  Poynting flux driven outflows from magnetized rotators are a plausible
explanation for gamma-ray burst engines. We suggest a new possibility for how
such outflows might transfer energy into radiating particles. We argue that the
Poynting flux drives non-linearly unstable large amplitude electromagnetic
waves (LAEMW) which ``break'' at radii $r_t \sim 10^{14} $ cm where the MHD
approximation becomes inapplicable. In the ``foaming'' (relativisticly
reconnecting) regions formed during the wave breaks the random electric fields
stochastically accelerate particles to ultrarelativistic energies which then
radiate in turbulent electromagnetic fields. The typical energy of the emitted
photons is a fraction of the fundamental Compton energy $ \epsilon \sim f \hbar
c/r_e $ with $f \sim 10^{-3}$ plus additional boosting due to the bulk motion
of the medium. The emission properties are similar to synchrotron radiation,
with a typical cooling time $\sim 10^{-4}$ sec. During the wave break, the
plasma is also bulk accelerated in the outward radial direction and at larger
radii can produce afterglows due to the interactions with external medium. The
near equipartition fields required by afterglow models maybe due to magnetic
field regeneration in the outflowing plasma (similarly to the field generation
by LAEMW of laser-plasma interactions) and mixing with the upstream plasma.
