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2004ApJ...601..142C - Astrophys. J., 601, 142-150 (2004/January-3)

Stacking searches for gamma-ray emission above 100 MeV from radio and Seyfert galaxies.

CILLIS A.N., HARTMAN R.C. and BERTSCH D.L.

Abstract (from CDS):

The EGRET telescope on board Compton Gamma Ray Observatory detected more than 60 sources of high-energy gamma radiation associated with active galactic nuclei (AGNs). All but one of those belong to the blazar subclass; the only exception is the nearby radio galaxy Centaurus A. Since there is no obvious reason other than proximity to expect Cen A to be the only nonblazar AGN emitting in high-energy gamma rays, we have utilized the stacking'' technique to search for emission above 100 MeV from two nonblazar AGN subclasses, radio galaxies and Seyfert galaxies. Maps of gamma-ray counts, exposure, and diffuse background have been created, then co-added in varying numbers based on sorts by redshift, 5 GHz flux density, and optical brightness, and finally tested for gamma-ray emission. No detection significance greater than 2 σ has been found for any subclass, sorting parameter, or number of objects co-added. Monte Carlo simulations have also been performed to validate the technique and estimate the significance of the results.

Journal keyword(s): Galaxies: Active - Galaxies: Seyfert - Gamma Rays: Observations

CDS comments: table 2 : NGC 1235 is a misprint for NGC 1233