Nuclear Composition of Gamma-Ray Burst Fireballs
Abstract
We study three processes that shape the nuclear composition of the fireballs in gamma-ray bursts (GRBs): (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 are shown to 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. First, as shown in previous works, neutrons can lead to observable multi-GeV neutrino emission. Second, as we show in an accompanying paper, the neutrons impact the explosion dynamics at radii up to 10^{17} cm and change the mechanism of the GRB afterglow emission.Keywords
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