Atomic X-ray Spectroscopy of Accreting Black Holes

Current astrophysical research suggests that the most persistently luminous objects in the Universe are powered by the flow of matter through accretion disks onto black holes. Accretion disk systems are observed to emit copious radiation across the electromagnetic spectrum, each energy band providing access to rather distinct regimes of physical conditions and geometric scale. X-ray emission probes the innermost regions of the accretion disk, where relativistic effects prevail. While this has been known for decades, it also has been acknowledged that inferring physical conditions in the relativistic regime from the behavior of the X-ray continuum is problematic and not satisfactorily constraining. With the discovery in the 1990s of iron X-ray lines bearing signatures of relativistic distortion came the hope that such emission would more firmly constrain models of disk accretion near black holes, as well as provide observational criteria by which to test general relativity in the strong field limit. Here we provide an introduction to this phenomenon. While the presentation is intended to be primarily tutorial in nature, we aim also to acquaint the reader with trends in current research. To achieve these ends, we present the basic applications of general relativity that pertain to X-ray spectroscopic observations of black hole accretion disk systems, focusing on the Schwarzschild and Kerr solutions to the Einstein field equations. To this we add treatments of the fundamental concepts associated with the theoretical and modeling aspects of accretion disks, as well as relevant topics from observational and theoretical X-ray spectroscopy.Comment: 63 pages, 21 figures, Einstein Centennial Review Article, Canadian Journal of Physics, in pres

Comparison of the expression of interferon gamma, IL2, IL4, and lymphotoxin mRNA in experimental autoimmune uveoretinitis.

The aim of this study was to investigate the T lymphocyte subsets involved in experimental autoimmune uveoretinitis (EAU) by quantifying the numbers of cells expressing mRNA for each of the lymphokines interferon gamma, interleukin 2, interleukin 4, and lymphotoxin throughout the disease process. Lewis rats were immunised with retinal S-antigen to provide a model of inflammatory eye disease. In situ hybridisation using cDNA probes specific for interferon gamma, IL2, IL4, and lymphotoxin mRNA were utilised to localise lymphokine mRNA expression by infiltrating cells and the numbers of positive cells counted. Localisation of mRNA for all four probes was found on increasing cell numbers as the disease process progressed. Similar numbers of cells expressed mRNA for each lymphokine, generally a small percentage of the T lymphocyte total. Activated cells within the eye express mRNA for interferon gamma, IL2, IL4, and lymphotoxin in EAU suggesting a mixed population of T lymphocyte subsets