  Magnetic fields may play a dominant role in gamma-ray bursts, and recent
observations by the Fermi satellite indicate that GeV radiation, when detected,
arrives delayed by seconds from the onset of the MeV component. Motivated by
this, we discuss a magnetically dominated jet model where both magnetic
dissipation and nuclear collisions are important. We show that, for parameters
typical of the observed bursts, such a model involving a realistic jet
structure can reproduce the general features of the MeV and a separate GeV
radiation component, including the time delay between the two. The model also
predicts a multi-GeV neutrino component.
