EGRET Limits on High-Energy Gamma-Ray Emission from X-Ray-- and Low-Energy Gamma-Ray--selected Seyfert Galaxies
Michelson, P. F.; Nolan, P. L.; Thompson, D. J.; Sreekumar, P.; Kanbach, G.; Mayer-Hasselwander, H. A.; Hartman, R. C.; Dingus, B. L.; Fichtel, C. E.; Lin, Y. C.; Hunter, S. D.; Kniffen, D. A.; Mattox, J. R.; von Montigny, C.; Schneid, E.; Bertsch, D. L.
Abstract
A sample of 22 Seyfert galaxies, 11 type 1 and two type 2 galaxies selected according to their X-ray fluxes in the AGN survey catalogs of EXOSAT and Ginga, two additional type 1 galaxies for which detections in low-energy gamma rays have been reported in the past, plus six more type 1 galaxies and one unclassified Seyfert that have been studied by the OSSE collaboration, have been examined for high-energy gamma ray emission in observations by the EGRET telescope on the Compton Observatory. No high-energy gamma-ray emission has been detected from any of them. The 2 σ upper limits of the gamma-ray fluxes above 100 MeV for these 22 Seyfert galaxies are given here. The significance of these negative results is discussed. Implications of the EGRET result for NGC 4151 are discussed in more detail.