  Although the observed spectra for gamma-ray burst (GRB) prompt emission is
well constrained, the underlying radiation mechanism is still not very well
understood. We explore photospheric emission in GRB jets by modelling the
Comptonization of fast cooled synchrotron photons whilst the electrons and
protons are accelerated to highly relativistic energies by repeated energy
dissipation events as well as Coulomb collisions. In contrast to the previous
simulations, we implement realistic photon-to-particle number ratios of
$N_{\gamma}/N_e \sim 10^{5}$ or higher, that are consistent with the observed
radiation efficiency of relativistic jets. Using our Monte Carlo radiation
transfer (MCRaT) code, we can successfully model the prompt emission spectra
when the electrons are momentarily accelerated to highly relativistic energies
(Lorentz factor $\sim 50-100$) after getting powered by $\sim30-50$ episodic
dissipation events in addition to their Coulomb coupling with the jet protons,
and for baryonic outflows that originate from moderate optical depths
$\sim20-30$. We also show that the resultant shape of the photon spectrum is
practically independent of the initial photon energy distribution and the jet
baryonic energy content, and hence independent of the emission mechanism.
