The spectrum of Gamma-ray Burst: a clue

Understand

In this work we numerically calculate the thermal radiation efficiency of the baryonic outflow.

• The possible outflow acceleration in the transparent stage, which lowers thermal radiation efficiency, has been taken into account.
• In the standard internal shock model for the prompt emission, the fast shells should move with a typical Lorentz factor $\gtrsim 5 \Gamma_{\rm i}$ otherwise the GRB efficiency will be in disagreement with the observations, where $\Gamma_{\rm i}$ is the bulk Lorentz factor of the shocked/emitting region.
• The photosphere radius of these fast shells is small and the thermal radiation is too strong to be effectively outshone by the internal shock emission.