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Simultaneous multiwavelength observations of the second exceptional gamma-ray flare of PKS 2155-304 in July 2006

F. Aharonian A.G. Akhperjanian G. Anton U. Barres de Almeida A.R. Bazer-Bachi 1 Y. Becherini 2 B. Behera K. Bernlöhr A. Bochow C. Boisson 3 V. Borrel 1 T. Boutelier 4 I. Braun E. Brion 5 J. Brucker P. Brun 5 R. Bühler T. Bulik I. Büsching P.M. Chadwicks A. Charbonnier 6 R.C.G. Chaves A. Cheesebrough L.-M. Chounet 7 A.C. Clapson G. Coignet 8 M. Dalton M.K. Daniel I.D. Davids B. Degrange 7 C. Deil H.J. Dickinson A. Djannati-Ataï 9 W. Domainko L.O'C. Drury F. Dubois 8 G. Dubus 4 J. Dyks M. Dyrda K. Egberts D. Emmanoulopoulos P. Espigat 2 C. Farnier 10 F. Feinstein 10 A. Fiasson 10 A. Förster G. Fontaine 7 M. Füßling S. Gabici Y.A. Gallant 10 L. Gérard 2 B. Giebels 7 J.F. Glicenstein 5 B. Glück P. Goret 5 D. Hauser M. Hauser S. Heinz G. Heinzelmann G. Henri 4 G. Hermann J.A. Hinton A. Hoffmann W. Hofmann M. Holleran S. Hoppe D. Horns A. Jacholkowska 6 O.C. de Jager I. Jung K. Katarzynski U. Katz E. Kendziorra M. Kerschhagg D. Khangulyan B. Khélifi 7 D. Keogh Nu. Komin 5 K. Kosack G. Lamanna 8 J.-P. Lenain 3 T. Lohse V. Marandon 2 J.M. Martin 3 O. Martineau-Huynh 6 A. Marcowith 10 C. Masterson D. Maurin 6 T.J.L. Mccomb M.C. Medina 3 R. Moderski Emmanuel Moulin 5 M. Naumann-Godo 7 M. de Naurois 6 D. Nedbal D. Nekrassov J. Niemiec S.J. Nolan S. Ohm J.-P. Olive 1 E. de Ona Wilhelmi 2 K.J. Orford M. Ostrowski M. Panter M. Paz Arribas G. Pedaletti G. Pelletier 4 P.-O. Petrucci 4 S. Pita 2 G. P¨uhlhofer M. Punch 2 A. Quirrenbach B.C. Raubenheimer M. Raue S.M. Rayner M. Renaud 2 F. Rieger J. Ripken L. Rob S. Rosier-Lees 8 G. Rowell B. Rudak C.B. Rulten J. Ruppel V. Sahakian A. Santangelo R. Schlickeiser F. Schock R. Schroder U. Schwanke S. Schwarzburg S. Schwemmer A. Shalchi J.L. Skilton H. Sol 3 D. Spangler Ł. Stawarz R. Steenkamp C. Stegmann G. Superina 7 A. Szostek 4 P.H. Tam J.-P. Tavernet 6 R. Terrier 2 O. Tibolla C. van Eldik G. Vasileiadis 10 C. Venter L. Venter 3 J.P. Vialle 8 P. Vincent 6 M. Vivier 5 H.J. Volk F. Volpe 7 S.J. Wagner M. Ward A.A. Zdziarski A. Zech
Abstract : Simultaneous HESS/CHANDRA/optical observations were performed on the BL Lac object PKS 2155-304 in the night of July 29-30 2006, when the source underwent its second major gamma-ray outburst in Summer 2006. This event took place about 44 hours after the July 28 outburst, known for its ultrafast variability. An unprecedented 6 to 8 hours of uninterrupted coverage was achieved, with spectra and light curves measured down to 7 and 2-minute timescales, respectively. The gamma-ray flux reached a maximum of 11x the Crab flux (>400 GeV), with rise/decay timescales of ~1 hour, plus a few smaller-amplitude flares superimposed on the decaying phase. The emission in the X-ray and VHE bands is strongly correlated, both in flux and spectrum, with no evidence of lags. The VHE spectrum shows a curvature that is variable with time and stronger at higher fluxes. The huge VHE variations (22x) are only accompanied by small-amplitude X-ray and optical variations (factor 2 and 15% respectively). The source has shown for the first time in an HBL a large Compton dominance (L_C/L_S ~10) -- rapidly evolving -- and a cubic relation between VHE and X-ray flux variations, during a decaying phase. These results challenge the common scenarios for the TeV-blazar emission.
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Submitted on : Friday, August 21, 2009 - 4:42:04 PM
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F. Aharonian, A.G. Akhperjanian, G. Anton, U. Barres de Almeida, A.R. Bazer-Bachi, et al.. Simultaneous multiwavelength observations of the second exceptional gamma-ray flare of PKS 2155-304 in July 2006. Astronomy and Astrophysics - A&A, EDP Sciences, 2009, 502, pp.749-770. ⟨10.1051/0004-6361/200912128⟩. ⟨in2p3-00410643⟩



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