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New constraints on the Mid-IR EBL from the HESS discovery of VHE gamma rays from 1ES 0229+200

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-Atai 7 W. Domainko L.O'C. Drury F. Dubois G. Dubus 4 J. Dyks K. Egberts D. Emmanoulopoulos P. Espigat 7 C. Farnier 8 F. Feinstein 8 A. Fiasson 8 A. Forster G. Fontaine 5 Seb. Funk M. Fusling Y.A. Gallant 8 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 8 O.C. de Jager I. Jung K. Katarzynski E. Kendziorra M. Kerschhaggl B. Khelifi 5 D. Keogh Nu. Komin 8 K. Kosack G. Lamanna 6 I.J. Latham A. Lemiere 7 M. Lemoine-Goumard 5 J.-P. Lenain 2 T. Lohse J.M. Martin 2 O. Martineau-Huynh 9 A. Marcowith 8 C. Masterson D. Maurin 9 G. Maurin 7 T.J.L. Mccomb R. Moderski Emmanuel Moulin 3 M. de Naurois 9 D. Nedbal S.J. Nolan S. Ohm J.-P. Olive 1 E. de Ona Wilhelmi 7 K.J. Orford J.L. Osborne M. Ostrowski M. Panter G. Pedaletti G. Pelletier 4 P.-O. Petrucci 4 S. Pita 10 G. Puhlhofer M. Punch 10 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 9 R. Terrier 10 C. van Eldik G. Vasileiadis 8 C. Venter J.P. Vialle 6 P. Vincent 9 M. Vivier 3 H.J. Volk F. Volpe 5 S.J. Wagner M. Ward A.A. Zdziarski A. Zech 2
Abstract : Aims:To investigate the very high energy (VHE: >100 GeV) γ-ray emission from the high-frequency peaked BL Lac 1ES 0229+200. Methods: Observations of 1ES 0229+200 at energies above 580 GeV were performed with the High Energy Stereoscopic System (HESS) in 2005 and 2006. Results: 1ES 0229+200 is discovered by HESS to be an emitter of VHE photons. A signal is detected at the 6.6σ level in the HESS observations (41.8 h live time). The integral flux above 580 GeV is (9.4±1.5_stat±1.9_syst) × 10-13 cm-2 s-1, corresponding to ~1.8% of the flux observed from the Crab Nebula. The data show no evidence for significant variability on any time scale. The observed spectrum is characterized by a hard power law (Γ = 2.50±0.19_stat±0.10_syst) from 500 GeV to ~15 TeV. Conclusions: The high-energy range and hardness of the observed spectrum, coupled with the object's relatively large redshift (z = 0.1396), enable the strongest constraints so far on the density of the Extragalactic Background Light (EBL) in the mid-infrared band. Assuming that the emitted spectrum is not harder than Γ_int ≈ 1.5, the HESS data support an EBL spectrum ∝λ-1 and density close to the lower limit from source counts measured by Spitzer, confirming the previous indications from the HEGRA data of 1ES 1426+428 (z=0.129). Irrespective of the EBL models used, the intrinsic spectrum of 1ES 0229+200 is hard, thus locating the high-energy peak of its spectral energy distribution above a few TeV.
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Submitted on : Monday, October 1, 2007 - 1:41:06 PM
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F. Aharonian, A.G. Akhperjanian, U. Barres de Almeida, A.R. Bazer-Bachi, B. Behera, et al.. New constraints on the Mid-IR EBL from the HESS discovery of VHE gamma rays from 1ES 0229+200. Astronomy and Astrophysics - A&A, EDP Sciences, 2007, 475, pp.L9-L13. ⟨10.1051/0004-6361:20078462⟩. ⟨in2p3-00175791⟩

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