Diffuse Galactic gamma‐ray emission above 1 MEV

The diffuse continuum γ‐ray emission from the Galaxy provides a unique tracer of cosmic rays. The emission above ∼50 MeV is well studied by the SAS‐2 and COS‐B satellites and can soon be analyzed with better angular resolution and sensitivity now the all‐sky survey by the EGRET telescope aboard the Compton Observatory has been completed. Information for the 1–50 MeV range was far more limited prior to the launch of the Compton Observatory. The COMPTEL telescope on this observatory provides for the first time extensive imaging possibilities at MeV energies. This paper presents a global review of the diffuse gamma radiation between about 1 MeV and 10 GeV, with emphasis on implications for the low‐energy cosmic‐ray electron spectrum and the distribution of cosmic rays in the Galaxy. A complementary review on the diffuse emission below 1 MeV is given by R. Ramaty in this volume.