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Long-term monitoring of PKS 2155−304 with ATOM and H.E.S.S. : investigation of optical/γ-ray correlations in different spectral states.

H.E.S.S.Collaboration, and Abramowski, A. and Aharonian, F. and Ait Benkhali, F. and Akhperjanian, A.G. and Angüner, E.O. and Backes, M. and Balenderan, S. and Balzer, A. and Barnacka, A. and Becherini, Y. and Becker Tjus, J. and Berge, D. and Bernhard, S. and Bernlöhr, K. and Birsin, E. and Biteau, J. and Böttcher, M. and Boisson, C. and Bolmont, J. and Bordas, P. and Bregeon, J. and Brun, F. and Brun, P. and Bryan, M. and Bulik, T. and Carrigan, S. and Casanova, S. and Chadwick, P. M. and Chakraborty, N. and Chalme-Calvet, R. and Chaves, R.C.G. and Chrétien, M. and Colafrancesco, S. and Cologna, G. and Conrad, J. and Couturier, C. and Cui, Y. and Dalton, M. and Davids, I.D. and Degrange, B. and Deil, C. and deWilt, P. and Djannati-Ataï, A. and Domainko, W. and Donath, A. and Drury, L. O'C. and Dubus, G. and Dutson, K. and Dyks, J. and Dyrda, M. and Edwards, T. and Egberts, K. and Eger, P. and Espigat, P. and Farnier, C. and Fegan, S. and Feinstein, F. and Fernandes, M.V. and Fernandez, D. and Fiasson, A. and Fontaine, G. and Förster, A. and Füßling, M. and Gabici, S. and Gajdus, M. and Gallant, Y.A. and Garrigoux, T. and Giavitto, G. and Giebels, B. and Glicenstein, J.F. and Gottschall, D. and Grondin, M.-H. and Grudzińska, M. and Hadsch, D. and Häffner, S. and Hahn, J. and Harris, J. and Heinzelmann, G. and Henri, G. and Hermann, G. and Hervet, O. and Hillert, A. and Hinton, J.A. and Hofmann, W. and Hofverberg, P. and Holler, M. and Horns, D. and Ivascenko, A. and Jacholkowska, A. and Jahn, C. and Jamrozy, M. and Janiak, M. and Jankowsky, F. and Jung, I. and Kastendieck, M.A. and Katarzyński, K. and Katz, U. and Kaufmann, S. and Khélifi, B. and Kieffer, M. and Klepser, S. and Klochkov, D. and Kluźniak, W. and Kolitzus, D. and Komin, Nu. and Kosack, K. and Krakau, S. and Krayzel, F. and Krüger, P.P. and Laffon, H. and Lamanna, G. and Lefaucheur, J. and Lefranc, V. and Lemière, A. and Lemoine-Goumard, M. and Lenain, J.-P. and Lohse, T. and Lopatin, A. and Lu, C.-C. and Marandon, V. and Marcowith, A. and Marx, R. and Maurin, G. and Maxted, N. and Mayer, M. and McComb, T.J.L. and Méhault, J. and Meintjes, P.J. and Menzler, U. and Meyer, M. and Mitchell, A.M.W. and Moderski, R. and Mohamed, M. and Morå, K. and Moulin, E. and Murach, T. and de Naurois, M. and Niemiec, J. and Nolan, S. J. and Oakes, L. and Odaka, H. and Ohm, S. and Opitz, B. and Ostrowski, M. and Oya, I. and Panter, M. and Parsons, R.D. and Paz Arribas, M. and Pekeur, N.W. and Pelletier, G. and Perez, J. and Petrucci, P.-O. and Peyaud, B. and Pita, S. and Poon, H. and Pühlhofer, G. and Punch, M. and Quirrenbach, A. and Raab, S. and Reichardt, I. and Reimer, A. and Reimer, O. and Renaud, M. and de los Reyes, R. and Rieger, F. and Rob, L. and Romoli, C. and Rosier-Lees, S. and Rowell, G. and Rudak, B. and Rulten, C.B. and Sahakian, V. and Salek, D. and Sanchez, D. A. and Santangelo, A. and Schlickeiser, R. and Schüssler, F. and Schulz, A. and Schwanke, U. and Schwarzburg, S. and Schwemmer, S. and Sol, H. and Spanier, F. and Spengler, G. and Spies, F. and Stawarz, Ł. and Steenkamp, R. and Stegmann, C. and Stinzing, F. and Stycz, K. and Sushch, I. and Tavernet, J.-P. and Tavernier, T. and Taylor, A.M. and Terrier, R. and Tluczykont, M. and Trichard, C. and Valerius, K. and van Eldik, C. and van Soelen, B. and Vasileiadis, G. and Veh, J. and Venter, C. and Viana, A. and Vincent, P. and Vink, J. and Völk, H.J. and Volpe, F. and Vorster, M. and Vuillaume, T. and Wagner, S.J. and Wagner, P. and Wagner, R.M. and Ward, M. and Weidinger, M. and Weitzel, Q. and White, R. and Wierzcholska, A. and Willmann, P. and Wörnlein, A. and Wouters, D. and Yang, R. and Zabalza, V. and Zaborov, D. and Zacharias, M. and Zdziarski, A.A. and Zech, A. and Zechlin, H.-S. (2014) 'Long-term monitoring of PKS 2155−304 with ATOM and H.E.S.S. : investigation of optical/γ-ray correlations in different spectral states.', Astronomy & astrophysics., 571 . A39.

Abstract

In this paper we report on the analysis of all the available optical and very high-energy γ-ray (>200 GeV) data for the BL Lac object PKS 2155−304, collected simultaneously with the ATOM and H.E.S.S. telescopes from 2007 until 2009. This study also includes X-ray (RXTE, Swift) and high-energy γ-ray (Fermi-LAT) data. During the period analysed, the source was transitioning from its flaring to quiescent optical states, and was characterized by only moderate flux changes at different wavelengths on the timescales of days and months. A flattening of the optical continuum with an increasing optical flux can be noted in the collected dataset, but only occasionally and only at higher flux levels. We did not find any universal relation between the very high-energy γ-ray and optical flux changes on the timescales from days and weeks up to several years. On the other hand, we noted that at higher flux levels the source can follow two distinct tracks in the optical flux–colour diagrams, which seem to be related to distinct γ-ray states of the blazar. The obtained results therefore indicate a complex scaling between the optical and γ-ray emission of PKS 2155−304, with different correlation patterns holding at different epochs, and a γ-ray flux depending on the combination of an optical flux and colour rather than a flux alone.

Item Type:Article
Keywords:Radiation mechanisms: non-thermal, Galaxies: active, Black hole physics, BL Lacertae objects: individual: PKS 2155-304, Galaxies: jets, Gamma rays: galaxies.
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Status:Peer-reviewed
Publisher Web site:http://dx.doi.org/10.1051/0004-6361/201424142
Publisher statement:Reproduced with permission from Astronomy & Astrophysics, © ESO, 2014.
Date accepted:10 July 2014
Date deposited:21 April 2015
Date of first online publication:November 2014
Date first made open access:No date available

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