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Simultaneous observations of PKS 2155-304 with H.E.S.S., Fermi, RXTE and ATOM: spectral energy distributions and variability in a low state

F. Aharonian A.G. Akhperjanian G. Anton U. Barres de Almeida A.R. Bazer-Bachi 1 Y. Becherini 2 B. Behera K. Bernl¨ohr C. Boisson 3 A. Bochow V. Borrel 1 E. Brion 4 J. Brucker P. Brun 4 R. B¨uhler T. Bulik I. B¨usching T. Boutelier 5 P.M. Chadwick 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 5 J. Dyks M. Dyrda K. Egberts D. Emmanoulopoulos P. Espigat 2 C. Farnier 10 F. Feinstein 10 A. Fiasson 10 A. F¨orster G. Fontaine 7 M. F¨usling S. Gabici Y.A. Gallant 10 L. Gérard 2, * B. Giebels 7 B. J.F. Glicenstein 4 B. Gl¨uck P. Goret 4 D. G¨ohring D. Hauser M. Hauser S. Heinz G. Heinzelmann G. Henri 5 G. Hermann J.A. Hinton A. Hoffmann W. Hofmann M. Holleran S. Hoppe D. Horns A. Jacholkowska 6 O.C. de Jager C. Jahn I. Jung K. Katarzy'Nski U. Katz S. Kaufmann E. Kendziorra M. Kerschhaggl D. Khangulyan B. Kh'Elifi 7 D. Keogh W. Klu'Zniak Nu. Komin 4 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 D. Maurin 6 T.J.L. Mccomb M.C. Medina 3 R. Moderski Emmanuel Moulin 4 M. Naumann-Godo 7 M. de Naurois 6 D. Nedbal D. Nekrassov J. Niemiec S.J. Nolan S. Ohm J.-F. Olive 1 E. de O˜na K.J. Orford M. Ostrowski M. Panter M. Paz Arribas G. Pedaletti G. Pelletier 5 P.-O. Petrucci 5 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 A J. Ruppel V. Sahakian A. Santangelo R. Schlickeiser F.M. Sch¨ock R. Schr¨oder U. Schwanke S. Schwarzburg S. Schwemmer A. Shalchi J.L. Skilton H. Sol 3 D. Spangler L. Stawarz R. Steenkamp C. Stegmann G. Superina 7 A. Szostek 5 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 4 H.J. V¨olk F. Volpe 7 S.J. Wagner M. Ward A.A. Zdziarski A. Zech 3 A. A. Abdo Markus Ackermann Marco Ajello W. B. Atwood Magnus Axelsson Luca Baldini Jean Ballet 11 Guido Barbiellini D. Bastieri M. Battelino B. M. Baughman K. Bechtol R. Bellazzini B. Berenji E. D. Bloom E. Bonamente A. W. Borgland J. Bregeon A. Brez M. Brigida Pascal Bruel 7 G. A. Caliandro R. A. Cameron P. A. Caraveo J. M. Casandjian 11 E. Cavazzuti C. Cecchi E. Charles A. Chekhtman A. W. Chen C. C. Cheung J. Chiang S. Ciprini R. Claus J. Cohen-Tanugi 10 J. Conrad L. Costamante S. Cutini C. D. Dermer A. de Angelis F. de Palma S. W. Digel E. Do Couto E Silva P. S. Drell R. Dubois D. Dumora 12 C. Favuzzi S. J. Fegan 7 E. C. Ferrara P. Fleury 7 W. B. Focke M. Frailis Y. Fukazawa S. Funk P. Fusco F. Gargano D. Gasparrini N. Gehrels S. Germani N. Giglietto F. Giordano M.-H. Grondin 12 J. E. Grove L. Guillemot 12 S. Guiriec 10 Y. Hanabata A. K. Harding M. Hayashida E. Hays D. Horan 7 G. J'Ohannesson A. S. Johnson R. P. Johnson W. N. Johnson M. Kadler T. Kamae H. Katagiri J. Kataoka M. Kerr J. Kn¨odlseder 1 F. Kuehn M. Kuss J. Lande L. Latronico S.-H. Lee M. Lemoine-Goumard 12 F. Longo F. Loparco B. Lott 12 M. N. Lovellette G. M. Madejski A. Makeev M. N. Mazziotta J. E. Mcenery C. Meurer P. F. Michelson W. Mitthumsiri T. Mizuno A. A. Moiseev C. Monte M. E. Monzani A. Morselli I. V. Moskalenko S. Murgia P. L. Nolan E. Nuss 10 T. Ohsugi N. Omodei E. Orlando J. F. Ormes D. Paneque J. H. Panetta B D. Parent 12 V. Pelassa 10 M. Pepe M. Pesce-Rollins F. Piron 10 T.A. Porter S. Rain'O M. Razzano A. Reimer O. Reimer T. Reposeur 12 S. Ritz A. Y. Rodriguez F. Ryde H. F.-W. Sadrozinski D. Sanchez 7 A. Sander J. D. Scargle T. L. Schalk A. Sellerholm C. Sgr'O M. Shaw David Stanley Smith 12 G. Spandre P. Spinelli Jean-Luc Starck 11 M. S. Strickman H. Tajima H. Takahashi T. Takahashi T. Tanaka J. G. Thayer D. J. Thompson L. Tibaldo D. F. Torres G. Tosti A. Tramacere Y. Uchiyama T. L. Usher N. Vilchez 1 M. Villata V. Vitale A. P. Waite K. S. Wood T. Ylinen
Abstract : We report on the first simultaneous observations that cover the optical, X-ray, and high energy gamma-ray bands of the BL Lac object PKS 2155-304. The gamma-ray bands were observed for 11 days, between 25 August and 6 September 2008, jointly with the Fermi Gamma-ray Space Telescope and the H.E.S.S. atmospheric Cherenkov array, providing the first simultaneous MeV-TeV spectral energy distribution with the new generation of gamma-ray telescopes. The ATOM telescope and the RXTE and Swift observatories provided optical and X-ray coverage of the low-energy component over the same time period. The object was close to the lowest archival X-ray and Very High Energy state, whereas the optical flux was much higher. The light curves show relatively little (~30%$) variability overall when compared to past flaring episodes, but we find a clear optical/VHE correlation and evidence for a correlation of the X-rays with the high energy spectral index. Contrary to previous observations in the flaring state, we do not find any correlation between the X-ray and VHE components. Although synchrotron self-Compton models are often invoked to explain the SEDs of BL Lac objects, the most common versions of these models are at odds with the correlated variability we find in the various bands for PKS 2155-304.
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Submitted on : Friday, April 24, 2009 - 11:07:24 AM
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F. Aharonian, A.G. Akhperjanian, G. Anton, U. Barres de Almeida, A.R. Bazer-Bachi, et al.. Simultaneous observations of PKS 2155-304 with H.E.S.S., Fermi, RXTE and ATOM: spectral energy distributions and variability in a low state. Astrophysical Journal Letters, IOP Science, 2009, 696, pp.L150-L155. ⟨10.1088/0004-637X/696/2/L150⟩. ⟨in2p3-00378403⟩

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