THE BROAD-BAND HIGH-ENERGY SPECTRUM OF CYG X-1

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 tha t broad band spectra should be used to constrain the models. To find a model which can overcome this problem, we have collected broad band d ata from 1 keV to 1 MeV. We describe this spectrum by a new self-consi stent accretion disk corona model where the corona is situated above a cold disk. The coronal compactness is l(C) = 0.75 and the optical dep th of the corona is tau(e) = 0.18, resulting in an equilibrium tempera ture of approximate to 150 keV. We also report the tentative detection of a S K alpha- and a Si K alpha-fluorescent line, both being much we aker than the lines expected from our models.