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A. M. Beloborodov (CITA)
Three processes shape the nuclear composition of GRB fireballs: (1) neutronization in the central engine, (2) nucleosynthesis in the fireball as it expands and cools, and (3) spallation of nuclei in subsequent internal shocks. The fireballs have a neutron excess and a marginally successful nucleosynthesis. They are composed of free nucleons, \alpha-particles, and deuterium. A robust result is the survival of a significant neutron component, which has important implications. Besides making the fireball an interesting source of multi-GeV neutrinos, the neutrons play a dramatic role in the explosion at radii R=1016-1017 cm and change the mechanism of the GRB afterglow emission.
Bulletin of the American Astronomical Society,
© 2003. The American Astronomical Soceity.