Atomic X-ray spectroscopy of accreting black holes

Abstract

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. PACS Nos.: 32.30. Rj, 32.80.Hd, 95.30.Dr, 95.30.Sf, 95.85.Nv, 97.10.Gz. 97.80.Jp, 98.35.Mp, 98.62.Mw

Quasinormal modes of black holes and black branes

“…Their * The most pessimistic viewpoint on electromagnetic spin measurements is perhaps that of Miller and Turner: according to them, "with the uncertainty and debate on the physical processes that dominate the X-ray spectrum in this energy range [...] it is not currently possible to constrain the BH spin in a model-independent way" [771] (see also [772]). ♯ Liedahl and Torres [773] focus on the basic general relativistic equations, scattering processes and atomic transitions. Reynolds and Nowak [774] discuss theoretical problems in the modeling of relativistic disk lines.…”

The masses and spins of neutron stars and stellar-mass black holes

“…of an effect similar to "magnetic levitation" observed in the sun. Several reviews of disk reflection and related topics have been published (see, e.g., [10,256,253]). The level of detail in those reviews exceeds what is possible to provide in this spin-centered treatment, and the reader is referred to the prior work for additional nuances of disk reflection spectroscopy.…”

The variable X-ray spectrum of Markarian 766

“…A second way of obtaining the observed spectrum could be from a reflector of intermediate ionisation, Fe ionised in the range Fe XVIII-XXIV, such that the Kα line can be resonantly scattered and destroyed by the Auger effect (Ross et al 1996;Matt et al 1996;Zycki & Czerny 1994, see also Liedahl & Torres 2005). Resonant Auger destruction arises in the "reflion" models of Ross & Fabian (2005) and has already been suggested for a model incorporating a reflection component in Mrk 766 by Matt et al (2000).…”