Hard X-ray Spectrum of the Crab Nebula from HEAO-1 Gruber, D. E. ; Matteson, J. L. ; Knight, F. K. ; Rothschild, R. E. ; Nolan, P. L. ; Howe, S. ; Levine, A. M. ; Primini, F. A. Abstract Publication: Bulletin of the American Astronomical Society Pub Date: March 1980 Bibcode: 1980BAAS...12..541G