Observation of EGRET gamma-ray sources by an Extensive Air Shower experiment

Department of Physics, Sharif university of Technology, PO Box 11365–9161, Tehran, Iran e-mail: [khakian;bahmanabadi;samimi]@sharif.edu

Received: 23 June 2004
Accepted: 3 November 2004

Abstract

Ultra-high-energy ( TeV) Extensive Air Showers (EASs) have been monitored for a period of five years (1997–2003), using a small array of scintillator detectors in Tehran, Iran. The data have been analyzed taking into account the dependence of source counts on zenith angle. During a calendar year different sources come into the field of view of the detector at varying zenith angles. Because of varying thickness of the overlaying atmosphere, the shower count rate is extremely dependent on zenith angle, which has been carefully analyzed over time (Bahrnanabadi et al. 2002, Exp. Astron., 13, 39). High energy gamma-ray sources from the EGRET third catalogue where observed and the data were analyzed using an excess method. Upper limits were obtained for a number of EGRET sources, including 6 AGNs or probably AGNs and 4 unidentified sources.