Nucleosynthesis in the gamma-ray burst accretion disks and associated outflows

TL;DR

This paper explores nucleosynthesis in low accretion rate gamma-ray burst disks, revealing synthesis of unusual nuclei and confirming production of common heavy elements, with implications for observed X-ray afterglow lines.

Contribution

It is the first to analyze nucleosynthesis in advection-dominated GRB disks at low accretion rates, identifying new synthesized nuclei and linking them to observed emissions.

Findings

Unusual nuclei like 31P, 39K, 43Sc are synthesized in the disk.

Heavy elements such as iron, nickel, silicon are produced and ejected.

Heavy element emission lines observed in GRB X-ray afterglows.

Abstract

We investigate nucleosynthesis inside the gamma-ray burst (GRB) accretion disks formed by the Type II collapsars and outflows launched from these disks. We deal with accretion disks having relatively low accretion rates: 0.001 M_sun s^{-1} <~ Mdot <~ 0.01 M_sun s^{-1} and hence they are predominantly advection dominated. We report the synthesis of several unusual nuclei like 31P, 39K, 43Sc, 35Cl and various isotopes of titanium, vanadium, chromium, manganese and copper in the disk. We also confirm that isotopes of iron, cobalt, nickel, argon, calcium, sulphur and silicon get synthesized in the disk, as shown by previous authors. Much of these heavy elements thus synthesized are ejected from the disk and survive in the outflows. Indeed, emission lines of many of these heavy elements have been observed in the X-ray afterglows of several GRBs.