Could the unusual optical afterglow of GRB 000301c arise from a non-relativistic shock with energy injection?

Recent observations on the gamma-ray burst (GRB) 000301c afterglow show that one sharp break appears in the global optical/IR light curves, and in particular the decay slope at late times is as steep as about -3.0. This unusual feature is clearly inconsistent with the standard afterglow shock model. Here we propose a non-standard model for the afterglow of GRB 000301c, in which an initial ultra-relativistic shock in a dense medium ("dirty environment") rapidly evolved to the non-relativistic phase in 1 day after the burst. During such a phase, the shock was refreshed by a strongly magnetized millisecond pulsar through magnetic dipole radiation. This refreshment led to flattening of the light curves. After the energy injection, the afterglow decayed as if the electron distribution index of the shocked medium, , derived from the optical spectrum. Therefore, our model can provide a plausible explanation for the peculiar optical/IR afterglow light curves of GRB 000301c.