  Indications of a GeV component in the emission from GRBs are known since the
EGRET observations during the 1990's and they have been confirmed by the data
of the Fermi satellite. These results have, however, shown that our
understanding of GRB physics is still unsatisfactory. The new generation of
Cherenkov observatories and in particular the MAGIC telescope, allow for the
first time the possibility to extend the measurement of GRBs from several tens
up to hundreds of GeV energy range. Both leptonic and hadronic processes have
been suggested to explain the possible GeV/TeV counterpart of GRBs.
Observations with ground-based telescopes of very high energy photons (E>30
GeV) from these sources are going to play a key role in discriminating among
the different proposed emission mechanisms, which are barely distinguishable at
lower energies. MAGIC telescope observations of the GRB 090102 (z=1.547) field
and Fermi Large Area Telescope (LAT) data in the same time interval are
analysed to derive upper limits of the GeV/TeV emission. We compare these
results to the expected emissions evaluated for different processes in the
framework of a relativistic blast wave model for the afterglow. Simultaneous
upper limits with Fermi and a Cherenkov telescope have been derived for this
GRB observation. The results we obtained are compatible with the expected
emission although the difficulties in predicting the HE and VHE emission for
the afterglow of this event makes it difficult to draw firmer conclusions.
Nonetheless, MAGIC sensitivity in the energy range of overlap with space-based
instruments (above about 40 GeV) is about one order of magnitude better with
respect to Fermi. This makes evident the constraining power of ground-based
observations and shows that the MAGIC telescope has reached the required
performance to make possible GRB multiwavelength studies in the very high
energy range.
