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Title:
Implications of very rapid TeV variability in blazars
Authors:
Begelman, Mitchell C.; Fabian, Andrew C.; Rees, Martin J.
Affiliation:
AA(JILA, University of Colorado, Boulder, CO 80309-0440, USA; Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, CO 80309-0391, USA), AB(Institute of Astronomy, Madingley Road, Cambridge CB3 0HA), AC(Institute of Astronomy, Madingley Road, Cambridge CB3 0HA)
Publication:
Monthly Notices of the Royal Astronomical Society: Letters, Volume 384, Issue 1, pp. L19-L23. (MNRAS Homepage)
Publication Date:
02/2008
Origin:
MNRAS
MNRAS Keywords:
accretion, accretion discs, galaxies: active, BL Lacertae objects: individual: PKS2155-304, BL Lacertae objects: individual: Mrk501, galaxies: jets, gamma-rays: observations
DOI:
10.1111/j.1745-3933.2007.00413.x
Bibliographic Code:
2008MNRAS.384L..19B

Abstract

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.
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