  We present the multi-wavelength study of those gamma-ray bursts observed by
TAROT. These events are characterized by the presence at early time of a rising
in their optical light curves lasting a few hundred of seconds. In one case
(GRB 060904B), a flare occurs at similar time in the X-ray band, while in the
other cases the X-ray light curves appear smooth during the optical rise. We
investigate the possible nature of this behavior and conclude th at a
multi-component emission is mandatory to explain the optical-to-X-ray
afterglow.
