The intermediate r-process in core-collapse supernovae driven by the magneto-rotational instability [HEAP]

Magneto-rotational supernovae are a possible astrophysical site of r-process nucleosynthesis, however, we have insufficient understanding of the explosion mechanism, especially the enhancement process of magnetic fields. We investigated the nucleosynthetic properties of magneto-rotational supernovae, based on a new explosion mechanism induced by the magneto-rotational instability (MRI). We performed a series of axisymmetric hydrodynamical simulations, numerically resolving the MRI, with detailed microphysics including neutrino heating. Explosion models driven by neutrino heating enhanced by the MRI showed mildly neutron-rich ejecta producing weak r-process nuclei $A \sim 130$, while an explosion model with a significant effect of magnetic fields reproduces a solar-like r-process pattern. More commonly seen abundance patterns in our models are in between the weak and regular r-process, producing lighter and intermediate mass nuclei. This intermediate r-process exhibits a variety of r-process abundance distributions, compatible with several r-process patterns in metal-poor stars. The amount of Eu ejecta reaches $\sim 10^{-5} M_\odot$ in strong-jet models that agrees with predicted values in the chemical evolution of early galaxies. In contrast, heating-dominant explosions aided by the MRI have a significant value of Fe ($^{56}{\rm Ni}$) and Zn ejecta masses, i.e. a typical value of supernovae and a significant value comparable to hypernove, respectively. The results clearly indicate that the effect of the MRI is significant in magneto-rotational supernovae for investing nucleosynthesis from the iron-group to r-process nuclei.

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N. Nishimura, H. Sawai, T. Takiwaki, et. al.
Wed, 9 Nov 16

Comments: 7 pages, 5 figures; submitted to ApJL