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

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) gamma-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 ß_VHE = 1.10 +0.10 -0.13) on time scales larger than one day. An analysis of 5.5 yr of HE Fermi LAT data gives consistent results (ß_HE = 1.20 +0.21 -0.23, on time scales 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 (ß ~ 2) seen on shorter time scales 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.

11 pages, 16 figures

References in corpus (5)

• Observations of the Crab Nebula with H.E.S.S
• Stochastic Modeling of the Fermi/LAT Gamma-ray Blazar Variability
• The minijets-in-a-jet statistical model and the RMS-flux correlation
• Lognormal variability in BL Lacertae
• Long-term optical variability of PKS 2155-304

Cited by in corpus (18)

• Validation of open-source science tools and background model construction in $\gamma$-ray astronomy
• Connecting steady emission and Very High Energy flaring states in blazars: the case of Mrk 421
• Blazar variability power spectra from radio up to TeV photon energies: Mrk 421 and PKS 2155-304
• Flux Distribution of Gamma-Ray Emission in Blazars: The Example of Mrk 501
• Variability studies and modeling of the blazar PKS 2155-304 in the light of a decade of multi-wavelength observations
• X-ray Intraday Variability of the TeV Blazar PKS 2155-304 with Suzaku During 2005-2014
• Study of long-term flux and photon Index distributions of blazars using RXTE observations
• Particle acceleration in radio galaxies with flickering jets: GeV electrons to ultrahigh energy cosmic rays
• Optical variability power spectrum analysis of blazar sources on intranight timescales
• Galactic and Extragalactic Sources of Very High Energy Gamma-rays
• Simulations of Stochastic Long-Term Variability in Leptonic Models for External-Compton and Synchrotron Self-Compton Dominated Blazars
• Analysis methods to search for transient events in ground-based Very High Energy gamma-ray astronomy
• Optical monitoring in southern blazars. Analysis of variability and spectral colour behaviours
• Not so Swift: 20 years of multiwavelength observations of Mrk 421 and Mrk 501
• The H.E.S.S. extragalactic sky survey with the first decade of observations
• H.E.S.S.: The High Energy Stereoscopic System
• 20 years of monitoring: PKS 2155-304 and PKS 1510-089 in the eyes of Swift and Fermi. II. PKS 1510-089 and comparison
• Expected performance of the ALTO particle detector array designed for 200 GeV - 50 TeV gamma-ray astronomy