  We propose a model in which the photons generated through pair annihilation
at the centre of a gamma ray burst (GRB) are backscattered through Compton
scattering by an outflowing stellar cork. Using pair annihilation spectrum for
seed photons, we show that the obtained spectra are capable of reproducing the
low energy slopes in the observed prompt spectra of most GRBs. We predict that
the low energy photon index ({\alpha}) ranges typically between 0.2 and -1.65
while the high energy slopes \beta are steeper. The Spectral peak energies
({\epsilon} peak ) cover a range from a few 10 x KeV to few MeV. Surveys have
shown that the population of most bursts reside within these ranges. We further
predict steep decay of photon flux at very low energies.
