Spectra of infant supernovae (SNe) within a few days since the explosion provide new probes on the natures of SN progenitors and explosions. The ‘golden’ sample, for which very-early spectra are accompanied by long-term observations that provide comprehensive diagnostics, is still very limited. We propose GMOS-N rapid ToO spectroscopy within 24 hrs after the discovery, for 20 very young supernova (SN) candidates, aiming at catching > 6 infant SNe (and > 3 genuinely infant SNe). The targets are then followed by our intensive follow-up program with the Seimei and Kanata telescopes as they are rapidly brightened. Combined with model analyses, we will provide a complete picture for these SNe, aiming at substantially deepening our understanding on the origin of the final activity of massive stars as a core-collapse (CC) SN progenitors, and the (multiple-channel) evolution of white dwarfs (WDs) toward thermonuclear SNe Ia.
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