Non-dissipative photospheres in GRBs: Spectral appearance in the Fermi/GBM catalogue

Zeynep Acuner, Felix Ryde, Hoi-Fung Yu

A large fraction of gamma-ray burst (GRB) spectra are very hard below the peak. Indeed, the observed distribution of sub-peak power-law indices, $\alpha$, has been used as an argument f…