Nucleosynthesis inside Gamma-Ray Burst Accretion Disks

TL;DR

This study models nucleosynthesis within gamma-ray burst accretion disks and their winds, revealing layered compositions and significant production of nickel, copper, zinc, and neutron-rich nuclei, with implications for element synthesis in extreme astrophysical environments.

Contribution

It introduces a detailed one-dimensional model of nucleosynthesis in GRB accretion disks and winds, highlighting layered compositions and heavy element production, including neutron-rich nuclei.

Findings

Disks have five distinct compositional layers shifting inward with decreasing accretion rate.

Ni56 is abundantly ejected through the wind from the inner disk region.

Heavy elements like Cu63 and Zn64 are significantly produced in the wind.

Abstract

We investigate nucleosynthesis inside both a gamma-ray burst accretion disk and a wind launched from an inner region of the disk using one-dimensional models of the disk and wind and a nuclear reaction network. Far from a central black hole, the composition of accreting gas is taken to be that of an O-rich layer of a massive star before core collapse. We find that the disk consists of five layers characterized by dominant elements: O16, Si28, Fe54 (and Ni56), He4, and nucleons, and the individual layers shift inward with keeping the overall profiles of compositions as the accretion rate decreases. Ni56 are abundantly ejected through the wind from the inner region of the disk with the electron fraction \simeq 0.5. In addition to iron group, elements heavier than Cu, in particular Cu63 and Zn64, are massively produced through the wind. Various neutron-rich nuclei can be also produced in the wind from neutron-rich regions of the disk, though the estimated yields have large uncertainties.