Ariel V and Copernicus measurements of the X-ray variability of CYG X-1

The X-ray intensity and spectrum observations of Cyg X-1 from May 3 to May 15, 1975 using Ariel V are reported. Cyg X-1 was more intense, had a steeper spectrum and was generally more active than has been observed during the past two and one half years by Copernicus. The Copernicus data taken between 1972 and 1975, were searched for any systematic change in X-ray behavior which might herald a transition. One possibility is a variation in the orbital phase at which absorption events are seen. Data suggest a systematic change in phase of the absorption events on a time scale of a few years.