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H.E.S.S. observations of PKS 2155-304.

Aharonian, F and Akhperjanian, A. G. and Aye, K-M. and Bazer-Bachi, A. R. and Beilicke, M. and Benbow, W. and Berge, D. and Berghaus, P. and Bernlöhr, K. and Bolz, O. and Boisson, C. and Borgmeier, C. and Breitling, F. and Brown, A. M. and Bussons Gordo, J. and Chadwick, P. M. and Chitnis, V. R., V. R. and Chounet, L.-M. and Cornils, R. and Costamante, L. and Degrange, B. and Djannati-Ataï, A. and Drury, L. O'C. and Ergin, T. and Espigat, P. and Feinstein, F. and Fleury, P. and Fontaine, G. and Funk, S. and Gallant, Y. A. and Giebels, B. and Gillessen, S. and Goret, P. and Guy, J. and Hadjichristidis, C. and Hauser, M. and Heinzelmann, G. and Henri, G. and Hermann, G. and Hinton, J. A. and Hofmann, W. and Holleran, M. and Horns, D. and de Jager, O. C. and Jung, I. and Khélifi, B. and Komin, N. and Konopelko, A. and Latham, I. J. and Le Gallou, R. and Lemoine, M. and Lemière, A. and Leroy, N. and Lohse, T. and Marcowith, A. and Masterson, C. and McComb, T. J. L. and de Naurois, M. and Nolan, S. J. and Noutsos, A. and Orford, K. J. and Osborne, J. L. and Ouchrif, M. and Panter, M. and Pelletier, G. and Pita, S. and Pohl, M. and Pühlhofer, G. and Punch, M. and Raubenheimer, B. C. and Raue, M. and Raux, J. and Rayner, S. M. and Redondo, I. and Reimer, A. and Reimer, O. and Ripken, J. and Rivoal, M. and Rob, L. and Rolland, L. and Rowell, G. and Sahakian, V. and Saugé, L. and Schlenker, S. and Schlickeiser, R. and Schuster, C. and Schwanke, U. and Siewert, M. and Sol, H. and Steenkamp, R. and Stegmann, C. and Tavernet, J.-P. and Théoret, C. G. and Tluczykont, M. and van der Walt, D. J. and Vasileiadis, G. and Vincent, P. and Visser, B. and Völk, H. J. and Wagner, S. J. (2005) 'H.E.S.S. observations of PKS 2155-304.', Astronomy & astrophysics., 430 (3). pp. 865-875.

Abstract

The high-frequency peaked BL Lac PKS 2155-304 at redshift z=0.117 has been detected with high significance (~45sigma) 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 Gamma=3.32±0.06. An improved chi2 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 (~2sigma). 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

Item Type:Article
Keywords:Active galaxies, BL Lacertae objects, Gamma rays.
Full text:PDF - Published Version (295Kb)
Status:Peer-reviewed
Publisher Web site:http://dx.doi.org/10.1051/0004-6361:20041853
Record Created:29 May 2008
Last Modified:23 Jul 2014 22:18

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