Diagnosing GRB Prompt Emission Site with Spectral Cut-Off Energy

Understand

The site and mechanism of gamma-ray burst (GRB) prompt emission is still unknown.

• Although internal shocks have been widely discussed as the emission site of GRBs, evidence supporting other emission sites have been also suggested recently, including the closer-in photosphere where the fireball becomes transparent and further-out radii near the fireball deceleration radius where magnetic dissipation may be important.
• With the successful operation of the GLAST experiment, prompt high energy emission spectra from many GRBs would be detected in the near future.
• We suggest that the cut-off energy of the prompt emission spectrum from a GRB depends on both the fireball bulk Lorentz factor and the unknown emission radius from the central engine.