Upper limits on the MeV emission of Seyfert galaxies
The gamma-ray emission of Seyfert galaxies has fallen far short of pre-CGRO expectations. From a sample of 26 X-ray bright Seyfert galaxies, we do not detect a single object of this class in the energy range 0.75-3MeV in COMPTEL data. To derive a more stringent upper limit for the emission from these objects in the energy ranges 0.75-1MeV and 1-3MeV, we have summed a large number of COMPTEL observations acquired during Phase I of the CGRO mission. From a total of 50 observations of 26 individual X-ray selected Seyfert galaxies, we derive upper limits (2 σ) of 1.0x10^-7^photons/(cm^2^s keV) in the 0.75-1MeV band and 9.7x10^-9^photons/(cm^2^s keV) in the 1-3 MeV band, two orders of magnitude below previously reported detections. Our observations show that if emission at the level previously reported for NGC 4151 and MCG 8-11-11 occurs as a transient phenomenon in Seyfert galaxies, it has a duty cycle of less than 5%.
Astronomy and Astrophysics
European Southern Observatory (ESO)
M. Maisack, W. Collmar, P. Barr, H. Bloemen, W. Hermsen, G.G. Lichti, M. McConnell, V. Schönfelder, J.G. Stacy, H. Steinle, and O.R. Williams. UPPER LIMITS ON THE MEV EMISSION OF SEYFERT GALAXIES. 1995, Astron. Astrophys., 298, 400.