  The nearby GRB 060216/SN 2006aj was an extremely long, weak and very soft
GRB. It was peculiar in many aspects. We show here that the X-ray,
ultraviolet/optical and radio afterglow of GRB 060218 have to be attributed to
different physical processes arising from different emission regions. From the
several components in this burst's afterglow only the radio afterglow can be
interpreted in terms of the common external shock model. We infer from the
radio that the blast wave's kinetic energy was $\sim 10^{50}$ erg and the
circumburst matter had a constant rather than a wind profile. The lack of a
"jet break" up to 22 days implies that the outflow was wide $\theta_j >1$. Even
though the late X-ray afterglow decays normally it cannot result from an
external shock because of its very steep spectrum. Furthermore, the implied
kinetic energy would have produced far too much radio. We suggest that this
X-ray afterglow could be attributed to a continued activity of the central
engine that within the collapsar scenario could arise from fall-back accretion.
"Central engine afterglow" may be common in under-luminous GRBs where the
kinetic energy of the blast wave is small and the external shock does not
dominate over this component. Such under-luminous GRBs might be very common but
they are rarely recorded because they can be detected only from short
distances.
