The first simultaneous X-ray/gamma-ray observations of Cyg X-1 by Ginga and OSSE

Marek Gierlinski

Astronomical Observatory, Jagiellonian University, Cracow, Poland

Andrzej A. Zdziarski

Copernicus Astronomical Center, Warsaw, Poland

W. Neil Johnson and Bernard F. Phlips

E. O. Hulburt Center for Space Research, Naval Research Lab, Washington DC, U.S.A.

Ken Ebisawa

NASA/GSFC, Greenbelt, U.S.A.

Chris Done

Department of Physics, University of Durham, Durham, U.K.

We present the results of 4 simultaneous observations of Cygnus X-1 by Ginga and OSSE. The X-ray/gamma-ray spectra can be described by an intrinsic continuum and a component due to Compton reflection including an iron K alpha line. The intrinsic spectrum at X-ray energies is a power-law with a photon spectral index of Gamma=1.6. The intrinsic gamma-ray spectrum can be described by either a power-law without cutoff up to 150 keV, and an exponential cutoff above that energy, or by an exponentially cutoff power law and a second hard component resembling strongly Comptonized bremsstrahlung.