There are observational indications that relativistic outflows in AGNs are accelerated over distances that far exceed the scale of the central engine .
Examples include the radio galaxy NGC 6251 , where knots in the radio jets were inferred to accelerate from \sim 0.13 c at a distance of \sim 0.53 { pc } from the galactic nucleus to \sim 0.42 c at r = 1.0 { pc } , and the quasar 3C 345 , where the Lorentz factor of the radio knot C7 was deduced to increase from \sim 5 to > 10 as it moved from r = 3 { pc } to r = 20 { pc } .
It is argued , using exact semianalytic solutions of the relativistic MHD equations , that this behavior is a signature of magnetic acceleration .
The same basic driving mechanism may apply to the relativistic jets in AGNs , gamma-ray burst sources , and microquasars .