Observations of Selected AGN with HESS

F. Aharonian , A. G. Akhperjanian , A. R. Bazer-Bachi , M. Beilicke , W. Benbow , D. Berge , K. Bernlöhr , C. Boisson , O. Bolz , V. Borrel , I. Braun , F. Breitling , A. M. Brown , P. M. Chadwick , L.-M. Chounet (1) , R. Cornils , L. Costamante , B. Degrange (1) , H.J. Dickinson , A. Djannati-Ataï (2) , Drury L. O'C. , G. Dubus (1) , D. Emmanoulopoulos , P. Espigat (2) , F. Feinstein (3) , G. Fontaine (1) , Y. Fuchs , S. Funk , Y.A. Gallant (3) , B. Giebels (1) , S. Gillessen , J.F. Glicenstein , P. Goret , C. Hadjichristidis , M. Hauser , G. Heinzelmann , G. Henri , G. Hermann , J. A. Hinton , W. Hofmann , M. Holleran , D. Horns , A. Jacholkowska (3) , O.C. Dejager , B. Khélifi , Nu. Komin , A. Konopelko , I. J. Latham , R. Le Gallou , A. Lemière (2) , M. Lemoine-Goumard (1) , N. Leroy (1) , T. Lohse , J.M. Martin , O. Martineau-Huynh (4) , A. Marcowith , C. Masterson , T. J. L. Mccomb , M. de Naurois (4) , S. J. Nolan , A. Noutsos , K. J. Orford , J. L. Osborne , M. Ouchrif (4) , M. Panter , G. Pelletier , S. Pita (2) , G. Pühlhofer , M. Punch (2) , B. C. Raubenheimer , M. Raue , J. Raux (4) , S. M. Rayner , A. Reimer , O. Reimer , J. Ripken , L. Rob , L. Rolland (4) , G. Rowell , V. Sahakian , L. Saugé , S. Schlenker , R. Schlickeiser , C. Schuster , U. Schwanke , M. Siewert , H. Sol , D. Spangler , R. Steenkamp , C. Stegmann , J.-P. Tavernet (4) , R. Terrier (2) , C.G. Théoret (2) , M. Tluczykont (1) , G. Vasileiadis (3) , C. Venter , P. Vincent (4) , H. J. Völk , S. J. Wagner

1 LLR - Laboratoire Leprince-Ringuet
2 APC (UMR_7164) - AstroParticule et Cosmologie
3 LPTA - Laboratoire de Physique Théorique et Astroparticules
4 LPNHE - Laboratoire de Physique Nucléaire et de Hautes Énergies

A sample of selected active galactic nuclei (AGN) was observed in 2003 and 2004 with the High Energy Stereoscopic System (H.E.S.S.), an array of imaging atmospheric-Cherenkov telescopes in Namibia. The redshifts of these candidate very-high-energy (VHE, >100 GeV) gamma-ray emitters range from z=0.00183 to z=0.333. Significant detections were already reported for some of these objects, such as PKS 2155-304 and Markarian 421. Marginal evidence (3.1 sigma) 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 (stat) +/- 0.3 (syst)) x 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 hrs 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.

Mots clés: Galaxies: active; BL Lacertae objects: Individual; Gamma rays: observations

Domaines: Cosmologie et astrophysique extra-galactique [astro-ph.CO]; Astrophysique [astro-ph]

F. Aharonian, A. G. Akhperjanian, A. R. Bazer-Bachi, M. Beilicke, W. Benbow, et al.. Observations of Selected AGN with HESS. Astronomy and Astrophysics - A&A, 2005, 441, pp.465-472. ⟨10.1051/0004-6361:20053478⟩. ⟨in2p3-00024534⟩