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P. J. Wiita (GSU), ~ Gopal-Krishna (NCRA/TIFR), S. Dhurde (U Pune)
The effective values of apparent transverse velocity and flux boosting factors for the VLBI radio knots of blazar jets are found by integrating over the angular distributions of these quantities across the widths of jets with finite opening angles. For high bulk Lorentz factors (\Gamma > 10) variations across the jet can be quite large if the opening angle, \omega, is even a few degrees on sub-parsec scales. Resulting apparent speeds are often much slower than those obtained from the usual analyses that assume cylindrical jets (\omega = 0). For instance, for \Gamma = 100 and \omega = 5\circ, over 73% of sources would have v\rm app < 10 and 41% would actually appear subluminal. We thus reconcile the usually observed subluminal or mildly superluminal VLBI knot speeds with the very high (\Gamma > 20) Lorentz factors, required by the inverse Compton origin and rapid variability of TeV fluxes, as well as by intraday radio variability. It is therefore possible to associate the VLBI radio knots directly with shocks in the ultra-relativistic main jet flow, without invoking very rapid jet deceleration on parsec scales, requiring a spine-sheath geometry, or assuming extremely unlikely very small viewing angles.
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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.