PKS2005-489 at VHE: Four years of monitoring with HESS and simultaneous multi-wavelength observations

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; L. Costamante; M. Dalton; M. K. Daniel; I. D. Davids; B. Degrange; C. Deil; H. J. Dickinson; A. Djannati-Ataï; W. Domainko; L. O C Drury; F. Dubois; G. Dubus; J. Dyks; M. Dyrda; K. Egberts; P. Eger; P. Espigat; L. Fallon; C. Farnier; S. Fegan; F. Feinstein; 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; 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; V. Marandon; O. Martineau-Huynh; 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; B. Nicholas; J. Niemiec; S. J. Nolan; S. Ohm; J. F. Olive; E. De Oña Wilhelmi; 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; M. Renaud; F. Rieger; J. Ripken; L. Rob; S. Rosier-Lees; G. Rowell; B. Rudak; C. B. Rulten; J. Ruppel; V. Sahakian; A. Santangelo; R. Schlickeiser; F. M. Schöck; U. Schwanke; S. Schwarzburg; S. Schwemmer; A. Shalchi; M. Sikora; J. L. Skilton; H. Sol; Stawarz; R. Steenkamp; C. Stegmann; F. Stinzing; G. Superina; A. Szostek; P. H. Tam; J. P. Tavernet; R. Terrier; O. Tibolla; M. Tluczykont; C. Van Eldik; G. Vasileiadis; C. Venter; L. Venter; J. P. Vialle; P. Vincent; M. Vivier; H. J. Völk; F. Volpe; S. J. Wagner; M. Ward; A. A. Zdziarski; A. Zech

doi:10.1051/0004-6361/200913073

PKS2005-489 at VHE: Four years of monitoring with HESS and simultaneous multi-wavelength observations

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. BüschingT. Boutelier, P. M. Chadwick, A. Charbonnier, R. C G Chaves, A. Cheesebrough, L. M. Chounet, A. C. Clapson, G. Coignet, L. Costamante, M. Dalton, M. K. Daniel, I. D. Davids, B. Degrange, C. Deil, H. J. Dickinson, A. Djannati-Ataï, W. Domainko, L. O C Drury, F. Dubois, G. Dubus, J. Dyks, M. Dyrda, K. Egberts, P. Eger, P. Espigat, L. Fallon, C. Farnier, S. Fegan, F. Feinstein, 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, 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, V. Marandon, O. Martineau-Huynh, 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, B. Nicholas, J. Niemiec, S. J. Nolan, S. Ohm, J. F. Olive, E. De Oña Wilhelmi, 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, M. Renaud, F. Rieger, J. Ripken, L. Rob, S. Rosier-Lees, G. Rowell, B. Rudak, C. B. Rulten, J. Ruppel, V. Sahakian, A. Santangelo, R. Schlickeiser, F. M. Schöck, U. Schwanke, S. Schwarzburg, S. Schwemmer, A. Shalchi, M. Sikora, J. L. Skilton, H. Sol, Stawarz, R. Steenkamp, C. Stegmann, F. Stinzing, G. Superina, A. Szostek, P. H. Tam, J. P. Tavernet, R. Terrier, O. Tibolla, M. Tluczykont, C. Van Eldik, G. Vasileiadis, C. Venter, L. Venter, J. P. Vialle, P. Vincent, M. Vivier, H. J. Völk, F. Volpe, S. J. Wagner, M. Ward, A. A. Zdziarski, A. Zech

Physics and Astronomy (Twin Cities)

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

31 Scopus citations

Abstract

Aims: Our aim is to study the very high energy (VHE; E > 100 GeV) Γ-ray emission from BL Lac objects and the evolution in time of their broad-band spectral energy distribution (SED). Methods: VHE observations of the high-frequency peaked BL Lac object PKS 2005-489 were made with the High Energy Stereoscopic System (HESS) from 2004 through 2007. Three simultaneous multi-wavelength campaigns at lower energies were performed during the HESS data taking, consisting of several individual pointings with the XMM-Newton and RXTE satellites. Results: A strong VHE signal, ∼17ρ total, from PKS 2005-489 was detected during the four years of HESS observations (90.3 h live time). The integral flux above the average analysis threshold of 400 GeV is ∼3% of the flux observed from the Crab Nebula and varies weakly on time scales from days to years. The average VHE spectrum measured from ∼300 GeV to ∼5 TeV is characterized by a power law with a photon index, Γ = 3.20 ± 0.16_stat ± 0.10_syst At X-ray energies the flux is observed to vary by more than an order of magnitude between 2004 and 2005. Strong changes in the X-ray spectrum (ΔΓ_X ≈ 0.7) are also observed, which appear to be mirrored in the VHE band. Conclusions: The SED of PKS 2005-4 constructed for the first time with contemporaneous data on both humps, shows significant evolution. The large flux variations in the X-ray band, coupled with weak or no variations in the VHE band and a similar spectral behavior, suggest the emergence of a new, separate, harder emission component in September 2005.

Original language	English (US)
Article number	A52
Journal	Astronomy and Astrophysics
Volume	511
Issue number	1
DOIs	https://doi.org/10.1051/0004-6361/200913073
State	Published - 2010

Keywords

BL Lacertae objects: individual: PKS 2005-489
Galaxies: active
Gamma rays: galaxies
X-rays: individuals: PKS 2005-489

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10.1051/0004-6361/200913073

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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., Bulik, T., ... Zech, A. (2010). PKS2005-489 at VHE: Four years of monitoring with HESS and simultaneous multi-wavelength observations. Astronomy and Astrophysics, 511(1), Article A52. https://doi.org/10.1051/0004-6361/200913073

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, Costamante, L, Dalton, M, Daniel, MK, Davids, ID, Degrange, B, Deil, C, Dickinson, HJ, Djannati-Ataï, A, Domainko, W, Drury, LOC, Dubois, F, Dubus, G, Dyks, J, Dyrda, M, Egberts, K, Eger, P, Espigat, P, Fallon, L, Farnier, C, Fegan, S, Feinstein, F, 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, 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, Marandon, V, Martineau-Huynh, O, 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, Nicholas, B, Niemiec, J, Nolan, SJ, Ohm, S, Olive, JF, De Oña Wilhelmi, E, 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, Renaud, M, Rieger, F, Ripken, J, Rob, L, Rosier-Lees, S, Rowell, G, Rudak, B, Rulten, CB, Ruppel, J, Sahakian, V, Santangelo, A, Schlickeiser, R, Schöck, FM, Schwanke, U, Schwarzburg, S, Schwemmer, S, Shalchi, A, Sikora, M, Skilton, JL, Sol, H, Stawarz, Steenkamp, R, Stegmann, C, Stinzing, F, Superina, G, Szostek, A, Tam, PH, Tavernet, JP, Terrier, R, Tibolla, O, Tluczykont, M, Van Eldik, C, Vasileiadis, G, Venter, C, Venter, L, Vialle, JP, Vincent, P, Vivier, M, Völk, HJ, Volpe, F, Wagner, SJ, Ward, M, Zdziarski, AA & Zech, A 2010, 'PKS2005-489 at VHE: Four years of monitoring with HESS and simultaneous multi-wavelength observations', Astronomy and Astrophysics, vol. 511, no. 1, A52. https://doi.org/10.1051/0004-6361/200913073

@article{9682da23bf0542c2b824ba41ce7697fb,

title = "PKS2005-489 at VHE: Four years of monitoring with HESS and simultaneous multi-wavelength observations",

abstract = "Aims: Our aim is to study the very high energy (VHE; E > 100 GeV) Γ-ray emission from BL Lac objects and the evolution in time of their broad-band spectral energy distribution (SED). Methods: VHE observations of the high-frequency peaked BL Lac object PKS 2005-489 were made with the High Energy Stereoscopic System (HESS) from 2004 through 2007. Three simultaneous multi-wavelength campaigns at lower energies were performed during the HESS data taking, consisting of several individual pointings with the XMM-Newton and RXTE satellites. Results: A strong VHE signal, ∼17ρ total, from PKS 2005-489 was detected during the four years of HESS observations (90.3 h live time). The integral flux above the average analysis threshold of 400 GeV is ∼3% of the flux observed from the Crab Nebula and varies weakly on time scales from days to years. The average VHE spectrum measured from ∼300 GeV to ∼5 TeV is characterized by a power law with a photon index, Γ = 3.20 ± 0.16stat ± 0.10syst At X-ray energies the flux is observed to vary by more than an order of magnitude between 2004 and 2005. Strong changes in the X-ray spectrum (ΔΓX ≈ 0.7) are also observed, which appear to be mirrored in the VHE band. Conclusions: The SED of PKS 2005-4 constructed for the first time with contemporaneous data on both humps, shows significant evolution. The large flux variations in the X-ray band, coupled with weak or no variations in the VHE band and a similar spectral behavior, suggest the emergence of a new, separate, harder emission component in September 2005.",

keywords = "BL Lacertae objects: individual: PKS 2005-489, Galaxies: active, Gamma rays: galaxies, X-rays: individuals: PKS 2005-489",

author = "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 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 C} 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 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 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 V. Marandon and O. Martineau-Huynh 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 B. Nicholas and J. Niemiec and Nolan, {S. J.} and S. Ohm and Olive, {J. F.} and {De O{\~n}a Wilhelmi}, E. 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 M. Renaud 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 V. Sahakian and A. Santangelo and R. Schlickeiser and Sch{\"o}ck, {F. M.} and U. Schwanke and S. Schwarzburg and S. Schwemmer and A. Shalchi and M. Sikora and Skilton, {J. L.} and H. Sol and 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 {Van Eldik}, C. and G. Vasileiadis and C. Venter and L. Venter and Vialle, {J. P.} and P. Vincent and M. Vivier and V{\"o}lk, {H. J.} and F. Volpe and Wagner, {S. J.} and M. Ward and Zdziarski, {A. A.} and A. Zech",

year = "2010",

doi = "10.1051/0004-6361/200913073",

language = "English (US)",

volume = "511",

journal = "Astronomy and Astrophysics",

issn = "0004-6361",

publisher = "EDP Sciences",

number = "1",

}

TY - JOUR

T1 - PKS2005-489 at VHE

T2 - Four years of monitoring with HESS and simultaneous multi-wavelength observations

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 - 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 C

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 - 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 - 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 - Marandon, V.

AU - Martineau-Huynh, O.

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 - Nicholas, B.

AU - Niemiec, J.

AU - Nolan, S. J.

AU - Ohm, S.

AU - Olive, J. F.

AU - De Oña Wilhelmi, E.

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 - Renaud, M.

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 - Sahakian, V.

AU - Santangelo, A.

AU - Schlickeiser, R.

AU - Schöck, F. M.

AU - Schwanke, U.

AU - Schwarzburg, S.

AU - Schwemmer, S.

AU - Shalchi, A.

AU - Sikora, M.

AU - Skilton, J. L.

AU - Sol, H.

AU - Stawarz,

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 - Van Eldik, C.

AU - Vasileiadis, G.

AU - Venter, C.

AU - Venter, L.

AU - Vialle, J. P.

AU - Vincent, P.

AU - Vivier, M.

AU - Völk, H. J.

AU - Volpe, F.

AU - Wagner, S. J.

AU - Ward, M.

AU - Zdziarski, A. A.

AU - Zech, A.

PY - 2010

Y1 - 2010

N2 - Aims: Our aim is to study the very high energy (VHE; E > 100 GeV) Γ-ray emission from BL Lac objects and the evolution in time of their broad-band spectral energy distribution (SED). Methods: VHE observations of the high-frequency peaked BL Lac object PKS 2005-489 were made with the High Energy Stereoscopic System (HESS) from 2004 through 2007. Three simultaneous multi-wavelength campaigns at lower energies were performed during the HESS data taking, consisting of several individual pointings with the XMM-Newton and RXTE satellites. Results: A strong VHE signal, ∼17ρ total, from PKS 2005-489 was detected during the four years of HESS observations (90.3 h live time). The integral flux above the average analysis threshold of 400 GeV is ∼3% of the flux observed from the Crab Nebula and varies weakly on time scales from days to years. The average VHE spectrum measured from ∼300 GeV to ∼5 TeV is characterized by a power law with a photon index, Γ = 3.20 ± 0.16stat ± 0.10syst At X-ray energies the flux is observed to vary by more than an order of magnitude between 2004 and 2005. Strong changes in the X-ray spectrum (ΔΓX ≈ 0.7) are also observed, which appear to be mirrored in the VHE band. Conclusions: The SED of PKS 2005-4 constructed for the first time with contemporaneous data on both humps, shows significant evolution. The large flux variations in the X-ray band, coupled with weak or no variations in the VHE band and a similar spectral behavior, suggest the emergence of a new, separate, harder emission component in September 2005.

AB - Aims: Our aim is to study the very high energy (VHE; E > 100 GeV) Γ-ray emission from BL Lac objects and the evolution in time of their broad-band spectral energy distribution (SED). Methods: VHE observations of the high-frequency peaked BL Lac object PKS 2005-489 were made with the High Energy Stereoscopic System (HESS) from 2004 through 2007. Three simultaneous multi-wavelength campaigns at lower energies were performed during the HESS data taking, consisting of several individual pointings with the XMM-Newton and RXTE satellites. Results: A strong VHE signal, ∼17ρ total, from PKS 2005-489 was detected during the four years of HESS observations (90.3 h live time). The integral flux above the average analysis threshold of 400 GeV is ∼3% of the flux observed from the Crab Nebula and varies weakly on time scales from days to years. The average VHE spectrum measured from ∼300 GeV to ∼5 TeV is characterized by a power law with a photon index, Γ = 3.20 ± 0.16stat ± 0.10syst At X-ray energies the flux is observed to vary by more than an order of magnitude between 2004 and 2005. Strong changes in the X-ray spectrum (ΔΓX ≈ 0.7) are also observed, which appear to be mirrored in the VHE band. Conclusions: The SED of PKS 2005-4 constructed for the first time with contemporaneous data on both humps, shows significant evolution. The large flux variations in the X-ray band, coupled with weak or no variations in the VHE band and a similar spectral behavior, suggest the emergence of a new, separate, harder emission component in September 2005.

KW - BL Lacertae objects: individual: PKS 2005-489

KW - Galaxies: active

KW - Gamma rays: galaxies

KW - X-rays: individuals: PKS 2005-489

UR - http://www.scopus.com/inward/record.url?scp=79952822315&partnerID=8YFLogxK

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U2 - 10.1051/0004-6361/200913073

DO - 10.1051/0004-6361/200913073

M3 - Article

AN - SCOPUS:79952822315

SN - 0004-6361

VL - 511

JO - Astronomy and Astrophysics

JF - Astronomy and Astrophysics

IS - 1

M1 - A52

ER -

PKS2005-489 at VHE: Four years of monitoring with HESS and simultaneous multi-wavelength observations

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