Predicting Spectral Parameters in the Backscattering-dominated Model for the Prompt Phase of GRBs

We present new results of the backscattering-dominated prompt emission model in which the photons generated through pair annihilation at the center of a gamma-ray burst (GRB) are backscattered through Compton scattering by an outflowing stellar cork. Using a Comptonized pair annihilation spectrum accompanied by bremsstrahlung radiation for seed photons, we show that the obtained spectra produce a low-energy photon index in the range α ∼ −1.95 to −1.1, steeper high-energy slopes β ∼ −3.5 to −2.4, and spectral peak energies approximately a few KeV to a few tens of MeV. These findings are consistent with the values covered in GRB prompt phase observations.