spacetimes, i.e., Minkowski and (anti-)de Sitter universe, with an expanding impulsive gravitational wave. We derive the simple refraction formulae for particles crossing the impulse and describe the effect of nonvanishig cosmological constant. In the second part of this work we present a general method useful for geometrical and physical interpretation of arbitrary spacetimes in any dimension. It is based on the systematic analysis of the relative motion of free test particles. The equation of geodesic deviation is rewritten with respect to the natural orthonormal frame. We discuss the contributions given by a specific algebraic structure of the curvature tensor and the matter content of the universe. This formalism is subsequently used for investigation of the large class of nontwisting spacetimes. In particular, we analyse the motions in the nonexpanding Kundt and expanding Robinson--Trautman family of solutions.

A colisão de buracos negros é uma das fontes mais importantes de ondas gravitacionais e, em geral, a emissão anisotrópica da radiação causa um recuo do objeto final. Este cenário já é conhecido há décadas, mas foi somente com o recente avanço na relatividade numérica que as velocidades finais dos objetos radiantes foram computadas com precisão. Os valores encontrados podem ser altos o suficiente para exercerem um importante papel no crescimento de buracos negros super massivos via coleção de galáxias e na abundância de núcleos galáticos ativos contendo buracos negros. Este é um autêntico efeito da não linearidade de Relatividade Geral e esta tese fornece uma nova metodologia estudar alguns aspectos da dinâmica da colisão de buracos negros. Consideramos o horizonte como uma tela canônica que codifica as informações da evolução temporal do espaço-tempo. Com esta hipótese, fenômenos como o anti-kick, isto é, uma súbita desaceleração do sistema antes de atingir a velocidade final, são explicado em termos da dissipação das deformações do horizonte. Estudamos primeiramente o Espaço-tempo de Robinson-Trautman. Uma das solução mais simples das equações de Einstein, esta métrica nos fornece um poderoso modelo para investigar tanto a perda de massa quanto o recuo do objeto final. Mostramos que, quando as configurações iniciais tem simetria especular, a massa do buraco negro remanescente e a energia irradiada são completamente determinadas pela condição inicial. Com isso, obtemos as expressões analíticas dos resultados numéricos obtidos anteriormente na literatura. Além disto, com o auxilio do método espectral de Galerkin, analisamos o regime não linear das equações envolvidas e verificamos que se pode estimar a velocidade de recuo final com boa precisão a partir de medidas da assimetria da condição inicial. Introduzimos na seqüência a curvatura efetiva como uma medida das deformações intrínsecas ao horizonte. Além de considerar as deformações gerais, ela também inclui as diferenças entre os hemisférios norte e sul. No espaço-tempo de Robinson-Trautman, essa quantidade se correlaciona de uma forma injetora com a velocidade final. Para superar algumas limitações dessa solução, aplicamos o mesmo procedimento nos resultados da simulação numérica de uma colisão head-on. Neste caso, a curvatura efetiva, está na realidade, correlacionada com a aceleração do sistema. Refinamentos e generalizações desta técnica são também discutidos e propostos para trabalhos futuros. / Colliding black holes are one of the most important sources of gravitational waves and the anisotropic emission of the radiation generally causes the recoil of the final hole. This scenario has been known for decades, but it is only thanks to the recent progress in numerical relativity that the final velocity have been accurately computed. The values found can be large enough to play an important role in the growth of supermassive black holes via mergers of galaxies and on the number of galaxies containing them. This is a genuine nonlinear effect of general relativity and this thesis provides a new methodology to study some features on the dynamics of the collision. We propose that the horizon is a canonical screen, which encodes he information of its surroundings. With this assumption, phenomena such as the anti-kick, namely the sudden deceleration before reaching the final velocity, are explained in terms of the dissipation of the horizons deformation. We first study the Robinson-Trautman spacetime. One of the simplest solutions of Einsteins equations, it provides us with a powerful toymodel to investigate both the mass loss of the system and the recoil of the final object. We show that, for the case of reflectionsymmetric initial configurations, the mass of the remnant black-hole and the total energy radiated away are completely determined by the initial data, allowing us to obtain analytical expressions for some numerical results that had appeared in the literature. Moreover, by using the Galerkin spectral method to analyze the non-linear regime of the equations involved, we found that the recoil velocity can be estimated with good accuracy from some symmetry measures of the initial data. Then we introduce the effective urvature as a measure of intrinsic deformations on the horizon. Not only does it account for overall deformation, but also for the differences on the north and south hemispheres. In the Robinson-Trautman spacetime, this quantity correlates in an injective way with the final velocity. To overcome some caveats of this solutions, we apply the same procedure to the results given by numerical simulations of a head-on collision. In the case, the effective curvature is actually correlated with the acceleration of the system. Further improvement and generalizations of this technic is also discussed and proposed for future work.