In his theory of General Relativity, Einstein describes gravity as a geometric property of spacetime, which deforms in the presence of mass and energy. The accelerated motion of masses produces deformations, which propagate outward from their source at the speed of light. We refer to these radiated deformations as gravitational waves. Over the past several decades, the goal of the Laser Interferometer Gravitational-wave Observatory (LIGO) has been the search for direct evidence of gravitational waves from astrophysical sources, using ground based laser interferometers. As LIGO moves into its Advanced era (aLIGO), the direct detection of gravitational waves is inevitable. With the technology at hand, it is imperative that we have the tools to analyze the detector signal and examine the interesting astrophysical properties of the source. Some of the main targets of this search are coalescing compact binaries. In this thesis, I describe and evaluate bhextractor, a data analysis algorithm that uses Principal Component Analysis (PCA) to identify the main features of a set of gravitational waveforms produced by the coalescence of two black holes. Binary Black Hole (BBH) systems are expected to be among the most common sources of gravitational waves in the sensitivity band of aLIGO. However, the gravitational waveforms emitted by BBH systems are not well modeled and require computationally expensive Numerical Relativity (NR) simulations. bhextractor uses PCA to decompose a catalog of available NR waveforms into a set of orthogonal Principal Components (PCs), which efficiently select the major common features of the waveforms in the catalog and represent a portion of the BBH parameter space. From these PCs, we can reconstruct any waveform in the catalog, and construct new waveforms with similar properties. Using Bayesian analysis and Nested Sampling, one can use bhextractor to classify an arbitrary BBH waveform into one of the available catalogs and estimate the parameters of the gravitational wave source.

京都大学 / 新制・課程博士 / 博士(理学) / 甲第24404号 / 理博第4903号 / 新制||理||1700(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 田中 貴浩, 准教授 久徳 浩太郎, 教授 橋本 幸士 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

This dissertation covers two di erent but related topics: the construction of new black hole solutions and the study of the microscopic origin of black hole entropy. In the solution part, two di erent sets of new solutions are found. The rst concerns a Plebanski-Demianski type solution in the ve-dimensional pure Einstein gravity, and the second concerns a three-charge (two of which equal) two-rotation solution to the ve-dimensional maximal supergravity. Obtaining new and interesting black hole solutions is an important and challenging task in studying general relativity and its extensions. During the past decade, the solutions become even more important because they might nd applications in the study of the gauge/gravity duality, which is currently in the central stage of the quantum gravity research. The Kerr/CFT correspondence is a recently propose example of the gauge/gravity duality. In the entropy part, we explicitly show that the Kerr/CFT correspondence can be applied to all known extremal stationary and axisymmetric black holes. We improve over previous works in showing that this can be done in a general fashion, rather than testing di erent solutions case by case. This e ort makes it obvious that the common structure of the near horizon metric for all known extremal stationary and axisymmetric black holes is playing a key role in the success of the Kerr/CFT correspondence. The discussion is made possible by the identi cation of two general ans atze that cover all such known solutions.

Remarkably, an astrophysical black hole has only two attributes: its mass and its spin angular momentum. Spin is often associated with the exotic behavior that black holes manifest such as the production of relativistic and energetic jets. In this thesis, we advance one of the two primary methods of measuring black hole spin, namely, the continuum-fitting method by (1) improving the methodology; (2) testing two foundational assumptions; and (3) measuring the spins of two stellar-mass black holes in X-ray binary systems. Methodology: We present an empirical model of Comptonization that self-consistently generates a hard power-law component by upscattering thermal accretion disk photons as they traverse a hot corona. We show that this model enables reliable measurements of spin for far more X-ray spectral data and for more sources than previously thought possible. Testing the foundations: First, by an exhaustive study of the X-ray spectra of LMC X–3, we show that the inner radius of its accretion disk is constant over decades and unaffected by source variability. Identifying this fixed inner radius with the radius of the innermost stable circular orbit in general relativity, our findings establish a firm foundation for the measurement of black hole spin. Secondly, we test the customary assumption that the inclination angles of the black-hole’s spin axis and the binary’s orbital axis are the same; for XTE J1550–564 we show that they are aligned to within \(12^{\circ}\) by modeling the kinematics of the large-scale jets of this microquasar. Measuring spins: We have made the first accurate continuum-fitting spin measurements of the black hole primaries in H1743–322 and XTE J1550–564. For this latter black hole, we have also measured its spin using the other leading method, namely, modeling the broad red wing of the \(Fe K\alpha\) line. As we show, these two independent measurements of spin are in agreement. / Astronomy

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第22251号 / 理博第4565号 / 新制||理||1655(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 嶺重 慎, 准教授 前田 啓一, 教授 長田 哲也 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

Variable emission from Sgr A*, the luminous counterpart to the super-massive black hole at the center of our Galaxy, arises from the innermost portions of the accretion flow. Better characterization of the variability is important for constraining models of the low-luminosity accretion mode powering Sgr A*, and could further our ability to use variable emission as a probe of the strong gravitational potential in the vicinity of the 4 x 10(6) M-circle dot black hole. We use the Herschel Spectral and Photometric Imaging Receiver (SPIRE) to monitor Sgr. A* at wavelengths that are difficult or impossible to observe from the ground. We find highly significant variations at 0.25, 0.35, and 0.5 mm, with temporal structure that is highly correlated across these wavelengths. While the variations correspond to < 1% changes in the total intensity in the Herschel beam containing Sgr. A*, comparison to independent, simultaneous observations at 0.85 mm strongly supports the reality of the variations. The lowest point in the light curves, similar to 0.5 Jy below the time-averaged flux density, places a lower bound on the emission of Sgr. A* at 0.25 mm, the first such constraint on the THz portion of the spectral energy distribution. The variability on few hour timescales in the SPIRE light curves is similar to that seen in historical 1.3 mm data, where the longest time series is available, but the distribution of variations in the sub-mm do not show a tail of large-amplitude variations seen at 1.3 mm. Simultaneous X-ray photometry from XMM-Newton shows no significant variation within our observing period, which may explain the lack of very large submillimeter variations in our data if X-ray and submillimeter flares are correlated.

Degree of Master of Science by research only: A dissertation submitted to the faculty of science, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Master of Science. Department of Physics Faculty of Science University of the Witwatersrand January 4, 2016 / Quasi-simultaneous observations of a flaring blazar source at multiple frequencies, offer an unprecedented view of the region surrounding a supermassive black hole during a large energy outburst. Blazars are active galaxies that host a super massive black hole releasing large amounts of energy through narrow jets of highly relativistic plasma located along the polar axes. Within these jets, electrons and protons move at relativistic speeds creating interactions that generate radio waves and gamma-rays that travel down the jet towards the observer. Based on the angle of inclination of the source towards the observer ( < 20◦), we can study relativistically boosted emission to peer into regions where high-energy particles (gamma-rays) are thought to be generated. Using high cadence monitoring campaigns, both the slow and fast variations in the source flux can be traced in detail revealing spatial and temporal information about the source state and activity. In this dissertation I studied the physics behind the variable behavior of the bright blazar PKS 1424-418, also known as J1427-4206. PKS 1424-418 is a Southern Hemisphere blazar that recently underwent a number of flaring events detected by FERMI-LAT. The study was specifically concerned with the behavior of PKS 1424-418 during the outburst/flaring events that occurred between 19 October 2012 and 9 October 2013. PKS 1424-418’s daily gamma-ray flux reached an average of 1.4 ± 0.2 x 10−6 ph cm−2 s−1 for E > 100 MeV, triggering radio follow up observations with the Hartebeesthoek Radio Astronomy Observatory 26 m radio telescope at 2.3-GHz, 4.8-GHz, 8.4-GHz and 12.2-GHz frequencies. The objective was to examine the nature of the relationship between the high-energy gamma rays detected by FERMI-LAT and the low-energy radio waves detected by the Hart26m radio telescope. In the study we investigated the relationship between the two energy regimes using Discrete cross-correlation functions to estimate the time-lags between two corresponding frequencies. We also studied the spectral index variation to establish the source behavior over the observing period at multiple epochs. A Lomb-Scargle periodicity search was also performed to investigate whether some periodic modulation was present in the gamma-ray data as it varied quite dramatically on shorter time-scales. Observations in gamma-rays and radio frequencies were done using the All-Sky mode and drift scan technique respectively at the different frequencies. Results indicated the existence of a strong correlation between the gamma-ray and radio data, with the gamma rays leading the radio. With each gamma-ray flaring event the radio spectra indicated some spectral hardening and the possibility of an 86 day gamma-ray period in the shorter term flares was also established in the study. This study however only shows the large scale relationship between time-series over the entire observing period. On smaller scales, each gamma-ray and radio flare is unique and as such requires individual analysis for each respective component. to successfully achieve this, more data is needed to confirm the individual radio flaring periods. Observations at VLBI scales are extremely useful in this kind of work and instrumental in studying the source structure behavior during flaring and will form part of the future work planned for studying blazar source variability.

Essa dissertação consiste de uma revisão dos resultados clássicos sobre a termodinâmica de buracos negros bem como de uma análise crítica das extensões recentes da relação entre a termodinâmica e a dinâmica gravitacional e suas implicações. / This dissertation consists of a revision of the classical results concerning the thermodynamics of black holes as well as a critical analysis of the recent extensions of the relationship between thermodynamics and the gravitational dynamics and its implications.

The study of geodesics is of intrinsic significance in the study of the geometry of space-time. In this thesis null, space-like and time-like geodesics are studied in the case of the space-times of Schwarzschild, Reissner-Nordstrouml;m and Kerr black holes. These space-times have been investigated with varying degrees of thoroughness in many articles and some books. However, there are some significant gaps in these treatments and the central aim of this thesis is to fill these gaps where necessary. Moreover, the following topics are covered for the first time. 1. In Chapter 4 a thorough treatment of the space-like geodesics of the Schwarzschild solutions has been given. These geodesics are the trajectories of Tachyons (faster than light particles) and are treated in a complete manner. This has been done by obtaining exact solutions and solving them numerically. 2. In Part II all solutions for geodesics for a Reissner-Nordstrouml;m black hole have been given in complete detail, i.e. time-like, null and space-like geodesics and orbit of a charged particle. 3. In Chapter 14 all solutions for geodesics in the equatorial plane of a Kerr black hole have been given in complete detail, i.e. time-like, null and space-like geodesics. 4. The study of special types of non-equatorial geodesics for a Kerr black hole have been given in complete detail, i.e. time-like (Chapter 17), null (Chapter 15) and space-like (Chapter 16). This has been done in order to distinguish the qualitatively different types of solutions. Calculation of the explicit formulas, which describe these geodesics, as well as numerically computed diagrams representing the geodesics have been incorporated in these studies. The following subjects have been also treated: 5. Solutions for the geodesics in Reissner-Nordstrouml;m black holes with |Q_*| gt;= M, which are black holes with one (|Q_*| = M) or no horizon (|Q_*|gt; M) (Chapter 8). 6. Solutions of geodesics in extreme and fast Kerr black holes, i.e. black holes with a = M (extreme) and a gt; M (fast). As in the case of |Q_*| gt; M, fast black holes have naked singularities (Chapter 14). 7. Some general observations about orbit types of the Kerr black holes regarding relationships between parameters such as angular momentum, energy, Carter constant and mass and angular momentum of black holes (Chapter 13). 8. Some corrections to errors found in the literature. While it has not been possible to cover all different cases which occur for possible relations amongst the parameters specifying a general black hole, interesting geodesics have, however, been studied and a more thorough presentation of the properties of geodesics has now been given.

One of the most important predictions of General Relativity, Einstein’s theory of gravity, is the existence of gravitational radiation. The strongest source of such radiation is expected to come from the merging of black holes. Upgrades to large ground based interferometric detectors (LIGO, VIRGO, GEO 600) have increased their sensitivity to the point that the first direct observation of a gravitational wave is expected to occur within the next few years. The chance of detection is greatly improved by the use of simulated waveforms which can be used as templates for signal processing. Recent advances in numerical relativity have allowed for long stable evolution of black hole mergers and the generation of expected waveforms. openGR is a modular, open framework black hole evolution code developed at The University of Texas at Austin Center for Relativity. Based on the BSSN (strongly hyperbolic) formulation of Einstein’s equations and the moving puncture method, we are able to model the evolution of a binary black hole system through the merger and extract the gravitational radiation produced. Although we are generally interested in binary interactions, openGR is capable of handling any number of black holes. This work serves as an overview of the capabilities of openGR and a demonstration of the physics it can be used to explore. / text