  The paper is devoted to the analysis of particle acceleration in Gamma-Ray
Bursts and its radiative consequences. Therefore we get on one hand constraints
on the physics and on the other hand possible signatures of particle
acceleration that could be recorded by the new gamma ray instruments. We have
previously shown that UHECRs can be generated in GRBs even with conservative
assumptions on the magnetic field and the scattering capability of its
perturbations, provided that a suitable relativistic Fermi process is at work
during the so-called "internal shock" phase. We extend here the analysis of the
consequences of these assumptions to the whole prompt emission of both
electrons and protons. Indeed, assuming that the magnetic field decays in
$1/r^2$ and that the scattering time of particles is longer than the Bohm's
assumption, in particular with a rule derived from Kolmogorov scaling, we show
with no other parameter adaptation that the intensity of the subequipartition
magnetic field, that: i) UHECRs can be generated with a sufficient flux within
the GZK-sphere to account for the CR-spectrum at the ankle. ii) The peak energy
of the gamma spectrum around 100 keV, namely the so-called $E_{peak}$, is
conveniently explained. iii) A thermal component below the $E_{peak}$ is often
unavoidable. iv) The cosmic rays could radiate gamma rays around 67 MeV (in the
co-moving frame, which implies $\simeq 20$ GeV for the observer) due to
$\pi^0$-decay and a low energy neutrino emission (around 0.2 GeV) associated to
neutron decay and also neutrinos of energy between 5 and 150 GeV from muon
decay. v) The UHECRs radiate high energy gamma rays between a few tens of MeV
and 10 GeV (taking the pair creation process into account) due to their
synchrotron emission with a sufficient flux to be observable.
