Program: GN-2021A-Q-200

We propose late-time spectroscopy of 10 − 15 supernovae (SNe) by FOCAS and SWIMS, aiming at connecting the properties of SNe soon after the explosion (in the first few days, by Seimei telescope) to the late phases (> 200 days, by Subaru). The earliest-phase data are sensitive to the properties of the outermost ejecta and the closest circum-stellar media (CSM), while the late-phase data provide totally different diagnostics on the nature of the progenitor, explosion, and the CSM in a larger scale. As Seimei and Tomo-e have started operation, it is time to connect these different diagnosing observations and seek for a unified picture of these stellar explosions. In S21A, the oppatunity of SWIMS operation will strenghten the science cases substantially from our previous programs using only FOCAS. Our main goals are (1) to identify an origin of the massive star activity in the final few years, and (2) to map different progenitors and explosoin mechanisms to sub classes in the diverse SN Ia zoo.