Please use this identifier to cite or link to this item: http://hdl.handle.net/2381/19058
Title: VHE gamma-ray emission of PKS 2155-304: spectral and temporal variability
Authors: Abramowski, A.
Acero, F.
Aharonian, F.
Akhperjanian, A. G.
Anton, G.
de Almeida UB
Bazer-Bachi, A. R.
Becherini, Y.
Behera, B.
Benbow, W.
Bernloehr, K.
Terrier, R.
Tibolla, O.
Tluczykont, M.
Brun, P.
Chadwick, P. M.
Valerius, K.
Kossakowski, R.
Chaves, R. C. G.
Klochkov, D.
Cheesebrough, A.
Kaufmann, S.
Chounet, L. -. M.
Clapson, A. C.
Coignet, G.
Conrad, J.
Costamante, L.
Dalton, M.
Daniel, M. K.
Masbou, J.
Lamanna, G.
Kluzniak, W.
Kerschhaggl, M.
Davids, I. D.
Degrange, B.
Deil, C.
Dickinson, H. J.
Djannati-Atai, A.
Domainko, W.
Drury, L. O.
Dubois, F.
Dubus, G.
Dyks, J.
Khangulyan, D.
Kneiske, T.
Lenain, J. -. P.
Maurin, D.
Dyrda, M.
Egberts, K.
Eger, P.
Espigat, P.
Fallon, L.
Farnier, C.
Fegan, S.
Khelifi, B.
Feinstein, F.
Komin, N.
Fernandes, M. V.
Lohse, T.
Fiasson, A.
McComb, T. J. L.
Foerster, A.
Fontaine, G.
Fuessling, M.
Gabici, S.
de Naurois M
Gallant, Y. A.
Gerard, L.
Moulin, E.
Gerbig, D.
Giebels, B.
Lu, C. -. C.
Glicenstein, J. F.
Glueck, B.
Medina, M. C.
Goret, P.
Keogh, D.
Goering, D.
Hampf, D.
Hauser, M.
Kosack, K.
Heinz, S.
Heinzelmann, G.
Henri, G.
Marandon, V.
Hermann, G.
Hinton, J. A.
Vorobiov, S.
Hoffmann, A.
Mehault, J.
Hofmann, W.
Hofverberg, P.
Bochow, A.
Holleran, M.
Hoppe, S.
Horns, D.
Jacholkowska, A.
Naumann-Godo, M.
Nekrassov, D.
de Jager OC
Jahn, C.
Jung, I.
Katarzynski, K.
Moderski, R.
Nedbal, D.
Katz, U.
Viana, A.
Nguyen, N.
van Eldik C
Nicholas, B.
Niemiec, J.
Nolan, S. J.
Ohm, S.
Olive, J. -. F.
Wilhelmi, E. D. O.
Opitz, B.
Boisson, C.
Wagner, S. J.
Vincent, P.
Vasileiadis, G.
Orford, K. J.
Ostrowski, M.
Panter, M.
Arribas, M. P.
Pedaletti, G.
Pelletier, G.
Petrucci, P. -. O.
Pita, S.
Puehlhofer, G.
Punch, M.
Venter, C.
Vivier, M.
Ward, M.
Bolmont, J.
Quirrenbach, A.
Raubenheimer, B. C.
Raue, M.
Rayner, S. M.
Reimer, O.
Renaud, M.
de los Reyes R
Venter, L.
Rieger, F.
Voelk, H. J.
Ripken, J.
Zdziarski, A. A.
Rob, L.
Borrel, V.
Rosier-Lees, S.
Rowell, G.
Rudak, B.
Rulten, C. B.
Buesching, I.
Ruppel, J.
Ryde, F.
Buehler, R.
Sahakian, V.
Santangelo, A.
Zech, A.
Schlickeiser, R.
Schoeck, F. M.
Brucker, J.
Schoenwald, A.
Vialle, J. P.
Schwanke, U.
Schwarzburg, S.
Schwemmer, S.
Volpe, F.
Shalchi, A.
Sushch, I.
Sikora, M.
Zechlin, H. -. S.
Skilton, J. L.
Sol, H.
Marcowith, A.
Stawarz, L.
Brun, F.
Steenkamp, R.
Stegmann, C.
Boutelier, T.
Stinzing, F.
Superina, G.
Szostek, A.
Tam, P. H.
Bulik, T.
Charbonnier, A.
Tavernet, J. -. P.
First Published: 1-Sep-2010
Publisher: EDP Sciences for European Southern Observatory (ESO)
Citation: Astronomy & Astrophysics, 2010, 520
Abstract: Context. Observations of very high-energy γ-rays from blazars provide information about acceleration mechanisms occurring in their innermost regions. Studies of variability in these objects lead to a better understanding of the mechanisms in play. Aims. To investigate the spectral and temporal variability of VHE (>100 GeV) γ-rays of the well-known high-frequency-peaked BL Lac object PKS 2155–304 with the HESS imaging atmospheric Cherenkov telescopes over a wide range of flux states. Methods. Data collected from 2005 to 2007 were analyzed. Spectra were derived on time scales ranging from 3 years to 4 min. Light curve variability was studied through doubling timescales and structure functions and compared with red noise process simulations. Results. The source was found to be in a low state from 2005 to 2007, except for a set of exceptional flares that occurred in July 2006. The quiescent state of the source is characterized by an associated mean flux level of (4.32 ± 0.09stat ± 0.86syst) × 10-11 cm-2 s-1 above 200 GeV, or approximately of the Crab Nebula, and a power-law photon index of Γ = 3.53 ± 0.06stat ± 0.10syst. During the flares of July 2006, doubling timescales of ~2 min are found. The spectral index variation is examined over two orders of magnitude in flux, yielding different behavior at low and high fluxes, which is a new phenomenon in VHE γ-ray emitting blazars. The variability amplitude characterized by the fractional rms Fvar is strongly energy-dependent and is . The light curve rms correlates with the flux. This is the signature of a multiplicative process that can be accounted for as a red noise with a Fourier index of ~2. Conclusions. This unique data set shows evidence of a low-level γ-ray emission state from PKS 2155–304 that possibly has a different origin than the outbursts. The discovery of the light curve lognormal behavior might be an indicator of the origin of aperiodic variability in blazars.
DOI Link: 10.1051/0004-6361/201014484
ISSN: 0004-6361
Links: http://hdl.handle.net/2381/19058
http://www.aanda.org/articles/aa/abs/2010/12/aa14484-10/aa14484-10.html
Version: Publisher Version
Status: Peer-reviewed
Type: Journal Article
Rights: Copyright © 2010 ESO. Reproduced with permission from Astronomy & Astrophysics, © ESO.
Appears in Collections:Published Articles, Dept. of Physics and Astronomy

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