**3. Prompt Emission from a Structured Jet**

The origin of the prompt emission of GRBs is not well understood yet. Generally speaking, the emission is thought to be powered by some mechanism that dissipates the dominant form of energy in the jet (either kinetic or magnetic), transforming it into internal energy. In most scenarios, part of the latter takes the form of relativistic particles with a non-thermal energy distribution, which produces the observed emission by means of some radiative process at the photosphere or beyond [154]. Different dissipation mechanisms operating within the relativistic outflow and different radiation mechanisms (typically synchrotron or inverse Compton) have been proposed, but no compelling evidence has been found yet in support of any of the envisaged scenarios. Still, the jet structure might have a leading role in explaining at least some of the prompt emission features.
