Nucleosynthesis of r-process elements in GRB engines

We model the nucleosynthesis in black hole accretion disks, and it’s neighbouring region, at the base of a gamma ray burst. The result is abundant production of light isotopes, as well as heavier elements with mass numbers in the range A~60- 80, which corresponds to the first maximum of nuclide production in the process of rapid neutron capture (r-process). Isotopes are created mainly on the surface of accretion disk and in the area beyond it, where they are carried by the magnetized, neutrino-driven wind.


Figure above shows the distribution of the relative abundance of the isotope Nickel-60 in the outflows from the accretion torus around a black hole in GRB engine, within the distance of 500 gravitational radii. Black hole mass is 3 Solar masses, and its spin a=0.9. Computations of nucleosynthesis were based on the NSE (nuclear statistical equilibrium) conditions, and performed on the basis of GR MHD simulation results of the gamma ray burst engine model. Figure made by Katarzyna Wojczuk.


Figure above shows the integrated abundances of heavy isotopes in the function of their mass number, A. The computations of NSE equlibria were performed for the axisymmetric GRB engine models with three values of black hole spin. Other parameters of the engine (BH mass, torus mass, magnetization) were kept constant. Figure: by Katarzyna Wojczuk.

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