Gamma-ray burst emission mechanisms

Gamma-ray burst emission mechanisms are physical processes proposed to produce bursts’ prompt gamma rays and later radiation, chiefly through synchrotron, inverse-Compton, or photospheric emission.

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Synchrotron radiation: Radiation emitted by charged particles spiraling through magnetic fields. Relativistic electrons in burst outflows can produce broad prompt spectra this way.
Relativistic jet: A narrow outflow of matter and energy moving at a speed close to the speed of light. The emitting plasma is carried outward in a jet moving at extreme relativistic speed.
GRB 080916C: A bright gamma-ray burst detected by the Fermi Gamma-ray Space Telescope in 2008. Its broad spectrum and high-energy photons constrain emission and transparency models.
Synchrotron line of death: A proposed incompatibility between some observed gamma-ray burst spectral slopes and simple optically thin synchrotron predictions. It highlights where the simplest synchrotron model may fail to match prompt spectra.
Inverse Compton scattering: A process in which energetic electrons transfer energy to lower-energy photons by scattering them. It can boost seed photons to gamma-ray energies in burst outflows.
Relativistic beaming: The concentration of radiation into a narrow direction when its source moves relativistically toward an observer. It helps explain why a compact emitting region can appear exceptionally bright.
GRB 090902B: A gamma-ray burst detected by Fermi in 2009 with a prominent quasi-thermal spectral component. Its thermal-looking component is a key case for photospheric emission.
Fast cooling problem: The mismatch between predicted steep low-energy synchrotron spectra from rapidly cooling electrons and many observed burst spectra. It challenges standard synchrotron interpretations of prompt emission.
Photospheric emission: Radiation released near the surface where an expanding plasma becomes transparent to photons. A burst’s hot, opaque jet can produce a thermal component at its photosphere.
Fermi acceleration: A process that increases particle energy through repeated encounters with moving magnetic structures or shock fronts. It is one proposed way to create the energetic electrons that radiate in bursts.