  We calculate radio-to-X-ray light curves for afterglows caused by non-thermal
emission from a highly relativistic blast wave, which is inferred from the
gamma-ray flux detected in GRB 980425 and from the very bright radio emission
detected in SN 1998bw. We find that the observed gamma-ray and radio light
curves are roughly reproduced by the synchrotron emission from a relativistic
fireball. The optical flux predicted for the non-thermal emission is well below
that of the thermal emission observed for SN 1998bw so that it will not be seen
at least for a few years. The model predicts the X-ray flux just above the
detection limit of BeppoSAX for the epoch when it was pointed to the field of
GRB980425. Therefore, the nondetection of X-ray and optical afterglows is
consistent with the model. The models presented here are consistent with the
physical association between SN 1998bw and GRB980425, and lend further support
to the idea that this object might correspond to an event similar to the
``hypernova'' or ``collapsar'' -- events in which the collapse of a massive
star forms a rotating black hole surrounded by a disk of the remnant stellar
mantle.
