Implications of very rapid TeV variability in blazars

By M. Begelman, A. C. Fabian, Martin J. Rees. 2007

218 citations recorded by the source corpus.

We discuss the implications of rapid (few-minute) variability in the TeV flux of blazars, which has been observed recently with the HESS and MAGIC telescopes. The variability time-scales seen in PKS 2155−304 and Mrk 501 are much shorter than inferred light-crossing times at the black hole horizon, suggesting that the variability involves enhanced emission in a small region within an outflowing jet. The enhancement could be triggered by dissipation in part of the black hole magnetosphere at the base of the outflow, or else by instabilities in the jet itself. By considering the energetics of the observed flares, along with the requirement that TeV photons escape without producing pairs, we deduce that the bulk Lorentz factors in the jets must be ≳50. The distance of the emission region from the central black hole is less well-constrained. We discuss possible consequences for multi-wavelength observations.

Subfields: Atomic and Molecular Physics, and Optics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/b48c1507758b7ef3b661b1843af8795f8da60a97

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Citations in the corpus

Fast TeV variability in blazars: jets in a jet (2009, background): “Causalityarguments for the emitting region limit its size to be smaller than l′ < Γemctf = 9× 1014Γj,1σ1/22 tf ,300 cm (e.g. Begelman et al. 2008).”
Reconnection-driven plasmoids in blazars: fast flares on a slow envelope (2012, background): “A high Doppler factorδp >∼ 50 of the emitting material is required for the escape of the TeV radiation from the soft radiation field of the jet without extensive pair creation (Begelman et al. 2008).”
Synchrotron Self-Compton Analysis of TeV X-Ray-Selected BL Lacertae Objects (2008, methodology): “For fits to the full optical/UV/X-ray spectra for PKS 2155–304, we find that very large Doppler factors ( δD & 60 for PKS 2155–304) are necessary to explain high energy emission with the SSC mechanism (similar to the findings of Begelman et al. 2008).”
BLAZARS AS ULTRA-HIGH-ENERGY COSMIC-RAY SOURCES: IMPLICATIONS FOR TeV GAMMA-RAY OBSERVATIONS (2011, background): “…CASCADES Theγγ opacity argument allows us to place constraints on δ in BL Lac objects observed at TeV energies, and requires δ & 60 for PKS 2155-304 (Begelman et al. 2008) for the major July/August 2006 TeV flares (Aharonian et al. 2007a), and δ & 100 to be furthermore consistent with…”
Non-thermal particle acceleration in collisionless relativistic electron-proton reconnection (2016, background): “To avoid excessive pair production, which would prevent the gamma rays from escaping, the flaring regions must have local bulk Lorentz factors that exceed the mean for the jet by a factor of a few (Begelman et al. 2008).”
MINUTE-TIMESCALE >100 MeV γ-RAY VARIABILITY DURING THE GIANT OUTBURST OF QUASAR 3C 279 OBSERVED BY FERMI-LAT IN 2015 JUNE (2016, background): “In the synchrotron scenario, they also require extremely efficient particle acceleration, going beyond the established picture of the blazar sequence (Ghisellini et al. 1998).”
LEPTONIC AND HADRONIC MODELING OF FERMI-DETECTED BLAZARS (2013, background): “However, the very fast (timescales of a few minutes) variability of some TeV blazars (Albert et al. 2007; Aharonian et al. 2007) poses severe problems for single-zone models of blazars due to the required extremely high bulk Lorentz factors (Begelman et al. 2008).”
THE INTERNAL-COLLISION-INDUCED MAGNETIC RECONNECTION AND TURBULENCE (ICMART) MODEL OF GAMMA-RAY BURSTS (2010, background): “The data demand some smallscale enhanced emission units (Begelman et al. 2008; Giannios et al. 2009).”
FERMI LARGE AREA TELESCOPE VIEW OF THE CORE OF THE RADIO GALAXY CENTAURUS A (2010, background): “…from very-long baseline interferometry59 (VLBI) superluminal observations; e.g., Γj & 50 is required for a recent outburst from PKS 2155-60 304 (e.g., Begelman et al. 2008; Finke et al. 2008).61 Since blazars are strong sources of beamed γ-rays, it is natural to think that radio galaxies may62 be…”