Gamma-ray follow-up studies on η Carinae

The increased exposure in conjunction with the improved instrumental response functions of the Fermi-LAT now allows a more detailed investigation of location, spectral shape and flux time history of the observed γ-ray emission at the position of η Carinae. We detect a weak but regular flux decrease over time. This can be understood and interpreted in a colliding-wind binary scenario for orbital modulation of the γ-ray emission. We find that the spectral shape of the γ-ray signal agrees with a single emitting particle population in combination with significant absorption by γ-γ pair production. Concluding, we are able to report on the first unambiguous detection of GeV γ-ray emission from a colliding-wind massive star binary. Studying the correlation of the flux decrease with the orbital separation of the binary components allows us to predict the behaviour up to the next periastron passage in 2014.