MeV seed photons produced in shocks in a variable ultrarelativistic outflow gain energy by the Fermi mechanism, because the photons Compton scatter off relativistically colliding shells. The Fermi-modified high-energy photon spectrum has a nonuniversal slope and a universal cutoff. A significant increase in the total radiative efficiency is possible. In some gamma-ray bursts, most of the power might be emitted at the high-energy cutoff for this mechanism, which would be close to 100 MeV for outflows with a mean bulk Lorentz factor of 100.
- Gamma rays: bursts
- Radiation mechanisms: nonthermal
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science