VHE gamma-ray emission of PKS 2155-304: spectral and temporal variability
Creators: name: HESS Collaboration
name: Abramowski, A.
name: Acero, F.
name: Aharonian, F.
name: Akhperjanian, A. G.
name: Anton, G.
name: de Almeida, U. Barres
name: Bazer-Bachi, A. R.
name: Becherini, Y.
name: Behera, B.
name: Benbow, W.
name: Bernlohr, K.
name: Bochow, A.
name: Boisson, C.
name: Bolmont, J.
name: Borrel, V.
name: Brucker, J.
name: Brun, F.
name: Brun, P.
name: Buhler, R.
name: Bulik, T.
name: Busching, I.
name: Boutelier, T.
name: Chadwick, P. M.
name: Charbonnier, A.
name: Chaves, R. C. G.
name: Cheesebrough, A.
name: Conrad, J.
name: Chounet, L. -M.
name: Clapson, A. C.
name: Coignet, G.
name: Costamante, L.
name: Dalton, M.
name: Daniel, M. K.
name: Davids, I. D.
name: Degrange, B.
name: Deil, C.
name: Dickinson, H. J.
name: Djannati-Atai, A.
name: Domainko, W.
name: Drury, L. O'C.
name: Dubois, F.
name: Dubus, G.
name: Dyks, J.
name: Dyrda, M.
name: Egberts, K.
name: Eger, P.
name: Espigat, P.
name: Fallon, L.
name: Farnier, C.
name: Fegan, S.
name: Feinstein, F.
name: Fernandes, M. V.
name: Fiasson, A.
name: Foerster, A.
name: Fontaine, G.
name: Fussling, M.
name: Gabici, S.
name: Gallant, Y. A.
name: Gerard, L.
name: Gerbig, D.
name: Giebels, B.
name: Glicenstein, J. F.
name: Glueck, B.
name: Goret, P.
name: Goering, D.
name: Hampf, D.
name: Hauser, M.
name: Heinz, S.
name: Heinzelmann, G.
name: Henri, G.
name: Hermann, G.
name: Hinton, J. A.
name: Hoffmann, A.
name: Hofmann, W.
name: Hofverberg, P.
name: Holleran, M.
name: Hoppe, S.
name: Horns, D.
name: Jacholkowska, A.
name: de Jager, O. C.
name: Jahn, C.
name: Jung, I.
name: Katarzynski, K.
name: Katz, U.
name: Kaufmann, S.
name: Kerschhaggl, M.
name: Khangulyan, D.
name: Khelifi, B.
name: Keogh, D.
name: Klochkov, D.
name: Kluzniak, W.
name: Kneiske, T.
name: Komin, Nu.
name: Kosack, K.
name: Kossakowski, R.
name: Lamanna, G.
name: Lenain, J. -P.
name: Lohse, T.
name: Lu, C. -C.
name: Marandon, V.
name: Marcowith, A.
name: Masbou, J.
name: Maurin, D.
name: McComb, T. J. L.
name: Medina, M. C.
name: Mehault, J.
name: Moderski, R.
name: Moulin, E.
name: Naumann-Godo, M.
name: de Naurois, M.
name: Nedbal, D.
name: Nekrassov, D.
name: Nguyen, N.
name: Nicholas, B.
name: Niemiec, J.
name: Nolan, S. J.
name: Ohm, S.
name: Olive, J-F.
name: Wilhelmi, E. de Ona
name: Opitz, B.
name: Orford, K. J.
name: Ostrowski, M.
name: Panter, M.
name: Arribas, M. Paz
name: Pedaletti, G.
name: Pelletier, G.
name: Petrucci, P. -O.
name: Pita, S.
name: Puehlhofer, G.
name: Punch, M.
name: Quirrenbach, A.
name: Raubenheimer, B. C.
name: Raue, M.
name: Rayner, S. M.
name: Reimer, O.
name: Renaud, M.
name: Reyes, R. de los
name: Rieger, F.
name: Ripken, J.
name: Rob, L.
name: Rosier-Lees, S.
name: Rowell, G.
name: Rudak, B.
name: Rulten, C. B.
name: Ruppel, J.
name: Ryde, F.
name: Sahakian, V.
name: Santangelo, A.
name: Schlickeiser, R.
name: Schoeck, F. M.
name: Schoenwald, A.
name: Schwanke, U.
name: Schwarzburg, S.
name: Schwemmer, S.
name: Shalchi, A.
name: Sushch, I.
name: Sikora, M.
name: Skilton, J. L.
name: Sol, H.
name: Stawarz, L.
name: Steenkamp, R.
name: Stegmann, C.
name: Stinzing, F.
name: Superina, G.
name: Szostek, A.
name: Tam, P. H.
name: Tavernet, J. -P.
name: Terrier, R.
name: Tibolla, O.
name: Tluczykont, M.
name: Valerius, K.
name: van Eldik, C.
name: Vasileiadis, G.
name: Venter, C.
name: Venter, L.
name: Vialle, J. P.
name: Viana, A.
name: Vincent, P.
name: Vivier, M.
name: Voelk, H. J.
name: Volpe, F.
name: Vorobiov, S.
name: Wagner, S. J.
name: Ward, M.
name: Zdziarski, A. A.
name: Zech, A.
name: Zechlin, H. -S.
Publisher: name: arXiv
Year: 2010
Subjects: subject: High Energy Astrophysical Phenomena (astro-ph.HE)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: Observations of very high energy gamma-rays from blazars provide information about acceleration mechanisms occurring in their innermost regions. Studies of variability in these objects allow a better understanding of the mechanisms at play. To investigate the spectral and temporal variability of VHE (&gt;100 GeV) gamma-rays of the well-known high-frequency-peaked BL Lac object PKS 2155-304 with the H.E.S.S. imaging atmospheric Cherenkov telescopes over a wide range of flux states. Data collected from 2005 to 2007 are analyzed. Spectra are derived on time scales ranging from 3 years to 4 minutes. Light curve variability is studied through doubling timescales and structure functions, and is compared with red noise process simulations. The source is found to be in a low state from 2005 to 2007, except for a set of exceptional flares which occurred in July 2006. The quiescent state of the source is characterized by an associated mean flux level of 4.32 +/-0.09 x 10^-11 cm^-2 s^-1 above 200 GeV, or approximately 15% of the Crab Nebula, and a power law photon index of 3.53 +/-0.06. 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 behaviour at low and high fluxes,which is a new phenomenon in VHE gamma-ray emitting blazars. The variability amplitude characterized by the fractional r.m.s. is strongly energy-dependent and is proportional to E^(0.19 +/- 0.01). The light curve r.m.s. correlates with the flux. This is the signature of a multiplicative process which can be accounted for as a red noise with a Fourier index of ~2. This unique data set shows evidence for a low level gamma-ray emission state from PKS 2155-304, which possibly has a different origin than the outbursts. The discovery of the light curve lognormal behaviour might be an indicator ..
description: 17 pages, 13 figures, Accepted for publication to Astronomy &amp; Astrophysics