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

2012-10-24T08:53:43Z (GMT) by F. Acero F. Aharonian A. G. Akhperjanian G. Anton de Almeida UB A. R. Bazer-Bachi Y. Becherini B. Behera W. Benbow K. Bernloehr A. Bochow U. Katz J. Ripken S. Kaufmann M. Kerschhaggl D. Khangulyan M. Dalton B. Khelifi D. Keogh D. Klochkov W. Kluzniak G. Superina de Naurois M G. Pelletier T. Kneiske L. Rob N. Komin K. Kosack S. Schwarzburg R. Kossakowski G. Lamanna J. -. P. Lenain P. Espigat T. Lohse V. Marandon O. Martineau-Huynh A. Marcowith J. Bolmont S. Rosier-Lees D. Nedbal S. Schwemmer J. Masbou D. Maurin A. Szostek T. J. L. McComb D. Nekrassov B. Nicholas J. Niemiec C. Boisson S. J. Nolan S. Ohm L. Costamante A. Shalchi P. -. O. Petrucci P. H. Tam J. -. F. Olive E. D. O. Wilhelmi K. J. Orford S. Pita G. Puehlhofer M. Punch G. Coignet A. Quirrenbach B. C. Raubenheimer P. Eger J. -. P. Tavernet G. Rowell M. Raue S. M. Rayner M. Renaud B. Rudak C. B. Rulten J. Ruppel K. Egberts V. Sahakian A. Santangelo R. Moderski M. Sikora R. Schlickeiser J. Brucker F. M. Schoeck J. L. Skilton H. Sol L. Stawarz D. Gerbig R. Steenkamp F. Brun R. Terrier C. Stegmann M. K. Daniel F. Stinzing O. Tibolla M. Tluczykont van Eldik C A. Hoffmann P. Brun I. D. Davids G. Vasileiadis L. Fallon C. Venter L. Venter B. Giebels J. P. Vialle P. Vincent M. Vivier M. P. Arribas H. J. Voelk F. Volpe S. J. Wagner M. Ward B. Degrange C. Farnier R. Buehler J. F. Glicenstein A. A. Zdziarski A. Zech W. Hofmann H. E. S. S. Collaboration T. Bulik I. Buesching T. Boutelier P. M. Chadwick A. Charbonnier R. C. G. Chaves J. Mehault B. Glueck C. Deil P. Hofverberg A. Cheesebrough L. -. M. Chounet A. C. Clapson H. J. Dickinson A. Djannati-Atai W. Domainko M. C. Medina L. O. Drury F. Dubois M. Panter M. Holleran S. Fegan G. Dubus J. Dyks M. Dyrda F. Feinstein A. Fiasson A. Foerster M. Ostrowski G. Fontaine M. Fuessling V. Borrel P. Goret S. Gabici Y. A. Gallant L. Gerard D. Goering M. Hauser S. Heinz F. Rieger G. Heinzelmann G. Henri S. Hoppe G. Hermann E. Moulin J. A. Hinton D. Horns A. Jacholkowska de Jager OC U. Schwanke C. Jahn M. Naumann-Godo I. Jung G. Pedaletti K. Katarzynski
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, . 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 () 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.