| Abstract: | The mechanism responsible for the prompt gamma-ray emission of a gamma-ray burst continues to
remain an enigma. The detailed analysis of the spectrum of GRB 131014A observed by the Fermi
gamma ray burst monitor and Large Area Telescope has revealed an unconventional spectral shape that
significantly deviates from the typical Band function. The spectrum exhibits three distinctive breaks
and an extended power law at higher energies. Furthermore, the lower end of the spectrum aligns with
power-law indices greater than -0.5, and in the brightest region of the burst, these values approach +1.
The lowest spectral break is thereby found to be consistent with a blackbody. These observed spectral
characteristics strongly suggest the radiation process to be inverse Compton scattering in an optically
thin region. Applying the empirical fit parameters for physical modeling, we find that the kinetic
energy of the GRB jet of bulk Lorentz factor, Γ ∼ 400, gets dissipated just above the photosphere,
approximately at a radius of ∼ 1014 cm. The electrons involved in this process are accelerated to a
power-law index of δ = −1.5, and the minimum electron Lorentz factor, γmin , is approximately 3. In
summary, this study provides a comprehensive identification and detailed modeling of optically thin
inverse Compton scattering in the prompt emission of GRB 131014A. |
