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Discovery of Very High Energy Gamma-Ray Emission from the BL Lac Object H2356-309 with the H.E.S.S. Cherenkov Telescopes

F. Aharonian A. G. Akhperjanian A. R. Bazer-Bachi 1 M. Beilicke W. Benbow D. Berge K. Bernlöhr C. Boisson 2 O. Bolz V. Borrel 1 I. Braun F. Breitling A. M. Brown R. Bühler I. Büsching S. Carrigan P. M. Chadwick L.-M. Chounet 3 R. Cornils L. Costamante B. Degrange 3 H. J. Dickinson A. Djannati-Ataï 4 L. O'C. Drury G. Dubus 3 K. Egberts D. Emmanoulopoulos P. Espigat 4 F. Feinstein 5 E. Ferrero G. Fontaine 3 Seb. Funk S. Funk Y.A. Gallant 5 B. Giebels 3 J. F. Glicenstein 6 P. Goret 6 C. Hadjichristidis D. Hauser M. Hauser G. Heinzelmann G. Henri 7 G. Hermann J. A. Hinton W. Hofmann M. Holleran D. Horns A. Jacholkowska 5 O. C. de Jager B. Khélifi 3 Nu. Komin A. Konopelko I. J. Latham R. Le Gallou A. Lemière 4 M. Lemoine-Goumard 3 T. Lohse J. M. Martin O. Martineau-Huynh A. Marcowith 1 C. Masterson T. J. L. Mccomb M. de Naurois D. Nedbal S. J. Nolan A. Noutsos K. J. Orford J. L. Osborne M. Ouchrif M. Panter G. Pelletier 7 S. Pita 4 G. Pühlhofer M. Punch 8 B. C. Raubenheimer M. Raue S. M. Rayner A. Reimer O. Reimer J. Ripken L. Rob L. Rolland G. Rowell V. Sahakian L. Saugé 7 S. Schlenker R. Schlickeiser U. Schwanke H. Sol 2 D. Spangler F. Spanier R. Steenkamp C. Stegmann G. Superina 3 J.-P. Tavernet R. Terrier 4 C.G. Théoret 4 M. Tluczykont 3 C. van Eldik G. Vasileiadis 5 C. Venter P. Vincent H. J. Völk S. J. Wagner M. Ward
Abstract : The extreme synchrotron BL Lac object H2356-309, located at a redshift of z = 0.165, was observed from June to December 2004 with a total exposure of approx. 40 h live-time with the H.E.S.S. (High Energy Stereoscopic System) array of atmospheric-Cherenkov telescopes (ACTs). Analysis of this data set yields, for the first time, a strong excess of 453 gamma-rays (10 standard deviations above background) from H2356-309, corresponding to an observed integral flux above 200 GeV of I(>200GeV) = (4.1+-0.5) 10^12 cm^-2.s^-1 (statistical error only). The differential energy spectrum of the source between 200 GeV and 1.3 TeV is well-described by a power law with a normalisation (at 1 TeV) of N_0 = (3.00 +- 0.80_stat +- 0.31_sys) 10^-13 cm^-2.s^-1.TeV^-1 and a photon index of Gamma = 3.09 +- 0.24_stat +- 0.10_sys. H2356-309 is one of the most distant BL Lac objects detected at very-high-energy gamma-rays so far. Results from simultaneous observations from ROTSE-III (optical), RXTE (X-rays) and NRT (radio) are also included and used together with the H.E.S.S. data to constrain a single-zone homogeneous synchrotron self-Compton (SSC) model. This model provides an adequate fit to the H.E.S.S. data when using a reasonable set of model parameters.
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Submitted on : Tuesday, June 12, 2007 - 3:53:20 PM
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F. Aharonian, A. G. Akhperjanian, A. R. Bazer-Bachi, M. Beilicke, W. Benbow, et al.. Discovery of Very High Energy Gamma-Ray Emission from the BL Lac Object H2356-309 with the H.E.S.S. Cherenkov Telescopes. Astronomy and Astrophysics - A&A, EDP Sciences, 2006, 455, pp.461-466. ⟨10.1051/0004-6361:20054732⟩. ⟨in2p3-00124806⟩

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