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Observations of PKS 2155-304 in gamma-rays with H.E.S.S., and interpretation with simultaneous multiwavelength data

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Aharonian,  F.
Division Prof. Dr. Werner Hofmann, MPI for Nuclear Physics, Max Planck Society;

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Benbow,  W.
Division Prof. Dr. Werner Hofmann, MPI for Nuclear Physics, Max Planck Society;

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Costamante,  L.
Division Prof. Dr. Werner Hofmann, MPI for Nuclear Physics, Max Planck Society;

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Dubus,  G.
Division Prof. Dr. Werner Hofmann, MPI for Nuclear Physics, Max Planck Society;

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Horns,  D.
Division Prof. Dr. Werner Hofmann, MPI for Nuclear Physics, Max Planck Society;

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Pühlhofer,  Gerd
Division Prof. Dr. Werner Hofmann, MPI for Nuclear Physics, Max Planck Society;

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Citation

Fontaine, G., Aharonian, F., Benbow, W., Boisson, C., Costamante, L., Dubus, G., et al. (2005). Observations of PKS 2155-304 in gamma-rays with H.E.S.S., and interpretation with simultaneous multiwavelength data. In B. S. Acharya, S. Gupta, P. Jagadeesan, A. Jain, S. Karthikeyan, S. Morris, et al. (Eds.), Proceedings of the 29th International Cosmic Ray Conference (pp. 279-282). Navy Nagar, Colaba, Mumbai, MH-400005: Tata Institute of Fundamental Research.


Cite as: https://hdl.handle.net/11858/00-001M-0000-0011-87AB-A
Abstract
The high-frequency peaked BL Lac PKS 2155-304, at a redshift z = 0.117, has been detected with high significance at energies greater than 160 GeV, using the H.E.S.S. stereoscopic array of imaging atmospheric-Cherenkov telescopes in Namibia. A strong signal is found in each of the data sets corresponding to dark periods in 2002 & 2003. Energy spectra are measured for these individual periods of data taking and are characterized by a steep power law with a 2003 time-averaged photon index of Γ = 3.34 ± 0.05 (± 0.10 syst). In late 2003, observations of PKS 2155-304 were performed simultaneously with H.E.S.S., the PCA on board the RXTE satellite, the ROTSE optical telescope, and with the Nançay decimetric radiotelescope. Results from these data represent the first simultaneous detections over such a wide energy range, and establish that the source was in a low or quiescent state at that time. During this low state, 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. A broadband spectral energy distribution (SED) is obtained from these simultaneous multiwavelength observations, and is used to place constraints on emission model parameters, taking into account the effect of Extragalactic Background Light absorption. In contrast, preliminary results from a similar multiwavelength campaign in 2004 show a higher activity state, and suggest a correlation between the gamma-ray and the X-ray fluxes.