Intensity and spectral variations of Cyg X-1 observed from balloons

Observations of Cyg X-1 with a 20 to 200 keV balloon carried x-ray telescope in 1969, 1970, and 1972 are presented. These results reveal the following characteristics of Cyg X-1: The steep spectrum observed at E less than 10 keV during the ''radio quiet'' phase can extend to 200 keV. This phase may have lasted 21 months (July 1969 to March 1971). The flux at 30 keV can vary from 1.1 x 10-2 to 1.4 x 10-3 ph (cm2-sec-keV)-1 and that at 100 keV from 1.4 x 10-3 to 10-4. The low flux values are factors of 3 and 8 below the ''normal'' values at 30 and 100 keV respectively, are rarely observed, and may be associated with the early phase of the 1971 April x-ray transition. During some one hour periods the intensity remained constant to approximately 20% and during other periods it varied a factor 2 in 5 minutes and a factor 10 in 1 hour. Complex spectral variations accompanied the intensity changes