Extended Data Fig. 8: ECSN rate estimators.

Comparison of the ECSN rate estimates: ‘SAGB’ is the SAGB mass window from stellar evolutionary calculations at solar metallicity⁵; ‘IIn’ is the observed Type IIn SN rate from a volume-limited (≤60 Mpc) sample⁷⁵; ‘IIn-P+2018zd’ is a rough lower limit of the Type IIn-P SN rate within 60 Mpc combined with SN 2018zd (Methods); ‘ILRT’ is a rough estimate from ILRTs within 30 Mpc⁸⁷; ‘NS’ is an estimated rate from the bimodality in the neutron star mass distribution³¹ assuming that the low-mass and high-mass peaks originate from ECSNe and Fe CCSNe, respectively; and ‘⁸⁶Kr’ is an upper limit from the ECSN nucleosynthesis calculation⁷⁶ assuming that ECSNe are the dominant production source of ⁸⁶Kr. The conversion between the fraction of all CCSNe and the SAGB mass window is performed assuming the Salpeter initial mass function with lower and upper CCSN mass limits of 7.5 M_⊙ and 120 M_⊙ (respectively) and maximum and minimum SAGB masses of 9.25 M_⊙ and 9.25 M_⊙ − ΔM_SAGB (respectively) at solar metallicity⁵. The grey vertical dotted line is where the minimum SAGB mass equals the assumed lower CCSN mass limit of 7.5 M_⊙. The grey shaded region shows a rough ECSN rate constraint by the IIn-P+2018zd lower limit and the nucleosynthesis upper limit.