Long‐term temporal and spectral variation of Cygnus X‐1 observed by BATSE

Preliminary BATSE results for Cygnus X‐1, analyzed by Earth occultation with the standard Mission Operations System (MOPS), show dramatic temporal varations of the broad‐band (20–2000 keV) emission with time scale of the order of days. We report here preliminary results of a study of the temporal and spectral variability of the source using the newly developed ‘‘Enhanced Earth Occultation Analysis’’ developed at JPL. From 25 October to 27 November 1991, variations in spectral form between a Comptonized and power‐law shape were noted. The average photon flux in the 45–140 keV band is near the γ2 level.