S21A0003

As the booming development of wide-field survey facilities, breakthroughs in time-domain astronomy have been made in 2010s. The large aperture of the Subaru telescope and the wide field of the Hyper Suprime-Cam (HSC) make Subaru/HSC the most powerful survey facility of studying type Ia supernovae (SNe Ia) soon after their explosions. Here, we propose a six half-night deep multiband imaging survey which is optimized to catch the first light of SNe Ia at redshifts below 0.2. By balancing the observing depth, survey period, and total survey area of the Subaru/HSC observation, a half dozen ultra-early SNe Ia with brightness >∼ 300 times fainter than the peak can be discovered, and particularly, the deepest photometry of early-phase SNe Ia by far (i.e. even deeper than that of the best-observed SN Ia in history, SN 2011fe) can be promisingly achieved. The deepest early-phase photometry and ultra-early spectroscopies with Subaru/HSC and synergistic Gemini/GMOS observations not only can tightly constrain or directly identify/rule out specific kinds of single-degenerate progenitor systems but also can test the double white-dwarf merger scenario by constraining the nearby CSM distribution for the first time.

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