Short-term VHE variability in blazars: PKS 2155-304

Abstract

Context: The $\gamma$-ray blazar PKS 2155-304 has attracted considerable attention because of its extreme TeV variability characteristics during an exceptional flaring period in 2006. Among the observed key findings are (i) a minimum variability timescale as short as $\sim 200$ sec and (ii) highly variable TeV emission, which in the frequency interval [$10^{-4}$ Hz, $10^{-2}$ Hz] can be described by a log-normal distribution and suggests an underlying multiplicative (and not additive) process. Aims: Simultaneously accounting for these findings appears difficult within conventional approaches. Following earlier suggestions for the TeV blazar Mkn 501, we explore a possible scenario where PKS 2155-304 is supposed to harbor a supermassive binary black hole system and where the observed TeV variability is dominated by emission from the less massive black hole. Methods: We analyze the constraints on the very high energy (VHE) source imposed by the observed variability characteristics and the integrated VHE luminosity output, and discuss its implications for a binary black hole system. Results: We show that for a secondary mass of $m_{\mathrm{BH}}\sim 10^7{M}_{\odot }$, fluctuations in the disk accretion rate that feed the jet could account for the observed red-noise type variability process down to frequencies of $\sim 10^{-2}$ Hz. Jet curvature induced by orbital motion, on the other hand, could further relax constraints on the intrinsic jet speeds. Conclusions: Because a binary system can lead to different (yet not independent) periodicities in different energy bands, a longterm (quasi-) periodicity analysis could offer important insights into the real nature of the central engine of PKS~2155-304.

5 pages, 1 figure; A&A in press

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• Implications of very rapid TeV variability in blazars
• Rapid variability in TeV blazars: the case of PKS 2155-304
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Cited by in corpus (12)

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• The minijets-in-a-jet statistical model and the RMS-flux correlation
• Characterizing the gamma-ray long-term variability of PKS 2155-304 with H.E.S.S. and Fermi-LAT
• Expected signatures from hadronic emission processes in the TeV spectra of BL Lac objects
• Charge-starved, relativistic jets and blazar variability
• The first GeV flare of the radio-loud narrow-line Seyfert 1 galaxy PKS 2004-447
• The Cluster-Scale Environment of PKS 2155-304
• Search for periodicities in High Energy AGNs with a time-domain approach
• TANAMI: Tracking Active Galactic Nuclei with Austral Milliarcsecond Interferometry. III. First-epoch S band images
• Convex X-ray Spectra of PKS 2155-304 and Constraints on the Minimum Electron Energy
• About 300 days optical quasi-periodic oscillations in the long-term light curves of the blazar PKS 2155-304
• VHE $\gamma$-ray observations of bright BL Lacs with the Large-Sized Telescope prototype (LST-1) of the CTAO