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. Chounet (1) , R. Cornils , L. Costamante , B. Degrange (1) , H. J. Dickinson , A. Djannati-Ataï (2) , Drury L. O'C. , G. Dubus (1) , D. Emmanoulopoulos , P. Espigat (2) , F. Feinstein (3) , G. Fontaine (1) , Y. Fuchs , S. Funk , Y.A. Gallant (3) , B. Giebels (1) , 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. Jacholkowska (3) , O. C. Jager De , B. Khélifi , Nu. Komin , A. Konopelko , I. J. Latham , R. Gallou Le , A. Lemière (2) , M. Lemoine-Goumard (1) , N. Leroy (1) , T. Lohse , J. M. Martin , O. Martineau-Huynh (4) , A. Marcowith , C. Masterson , T. J. L. Mccomb , M. Naurois De (4) , S. J. Nolan , A. Noutsos , K. J. Orford , J. L. Osborne , M. Ouchrif (4) , M. Panter , G. Pelletier , S. Pita , G. Pühlhofer , M. Punch (2) , B. C. Raubenheimer , M. Raue , J. Raux (4) , S. M. Rayner , A. Reimer , O. Reimer , J. Ripken , L. Rob , L. Rolland (4) , 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. Tavernet (4) , R. Terrier (2) , C.G. Théoret (2) , M. Tluczykont (1) , G. Vasileiadis (3) , C. Venter , P. Vincent (4) , H. J. Völk , S. J. Wagner

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

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.

Mots clés: BL Lacertae objects: Individual: PKS 2155-304; galaxie: active; gamma rays: observations; X-rays:galaxies; radiation mechanisms: non thermal

Domaines: Cosmologie et astrophysique extra-galactique [astro-ph.CO]; Astrophysique [astro-ph]

F. Aharonian, A. G. Akhperjanian, A. R. Bazer-Bachi, M. Beilicke, W. Benbow, et al.. Multi-wavelength observations of PKS 2155-304 with H.E.S.S. Astronomy and Astrophysics - A&A, 2005, 442, pp.895-907. ⟨10.1051/0004-6361:20053353⟩. ⟨in2p3-00024349⟩