The γ-ray emission from the Seyfert galaxy NGC 4151

Light curves at X-ray, ultraviolet, optical and infrared wavelengths of NGC 4151 over the period 1977–1980 are presented together with a summary of the large amount of observational data relating to this Seyfert galaxy. Intensity variations in different wavebands are discussed and compared with recent low energy γ-ray observations of this object. The positive measurement of gamma-radiation in May 1977 is shown to have been characterised by a high optical state and a possible infrared maximum. The data presented are compared with the predictions of some emission mechanisms, which have been proposed to account for the gamma-radiation. In particular, a synchrotron self-Compton model, which relates the infrared/optical emission to the X-ray/low energy γ-ray emission is discussed.