Implications of very rapid TeV variability in blazars

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, s...

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Bibliographic Details
Published in:Monthly notices of the Royal Astronomical Society. Letters Vol. 384; no. 1; pp. L19 - L23
Main Authors: Begelman, Mitchell C., Fabian, Andrew C., Rees, Martin J.
Format: Journal Article
Language:English
Published: Oxford, UK Blackwell Science Ltd 01.02.2008
Blackwell Publishing Ltd
Subjects:
accretion
accretion discs
accretion, accretion discs
BL Lacertae objects: individual: Mrk 501
BL Lacertae objects: individual: PKS 2155−304
galaxies: active
galaxies: jets
gamma-rays: observations
ISSN:1745-3925, 1745-3933
Online Access:Get full text
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Summary: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.
Bibliography:istex:4E61A45B55CAD09F9302CB7F03DBA340098D12CB
ark:/67375/HXZ-MVQ3LVL3-5
ISSN:1745-3925
1745-3933
DOI:10.1111/j.1745-3933.2007.00413.x