The TAROT archive rising afterglows

The TAROT telescopes (Tlescopes Action Rapide pour les Objets Transitoires) are two robotic observatories designed to observe the prompt optical emission counterpart and the early afterglow of gamma ray bursts (GRBs). 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 that a multi-component emission is mandatory to explain the optical-to-X-ray afterglow.