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For refcode 1995A&A...298..400M:
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Copyright by European Southern Observatory (ESO). Reproduced by permission
1995A&A...298..400M Upper limits on the MeV emission of Seyfert galaxies M. Maisack, W. Collmar, P. Barr, H. Bloemen, W. Hermsen, C.C. Lichti, M. McConnell, V. Schonfelder, J.G. Stacy, H. Steinle, and O.R. Williams Max-Planck-Institut fur extraterrestrische Physik, D-85740 Garching, Germany SRON-Leiden, P.O. Box 9504, NL-2300 RA Leiden, The Netherlands University of New Hampshire, Durham NH 03824, USA Astrophysics Division, ESTEC, NL-2200 AG Nordwijk, The Netherlands Astronomisches Institut der Universitat Tubingen, D-72076 Tubingen, Germany Received 1 April 1994/Accepted 3 November 1994 Abstract. 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 0.75-3 MeV in COMPTEL data. To derive a more stringent upper limit for the emission from these objects in the energy ranges 0.75-1 MeV and I -3 MeV, 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 {sigma}) of 1.0 x 10^-7^ photons / (cm^2^ s keV) in the 0.75-1 MeV band and 9.7 x 10^-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%. Key words: galaxies: active Seyfert - gamma rays: observations
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