The electron-capture origin of supernova 2018zd

In the transitional mass range between white dwarf formation and iron core-collapse supernovae, stars are theoretically expected to become super-asymptotic giant branch stars with a degenerate O+Ne+Mg core, and electron capture onto Ne and Mg nuclei should initiate core collapse. In this talk, I will present six indicators of electron-capture supernovae and show how our observations of supernova 2018zd fulfill them: progenitor identification, circumstellar material, chemical composition, explosion energy, light curve, and nucleosynthesis. Then I will discuss the implications of this identification on the complex stellar evolution, supernova physics, cosmic nucleosynthesis, and remnant populations.