The Hard X-ray Spectrum of Cyg X-1 from HEAO-1 Nolan, P. L. ; Gruber, D. E. ; Matteson, J. L. ; Knight, F. K. ; Primini, F. ; Levine, A. ; Lewin, W. Abstract Publication: Bulletin of the American Astronomical Society Pub Date: December 1979 Bibcode: 1979BAAS...11..721N