The Low-Energy Spectral Index of Gamma-Ray Burst Prompt Emission from Internal Shocks

The prompt emission of most gamma-ray bursts (GRBs) typically exhibits a non-thermal Band component. synchrotron radiation in the popular internal shock model is generally put forward to explain such However, low-energy photon index α∼−1.5 predicted by inconsistent with observed value α∼−1. Here, we investigate evolution magnetic field during propagation shocks within an ultrarelativistic outflow, and revisit fast cooling shock-accelerated electrons via for this evolutional field. We find that first nearly constant then decays as B′∝t−1, which leads reasonable range index, −3/2<α<−2/3. In addition, if rising electron injection rate GRB introduced, α reaches −2/3 more easily. thus fit spectra 080916c 080825c.