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Multi-wavelength observations of PKS 2155-304 with HESS.

Aharonian, F. and Akhperjanian, A. G. and Bazer-Bachi, A. R. and Beilicke, M. and Benbow, W. and Berge, D. and Bernlohr, K. and Boisson, C. and Bolz, O. and Borrel, V. and Braun, I. and Breitling, F. and Brown, A. M. and Chadwick, P. M. and Chounet, L. M. and Cornils, R. and Costamante, L. and Degrange, B. and Dickinson, H. J. and Djannati-Atai, A. and Drury, L. O. and Dubus, G and Emmanoulopoulos, D. and Espigat, P. and Feinstein, F. and Fontaine, G. and Fuchs, Y. and Funk, S. and Gallant, Y. A. and Giebels, B. and Gillessen, S. and Glicenstein, J. F. and Goret, P. 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 Jacholkowska, A. and de Jager, O. C. and Khelifi, B. and Komin, N. and Konopelko, A. and Latham, I. J. and Le Gallou, R. and Lemiere, A. and Lemoine-Goumard, M. and Leroy, N. and Lohse, T. and Martin, J. M. and Martineau-Huynh, O. 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 Puhlhofer, G. and Punch, M. and Raubenheimer, B. C. and Raue, M. and Raux, J. and Rayner, S. M. and Reimer, A. and Reimer, O. and Ripken, J. and Rob, L. and Rolland, L. and Rowell, G. and Sahakian, V. and Sauge, L. and Schlenker, S. and Schlickeiser, R. and Schuster, C. and Schwanke, U. and Siewert, M. and Sol, H. and Spangler, D. and Steenkamp, R. and Stegmann, C. and Tavernet, J. P. and Terrier, R. and Theoret, C. G. and Tluczykont, M. and Vasileiadis, G. and Venter, C. and Vincent, P. and Volk, H. J. and Wagner, S. J. (2005) 'Multi-wavelength observations of PKS 2155-304 with HESS.', Astronomy & astrophysics., 442 (3). pp. 895-907.


The High Energy Stereoscopic System (HESS) has observed the high-frequency peaked BL Lac object PKS 2155- 304 in 2003 between October 19 and November 26 in Very High Energy (VHE) gamma-rays (E >= 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. A transient X-ray event with a 1500 s timescale is detected, making this the fastest X-ray flare seen in this object. No correlation can be established between the X-ray and the gamma-ray fluxes, or any of the other wavebands, over the small range of observed variability. The average HESS spectrum shows a very soft power law shape with a photon index of 3.37 +/- 0.07(stat) +/- 0.10(sys). 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 PKS 2155- 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. These parameters are found to be sensitive to the model of Extragalactic Background Light (EBL) that attenuates the VHE signal at this source's redshift (z = 0.117).

Item Type:Article
Keywords:Active galaxies, Energy gamma Rays, Observations, X-rays, Radiation mechanisms, Non thermal, BL-LAC objects, Atmospheric Cherenkov telescopes, Synchrotron-proton blazar, Active galactic nuclei, Simultaneous x-ray, Tev blazars, Spectral variability.
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Publisher statement:Reproduced with permission from Astronomy & Astrophysics, © ESO
Date accepted:No date available
Date deposited:29 May 2008
Date of first online publication:November 2005
Date first made open access:No date available

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