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

1 CESR - Centre d'étude spatiale des rayonnements
2 LUTH (UMR_8102) - Laboratoire Univers et Théories
3 LLR - Laboratoire Leprince-Ringuet
4 APC (UMR_7164) - AstroParticule et Cosmologie
5 LPTA - Laboratoire de Physique Théorique et Astroparticules
6 DAPNIA - Département d'Astrophysique, de physique des Particules, de physique Nucléaire et de l'Instrumentation Associée
7 LAOG - Laboratoire d'Astrophysique de Grenoble
8 APC - AHE - APC - Astrophysique des Hautes Energies

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.

Mots clés: gamma rays: observations; galaxies: active; galaxies: BL Lacertae objects: individual: H 2356-309

Domaines: Cosmologie et astrophysique extra-galactique [astro-ph.CO]; 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.. 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, 2006, 455, pp.461-466. ⟨10.1051/0004-6361:20054732⟩. ⟨in2p3-00124806⟩