期刊
ASTRONOMY & ASTROPHYSICS
卷 511, 期 -, 页码 -出版社
EDP SCIENCES S A
DOI: 10.1051/0004-6361/200913073
关键词
galaxies: active; BL Lacertae objects: individual: PKS 2005-489; gamma rays: galaxies; X-rays: individuals: PKS 2005-489
资金
- German Ministry for Education and Research (BMBF)
- Max Planck Society
- French Ministry for Research
- CNRS-IN2P3
- CNRS
- UK Science and Technology Facilities Council (STFC)
- Charles University
- Polish Ministry of Science and Higher Education
- South African Department of Science and Technology
- National Research Foundation
- University of Namibia
- ESA Member States
- NASA
- STFC [PP/E001645/2] Funding Source: UKRI
- Science and Technology Facilities Council [PP/E001319/1, ST/F002963/1, PP/E001645/2] Funding Source: researchfish
Aims. Our aim is to study the very high energy (VHE; E > 100 GeV) gamma-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, similar to 17 sigma 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 similar to 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 similar to 300 GeV to similar to 5 TeV is characterized by a power law with a photon index, Gamma = 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 (Delta Gamma(X) approximate to 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.
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