HEAO-1 Modulation Collimator Observations of X-Ray Seyferts and Other Active Galactic Nuclei. Griffiths, R. E. ; Bradt, H. ; Briel, U. ; Doxsey, R. E. ; Johnston, M. ; Schwartz, D. A. ; Schwarz, J. Abstract Publication: Bulletin of the American Astronomical Society Pub Date: June 1978 Bibcode: 1978BAAS...10..503G