  Randomly oriented relativistic emitters in a relativistically expanding shell
provides an alternative to internal shocks as a mechanism for producing GRBs'
variable light curves with efficient conversion of energy to radiation. In this
model the relativistic outflow is broken into small emitters moving
relativistically in the outflow's rest frame. Variability arises because an
observer sees an emitter only when its velocity points towards him so that only
a small fraction of the emitters are seen by a given observer. Models with
significant relativistic random motions require converting and maintaining a
large fraction of the overall energy into these motions. While it is not clear
how this is achieved, we explore here, using two toy models, the constraints on
parameters required to produce light curves comparable to the observations. We
find that a tight relation between the size of the emitters and the bulk and
random Lorentz factors is needed and that the random Lorentz factor determines
the variability. While both models successfully produce the observed
variability there are several inconsistencies with other properties of the
light curves. Most of which, but not all, might be resolved if the central
engine is active for a long time producing a number of shells, resembling to
some extent the internal shocks model.
