Another correlated X-ray-radio transition in Cygnus X-1

It is reported that in February 1976 the x-ray and radio emission from Cyg X-1 underwent a simultaneous transition, similar to that observed in March 1971 when the source was first detected at radio frequencies. Observations were made with the Westerbork synthesis radio telescope at 1415 MHz. Comparisons of the measurements showed no significant changes in the flux densities of sources in the observed field except for Cyg X-1. The results are shown graphically and in tabular form, and are discussed. Possible explanations are advanced for the observed anti-correlation observed in the x-ray and radio behaviour during transitions. (U.K.)