Radio Variability of HDE 226868 (cygnus X-1)

Radio observations of HDE 226868 (Cyg X-1) at 2695 and 8085 MHz made between 1971 February 23 and 1972 October 21 show that (1) the radio flux of this spectroscopic binary went from less than 0.005 f.u. on 1971 March 22 to 0.02 f.u. on 1971 March 31, just as the X-ray flux of Cyg X-1 was beginning a significant change in average level; (2) a significant change from a mean level of 0.015 f.u. to 0.018 f.u. occurred at both frequendes between 1972 April 25 and 1972 September 3; and (3) radio variability on a time scale of days definitely occurred during October 1972 and may have occurred at other times. Subject headings: radio sources - spectroscopic binaries - variable stars - X-ray sources