A review of Cygnus X-1 soft γ-ray observations

Since the first discovery of Cygnus X- I in the mid 1960's, the source has been the subject of intense soft gamma-ray (30 keV - 10 MeV) observations by many balloon and satellite experiments. A large body of spectral and temporal information about the source has been gathered to date. While these results have significantly enhanced our understanding of the Cygnus X-1 system, they have also raised new questions that need to be addressed by future missions. This paper provides a brief summary of some of the important long-term temporal and spectral results obtained over the last thirty years, and discusses the current status and issues that need to be addressed by upcoming missions.