The Laser Interferometer Space Antenna (LISA) will be the first gravitational wave detector in space. The European Space Agency has selected LISA as a large mission scheduled to launch in the mid-2030s. The sensitivity of LISA to gravitational waves is limited at low frequencies by force disturbances acting on the otherwise free-falling test masses. Among the stray forces relevant to the LISA noise budget, we find the ones that arise from the electrostatic interaction between the test masses and the surrounding capacitive sensor. Most of such electrostatic forces scale with the electric charge deposited on the test masses. This problem is aggravated by the fact that isolated objects in space, such as the floating LISA test masses, accumulate electric charge due to the constant bombardment of cosmic rays and solar energetic particles. We, therefore, understand that if the test masses were not discharged, the electrostatic disturbances could spoil the performance of the whole mission at low frequency. The precursor LISA Pathfinder (LPF) mission proved that the test mass charge could be successfully managed with a contactless system based on photoelectric charge transfer. The light sources required for photoemission in LISA Pathfinder were mercury-vapor lamps emitting photons in the UV range. In this thesis, we will present our on-ground testing campaign of a prototype Charge Management System for LISA, which relies on UV-LEDs as light sources. LEDs, compared to mercury-vapor lamps, can emit short pulses of UV light (~10 ns), which can be synchronized with the time-varying electrostatic fields around the test mass. For this reason, we studied new discharge strategies made possible by adopting UV-LEDs characterized by pulsed illumination synced with the capacitive sensing injection bias. Our measurements indicate that UV-LEDs offer significant advantages regarding the flexibility and robustness of the Charge Management System. Moreover, the new illumination patterns offered by UV-LEDs allow fine-tuning the TM equilibrium potential without introducing local DC fields, easing the implementation of the continuous discharge mode to manage the TM potential. Finally, we investigated the charge noise introduced by the continuous discharge mode and verified that it could be kept within the LISA requirements. We will present hereafter the outline of the thesis. In the first chapter, we present a mandatory introduction to gravitational waves and the LISA mission. In the second chapter, we present the instrument used for our experimental campaign, namely the four-test-masses torsion pendulum at the University of Trento. We also present the electrostatic model and the measurement techniques used to evaluate the electric charge on the pendulum test mass. In the third chapter, we introduce the concept of apparent yield, which is a figure of merit of the charge management system performance. We also present our experimental measurement, which encompasses tests on several UV-LEDs in different illumination patterns. In the fourth chapter, we derive a simple photoemission model, which is useful for interpreting the apparent yield data acquired. We will also use the model to fit the experimental data and extract estimates of the microscopic parameters that affect the photoemission from metallic surfaces, e.g. work function or quantum yield. In the fifth chapter, we present a model and our torsion pendulum measurements for the charge noise induced on the test masses when continuously illuminated with UV light. Such noise arises from the discrete and intrinsically stochastic nature of photoelectric charge transfer. Finally, in the last chapter, we will wrap up by presenting the problems encountered and the "lessons learned" during the years-long experimental endeavor.

[Truncated abstract] As gravitational wave detectors approach sensitivities that will allow observations to become routine, astrophysics lies on the cusp of an exciting new era. Potential sources will include transients such as merging neutron stars and black holes, supernova explosions or the engines that power gamma-ray bursts. This thesis will be devoted to the astrophysical gravitational wave background signal produced by cosmological populations of such transient signals. Particular attention will be devoted to the observation-time dependence imposed on the individual sources that accumulate to produce a gravitational wave background signal. The ultimate aim is to determine what information is encoded in the temporal evolution of such a signal. To lay the foundations for further investigation, the stochastic gravitational wave background signal from neutron star birth throughout the Universe has been calculated. In view of the uncertainties in both the single-source emissions and source rate histories, several models of each are employed. The results show that that the resulting signals are only weakly dependent on the source-rate evolution model and that prominent features in the single-source spectra can be related to the background spectra. In comparison with previous studies, the use of relativistic single-source gravitational wave waveforms rather than Newtonian models and a more slowly evolving source-rate density results in a 1 { 2 order of magnitude reduction in signal. ... A comparison with the more commonly used brightness distribution of events shows that when applying both methods to a data stream containing a background of Gaussian distributed false alarms, the brightness distribution yielded lower standard errors, but was biased by the false alarms. In comparison, a fitting procedure based on the time evolution of events was less prone to errors resulting from false alarms, but as fewer events contributed to the data, had a lower resolution. In further support of the time dependent signature of transient events, an alternative technique is fiapplied to the same source population. In this case, the local rate density is probed by measuring the statistical compatibility of the filtered data against synthetic time dependent data. Although this method is not as compact as the fitting procedure, the rate estimates are compatible. To further investigate how the observation time dependence of transient populations can be used to constrain global parameters, the method is applied to Swift long gamma-ray burst data. By considering a distribution in peak °ux rather than a gravitational wave amplitude, gamma-ray bursts can be considered as a surrogate for resolved gravitational wave transients. For this application a peak °ux{observation time relation is described that takes the form of a power law that is invariant to the luminosity distribution of the sources. Additionally, the method is enhanced by invoking time reversal invariance and the temporal cosmological principle. Results are presented to show that the peak °ux{observation time relation is in good agreement with recent estimates of source parameters. Additionally, to show that the intrinsic time dependence allows the method to be used as a predictive tool, projections are made to determine the upper limits in peak °ux of future gamma-ray burst detections for Swift.

[Truncated abstract] Interferometric gravitational wave detectors are being built around the world with continually improving measurement sensitivities. Noise levels from sources that are intrinsic to these detectors must be reduced to a level below the gravita- tional wave signal. Seismic noise in the low frequency range, which is within the gravitational wave detection bandwidth, is a concern for earth-based detectors. This thesis presents research and development of a high performance vibration isolation system that is designed to attenuate seismic noise. The final design will be used as part of a fully working interferometer at the Australian International Gravitational Observatory (AIGO). Pendulums and springs are conventionally used for the horizontal and vertical vibration isolation components respectively. A complete system comprises of a cascade of these components, each stage dramatically improving the level of isola- tion. The residual motion at the test mass level is thus reduced but is dominated by the normal mode resonances of the chain. A simple and effective method to reduce residual motion further is to add ultra-low frequency pre-isolation stages which suspend the chain. The Roberts Linkage is a relatively new and simple geometrical structure that is implemented in the pre-isolation stages. Here we present experimental results of improving isolation based on mathematical mod- elling. The attenuation of seismic noise in the vertical direction is almost as important as that in the horizontal direction, due to cross-coupling between the two planes. To help improve the vertical performance a lightweight Euler spring that stores no static energy was implemented into the AIGO suspension system. ... Theoretical and experimental results are presented and discussed. Currently the AIGO laboratory consists of two 80 m length arms. They are aligned along the east and south directions. One of AIGO's top priorities is the installation of two complete vibration isolators in the east arm to form a Fabry-Perot cavity. Assembling two suspension systems will enable more accurate performance measurements of the tuned isolators. This would significantly reduce the measurement noise floor as well as eliminate the seismic noise spectrum due to referencing with the ground motion. The processes involved in preparing such a task is presented, including clean room preparation, tuning of each isolator stage, and local control schematics and methods. The status of the AIGO site is also presented.

<p dir="ltr">Neutron star mergers generate powerful gravitational waves and various types of electromagnetic signals, including gamma-ray bursts (GRB), kilonovae, and their afterglows. Observing and modeling these signals help us understand the physical processes of the merger events. Radiation from mergers can also serve as probes to study nuclear physics and cosmology. In this report, I focus on two types of signals: the GRB afterglow and the kilonova. GRB afterglows are non-thermal radiation produced by the interaction of relativistic jets and circumburst material, where the jets are launched perpendicular to the merger plane. Kilonovae are the thermal radiation emitted from the hot materials ejected during the merger. Besides the modeling of these objects, I also investigate their application in multimessenger astrophysics, especially the constraint on the expansion rate of the Universe. </p><p dir="ltr">First, I developed a GRB afterglow model to account for the off-axis observation of a structured jet. Using a jet structure derived from a three-dimensional general relativistic magnetohydrodynamic simulation, we performed a joint analysis of the multimessenger data of the neutron star merger event GW170817, including the gravitational wave data and GRB afterglow data in the radio band. We have tightly constrained the observing angle of GW170817 and broken the degeneracy between the inclination angle and luminosity distance measured in gravitational waves. With a better constrained distance, we improved the standard siren measurement of the Hubble constant to $H_0 = 69.5\pm 4\ \mathrm{km\ s^{-1}\ Mpc^{-1}}$. The error bar has been reduced by a factor of 2. This work demonstrates that the modeling of off-axis GRB afterglow can significantly improve the standard siren method, provided that we have a reliable jet structure.</p><p dir="ltr">Second, I upgrade the GRB afterglow model in the first work, extending it to the late time where lateral spreading of the GRB jet becomes important. In this model, the ultra-relativistic blastwave is approximated by an infinitely thin two-dimensional surface. With this approximation, the hydrodynamic equations can be analytically integrated over the radius. Further assuming axial symmetry, the three-dimensional hydrodynamic simulation can be reduced to one dimension, which significantly increases the computational efficiency. We have compared our method to full numerical simulations and existing GRB afterglow modeling tools. The comparison shows good agreement and verifies our approach. Compared to these tools, our model has better flexibility and is applicable in a broader context. This method has been developed into a numerical code, \texttt{jetsimpy}, which we have provided to the community. It will serve as a powerful tool in the era of multimessenger astrophysics.</p><p dir="ltr">Finally, I investigate the possibility of long-lived massive neutron stars as neutron star merger remnants. A long-lived massive neutron star can inject a significant amount of energy into the merger ejecta, boosting the luminosity of kilonova by several orders of magnitude. However, this type of event has not yet been observed in optical sky surveys. We developed a boosted kilonova model with a detailed calculation of the photoionization process to better describe the efficiency of energy injection from spin down power to the ejecta. Our study found that boosted kilonovae, if commonly occurring, they should have already been observed given the accumulated time in sky surveys. As a result, the absence of detection implies that long-lived massive neutron stars as neutron star merger remnants are likely to be rare in the Universe.</p>

The motion of a test particle in the Schwarzschild background models the merger of a compact object binary with extremely different masses known in the literature as Extreme Mass Ratio Inspiral. In the simplest geodesic approxima- tion, this motion is integrable and there is no chaos. When one takes the spin of the smaller body into account, integrability is broken and prolonged resonances along with chaotic orbits appear. By employing the methods of Poincaré surface of section, rotation number and recurrence analysis we show for the first time that there is chaos for astrophysically relevant spin values. We propose a uni- versal method of measuring widths of resonances in perturbations of geodesic motion in the Schwarzschild spacetime using action-angle-like variables. We ap- ply this novel method to demonstrate that one of the most prominent resonances is driven by second order in spin terms by studying its growth, supporting the expectation that chaos will not play a dominant role in Extreme Mass Ratio Inspirals. Last but not least, we compute gravitational waveforms in the time- domain and establish that they carry information on the motion's dynamics. In particular, we show that the time series of the gravitational wave strain can be used to discern regular from chaotic motion of the source. 1

Cette thèse présente les résultats de la recherche de signaux impulsionnels d’ondes gravitationnelles associés aux sursauts gamma dans les données 2009-2010 des interféromètres LIGO-Virgo. L’étude approfondie des mécanismesd’émission d’ondes gravitationnelles par les progéniteurs de sursauts gamma, ainsi que des mécanismes d’émission de rayons gamma eux-mêmes, permet de déterminer les caractéristiques essentielles du signal à détecter : polarisation, délai temporel, etc ... Cette connaissance de l’émission conjointe permet alors de construire une méthode d’analyse qui inclut les a priori astrophysiques. Cette méthode est de plus robuste vis-à-vis des bruits transitoires présents dans les données. L’absence de détection nous permet de placer des limites observationnelles inédites sur la population des sursauts gamma. / In this thesis we present the results of the search for gravitational wave bursts associated with gamma-ray bursts in the 2009-2010 data from the LIGOVirgo gravitational wave interferometer network. The study of gamma-ray bursts progenitors, both from the gamma-ray emission and the gravitational wave emission point of view, yields the characteristic of the sought signal: polarization, time delays, etc ... This knowledge allows the construction of a data analysis method which includes the astrophysical priors on joint gravitational wave and gamma-ray emission, and moreover which is robust to non-stationary transient noises, which are present in the data. The lack of detection in the analyzed data yields novel observational limits on the gamma-ray burst population.

Cette thèse présente les résultats de l'analyse all-sky STAMPAS de recherche de signaux transitoires longs d'ondes gravitationnelles, dans les données 2005-2007 des interféromètres LIGO et Virgo. Les ondes gravitationnelles sont des perturbations de la métrique de l'espace-temps, et les expériences Virgo et LIGO sont conçues pour les détecter. Ces expériences sont des interféromètres de Michelson, avec des bras longs respectivement de 3 km et 4 km, dont la luminosité en sortie est modifiée lors du passage d'une onde gravitationnelle.Jusqu'à très récemment, les pipelines de recherche de signaux transitoires se concentraient uniquement sur les signaux courts, qui durent moins d'une seconde, et sur les signaux de coalescence de binaires. STAMPAS est l'un des tout premiers pipelines entièrement dédiés à la recherche de signaux transitoires longs, qui durent d'une à plusieurs centaines de secondes.Ces signaux sont émis, entre autres, par les instabilités qui apparaissent pendant la violente création des proto-étoiles à neutrons. Les instabilités dans les supernovae à effondrement gravitationnel et celles des disques d'accrétion sont également de possibles sources de signaux transitoires longs. Les coalescences de binaires excentriques de trous noirs sont elles aussi censées émettre de puissantes ondes gravitationnelles pendant plusieurs secondes avant leur fusion.STAMPAS est basé sur la corrélation de données issues de deux interféromètres. On construit des cartes temps-fréquence à partir des données, et leurs pixels les plus significatifs sont agrégés et forment les "triggers" (candidats potentiels d'ondes gravitationnelles). Aucune hypothèse sur la provenance, le temps ou la forme des signaux recherchés n'est formulée.La première analyse effectuée avec STAMPAS a été réalisée à partir des données acquises entre 2005 et 2007 par les deux détecteurs LIGO. Après une sélection rigoureuse des "triggers", l'analyse en a révélé un taux proche du bruit Gaussien attendu, ce qui constitue un accomplissement majeur. Aucune onde gravitationnelle n'a été détectée, et nous avons établi des limites hautes sur les taux astrophysiques de plusieurs modèles de sources d'instabilités de disques d'accrétion et de coalescences de binaires excentriques de trous noirs. Le pipeline STAMPAS a montré qu'il sera efficace dans la recherche des signaux transitoires longs d'ondes gravitationnelles lors de la prochaine génération d'interféromètres. / 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.

The starting point of any general relativistic numerical simulation is a solution of the Hamiltonian and momentum constraints that (ideally) represents an astrophysically realistic scenario. This dissertation presents a new method to produce initial data sets for binary neutron stars with arbitrary spins and orbital eccentricities. The method only provides approximate solutions to the constraints. However, it was shown that the corresponding constraint violations subside after a few orbits, becoming comparable to those found in evolutions of standard conformally flat, helically symmetric binary initial data. This dissertation presents the first spinning neutron star binary simulations in circular orbits with a orbital eccentricity less then 0.01. The initial data sets corresponding to binaries with spins aligned, zero and anti-aligned with the orbital angular momentum were evolved in time. These simulations show the orbital “hang-up” effect previously seen in binary black holes. Additionally, they show orbital eccentricities that can be up to one order of magnitude smaller than those found in helically symmetric initial sets evolutions. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2013.

Através de várias simulações em um programa de elementos finitos fez-se uma série de estudos de uma esfera conectada a casadores de impedância mecânicos com dois formatos diferentes: "bico de passsarinho", criado nesta pesquisa, e "cogumelo". Por limitação de tempo de processamento computacional escolheu-se trabalhar com casadores de impedância mecânicos com formatos mais simples que os utilizados no detector Mário Schenberg. Constatou-se que os modos normais do sistema acoplado não são exatamente degenerados. Fica clara a dificuldade em se encontrar um grupo de casador de impedância mecânico que possa ser calibrado da mesma forma em todos os diferentes modos de detecção. Para o casador de impedância com formato de cogumelo foi identificado um conjunto de dimensões que permite que todos os transdutores sejam calibrados da mesma forma / Using simulation in Finite Element Modeling software a series of studies of a sphere connected to mechanical impedance mantchers with two different shapes: beak shape na mushroom shape. For computer processing limitation time, the work was done with simpler shapes than the one used in Mário schenberg Detector. It was shown that the system vibration normal modes are not exactly degenerated. It’s clear the dificcult in finding a set of mehanical macthers that can be calibrated in the same way in all the different detector modes

We study the evolution of binary black hole initial data schemes as alternatives to the standard puncture construction. These alternatives are based on post-Newtonian expansions that contain realistic gravitational waves. The first scheme is based on a second order post-Newtonian expansion in Arnowitt, Deser, and Misner transverse-traceless (ADMTT) gauge that has been re-summed to approach standard puncture data at the black holes. The other schemes are based on asymptotic matching of the 4-metrics of two tidally perturbed Schwarzschild solutions to post-Newtonian expansions at different orders. The alternatives are encouraging and lead to quasi-circular orbits and show gravitational radiation from the onset, as well as a reduction of spurious radiation. Deficiencies compared to punctures include more eccentricity during inspiral and larger constraint violations, since the alternative data sets only approximate solutions of Einstein's equations. / by George C. Reifenberger. / Thesis (Ph.D.)--Florida Atlantic University, 2013. / Includes bibliography. / Mode of access: World Wide Web. / System requirements: Adobe Reader.