VHE γ-ray emission of PKS2155-304: Spectral and temporal variability

A. Abramowski; F. Acero; F. Aharonian; A. G. Akhperjanian; G. Anton; U. Barres De Almeida; A. R. Bazer-Bachi; Y. Becherini; B. Behera; W. Benbow; K. Bernlöhr; A. Bochow; C. Boisson; J. Bolmont; V. Borrel; J. Brucker; F. Brun; P. Brun; R. Bühler; T. Bulik; I. Büsching; T. Boutelier; P. M. Chadwick; A. Charbonnier; R. C.G. Chaves; A. Cheesebrough; L. M. Chounet; A. C. Clapson; G. Coignet; J. Conrad; L. Costamante; M. Dalton; M. K. Daniel; I. D. Davids; B. Degrange; C. Deil; H. J. Dickinson; A. Djannati-Ataï; W. Domainko; L. O. Drury; F. Dubois; G. Dubus; J. Dyks; M. Dyrda; K. Egberts; P. Eger; P. Espigat; L. Fallon; C. Farnier; S. Fegan; F. Feinstein; M. V. Fernandes; A. Fiasson; A. Förster; G. Fontaine; M. Füßling; S. Gabici; Y. A. Gallant; L. Gérard; D. Gerbig; B. Giebels; J. F. Glicenstein; B. Glück; P. Goret; D. Göring; D. Hampf; M. Hauser; S. Heinz; G. Heinzelmann; G. Henri; G. Hermann; J. A. Hinton; A. Hoffmann; W. Hofmann; P. Hofverberg; M. Holleran; S. Hoppe; D. Horns; A. Jacholkowska; O. C. De Jager; C. Jahn; I. Jung; K. Katarzyński; U. Katz; S. Kaufmann; M. Kerschhaggl; D. Khangulyan; B. Khélifi; D. Keogh; D. Klochkov; W. Kluźniak; T. Kneiske; Nu Komin; K. Kosack; R. Kossakowski; G. Lamanna; J. P. Lenain; T. Lohse; C. C. Lu; V. Marandon; A. Marcowith; J. Masbou; D. Maurin; T. J.L. McComb; M. C. Medina; J. Méhault; R. Moderski; E. Moulin; M. Naumann-Godo; M. De Naurois; D. Nedbal; D. Nekrassov; N. Nguyen; B. Nicholas; J. Niemiec; S. J. Nolan; S. Ohm; J. F. Olive; E. De Oña Wilhelmi; B. Opitz; K. J. Orford; M. Ostrowski; M. Panter; M. Paz Arribas; G. Pedaletti; G. Pelletier; P. O. Petrucci; S. Pita; G. Pühlhofer; M. Punch; A. Quirrenbach; B. C. Raubenheimer; M. Raue; S. M. Rayner; O. Reimer; M. Renaud; R. De Los Reyes; F. Rieger; J. Ripken; L. Rob; S. Rosier-Lees; G. Rowell; B. Rudak; C. B. Rulten; J. Ruppel; F. Ryde; V. Sahakian; A. Santangelo; R. Schlickeiser; F. M. Schöck; A. Schönwald; U. Schwanke; S. Schwarzburg; S. Schwemmer; A. Shalchi; I. Sushch; M. Sikora; J. L. Skilton; H. Sol; L. Stawarz; R. Steenkamp; C. Stegmann; F. Stinzing; G. Superina; A. Szostek; P. H. Tam; J. P. Tavernet; R. Terrier; O. Tibolla; M. Tluczykont; K. Valerius; C. Van Eldik; G. Vasileiadis; C. Venter; L. Venter; J. P. Vialle; A. Viana; P. Vincent; M. Vivier; H. J. Völk; F. Volpe; S. Vorobiov; S. J. Wagner; M. Ward; A. A. Zdziarski; A. Zech; H. S. Zechlin

doi:10.1051/0004-6361/201014484

VHE γ-ray emission of PKS2155-304: Spectral and temporal variability

A. Abramowski
, F. Acero
, F. Aharonian
, A. G. Akhperjanian
, G. Anton
, U. Barres De Almeida
, A. R. Bazer-Bachi
, Y. Becherini
, B. Behera
, W. Benbow
, K. Bernlöhr
, A. Bochow
, C. Boisson
, J. Bolmont
, V. Borrel
, J. Brucker
, F. Brun
, P. Brun
, R. Bühler
, T. Bulik

I. Büsching, T. Boutelier, P. M. Chadwick, A. Charbonnier, R. C.G. Chaves, A. Cheesebrough, L. M. Chounet, A. C. Clapson, G. Coignet, J. Conrad, L. Costamante, M. Dalton, M. K. Daniel, I. D. Davids, B. Degrange, C. Deil, H. J. Dickinson, A. Djannati-Ataï, W. Domainko, L. O. Drury, F. Dubois, G. Dubus, J. Dyks, M. Dyrda, K. Egberts, P. Eger, P. Espigat, L. Fallon, C. Farnier, S. Fegan, F. Feinstein, M. V. Fernandes, A. Fiasson, A. Förster, G. Fontaine, M. Füßling, S. Gabici, Y. A. Gallant, L. Gérard, D. Gerbig, B. Giebels, J. F. Glicenstein, B. Glück, P. Goret, D. Göring, D. Hampf, M. Hauser, S. Heinz, G. Heinzelmann, G. Henri, G. Hermann, J. A. Hinton, A. Hoffmann, W. Hofmann, P. Hofverberg, M. Holleran, S. Hoppe, D. Horns, A. Jacholkowska, O. C. De Jager, C. Jahn, I. Jung, K. Katarzyński, U. Katz, S. Kaufmann, M. Kerschhaggl, D. Khangulyan, B. Khélifi, D. Keogh, D. Klochkov, W. Kluźniak, T. Kneiske, Nu Komin, K. Kosack, R. Kossakowski, G. Lamanna, J. P. Lenain, T. Lohse, C. C. Lu, V. Marandon, A. Marcowith, J. Masbou, D. Maurin, T. J.L. McComb, M. C. Medina, J. Méhault, R. Moderski, E. Moulin, M. Naumann-Godo, M. De Naurois, D. Nedbal, D. Nekrassov, N. Nguyen, B. Nicholas, J. Niemiec, S. J. Nolan, S. Ohm, J. F. Olive, E. De Oña Wilhelmi, B. Opitz, K. J. Orford, M. Ostrowski, M. Panter, M. Paz Arribas, G. Pedaletti, G. Pelletier, P. O. Petrucci, S. Pita, G. Pühlhofer, M. Punch, A. Quirrenbach, B. C. Raubenheimer, M. Raue, S. M. Rayner, O. Reimer, M. Renaud, R. De Los Reyes, F. Rieger, J. Ripken, L. Rob, S. Rosier-Lees, G. Rowell, B. Rudak, C. B. Rulten, J. Ruppel, F. Ryde, V. Sahakian, A. Santangelo, R. Schlickeiser, F. M. Schöck, A. Schönwald, U. Schwanke, S. Schwarzburg, S. Schwemmer, A. Shalchi, I. Sushch, M. Sikora, J. L. Skilton, H. Sol, L. Stawarz, R. Steenkamp, C. Stegmann, F. Stinzing, G. Superina, A. Szostek, P. H. Tam, J. P. Tavernet, R. Terrier, O. Tibolla, M. Tluczykont, K. Valerius, C. Van Eldik, G. Vasileiadis, C. Venter, L. Venter, J. P. Vialle, A. Viana, P. Vincent, M. Vivier, H. J. Völk, F. Volpe, S. Vorobiov, S. J. Wagner, M. Ward, A. A. Zdziarski, A. Zech, H. S. Zechlin

Universität Hamburg
Laboratoire Univers et Particules de Montpellier
Max-Planck-Institut für Kernphysik
Dublin Institute for Advanced Studies
Yerevan Physics Institute
Friedrich-Alexander University (FAU) Erlangen-Nürnberg and Universitätsklinikum Erlangen
Durham University
Centre national de la recherche scientifique
Astroparticule and Cosmol APC
Landessternwarte Heidelberg
Humboldt-Universität zu Berlin
LUTH - Laboratoire de l'Univers et de ses Theories
Universités Paris VI and VII
Universite Paris-Saclay
University of Warsaw
North-West University
Université Savoie Mont Blanc
Stockholm University
CNRS and MPG
University of Namibia
Nicolaus Copernicus Astronomical Center of the Polish Academy of Sciences
Institute for Nuclear Physics
Medical University of Innsbruck
Ruhr-University Bochum
University of Leicester
University of Tübingen
Nicolaus Copernicus University
Charles University
University of Adelaide
Jagiellonian University
KTH Royal Institute of Technology
University of Leeds

Research output: Contribution to journal › Article › peer-review

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 ± 0.09 _stat ± 0.86_syst) × 10^-11 cm ^-2 s^-1 above 200 GeV, or approximately 15\% of the Crab Nebula, and a power-law photon index of Γ = 3.53 ± 0.06 _stat ± 0.10_syst. 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 F _var is strongly energy-dependent and is E^0.19±0.01. 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.

Original language	English
Article number	A83
Journal	Astronomy and Astrophysics
Volume	520
Issue number	13
DOIs	https://doi.org/10.1051/0004-6361/201014484
Publication status	Published - 1 Jan 2010

Keywords

BL Lacertae objects: individual: PKS 2155-304
galaxies: active
galaxies: jets
gamma rays: general

Access to Document

10.1051/0004-6361/201014484

Cite this

Abramowski, A., Acero, F., Aharonian, F., Akhperjanian, A. G., Anton, G., Barres De Almeida, U., Bazer-Bachi, A. R., Becherini, Y., Behera, B., Benbow, W., Bernlöhr, K., Bochow, A., Boisson, C., Bolmont, J., Borrel, V., Brucker, J., Brun, F., Brun, P., Bühler, R., ... Zechlin, H. S. (2010). VHE γ-ray emission of PKS2155-304: Spectral and temporal variability. Astronomy and Astrophysics, 520(13), Article A83. https://doi.org/10.1051/0004-6361/201014484

@article{11e9574e3832420eb02f597e65163e53,

title = "VHE γ-ray emission of PKS2155-304: Spectral and temporal variability",

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 ± 0.09 stat ± 0.86syst) × 10-11 cm -2 s-1 above 200 GeV, or approximately 15\textbackslash{}\% of the Crab Nebula, and a power-law photon index of Γ = 3.53 ± 0.06 stat ± 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 F var is strongly energy-dependent and is E0.19±0.01. 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.",

keywords = "BL Lacertae objects: individual: PKS 2155-304, galaxies: active, galaxies: jets, gamma rays: general",

author = "A. Abramowski and F. Acero and F. Aharonian and Akhperjanian, \{A. G.\} and G. Anton and \{Barres De Almeida\}, U. and Bazer-Bachi, \{A. R.\} and Y. Becherini and B. Behera and W. Benbow and K. Bernl{\"o}hr and A. Bochow and C. Boisson and J. Bolmont and V. Borrel and J. Brucker and F. Brun and P. Brun and R. B{\"u}hler and T. Bulik and I. B{\"u}sching and T. Boutelier and Chadwick, \{P. M.\} and A. Charbonnier and Chaves, \{R. C.G.\} and A. Cheesebrough and Chounet, \{L. M.\} and Clapson, \{A. C.\} and G. Coignet and J. Conrad and L. Costamante and M. Dalton and Daniel, \{M. K.\} and Davids, \{I. D.\} and B. Degrange and C. Deil and Dickinson, \{H. J.\} and A. Djannati-Ata{\"i} and W. Domainko and Drury, \{L. O.\} and F. Dubois and G. Dubus and J. Dyks and M. Dyrda and K. Egberts and P. Eger and P. Espigat and L. Fallon and C. Farnier and S. Fegan and F. Feinstein and Fernandes, \{M. V.\} and A. Fiasson and A. F{\"o}rster and G. Fontaine and M. F{\"u}{\ss}ling and S. Gabici and Gallant, \{Y. A.\} and L. G{\'e}rard and D. Gerbig and B. Giebels and Glicenstein, \{J. F.\} and B. Gl{\"u}ck and P. Goret and D. G{\"o}ring and D. Hampf and M. Hauser and S. Heinz and G. Heinzelmann and G. Henri and G. Hermann and Hinton, \{J. A.\} and A. Hoffmann and W. Hofmann and P. Hofverberg and M. Holleran and S. Hoppe and D. Horns and A. Jacholkowska and \{De Jager\}, \{O. C.\} and C. Jahn and I. Jung and K. Katarzy{\'n}ski and U. Katz and S. Kaufmann and M. Kerschhaggl and D. Khangulyan and B. Kh{\'e}lifi and D. Keogh and D. Klochkov and W. Klu{\'z}niak and T. Kneiske and Nu Komin and K. Kosack and R. Kossakowski and G. Lamanna and Lenain, \{J. P.\} and T. Lohse and Lu, \{C. C.\} and V. Marandon and A. Marcowith and J. Masbou and D. Maurin and McComb, \{T. J.L.\} and Medina, \{M. C.\} and J. M{\'e}hault and R. Moderski and E. Moulin and M. Naumann-Godo and \{De Naurois\}, M. and D. Nedbal and D. Nekrassov and N. Nguyen and B. Nicholas and J. Niemiec and Nolan, \{S. J.\} and S. Ohm and Olive, \{J. F.\} and \{De O{\~n}a Wilhelmi\}, E. and B. Opitz and Orford, \{K. J.\} and M. Ostrowski and M. Panter and \{Paz Arribas\}, M. and G. Pedaletti and G. Pelletier and Petrucci, \{P. O.\} and S. Pita and G. P{\"u}hlhofer and M. Punch and A. Quirrenbach and Raubenheimer, \{B. C.\} and M. Raue and Rayner, \{S. M.\} and O. Reimer and M. Renaud and \{De Los Reyes\}, R. and F. Rieger and J. Ripken and L. Rob and S. Rosier-Lees and G. Rowell and B. Rudak and Rulten, \{C. B.\} and J. Ruppel and F. Ryde and V. Sahakian and A. Santangelo and R. Schlickeiser and Sch{\"o}ck, \{F. M.\} and A. Sch{\"o}nwald and U. Schwanke and S. Schwarzburg and S. Schwemmer and A. Shalchi and I. Sushch and M. Sikora and Skilton, \{J. L.\} and H. Sol and L. Stawarz and R. Steenkamp and C. Stegmann and F. Stinzing and G. Superina and A. Szostek and Tam, \{P. H.\} and Tavernet, \{J. P.\} and R. Terrier and O. Tibolla and M. Tluczykont and K. Valerius and \{Van Eldik\}, C. and G. Vasileiadis and C. Venter and L. Venter and Vialle, \{J. P.\} and A. Viana and P. Vincent and M. Vivier and V{\"o}lk, \{H. J.\} and F. Volpe and S. Vorobiov and Wagner, \{S. J.\} and M. Ward and Zdziarski, \{A. A.\} and A. Zech and Zechlin, \{H. S.\}",

year = "2010",

month = jan,

day = "1",

doi = "10.1051/0004-6361/201014484",

language = "English",

volume = "520",

journal = "Astronomy and Astrophysics",

issn = "0004-6361",

number = "13",

}

Abramowski, A, Acero, F, Aharonian, F, Akhperjanian, AG, Anton, G, Barres De Almeida, U, Bazer-Bachi, AR, Becherini, Y, Behera, B, Benbow, W, Bernlöhr, K, Bochow, A, Boisson, C, Bolmont, J, Borrel, V, Brucker, J, Brun, F, Brun, P, Bühler, R, Bulik, T, Büsching, I, Boutelier, T, Chadwick, PM, Charbonnier, A, Chaves, RCG, Cheesebrough, A, Chounet, LM, Clapson, AC, Coignet, G, Conrad, J, Costamante, L, Dalton, M, Daniel, MK, Davids, ID, Degrange, B, Deil, C, Dickinson, HJ, Djannati-Ataï, A, Domainko, W, Drury, LO, Dubois, F, Dubus, G, Dyks, J, Dyrda, M, Egberts, K, Eger, P, Espigat, P, Fallon, L, Farnier, C, Fegan, S, Feinstein, F, Fernandes, MV, Fiasson, A, Förster, A, Fontaine, G, Füßling, M, Gabici, S, Gallant, YA, Gérard, L, Gerbig, D, Giebels, B, Glicenstein, JF, Glück, B, Goret, P, Göring, D, Hampf, D, Hauser, M, Heinz, S, Heinzelmann, G, Henri, G, Hermann, G, Hinton, JA, Hoffmann, A, Hofmann, W, Hofverberg, P, Holleran, M, Hoppe, S, Horns, D, Jacholkowska, A, De Jager, OC, Jahn, C, Jung, I, Katarzyński, K, Katz, U, Kaufmann, S, Kerschhaggl, M, Khangulyan, D, Khélifi, B, Keogh, D, Klochkov, D, Kluźniak, W, Kneiske, T, Komin, N, Kosack, K, Kossakowski, R, Lamanna, G, Lenain, JP, Lohse, T, Lu, CC, Marandon, V, Marcowith, A, Masbou, J, Maurin, D, McComb, TJL, Medina, MC, Méhault, J, Moderski, R, Moulin, E, Naumann-Godo, M, De Naurois, M, Nedbal, D, Nekrassov, D, Nguyen, N, Nicholas, B, Niemiec, J, Nolan, SJ, Ohm, S, Olive, JF, De Oña Wilhelmi, E, Opitz, B, Orford, KJ, Ostrowski, M, Panter, M, Paz Arribas, M, Pedaletti, G, Pelletier, G, Petrucci, PO, Pita, S, Pühlhofer, G, Punch, M, Quirrenbach, A, Raubenheimer, BC, Raue, M, Rayner, SM, Reimer, O, Renaud, M, De Los Reyes, R, Rieger, F, Ripken, J, Rob, L, Rosier-Lees, S, Rowell, G, Rudak, B, Rulten, CB, Ruppel, J, Ryde, F, Sahakian, V, Santangelo, A, Schlickeiser, R, Schöck, FM, Schönwald, A, Schwanke, U, Schwarzburg, S, Schwemmer, S, Shalchi, A, Sushch, I, Sikora, M, Skilton, JL, Sol, H, Stawarz, L, Steenkamp, R, Stegmann, C, Stinzing, F, Superina, G, Szostek, A, Tam, PH, Tavernet, JP, Terrier, R, Tibolla, O, Tluczykont, M, Valerius, K, Van Eldik, C, Vasileiadis, G, Venter, C, Venter, L, Vialle, JP, Viana, A, Vincent, P, Vivier, M, Völk, HJ, Volpe, F, Vorobiov, S, Wagner, SJ, Ward, M, Zdziarski, AA, Zech, A & Zechlin, HS 2010, 'VHE γ-ray emission of PKS2155-304: Spectral and temporal variability', Astronomy and Astrophysics, vol. 520, no. 13, A83. https://doi.org/10.1051/0004-6361/201014484

TY - JOUR

T1 - VHE γ-ray emission of PKS2155-304

T2 - Spectral and temporal variability

AU - Abramowski, A.

AU - Acero, F.

AU - Aharonian, F.

AU - Akhperjanian, A. G.

AU - Anton, G.

AU - Barres De Almeida, U.

AU - Bazer-Bachi, A. R.

AU - Becherini, Y.

AU - Behera, B.

AU - Benbow, W.

AU - Bernlöhr, K.

AU - Bochow, A.

AU - Boisson, C.

AU - Bolmont, J.

AU - Borrel, V.

AU - Brucker, J.

AU - Brun, F.

AU - Brun, P.

AU - Bühler, R.

AU - Bulik, T.

AU - Büsching, I.

AU - Boutelier, T.

AU - Chadwick, P. M.

AU - Charbonnier, A.

AU - Chaves, R. C.G.

AU - Cheesebrough, A.

AU - Chounet, L. M.

AU - Clapson, A. C.

AU - Coignet, G.

AU - Conrad, J.

AU - Costamante, L.

AU - Dalton, M.

AU - Daniel, M. K.

AU - Davids, I. D.

AU - Degrange, B.

AU - Deil, C.

AU - Dickinson, H. J.

AU - Djannati-Ataï, A.

AU - Domainko, W.

AU - Drury, L. O.

AU - Dubois, F.

AU - Dubus, G.

AU - Dyks, J.

AU - Dyrda, M.

AU - Egberts, K.

AU - Eger, P.

AU - Espigat, P.

AU - Fallon, L.

AU - Farnier, C.

AU - Fegan, S.

AU - Feinstein, F.

AU - Fernandes, M. V.

AU - Fiasson, A.

AU - Förster, A.

AU - Fontaine, G.

AU - Füßling, M.

AU - Gabici, S.

AU - Gallant, Y. A.

AU - Gérard, L.

AU - Gerbig, D.

AU - Giebels, B.

AU - Glicenstein, J. F.

AU - Glück, B.

AU - Goret, P.

AU - Göring, D.

AU - Hampf, D.

AU - Hauser, M.

AU - Heinz, S.

AU - Heinzelmann, G.

AU - Henri, G.

AU - Hermann, G.

AU - Hinton, J. A.

AU - Hoffmann, A.

AU - Hofmann, W.

AU - Hofverberg, P.

AU - Holleran, M.

AU - Hoppe, S.

AU - Horns, D.

AU - Jacholkowska, A.

AU - De Jager, O. C.

AU - Jahn, C.

AU - Jung, I.

AU - Katarzyński, K.

AU - Katz, U.

AU - Kaufmann, S.

AU - Kerschhaggl, M.

AU - Khangulyan, D.

AU - Khélifi, B.

AU - Keogh, D.

AU - Klochkov, D.

AU - Kluźniak, W.

AU - Kneiske, T.

AU - Komin, Nu

AU - Kosack, K.

AU - Kossakowski, R.

AU - Lamanna, G.

AU - Lenain, J. P.

AU - Lohse, T.

AU - Lu, C. C.

AU - Marandon, V.

AU - Marcowith, A.

AU - Masbou, J.

AU - Maurin, D.

AU - McComb, T. J.L.

AU - Medina, M. C.

AU - Méhault, J.

AU - Moderski, R.

AU - Moulin, E.

AU - Naumann-Godo, M.

AU - De Naurois, M.

AU - Nedbal, D.

AU - Nekrassov, D.

AU - Nguyen, N.

AU - Nicholas, B.

AU - Niemiec, J.

AU - Nolan, S. J.

AU - Ohm, S.

AU - Olive, J. F.

AU - De Oña Wilhelmi, E.

AU - Opitz, B.

AU - Orford, K. J.

AU - Ostrowski, M.

AU - Panter, M.

AU - Paz Arribas, M.

AU - Pedaletti, G.

AU - Pelletier, G.

AU - Petrucci, P. O.

AU - Pita, S.

AU - Pühlhofer, G.

AU - Punch, M.

AU - Quirrenbach, A.

AU - Raubenheimer, B. C.

AU - Raue, M.

AU - Rayner, S. M.

AU - Reimer, O.

AU - Renaud, M.

AU - De Los Reyes, R.

AU - Rieger, F.

AU - Ripken, J.

AU - Rob, L.

AU - Rosier-Lees, S.

AU - Rowell, G.

AU - Rudak, B.

AU - Rulten, C. B.

AU - Ruppel, J.

AU - Ryde, F.

AU - Sahakian, V.

AU - Santangelo, A.

AU - Schlickeiser, R.

AU - Schöck, F. M.

AU - Schönwald, A.

AU - Schwanke, U.

AU - Schwarzburg, S.

AU - Schwemmer, S.

AU - Shalchi, A.

AU - Sushch, I.

AU - Sikora, M.

AU - Skilton, J. L.

AU - Sol, H.

AU - Stawarz, L.

AU - Steenkamp, R.

AU - Stegmann, C.

AU - Stinzing, F.

AU - Superina, G.

AU - Szostek, A.

AU - Tam, P. H.

AU - Tavernet, J. P.

AU - Terrier, R.

AU - Tibolla, O.

AU - Tluczykont, M.

AU - Valerius, K.

AU - Van Eldik, C.

AU - Vasileiadis, G.

AU - Venter, C.

AU - Venter, L.

AU - Vialle, J. P.

AU - Viana, A.

AU - Vincent, P.

AU - Vivier, M.

AU - Völk, H. J.

AU - Volpe, F.

AU - Vorobiov, S.

AU - Wagner, S. J.

AU - Ward, M.

AU - Zdziarski, A. A.

AU - Zech, A.

AU - Zechlin, H. S.

PY - 2010/1/1

Y1 - 2010/1/1

N2 - 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 ± 0.09 stat ± 0.86syst) × 10-11 cm -2 s-1 above 200 GeV, or approximately 15\% of the Crab Nebula, and a power-law photon index of Γ = 3.53 ± 0.06 stat ± 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 F var is strongly energy-dependent and is E0.19±0.01. 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.

AB - 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 ± 0.09 stat ± 0.86syst) × 10-11 cm -2 s-1 above 200 GeV, or approximately 15\% of the Crab Nebula, and a power-law photon index of Γ = 3.53 ± 0.06 stat ± 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 F var is strongly energy-dependent and is E0.19±0.01. 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.

KW - BL Lacertae objects: individual: PKS 2155-304

KW - galaxies: active

KW - galaxies: jets

KW - gamma rays: general

U2 - 10.1051/0004-6361/201014484

DO - 10.1051/0004-6361/201014484

M3 - Article

AN - SCOPUS:77957764207

SN - 0004-6361

VL - 520

JO - Astronomy and Astrophysics

JF - Astronomy and Astrophysics

IS - 13

M1 - A83

ER -

VHE γ-ray emission of PKS2155-304: Spectral and temporal variability

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