Hercules X-1; Spectral Hard X-ray Observations from HEAO-1. Gruber, D. E. ; Matteson, J. L. ; Baity, W. A. ; Peterson, L. E. ; Wheaton, W. A. ; Dobson, C. ; Campbell, P. ; Lewin, W. Abstract Publication: Bulletin of the American Astronomical Society Pub Date: March 1978 Bibcode: 1978BAAS...10R.433G