Institut für Astronomie und Astrophysik

Abteilung Astronomie

Preprint Kb/98

Accretion Disk Coronae

J. Wilms(1), J.B. Dove(2), M.A. Nowak(3), M.C. Begelman(3)

(1)Institut für Astronomie und Astrophysik, Astronomie, Universität Tübingen, Waldhäuser Str. 64, D-72076 Tübingen, Germany
(2)CASA, University of Colorado, Boulder, CO 80309-389, U.S.A.
(3)JILA, University of Colorado, Boulder, CO 80309-440, U.S.A.

1999, Highlights in X-ray Astronomy, ed. B. Aschenbach, MPE Report, in press

Abstract. The X-ray and gamma-ray spectra of the hard state of galactic black holes like Cyg X-1 and GX 339-4 have traditionally been described by Comptonization models, where soft photons are upscattered in a hot electron plasma. The geometry of this accretion disk corona system, however, has long been a mystery. Until recently it was mostly assumed that the source of the photons is an accretion disk sandwiched between two coronae. New broad band X-ray spectra from galactic black hole candidates, however, provide evidence that this simple picture has to be modified. Since Compton cooling operates at a high efficiency in the sandwich configuration, the corona cannot reach the high temperature needed for generating the observed hard spectra. Several geometries in which the hard spectra might be produced have been proposed: advection dominated accretion flows, the sphere+disk model, non-thermal electron distributions, or an intermediate ionization layer between the corona and the cold disk. We review these models and compare theoretical spectra from self-consistent accretion disk corona models to the X-ray data.

Key words: -

Paper (59k gzip'ed Postscript including figures)

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Jürgen Barnstedt (barnstedt AT astro.uni-tuebingen.de) Last updated 16-Nov-1998