Observations of the Very Young Type Ia Supernova 2019np with Early-excess Emission

Abstract

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Early Lightcurves of Type Ia Supernovae are Consistent with Nondegenerate Progenitor Companions

“…SN 2017cbv shows a very clear and well-resolved initial redward color evolution before overlapping with the blueward evolution after ≈5 days. The other two objects with early excesses (SNe 2017erp and 2018yu) display similar redward turns from between their first and second epochs, as does SN 2019np (discussed above and in Sai et al 2022, although again we don't confidently claim it as having an early excess). These "kinks" in the color evolution are more obvious in U − V than the range of early slopes in B − V , and presumably arise from the rapid cooling of the shocked ejecta in the early shock-dominated phase, before matching more typical color evolution in the later SNflux-dominated regime.…”

“…the outer ejecta, further proof that extremely early data (in this case within 12.4 hr of first light) can reveal key clues to the progenitor systems of SNe Ia. SN 2019np was also modeled in Sai et al (2022), which noted unusual early behavior and attributed it to Ni mixing. The residuals of SN 2019np do show behavior partly consistent with other early-bump objects, starting off with a > 5σ discrepancy with respect to the stretch template at the earliest epochs and decreasing over time, but the timescale of this behavior is significantly longer than for the other three objects with early bumps, lasting ∼10 days instead of the more expected ∼5 days.…”

“…Even for cases where these models are less successful at fitting the data (i.e. SN 2019np and the earliest data of SN 2018aoz, see Sai et al 2022;Ni et al 2022), the discrepancies reveal an exciting diversity of early lightcurve behavior. The sample size is small, but the strengths of early excesses and the distribution of viewing angles are statistically consistent with SNe Ia predominantly arising from Roche-lobe-overflowing single-degenerate progenitor systems.…”