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PKS2005-489 at VHE: four years of monitoring with HESS and simultaneous multi-wavelength observations
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2010 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 511, p. A52-Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
2010. Vol. 511, p. A52-
Keywords [en]
galaxies: active, BL Lacertae objects: individual: PKS 2005-489, gamma rays: galaxies, X-rays: individuals: PKS 2005-489
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics, Astroparticle Physics
Identifiers
URN: urn:nbn:se:lnu:diva-30254DOI: 10.1051/0004-6361/200913073ISI: 000275752400066OAI: oai:DiVA.org:lnu-30254DiVA, id: diva2:706030
Available from: 2014-03-18 Created: 2013-11-08 Last updated: 2017-12-05Bibliographically approved

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Becherini, Yvonne

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