Issue |
A&A
Volume 475, Number 2, November IV 2007
|
|
---|---|---|
Page(s) | L9 - L13 | |
Section | Letters | |
DOI | https://doi.org/10.1051/0004-6361:20078462 | |
Published online | 02 October 2007 |
Letter to the Editor
New constraints on the mid-IR EBL from the HESS discovery of VHE γ-rays from 1ES 0229+200
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
Toruń Centre for Astronomy, Nicolaus Copernicus University, Toruń, 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 Jagielloński, 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
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 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 (
) 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 (),
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
, the HESS data
support an EBL spectrum
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 (
).
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
© ESO, 2007
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