PKS 2005-489 at VHE: four years of monitoring with HESS and simultaneous multi-wavelength observations
Klochkov, D.; Santangelo, A.; Quirrenbach, A.; Ripken, J.; Farnier, C.; Tibolla, O.; Venter, C.; Schlickeiser, R.; Petrucci, P. -O.; Giebels, B.; Stawarz, Ł.; Sikora, M.; Fontaine, G.; Benbow, W.; Daniel, M. K.; Hauser, M.; Boisson, C.; Aharonian, F.; Akhperjanian, A. G.; Bazer-Bachi, A. R.; Bernlöhr, K.; Chadwick, P. M.; Chounet, L. -M.; Costamante, L.; Degrange, B.; Djannati-Ataï, A.; O'C. Drury, L.; Dubus, G.; Espigat, P.; Feinstein, F.; Gallant, Y. A.; Glicenstein, J. F.; Goret, P.; Heinzelmann, G.; Henri, G.; Hermann, G.; Hinton, J. A.; Hofmann, W.; Holleran, M.; Horns, D.; de Jager, O. C.; Khélifi, B.; Komin, Nu.; Martineau-Huynh, O.; Lohse, T.; Marcowith, A.; McComb, T. J. L.; de Naurois, M.; Nolan, S. J.; Orford, K. J.; Panter, M.; Pelletier, G.; Pita, S.; Pühlhofer, G.; Punch, M.; Raubenheimer, B. C.; Raue, M.; Rayner, S. M.; Rob, L.; Rowell, G.; Sahakian, V.; Schwanke, U.; Sol, H.; Steenkamp, R.; Stegmann, C.; Tavernet, J. -P.; Terrier, R.; Tluczykont, M.; Vasileiadis, G.; Vincent, P.; Völk, H. J.; Wagner, S. J.; Ward, M.; Heinz, S.; Kossakowski, R.; Lamanna, G.; Vialle, J. P.; Acero, F.; Chaves, R. C. G.; Renaud, M.; Barres de Almeida, U.; de Oña Wilhelmi, E.; Pedaletti, G.; Anton, G.; Becherini, Y.; Behera, B.; Bochow, A.; Bolmont, J.; Borrel, V.; Brucker, J.; Brun, F.; Brun, P.; Bühler, R.; Bulik, T.; Büsching, I.; Boutelier, T.; Charbonnier, A.; Cheesebrough, A.; Clapson, A. C.; Coignet, G.; Dalton, M.; Davids, I. D.; Deil, C.; Dickinson, H. J.; Domainko, W.; Dubois, F.; Dyks, J.; Dyrda, M.; Egberts, K.; Eger, P.; Fallon, L.; Fegan, S.; Fiasson, A.; Förster, A.; Füßling, M.; Gabici, S.; Gérard, L.; Gerbig, D.; Glück, B.; Göring, D.; Hoffmann, A.; Hofverberg, P.; Hoppe, S.; Jacholkowska, A.; Jahn, C.; Jung, I.; Katarzyński, K.; Katz, U.; Kaufmann, S.; Kerschhaggl, M.; Khangulyan, D.; Keogh, D.; Kluźniak, W.; Kneiske, T.; Kosack, K.; Lenain, J. -P.; Marandon, V.; Masbou, J.; Maurin, D.; Medina, M. C.; Méhault, J.; Moderski, R.; Moulin, E.; Naumann-Godo, M.; Nedbal, D.; Nekrassov, D.; Nicholas, B.; Niemiec, J.; Ohm, S.; Olive, J. -F.; Ostrowski, M.; Paz Arribas, M.; Rieger, F.; Rosier-Lees, S.; Rudak, B.; Rulten, C. B.; Ruppel, J.; Schöck, F. M.; Schwarzburg, S.; Schwemmer, S.; Shalchi, A.; Skilton, J. L.; Stinzing, F.; Superina, G.; Szostek, A.; Tam, P. H.; van Eldik, C.; Venter, L.; Vivier, M.; Volpe, F.; Zdziarski, A. A.; Zech, A.; H. E. S. S. Collaboration
France, Germany, Ireland, Armenia, United Kingdom, Poland, South Africa, Namibia, Czech Republic, Australia
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, ~17σ 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 (ΔΓX ≈ 0.7) are also observed, which appear to be mirrored in the VHE band.
Conclusions: The SED of PKS 2005-489, 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.