  Aims. The high-redshift (z = 4:048) gamma-ray burst GRB 060206 showed unusual
behavior, with a significant rebrightening by a factor of ~ 4 at about 3000 s
after the burst. We argue that this rebrightening implies that the central
engine became active again after the main burst produced by the first ejecta,
then drove another more collimated jet-like ejecta with a larger viewing angle.
The two ejecta both interacted with the ambient medium, giving rise to forward
shocks that propagated into the ambient medium and reverse shocks that
penetrated into the ejecta. The total emission was a combination of the
emissions from the reverse- and forward- shocked regions. We discuss how this
combined emission accounts for the observed rebrightening. Methods. We apply
numerical models to calculate the light curves from the shocked regions, which
include a forward shock originating in the first ejecta and a forward-reverse
shock for the second ejecta. Results. We find evidence that the central engine
became active again 2000 s after the main burst. The combined emission produced
by interactions of these two ejecta with the ambient medium can describe the
properties of the afterglow of this burst. We argue that the rapid rise in
brightness at ~ 3000 s in the afterglow is due to the off-axis emission from
the second ejecta. The precession of the torus or accretion disk of the central
engine is a natural explanation for the departure of the second ejecta from the
line of sight.
