In this thesis, I present work from three separate research projects associated with observations of X-ray binaries. Two of those revolve around spectral characteristics of neutron star low-mass X-ray binaries (NS-LMXBs), with a particular source, XTE J1701-462, playing a central role. First, I construct and study color-color and hardness-intensity diagrams (CDs and HIDs) for a large sample of NS-LMXBs using Rossi X-ray Timing Explorer (RXTE) data spanning ~15 years. I study in particular detail three sources whose complicated CDs/HIDs are strongly affected by secular motion -- Cyg X-2, Cir X-1, and GX 13+1 -- and show that Cyg X-2 and Cir X-1 display CD/HID evolution with strong similarities to the transient Z source XTE J1701-462, which was previously shown to have evolved through all subclasses of NS-LMXBs as a result of changes in mass accretion rate. I build on the results for XTE J1701-462, Cyg X-2, and Cir X-1 and rank all the sources in the sample based only on their CD/HID morphology. I speculate that this represents a rough ranking in terms of the relative ranges in mass accretion rate experienced by the sources. Next, I use data from RXTE, Swift, Chandra, and XMM-Newton to study the transition to quiescence and the first ~1200 days of the quiescent phase of XTE J1701-462 following the end of its extraordinarily luminous 19 month outburst in 2006-2007. I find that the crust of the neutron star cooled rapidly during the first ~200 days of quiescence, after having been heated out of thermal equilibrium with the core during the outburst; the source has subsequently shown slower cooling along with sporadic low-level accretion activity. I discuss the implications of the observed cooling behavior and low-level accretion, the former of which yields information on the internal properties of the neutron star. Finally, I use multiple Chandra observations to study the X-ray source populations in the late-type galaxies NGC 6946 and NGC 4485/4490. A particular emphasis is placed on investigating the long-term variability of the sources, several of which are ultraluminous. I present detailed source catalogs and characterize the populations -- which consist primarily of X-ray binaries -- using X-ray luminosity functions and CDs.

NASA's Chandra X-ray Observatory and ESA's XMM-Newton Observatory have been the pioneering satellites for studying the Universe with X-rays and the cornerstone of X-ray spectroscopy since their launches more than 20 years ago. The onboard gratings provide us a unique opportunity to distinguish individual spectral lines from different atoms thanks to their high energy resolutions. Enormous discoveries have been achieved by these two missions when observing a variety of X-ray-emitting astronomical objects, such as black holes, supernova remnants, clusters of galaxies, and stars. However, the data are limited to fairly bright X-ray sources. The recent JAXA's mission Hitomi opened a new window of high-resolution X-ray spectroscopy thanks to its onboard X-ray calorimeter. Although this mission was shortly terminated due to a mishap, Hitomi left behind a few sets of observations awaiting more data mining. The first half of this book introduces the history of high-resolution X-ray spectroscopy and different generations of X-ray spectrometers. A tutorial guide on how to reduce, analyze, and understand the astronomical data from Chandra, XMM-Newton, and Hitomi is also included. The second half of the book reviews past results obtained by the high-resolution spectrometers on these missions on multiple topics and discusses possible discoveries by upcoming missions in the next decade.

A collection of papers using the relative advantages of studying stellar mass and supermassive black holes. The topics discussed here include the state of the art in black hole observational and theoretical work-variability, spectroscopy, disk-jet connections, and multi-wavelength campaigns on black holes.

X-ray binaries are some of the most varied and perplexing systems known to astronomers. The compact object which accretes mass from its companion star may be a white dwarf, neutron star, or black hole, whereas the donor star can be a 'normal' star or a white dwarf. The various combinations differ widely in their behaviour, and this timely volume provides a unique reference of our knowledge to date of all of them.Fifteen specially written chapters by a team of the world's foremost researchers in the field explore all aspects of the X-ray binaries. They cover the X-ray, ultraviolet, optical and radio properties of these violent systems and address key issues such as: how were these systems formed, and what will be their fate; how can we understand X-ray bursts, and how the quasi-periodic oscillations; what is the connection between millisecond radio pulsars and low-mass X-ray binaries; and how does the magnetic field of a neutron star decay?This long awaited review provides graduate students and researchers with the standard reference on X-ray binaries for many years to come.

Mass determinations and X-ray energy spectral analyses are among the methods used to distinguish between the types of compact objects present in X-ray binary systems. We test a method of distinguishing between neutron stars and black holes proposed by Sunyaev and Revnivtsev where power density spectra are used, particularly in the 500-1000Hz range. Sunyaev and Revnivtsev found that only neutron stars appear to have significant power in this frequency range. We apply this criterion to 12 X-ray binary systems (six neutron stars and six black holes) using USA data and cannot reproduce Sunyaev and Revnivtsev's result. The reason for this discrepancy is most likely a USA instrumental effect which manifests itself as excess power in the frequency range of interest. Future work on correcting this problem should provide more accurate analyses that may yield a different result.

This book is a comprehensive introduction to the data analysis of ultraluminous X-ray sources. This book will provide the readers with a familiar environment in data analysis methods and the different software used in high energy astrophysical data analysis.