Characterizing the γ-ray long-term variability of PKS 2155 - 304 with H.E.S.S. and Fermi-LAT

H.E.S.S. Collaboration

Research output: Contribution to journalArticlepeer-review

30 Scopus citations

Abstract

Studying the temporal variability of BL Lac objects at the highest energies provides unique insights into the extreme physical processes occurring in relativistic jets and in the vicinity of super-massive black holes. To this end, the long-term variability of the BL Lac object PKS 2155-304 is analyzed in the high (HE, 100 MeV < E < 300 GeV) and very high energy (VHE, E > 200 GeV) γ-ray domain. Over the course of ∼9 yr of H.E.S.S. observations the VHE light curve in the quiescent state is consistent with a log-normal behavior. The VHE variability in this state is well described by flicker noise (power-spectral-density index βVHE = 1.10-0.13 +0.10) on timescales larger than one day. An analysis of ∼5.5 yr of HE Fermi-LAT data gives consistent results (βHE = 1.20-0.23 +0.21), on timescales larger than 10 days) compatible with the VHE findings. The HE and VHE power spectral densities show a scale invariance across the probed time ranges. A direct linear correlation between the VHE and HE fluxes could neither be excluded nor firmly established. These long-term-variability properties are discussed and compared to the red noise behavior (β ∼ 2) seen on shorter timescales during VHE-flaring states. The difference in power spectral noise behavior at VHE energies during quiescent and flaring states provides evidence that these states are influenced by different physical processes, while the compatibility of the HE and VHE long-term results is suggestive of a common physical link as it might be introduced by an underlying jet-disk connection.

Original languageEnglish
Article numberA39
JournalAstronomy and Astrophysics
Volume598
DOIs
StatePublished - 1 Feb 2017
Externally publishedYes

Keywords

  • BL Lacertae objects: individual: PKS 2155-304
  • Galaxies: active
  • Galaxies: jets
  • Galaxies: nuclei
  • Gamma rays: galaxies
  • Radiation mechanisms: non-thermal

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Fingerprint

Dive into the research topics of 'Characterizing the γ-ray long-term variability of PKS 2155 - 304 with H.E.S.S. and Fermi-LAT'. Together they form a unique fingerprint.

Cite this