Testing GRB models with the afterglow of GRB 090102
  We present the observations of the afterglow of gamma-ray burst GRB 090102.
Optical data taken by the TAROT, REM, GROND, together with publicly available
data from Palomar, IAC and NOT telescopes, and X-ray data taken by the XRT
instrument on board the Swift spacecraft were used. This event features an
unusual light curve. In X-rays, it presents a constant decrease with no hint of
temporal break from 0.005 to 6 days after the burst. In the optical, the light
curve presents a flattening after 1 ks. Before this break, the optical light
curve is steeper than that of the X-ray. In the optical, no further break is
observed up to 10 days after the burst. We failed to explain these observations
in light of the standard fireball model. Several other models, including the
cannonball model were investigated. The explanation of the broad band data by
any model requires some fine tuning when taking into account both optical and
X-ray bands.
