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Astronomy and Astrophysics 442 (2005) 895-907
Multi-wavelength observations of PKS 2155-304 with H.E.S.S
F. Aharonian, A. G. Akhperjanian, A. R. Bazer-Bachi, M. Beilicke, W. Benbow, D. Berge, K. Bernlöhr, C. Boisson, O. Bolz, V. Borrel, I. Braun, F. Breitling, A. M. Brown, P. M. Chadwick, L.-M. Chounet1, R. Cornils, L. Costamante, B. Degrange1, H. J. Dickinson, A. Djannati-Ataï2, Drury L. O'C., G. Dubus1, D. Emmanoulopoulos, P. Espigat2, F. Feinstein3, G. Fontaine1, Y. Fuchs, S. Funk, Y. A. Gallant3, B. Giebels1, S. Gillessen, J. F. Glicenstein, P. Goret, C. Hadjichristidis, M. Hauser, G. Heinzelmann, G. Henri, G. Hermann, J. A. Hinton, W. Hofmann, M. Holleran, D. Horns, A. Jacholkowska3, O. C. Jager De, B. Khélifi, Nu. Komin, A. Konopelko, I. J. Latham, R. Gallou Le, A. Lemière2, M. Lemoine-Goumard1, N. Leroy1, T. Lohse, J. M. Martin, O. Martineau-Huynh4, A. Marcowith, C. Masterson, T. J. L. Mccomb, M. Naurois De4, S. J. Nolan, A. Noutsos, K. J. Orford, J. L. Osborne, M. Ouchrif4, M. Panter, G. Pelletier, S. Pita, G. Pühlhofer, M. Punch2, B. C. Raubenheimer, M. Raue, J. Raux4, S. M. Rayner, A. Reimer, O. Reimer, J. Ripken, L. Rob, L. Rolland4, G. Rowell, V. Sahakian, L. Saugé, S. Schlenker, R. Schlickeiser, C. Schuster, U. Schwanke, M. Siewert, H. Sol, D. Spangler, R. Steenkamp, C. Stegmann, J.-P. Tavernet4, R. Terrier2, C.G. Théoret2, M. Tluczykont1, G. Vasileiadis3, C. Venter, P. Vincent4, H. J. Völk, S. J. Wagner
HESS Collaboration(s)

The High Energy Stereoscopic System (H.E.S.S.) has observed the high-frequency peaked BL Lac object PKS2155-304 in 2003 between October 19 and November 26 in Very High Energy (VHE) $\gamma$-rays (E $\geq$ 160 GeV for these observations). Observations were carried out simultaneously with the Proportional Counter Array (PCA) on board the Rossi X-ray Timing Explorer satellite (RXTE), the Robotic Optical Transient Search Experiment (ROTSE) and the Nancay decimetric radiotelescope (NRT). Intra-night variability is seen in the VHE band, the source being detected with a high significance on each night it was observed. Variability is also found in the X-ray and optical bands on kilosecond timescales, along with flux-dependent spectral changes in the X-rays. The average H.E.S.S. spectrum shows a very soft power law shape with a photon index of 3.37 $\pm$ 0.07${stat} \pm 0.10 {syst}. The energy outputs in the 2-10 keV and in the VHE gamma-ray range are found to be similar, with the X-rays and the optical fluxes at a level comparable to some of the lowest historical measurements, indicating that PKS2155-304 was in a low or quiescent state during the observations. Both a leptonic and a hadronic model are used to derive source parameters from these observations.
1 :  LLR - Laboratoire Leprince-Ringuet
2 :  APC - UMR 7164 - AstroParticule et Cosmologie
3 :  LPTA - Laboratoire de Physique Théorique et Astroparticules
4 :  LPNHE - Laboratoire de Physique Nucléaire et de Hautes Énergies
Physique/Astrophysique/Cosmologie et astrophysique extra-galactique

Planète et Univers/Astrophysique
BL Lacertae objects: Individual: PKS 2155-304 – galaxie: active – gamma rays: observations – X-rays:galaxies – radiation mechanisms: non thermal
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