Infant Type Ia Supernovae from the KMTNet. I. Multicolor Evolution and Populations

Le résumé fourni par la source

Abstract We conduct a systematic analysis of the early multiband light curves and colors of 19 Type Ia supernovae (SNe) from the Korea Microlensing Telescope Network SN Program, including 16 previously unpublished events. Seven are detected ≲1 day (as early as ≲1 hr) since the estimated epoch of first light and the rest ≲3 days. Some show excess emission within <0.5 day to ∼2 days, but most show pure power-law rises. Colors are initially diverse before ∼5 days, but converge to similar values at ∼10 days. We identify at least three populations based on 2–5 day color evolution: (1) “early-blues” exhibit slowly evolving colors consistent with a ∼17,000 K blackbody; (2) “early-reds” have initially blue B − V and red V − i colors that cannot simultaneously be fit with a blackbody—likely due to suppression of B- and i-band flux by Fe ii/iii and Ca ii—and evolve more rapidly; and (3) “early-yellows” evolve blueward, consistent with thermal heating from ∼8000–13,000 K. Distributions of early-blue and early-red colors are compatible with them being either distinct populations—with early-reds comprising (60 ± 15)% of them—or extreme ends of one continuous population, whereas the early-yellow population identified here is clearly distinct. Compared to the other populations, early-blues in our sample differ by exhibiting excess emission within 1–2 days, nearly constant peak brightness regardless of Δm 15(B) after standardization, and shallower Si ii features. Early-blues also prefer star-forming host environments, while early-yellows and, to a lesser extent, early-reds prefer quiescent ones. These preferences appear to indicate at least two Type Ia SN production channels based on stellar population age, while early-reds and early-blues may still share a common origin.

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