Volume 441, Number 2, October II 2005
|Page(s)||465 - 472|
|Published online||19 September 2005|
Observations of selected AGN with HESS
Max-Planck-Institut für Kernphysik, Heidelberg, Germany; e-mail: firstname.lastname@example.org;
2 Yerevan Physics Institute, Armenia;
3 Centre d'Étude Spatiale des Rayonnements, CNRS/UPS, Toulouse, France;
4 Universität Hamburg, Institut für Experimentalphysik, Germany;
5 Institut für Physik, Humboldt-Universität zu Berlin, Germany;
6 LUTH, UMR 8102 du CNRS, Observatoire de Paris, Section de Meudon, France;
7 University of Durham, Department of Physics, UK;
8 Laboratoire Leprince-Ringuet, IN2P3/CNRS, École Polytechnique, Palaiseau, France;
9 European Associated Laboratory for Gamma-Ray Astronomy, jointly supported by CNRS and MPG
10 APC, Paris, France;
11 Dublin Institute for Advanced Studies, Ireland;
12 Landessternwarte, Königstuhl, Heidelberg, Germany;
13 Laboratoire de Physique Théorique et Astroparticules, IN2P3/CNRS, Université Montpellier II, France;
14 Laboratoire d'Astrophysique de Grenoble, INSU/CNRS, Université Joseph Fourier, France;
15 DAPNIA/DSM/CEA, CE Saclay, Gif-sur-Yvette, France;
16 Unit for Space Physics, North-West University, Potchefstroom, South Africa;
17 Laboratoire de Physique Nucléaire et de Hautes Energies, IN2P3/CNRS, Universités Paris VI & VII, France;
18 Institut für Theoretische Physik, Lehrstuhl IV, Ruhr-Universität Bochum, Germany;
19 Institute of Particle and Nuclear Physics, Charles University, Prague, Czech Republic;
20 University of Namibia, Windhoek, Namibia;
Accepted: 16 June 2005
A sample of selected active galactic nuclei (AGN) was observed in 2003 and 2004 with the High Energy Stereoscopic System (HESS), an array of imaging atmospheric-Cherenkov telescopes in Namibia. The redshifts of these candidate very-high-energy (VHE, >100 GeV) γ-ray emitters range from to . Significant detections were already reported for some of these objects, such as PKS 2155-304 and Markarian 421. Marginal evidence (3.1σ) for a signal is found from large-zenith-angle observations of Markarian 501, corresponding to an integral flux of I(>1.65 TeV) = (1.5±0.6±0.3) 10-12 cm-2 s-1 or ~15% of the Crab Nebula flux. Integral flux upper limits for 19 other AGN, based on exposures of ~1 to ~8 h live time, and with average energy thresholds between 160 GeV and 610 GeV, range from 0.4% to 5.1% of the Crab Nebula flux. All the upper limits are the most constraining ever reported for these objects.
Key words: galaxies: active / BL Lacertae objects: general / gamma rays: observations
© ESO, 2005
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