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We summarize our current knowledge of neutron-star masses and radii. Recent instrumentation and computational advances have resulted in a rapid increase in the discovery rate and precise timing of radio pulsars in binaries in the past few years, leading to a large number of mass measurements. These discoveries show that the neutron-star mass distribution is much wider than previously thought, with three known pulsars now firmly in the 1.9-2.0-M⊙ mass range. For radii, large, high-quality data sets from X-ray satellites as well as significant progress in theoretical modeling led to considerable progress in the measurements, placing them in the 10-11.5-km range and shrinking their uncertainties, owing to a better understanding of the sources of systematic errors. The combination of the massive-neutron-star discoveries, the tighter radius measurements, and improved laboratory constraints of the properties of dense matter has already made a substantial impact on our understanding of the composition and bulk properties of cold nuclear matter at densities higher than that of the atomic nucleus, a major unsolved problem in modern physics. [ABSTRACT FROM AUTHOR]

Many shell supernova remnants are now known to radiate synchrotron X-rays. Several objects have also been detected in TeV gamma rays. Nonthermal X-rays and gamma rays can be produced in shell remnants by extremely energetic ions and electrons due to decay of π0 mesons produced in inelastic collisions between ions and thermal gas, or by electron synchrotron, bremsstrahlung, or inverse-Compton radiation. Thus observations at X-ray and gamma-ray wavelengths constrain the process of particle acceleration to high energies in the shock waves of supernova remnants. This review examines the relevant characteristics of Type Ia and core-collapse supernovae, the dynamics of their evolution through the Sedov blast-wave phase, the basic physics of diffusive shock acceleration, and the physics of the relevant radiative processes. It also reviews the current status of observations of shell remnants from X-rays to TeV gamma rays, and summarizes what we can learn about particle acceleration. [ABSTRACT FROM AUTHOR]

Relativistic X-ray emission lines from the inner accretion disks around black holes are reviewed. Recent observations with the Chandra X-ray Observatory, X-ray Multi-Mirror Mission-Newton, and Suzaku are revealing these lines to be good probes of strong gravitational effects. A number of important observational and theoretical developments are highlighted, including evidence of black hole spin and effects such as gravitational light bending, the detection of relativistic lines in stellar-mass black holes, and evidence of orbital-timescale line flux variability. In addition, the robustness of the relativistic disk lines against absorption, scattering, and continuum effects is discussed. Finally, prospects for improved measures of black hole spin and understanding the spin history of supermassive black holes in the context of black hole-galaxy coevolution are presented. The best data and most rigorous results strongly suggest that relativistic X-ray disk lines can drive new explorations of General Relativity and disk physics in the future. [ABSTRACT FROM AUTHOR]

Today's sensitive X-ray observations allow the study of populations of X-ray binaries in galaxies as distant as 20-30 Mpc. Photometric diagrams and luminosity functions applied to these populations provide a direct probe of the evolved binary component of different stellar populations. The study of the X-ray populations of E and SO galaxies has revamped the debate on the formation and evolution of low-mass X-ray binaries (LMXBs) and on the role of globular clusters in these processes. Though overall stellar mass drives the amount of X-ray binaries in old stellar populations, the amount of sources in star-forming galaxies is related to the star-formation rate. Short-lived, luminous, high-mass X-ray binaries (HMXBs) dominate these young X-ray populations. The most luminous sources in these systems are the debated ultraluminous X-ray sources (ULXs). Observations of the deep X-ray sky, and comparison with deep optical surveys, are providing the first evidence of the X-ray evolution of galaxies. [ABSTRACT FROM AUTHOR]

We review the properties and behavior of 20 X-ray binaries that contain a dynamically-confirmed black hole, 17 of which are transient systems. During the past decade, many of these transient sources were observed daily throughout the course of their typically year-long outburst cycles using the large-area timing detector aboard the Rossi X-Ray Timing Explorer. The evolution of these transient sources is complex. Nevertheless, there are behavior patterns common to all of them as we show in a comprehensive comparison of six selected systems. Central to this comparison are three X-ray states of accretion, which are reviewed and defined quantitatively. We discuss phenomena that arise in strong gravitational fields, including relativistically-broadened Fe lines, high-frequency quasi-periodic oscillations (100-450 Hz), and relativistic radio and X-ray jets. Such phenomena show us how a black hole interacts with its environment, thereby complementing the picture of black holes that gravitational wave detectors will provide. We sketch a scenario for the potential impact of timing/spectral studies of accreting black holes on physics and discuss a current frontier topic, namely, the measurement of black hole spin. [ABSTRACT FROM AUTHOR]