New results from long-term observations of Cyg X-1

Observations of Cyg X-1 between October 1974 and July 1975 reveal a persistent 5.6 day modulation of the 3 to 6 keV x-ray intensity, having a minimum in phase with superior conjunction of the HDE 226868 binary system. The modulation is found to be most pronounced just prior to the April to May 1975 increase of Cyg X-1, after which both the modulation and intensity are at their lowest values for the entire duration of the observations. These data imply that the x-ray emission from Cyg X-1 arises from the compact member of HDE 226868, and that the increase of April to May 1975 may have represented the depletion of accreting material which had not yet been mixed into a cylindrically symmetric accretion disk about the compact member