Please use this identifier to cite or link to this item: http://hdl.handle.net/2381/11153
Title: HESS 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.
Bernlohr, K.
Bolz, O.
Boisson, C.
Borgmeier, C.
Breitling, F.
Brown, A. M.
Gordo, J. B.
Chadwick, P. M.
Chitnis, V. R.
Chounet, L. M.
Cornils, R.
Costamante, L.
Degrange, B.
Djannati-Atai, A. D.
Drury, L. O.
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.
Khelifi, B.
Komin, N.
Konopelko, A.
Latham, IJ.
Le Gallou R.
Lemoine, M.
Lemiere, 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.
Puhlhofer, G.
Punch, M.
Raubenheimer, B. C.
Raue, M.
Raux, J.
Rayner, S. M.
RedondoO, I.
Reimer, A.
Reimer, O.
Ripken, J.
Rivoal, M.
Rob, L.
Rolland, L.
Rowell, G.
Sahakian, V.
Sauge, L.
Schlenker, S.
Schlickeiser, R.
Schuster, C.
Schwanke, U.
Siewert, M.
Sol, H.
Steenkamp, R.
Stegmann, C.
Tavernet, J. P.
Theoret, C. G.
Tluczykont, M.
van der Walt D. J.
Vasileiadis, G.
Vincent, P.
Visser, B.
Volk, H. J.
Wagner, S. J.
First Published: Feb-2005
Publisher: EDP Sciences for European Southern Observatory (ESO)
Citation: Astronomy & Astrophysics, 2005, 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 (~45 $\sigma$) 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 $\Gamma=3.32\pm0.06$. An improved $\chi^2$ 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 $\sigma$). 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.
DOI Link: 10.1051/0004-6361:20041853
ISSN: 0004-6361
Links: http://hdl.handle.net/2381/11153
http://www.aanda.org/articles/aa/abs/2005/06/aa1853/aa1853.html
Version: Publisher Version
Status: Peer-reviewed
Type: Journal Article
Rights: Copyright © 2005 ESO. Reproduced with permission from Astronomy & Astrophysics, © ESO.
Appears in Collections:Published Articles, Dept. of Physics and Astronomy

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