2021MNRAS.501.2764G

Hypernovae powered by magnetic jets launched from the surface of rapidly rotating millisecond magnetars are one of the leading models to explain broad-lined Type Ic supernovae (SNe Ic-BL), and have been implicated as an important source of metal enrichment in the early Universe. We investigate the nucleosynthesis in such jet-driven hypernovae using a parametrized, but physically motivated, approach that analytically relates an artificially injected jet energy flux to the power available from the energy in differential rotation in the protoneutron star. We find ejected ⁵⁶Ni masses of 0.05 -0.45 M_☉ in our most energetic models with explosion energy > 10⁵² erg. This is in good agreement with the range of observationally inferred values for SNe Ic-BL. The ⁵⁶Ni is mostly synthesized in the shocked stellar envelope, and is therefore only moderately sensitive to the jet composition. Jets with a high electron fraction Y_e = 0.5 eject more ⁵⁶Ni by a factor of 2 than neutron-rich jets. We can obtain chemical abundance profiles in good agreement with the average chemical signature observed in extremely metal-poor (EMP) stars presumably polluted by hypernova ejecta. Notably, [Zn/Fe] >= 0.5 is consistently produced in our models. For neutron-rich jets, there is a significant r-process component, and agreement with EMP star abundances in fact requires either a limited contribution from neutron-rich jets or a stronger dilution of r-process material in the interstellar medium than for the slow SN ejecta outside the jet. The high [C/Fe] >= 0.7 observed in many EMP stars cannot be consistently achieved due to the large mass of iron in the ejecta, however, and remains a challenge for jet-driven hypernovae based on the magnetorotational mechanism.