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Astronomy and Astrophysics 478 (2008) 387-393
Upper Limits from HESS active galactic nuclei Observations in 2005-2007
F. Aharonian, A.G. Akhperjanian, U. Barres De Almeida, A.R. Bazer-Bachi1, B. Behera, M. Beilicke, W. Benbow, K. Bernlohr, C. Boisson2, O. Bolz, V. Borrel1, I. Braun, E. Brion3, A.M. Brown, R. Buhler, T. Bulik, I. Busching, T. Boutelier4, S. Carrigan, P.M. Chadwick, L.-M. Chounet5, A.C. Clapson, G. Coignet6, R. Cornils, L. Costamante, M. Dalton, B. Degrange5, H.J. Dickinson, A. Djannati-Ataï7, W. Domainko, L.O'C. Drury, F. Dubois6, G. Dubus4, J. Dyks, K. Egberts, D. Emmanoulopoulos, P. Espigat7, C. Farnier8, F. Feinstein8, A. Fiasson8, A. Forster, G. Fontaine5, Seb. Funk, M. Fusling, Y.A. Gallant8, B. Giebels5, J.F. Glicenstein3, B. Gluck, P. Goret3, C. Hadjichristidis, D. Hauser, M. Hauser, G. Heinzelmann, G. Henri4, G. Hermann, J.A. Hinton, A. Hoffmann, W. Hofmann, M. Holleran, S. Hoppe, D. Horns, A. Jacholkowska8, O.C. de Jager, I. Jung, K. Katarzynski, E. Kendziorra, M. Kerschhaggl, B. Khelifi5, D. Keogh, Nu. Komin8, K. Kosack, G. Lamanna6, I.J. Latham, A. Lemiere7, M. Lemoine-Goumard5, J.-P. Lenain2, T. Lohse, J.M. Martin2, O. Martineau-Huynh9, A. Marcowith8, C. Masterson, D. Maurin9, G. Maurin7, T.J.L. Mccomb, R. Moderski, E. Moulin3, M. De Naurois9, D. Nedbal, S.J. Nolan, S. Ohm, J.-P. Olive1, E. De Ona Wilhelmi7, K.J. Orford, J.L. Osborne, M. Ostrowski, M. Panter, G. Pedaletti, G. Pelletier4, P.-O. Petrucci4, S. Pita7, G. Puhlhofer, M. Punch7, S. Ranchon6, B.C. Raubenheimer, M. Raue, S.M. Rayner, M. Renaud, J. Ripken, L. Rob, L. Rolland3, S. Rosier-Lees6, G. Rowell, B. Rudak, J. Ruppel, V. Sahakian, A. Santangelo, R. Schlickeiser, F. Schock, R. Schroder, U. Schwanke, S. Schwarzburg, S. Schwemmer, A. Shalchi, H. Sol2, D. Spangler, L. Stawarz, R. Steenkamp, C. Stegmann, G. Superina5, P.H. Tam, J.-P. Tavernet9, R. Terrier7, C. Van Eldik, G. Vasileiadis8, C. Venter, J.P. Vialle6, P. Vincent9, M. Vivier3, H.J. Volk, F. Volpe5, S.J. Wagner, M. Ward, A.A. Zdziarski, A. Zech2
HESS Collaboration(s)

AIMS: Very high energy (VHE; E>100 GeV) gamma-ray studies were performed for 18 active galactic nuclei (AGN) from a variety of AGN classes. METHODS: VHE observations of a sample of 14 AGN, considered candidate VHE emitters, were made with the High Energy Stereoscopic System (HESS) between January 2005 and July 2007. Large-zenith-angle observations of three northern AGN (Mkn 421, Mkn 501, 1ES 1218+304), known to emit VHE gamma rays, were also performed in order to sample their spectral energy distributions (SEDs) above 1 TeV. In addition, the VHE flux from 1ES 1101-232, previously detected by HESS in 2004-2005, was monitored during 2006 and 2007. RESULTS: As significant detections from the HESS observation program are reported elsewhere, the results reported here are primarily integral flux upper limits. The average exposure for each of the 14 VHE-candidate AGN is ~7 h live time, and the observations have an average energy threshold between 230 GeV and 590 GeV. Upper limits for these 14 AGN range from <0.9% to <4.9% of the Crab Nebula flux, and eight of these are the most constraining ever reported for the object. The brief (<2.2 h each) large-zenith-angle observations yield upper limits for Mkn 501 (<20% Crab above 2.5 TeV) and 1ES 1218+304 (<17% Crab above 1.0 TeV), and a marginal detection (3.5 sigma) of Mkn 421 (50% Crab above 2.1 TeV). 1ES 1101-232 was marginally detected (3.6 sigma, 1.7% Crab above 260 GeV) during the 2006 (13.7 h live time) observations, but not in the 2007 (4.6 h live time) data. The upper limit in 2007 (<1.9% Crab above 260 GeV) is below the average flux measured by HESS from 2004-2006.
1 :  CESR - Centre d'étude spatiale des rayonnements
2 :  LUTH - Laboratoire Univers et Théories
3 :  DAPNIA - Département d'Astrophysique, de physique des Particules, de physique Nucléaire et de l'Instrumentation Associée
4 :  LAOG - Laboratoire d'Astrophysique de Grenoble
5 :  LLR - Laboratoire Leprince-Ringuet
6 :  LAPP - Laboratoire d'Annecy le Vieux de Physique des Particules
7 :  APC - UMR 7164 - AstroParticule et Cosmologie
8 :  LPTA - Laboratoire de Physique Théorique et Astroparticules
9 :  LPNHE - Laboratoire de Physique Nucléaire et de Hautes Énergies
Physique/Astrophysique/Cosmologie et astrophysique extra-galactique

Planète et Univers/Astrophysique/Cosmologie et astrophysique extra-galactique

Planète et Univers/Astrophysique
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