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Upper Limits from HESS active galactic nuclei Observations in 2005-2007

F. Aharonian A.G. Akhperjanian U. Barres de Almeida A.R. Bazer-Bachi 1 B. Behera M. Beilicke W. Benbow K. Bernlohr C. Boisson 2 O. Bolz V. Borrel 1 I. Braun E. Brion 3 A.M. Brown R. Buhler T. Bulik I. Busching T. Boutelier 4 S. Carrigan P.M. Chadwick L.-M. Chounet 5 A.C. Clapson G. Coignet 6 R. Cornils L. Costamante M. Dalton B. Degrange 5 H.J. Dickinson A. Djannati-Ataï 7 W. Domainko L.O'C. Drury F. Dubois 6 G. Dubus 4 J. Dyks K. Egberts D. Emmanoulopoulos P. Espigat 8 C. Farnier 9 F. Feinstein 9 A. Fiasson 9 A. Forster G. Fontaine 5 Seb. Funk M. Fusling Y.A. Gallant 9 B. Giebels 5 J.F. Glicenstein 3 B. Gluck P. Goret 3 C. Hadjichristidis D. Hauser M. Hauser G. Heinzelmann G. Henri 4 G. Hermann J.A. Hinton A. Hoffmann W. Hofmann M. Holleran S. Hoppe D. Horns A. Jacholkowska 9 O.C. de Jager I. Jung K. Katarzynski E. Kendziorra M. Kerschhaggl B. Khelifi 5 D. Keogh Nu. Komin 9 K. Kosack G. Lamanna 6 I.J. Latham A. Lemiere 8 M. Lemoine-Goumard 5 J.-P. Lenain 2 T. Lohse J.M. Martin 2 O. Martineau-Huynh 10 A. Marcowith 9 C. Masterson D. Maurin 10 G. Maurin 8 T.J.L. Mccomb R. Moderski Emmanuel Moulin 3 M. de Naurois 10 D. Nedbal S.J. Nolan S. Ohm J.-P. Olive 1 E. de Ona Wilhelmi 8 K.J. Orford J.L. Osborne M. Ostrowski M. Panter G. Pedaletti G. Pelletier 4 P.-O. Petrucci 4 S. Pita 8 G. Puhlhofer M. Punch 8 S. Ranchon 6 B.C. Raubenheimer M. Raue S.M. Rayner M. Renaud J. Ripken L. Rob L. Rolland 3 S. Rosier-Lees 6 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. Sol 2 D. Spangler L. Stawarz R. Steenkamp C. Stegmann G. Superina 5 P.H. Tam J.-P. Tavernet 10 R. Terrier 8 C. van Eldik G. Vasileiadis 9 C. Venter J.P. Vialle 6 P. Vincent 10 M. Vivier 3 H.J. Volk F. Volpe 5 S.J. Wagner M. Ward A.A. Zdziarski A. Zech 2
Abstract : 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.
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Submitted on : Friday, February 29, 2008 - 4:21:25 PM
Last modification on : Friday, November 20, 2020 - 6:04:04 PM

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F. Aharonian, A.G. Akhperjanian, U. Barres de Almeida, A.R. Bazer-Bachi, B. Behera, et al.. Upper Limits from HESS active galactic nuclei Observations in 2005-2007. Astronomy and Astrophysics - A&A, EDP Sciences, 2008, 478, pp.387-393. ⟨10.1051/0004-6361:20078604⟩. ⟨in2p3-00189509⟩



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