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          Institute: MPI für Kernphysik     Collection: High-Energy Astrophysics     Display Documents

ID: 223191.0, MPI für Kernphysik / High-Energy Astrophysics
H.E.S.S. Observations of PKS 2155-304
Authors:Aharonian, F.; Akhperjanian, A. G.; Aye, K.-M.; Bazer-Bachi, A. R.; Beilicke, M.; Benbow, W.; Berge, D.; Berghaus, P.; Bernlöhr, K.; Bolz, O.; Boisson, C:; Borgmeier, C.; Breitling, F.; Brown, A. M.; Bussons Gordo, J.; Chadwick, P. M.; Chitnis, V. R.; Chounet, L.-M.; Cornils, R.; Costamante, L.; Degrange, B.; Djannati-Atai, A.; Drury, L.O'C.; Ergin, T.; Espigat, P.; Feinstein, F.; Fleury, P.; Fontaine, G.; Funk, S.; Gallant, Y. A.; Giebels, B.; Gillessen, S.; Goret, P.; Guy, J.; Hadjichristidis, C.; Hauser, M.; Heinzelmann, G.; Henri, G.; Hermann, G.; Hinton, J. A.; Hofmann, W.; Holleran, M.; Horns, D.; de Jager, O. C.; Jung, I.; Khélifi, B.; Komin, N.; Konopelko, A.; Latham, I. J.; Le Gallou, R.; Lemoine, M.; Lemière, A.; Leroy, N.; Lohse, T.; Marcowith, A.; Masterson, C.; McComb, T. J. L.; de Naurois, M.; Nolan, S. J.; Noutsos, A.; Orford, K. J.; Osborne, J. L.; Ouchrif, M.; Panter, M.; Pelletier, G.; Pita, S.; Pohl, M.; Pühlhofer, G.; Punch, M.; Raubenheimer, B. C.; Raue, M.; Raux, J.; Rayner, S. M.; Redondo, I.; Reimer, A.; Reimer, O.; Ripken, J.; Rivoal, M.; Rob, L.; Rolland, L.; Rowell, G.; Sahakian, V.; Saugé, L.; Schlenker, S.; Schlickeiser, R.; Schuster, C.; Schwanke, U.; Siewert, M.; Sol, H.; Steenkamp, R.; Stegmann, C.; Tavernet, J.-P-; Théoret, C. G.; Tluczykont, M.; van der Walt, D. J.; Vasileiadis, G.; Vincent, P.; Visser, B.; Völk, H. J.; Wagner, S. J.
Date of Publication (YYYY-MM-DD):2005-02-02
Title of Journal:Astronomy & Astrophysics
Journal Abbrev.:A&A
Issue / Number:3
Start Page:865
End Page:875
Copyright:© ESO 2005
Review Status:not specified
Audience:Experts Only
Abstract / Description:The high-frequency peaked BL Lac PKS 2155-304 at redshift z=0.117 has been detected with high significance (~45 ) at energies greater than 160 GeV, using the H.E.S.S. stereoscopic array of imaging air-Cherenkov telescopes in Namibia. A strong signal is found in each of the data sets corresponding to the dark periods of July and October, 2002, and June-September, 2003. The observed flux of VHE gamma rays shows variability on time scales of months, days, and hours. The monthly-averaged integral flux above 300 GeV varies between 10% and 60% of the flux observed from the Crab Nebula. Energy spectra are measured for these individual periods of data taking and are characterized by a steep power law with a time-averaged photon index of Γ= 3.32±0.06 . An improved per degree of freedom is found when either a power law with an exponential cutoff energy or a broken power law are fit to the time-averaged energy spectrum. However, the significance of the improvement is marginal (~2 ). The suggested presence of features in the energy spectrum may be intrinsic to the emission from the blazar, or an indication of absorption of TeV gamma rays by the extragalactic infrared background light.
Free Keywords:galaxies: active -- galaxies: BL Lacertae objects: individual: PKS 2155-304 -- gamma rays: observations
External Publication Status:published
Document Type:Article
Affiliations:MPI für Kernphysik/Group of H. J. Völk/High Energy Astrophysics (F. Aharonian)
MPI für Kernphysik/Group of W. Hofmann/Experimental High-Energy Astrophysics (M. Panter, G. Hermann)
External Affiliations:Yerevan Physics Institute, Armenia
University of Durham, Department of Physics, UK
Centre d'Etudes Spatiales des Rayonnements, CNRS/UPS Toulouse, France
Universität Hamburg, Institut für Experimentalphysik, Germany
Physique Corpusculaire et Cosmologie, IN2P3/CNRS, Collège de France, Paris, France
Institut für Physik, Humboldt-Universität zu Berlin, Germany
LUTH, UMR 8102 du CNRS, Observatoire de Paris, Section de Meudon, France
Groupe d'astroparticules de Montpellier, IN2P3/CNRS, Université Montpellier II, France
Laboratoire de Physique Nucléaire et de Hautes Energies, IN2P3/CNRS, Universités Paris VI & VII, France
European Associated Laboratory for Gamma-Ray Astronomy, jointly supported by CNRS and MPG
Laboratoire Leprince-Ringuet, IN2P3/CNRS, Ecole Polytechnique, Palaiseau, France
Dublin Institute for Advanced Studies, Ireland
Service d'Astrophysique. DAPNIA/DSM/CEA, CE Saclay, Gif-sur-Yvette, France
Landessternwarte, Königstuhl, Heidelberg, Germany
Laboratoire d'Astrophysique de Grenoble, INSU/CNRS, Université Joseph Fourier, France
Unit for Space Physics, North-West University, Potchefstroom, South Africa
Institut für theoretische Physik, Lehrstuhl IV, Ruhr-Universität Bochum, Germany
Institute of Particle and Nuclear Physics, Charles University, Prague, Czech Republic
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