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

Free access article

Issue		A&A Volume 475, Number 2, November IV 2007


Page(s)		L9 - L13
Section		Letters
DOI		http://dx.doi.org/10.1051/0004-6361:20078462

A&A 475, L9-L13 (2007)
DOI: 10.1051/0004-6361:20078462

Letter

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

F. Aharonian^{1, 2}, A. G. Akhperjanian³, U. Barres de Almeida⁴, A. R. Bazer-Bachi⁵, B. Behera⁶, M. Beilicke⁷, W. Benbow¹, K. Bernlöhr^{1, 8}, C. Boisson⁹, O. Bolz¹, V. Borrel⁵, I. Braun¹, E. Brion¹⁰, A. M. Brown⁴, R. Bühler¹, T. Bulik¹¹, I. Büsching¹², T. Boutelier¹³, S. Carrigan¹, P. M. Chadwick⁴, L.-M. Chounet¹⁴, A. C. Clapson¹, G. Coignet¹⁵, R. Cornils⁷, L. Costamante^{1, 16}, M. Dalton⁸, B. Degrange¹⁴, H. J. Dickinson⁴, A. Djannati-Ataï¹⁷, W. Domainko¹, L. O'C. Drury², F. Dubois¹⁵, G. Dubus¹³, J. Dyks¹¹, K. Egberts¹, D. Emmanoulopoulos⁶, P. Espigat¹⁷, C. Farnier¹⁸, F. Feinstein¹⁸, A. Fiasson¹⁸, A. Förster¹, G. Fontaine¹⁴, Seb. Funk⁸, M. Füßling⁸, Y. A. Gallant¹⁸, B. Giebels¹⁴, J. F. Glicenstein¹⁰, B. Glück¹⁹, P. Goret¹⁰, C. Hadjichristidis⁴, D. Hauser¹, M. Hauser⁶, G. Heinzelmann⁷, G. Henri¹³, G. Hermann¹, J. A. Hinton²⁰, A. Hoffmann²¹, W. Hofmann¹, M. Holleran¹², S. Hoppe¹, D. Horns²¹, A. Jacholkowska¹⁸, O. C. de Jager¹², I. Jung¹⁹, K. Katarzynski²², E. Kendziorra²¹, M. Kerschhaggl⁸, B. Khélifi¹⁴, D. Keogh⁴, Nu. Komin¹⁸, K. Kosack¹, G. Lamanna¹⁵, I. J. Latham⁴, A. Lemière¹⁷, M. Lemoine-Goumard¹⁴, J.-P. Lenain⁹, T. Lohse⁸, J. M. Martin⁹, O. Martineau-Huynh²³, A. Marcowith¹⁸, C. Masterson², D. Maurin²³, G. Maurin¹⁷, T. J. L. McComb⁴, R. Moderski¹¹, E. Moulin¹⁰, M. de Naurois²³, D. Nedbal²⁴, S. J. Nolan⁴, S. Ohm¹, J.-P. Olive⁵, E. de Oña Wilhelmi¹⁷, K. J. Orford⁴, J. L. Osborne⁴, M. Ostrowski²⁵, M. Panter¹, G. Pedaletti⁶, G. Pelletier¹³, P.-O. Petrucci¹³, S. Pita¹⁷, G. Pühlhofer⁶, M. Punch¹⁷, S. Ranchon¹⁵, B. C. Raubenheimer¹², M. Raue⁷, S. M. Rayner⁴, M. Renaud¹, J. Ripken⁷, L. Rob²⁴, L. Rolland¹⁰, S. Rosier-Lees¹⁵, G. Rowell²⁶, B. Rudak¹¹, J. Ruppel²⁷, V. Sahakian³, A. Santangelo²¹, R. Schlickeiser²⁷, F. Schöck¹⁹, R. Schröder²⁷, U. Schwanke⁸, S. Schwarzburg²¹, S. Schwemmer⁶, A. Shalchi²⁷, H. Sol⁹, D. Spangler⁴, L. Stawarz²⁵, R. Steenkamp²⁸, C. Stegmann¹⁹, G. Superina¹⁴, P. H. Tam⁶, J.-P. Tavernet²³, R. Terrier¹⁷, C. van Eldik¹, G. Vasileiadis¹⁸, C. Venter¹², J. P. Vialle¹⁵, P. Vincent²³, M. Vivier¹⁰, H. J. Völk¹, F. Volpe¹⁴, S. J. Wagner⁶, M. Ward⁴, A. A. Zdziarski¹¹, and A. Zech⁹

¹ Max-Planck-Institut für Kernphysik, Heidelberg, Germany
e-mail: [Wystan.Benbow;Luigi.Costamante]@mpi-hd.mpg.de
² Dublin Institute for Advanced Studies, Ireland
³ Yerevan Physics Institute, Armenia
⁴ University of Durham, Department of Physics, UK
⁵ Centre d'Étude Spatiale des Rayonnements, CNRS/UPS, Toulouse, France
⁶ Landessternwarte, Universität Heidelberg, Königstuhl, Germany
⁷ Universität Hamburg, Institut für Experimentalphysik, Germany
⁸ Institut für Physik, Humboldt-Universität zu Berlin, Germany
⁹ LUTH, Observatoire de Paris, CNRS, Université Paris Diderot, Meudon, France
¹⁰ DAPNIA/DSM/CEA, CE Saclay, Gif-sur-Yvette, France
¹¹ Nicolaus Copernicus Astronomical Center, Warsaw, Poland
¹² Unit for Space Physics, North-West University, Potchefstroom, South Africa
¹³ Laboratoire d'Astrophysique de Grenoble, INSU/CNRS, Université Joseph Fourier, France
¹⁴ Laboratoire Leprince-Ringuet, École Polytechnique, CNRS/IN2P3, Palaiseau, France
¹⁵ Laboratoire d'Annecy-le-Vieux de Physique des Particules, CNRS/IN2P3, Annecy-le-Vieux, France
¹⁶ European Associated Laboratory for Gamma-Ray Astronomy, jointly supported by CNRS and MPG
¹⁷ Astroparticule et Cosmologie (APC), CNRS, Université Paris 7 Denis Diderot, France
¹⁸ Laboratoire de Physique Théorique et Astroparticules, CNRS/IN2P3, Université Montpellier II, France
¹⁹ Universität Erlangen-Nürnberg, Physikalisches Institut, Germany
²⁰ School of Physics & Astronomy, University of Leeds, UK
²¹ Institut für Astronomie und Astrophysik, Universität Tübingen, Germany
²² Torun Centre for Astronomy, Nicolaus Copernicus University, Torun, Poland
²³ LPNHE, Université Pierre et Marie Curie Paris 6, Université Denis Diderot Paris 7, CNRS/IN2P3, France
²⁴ Institute of Particle and Nuclear Physics, Charles University, Prague, Czech Republic
²⁵ Obserwatorium Astronomiczne, Uniwersytet Jagiellonski, Kraków, Poland
²⁶ School of Chemistry & Physics, University of Adelaide, Australia
²⁷ Institut für Theoretische Physik, Lehrstuhl IV, Ruhr-Universität Bochum, Germany
²⁸ University of Namibia, Windhoek, Namibia

(Received 10 August 2007 / Accepted 23 September 2007)

Abstract
Aims.To investigate the very high energy (VHE: >100 GeV) $\gamma$ -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 6.6 $\sigma$ level in the HESS observations (41.8 h live time). The integral flux above 580 GeV is $(9.4\pm1.5_{\rm stat}\pm1.9_{\rm syst}) \times 10^{-13}$ 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 ( $\Gamma = 2.50\pm0.19_{\rm stat}\pm0.10_{\rm syst}$ ) 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 $\Gamma_{\rm int} \approx 1.5$ , the HESS data support an EBL spectrum $\propto$ $\lambda^{-1}$ 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.

Key words: galaxies: BL lacertae objects: individual: 1ES 0229+200 -- gamma rays: observations

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Letter

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

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