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Preprint 01d/96

The Broad-Band High Energy Spectrum of Cyg X-1

J. Wilms(1,2), J.B. Dove(2,3), M. Maisack(1), and R. Staubert(1)

(1)Institut für Astronomie und Astrophysik, Astronomie, Universität Tübingen, Waldhäuser Str. 64, D-72076 Tübingen, Germany
(2)JILA, University of Colorado, C.B. 440, Boulder, CO 80307, U.S.A.
(3)APAS, University of Colorado, C.B. 391, Boulder, CO 80307, U.S.A.

Contribution to the 3rd COMPTON Gamma Ray Observatory Symposium, München, Germany, June 12-14, 1995
accepted by Astronomy & Astrophysics Suppl.

Abstract. The X-ray spectrum of the prominent galactic black hole candidate Cyg X-1 has historically been modeled by thermal Comptonization or Compton reflection models. However, data from instruments covering different energy ranges have produced different model parameters, indicating that broad band spectra should be used to constrain the models. To find a model which can overcome this problem, we have collected broad band data from 1 keV to 1 MeV. We describe this spectrum by a new self-consistent accretion disk corona model where the corona is situated above a cold disk. The coronal compactness is l_C=0.75 and the optical depth of the corona is tau_e=0.18, resulting in an equilibrium temperature of ~150 keV. We also report the tentative detection of a S K alpha- and a Si Kalpha-fluorescent line, both being much weaker than the lines expected from our models.

Key words: Accretion, accretion disks - Stars: binaries: general - X-rays: general - X-rays: stars

Addendum: (not included in the paper!) The S- and Si-lines were erroneously created by a bug in the response-matrix of BBXRT. See also Wilms et al. in the preprint 13/96.

Paper (33k gzip'ed Postscript including figures)

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