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%.



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Astronomy and Astrophysics


European Southern Observatory (ESO)

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