Please use this identifier to cite or link to this item:
https://hdl.handle.net/2440/62931
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dc.contributor.author | Nicholas, B. | - |
dc.contributor.author | Rowell, G. | - |
dc.date.issued | 2010 | - |
dc.identifier.citation | Astronomy and Astrophysics: a European journal, 2010; 520(13):1-16 | - |
dc.identifier.issn | 0004-6361 | - |
dc.identifier.issn | 1432-0746 | - |
dc.identifier.uri | http://hdl.handle.net/2440/62931 | - |
dc.description.abstract | Context. Observations of very high-energy γ-rays from blazars provide information about acceleration mechanisms occurring in their innermost regions. Studies of variability in these objects lead to a better understanding of the mechanisms in play. Aims. To investigate the spectral and temporal variability of VHE (>100 GeV) γ-rays of the well-known high-frequency-peaked BL Lac object PKS 2155–304 with the HESS imaging atmospheric Cherenkov telescopes over a wide range of flux states. Methods. Data collected from 2005 to 2007 were analyzed. Spectra were derived on time scales ranging from 3 years to 4 min. Light curve variability was studied through doubling timescales and structure functions and compared with red noise process simulations. Results. The source was found to be in a low state from 2005 to 2007, except for a set of exceptional flares that occurred in July 2006. The quiescent state of the source is characterized by an associated mean flux level of (4.32 ± 0.09stat ± 0.86syst) × 10-11 cm-2 s-1 above 200 GeV, or approximately of the Crab Nebula, and a power-law photon index of Γ = 3.53 ± 0.06stat ± 0.10syst. During the flares of July 2006, doubling timescales of ~2 min are found. The spectral index variation is examined over two orders of magnitude in flux, yielding different behavior at low and high fluxes, which is a new phenomenon in VHE γ-ray emitting blazars. The variability amplitude characterized by the fractional rms Fvar is strongly energy-dependent and is . The light curve rms correlates with the flux. This is the signature of a multiplicative process that can be accounted for as a red noise with a Fourier index of ~2. Conclusions. This unique data set shows evidence of a low-level γ-ray emission state from PKS 2155–304 that possibly has a different origin than the outbursts. The discovery of the light curve lognormal behavior might be an indicator of the origin of aperiodic variability in blazars. | - |
dc.description.statementofresponsibility | A. Abramowski... B. Nicholas... G. Rowell... et al. | - |
dc.language.iso | en | - |
dc.publisher | E D P Sciences | - |
dc.rights | © ESO, 2010 | - |
dc.source.uri | http://dx.doi.org/10.1051/0004-6361/201014484 | - |
dc.subject | gamma rays: general | - |
dc.subject | galaxies: active | - |
dc.subject | galaxies: jets | - |
dc.subject | BL Lacertae objects: individual: PKS 2155–304 | - |
dc.title | VHE γ-ray emission of PKS 2155-304: spectral and temporal variability | - |
dc.title.alternative | VHE gamma-ray emission of PKS 2155-304: spectral and temporal variability | - |
dc.type | Journal article | - |
dc.contributor.organisation | H.E.S.S. Collaboration | - |
dc.identifier.doi | 10.1051/0004-6361/201014484 | - |
pubs.publication-status | Published | - |
dc.identifier.orcid | Rowell, G. [0000-0002-9516-1581] | - |
Appears in Collections: | Aurora harvest Chemistry and Physics publications IPAS publications |
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File | Description | Size | Format | |
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hdl_62931.pdf | Published version | 945.49 kB | Adobe PDF | View/Open |
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