The Spectacular Ultraviolet Flash from the Peculiar Type Ia Supernova 2019yvq

Abstract

Early observations of Type Ia supernovae (SNe Ia) provide essential clues for understanding the progenitor system that gave rise to the terminal thermonuclear explosion. We present exquisite observations of SN 2019yvq, the second observed SN Ia, after iPTF 14atg, to display an early flash of emission in the ultraviolet (UV) and optical. Our analysis finds that SN 2019yvq was unusual, even when ignoring the initial flash, in that it was moderately underluminous for a SN Ia (M g ≈ −18.5 mag at peak) yet featured very high absorption velocities (v ≈ 15, 000 km s −1 for Si II λ6355 at peak). We find that many of the observational features of SN 2019yvq, aside from the flash, can be explained if the explosive yield of radioactive 56 Ni is relatively low (we measure M56 Ni = 0.31 ± 0.05 M) and it and other iron-group elements are concentrated in the innermost layers of the ejecta. To explain both the UV/optical flash and peak properties of SN 2019yvq we consider four different models: interaction between the SN ejecta and a nondegenerate companion, extended clumps of 56 Ni in the outer ejecta,

ZTF Early Observations of Type Ia Supernovae. II. First Light, the Initial Rise, and Time to Reach Maximum Brightness

“…We constrain the presence of extreme optical flashes in SNe Ia by searching our sample for sources with light curves that initially decline before following the typical rise of an SN Ia. While this simple criterion excludes events that exhibit an early bump, such as SNe 2017cbv and 2018oh, ZTF has found SNe Ia with an early optical flash (e.g., SN 2019yvq; see Miller et al (2020)). Furthermore, the detection of bumps, as opposed to "flashes" where the flux is observed to decline, requires physical models of the early emission (e.g., Levanon & Soker 2017), and cannot be captured by the empirical power-law models used in this study.…”

“…Finally, we conclude with a 15 There are claims of companion interaction based on short-lived optical "bumps" in the early light curves of individual SNe (e.g., Cao et al 2015;Marion et al 2016;Hosseinzadeh et al 2017;Dimitriadis et al 2019). Alternative models (e.g., Dessart et al 2014;Piro & Morozova 2016;Levanon & Soker 2017;Polin et al 2019; utilizing different physical scenarios can produce similar bumps, leading many (e.g., Kromer et al 2016;Noebauer et al 2017;Miller et al 2018Miller et al , 2020Shappee et al 2018Shappee et al , 2019 to appeal to alternative explanations to ejecta-companion interaction.…”

Exploring the diversity of double detonation explosions for type Ia supernovae: Effects of the post-explosion helium shell composition

“…of 17.6±0.7 d. The longer rise time of the IME-dominated models is more typical of normal SNe Ia (e.g. Ganeshalingam et al 2011;Firth et al 2015;Miller et al 2020a). Although in general we find that models with IGE-dominated shells show shorter rise times, there are some notable exceptions.…”

“…In Fig. 14(c), we compare a double-detonation model to SN 2019yvq (Miller et al 2020a). SN 2019yvq was a somewhat peculiar SN -it was slightly under-luminous, but showed high ve- locity spectral features.…”

“…Bianco et al 2011;Olling et al 2015;Papadogiannakis et al 2019;Miller et al 2020b) have shown that the evidence for clear bumps is relatively rare, but a few candidate objects have been proposed (e.g. Jiang et al 2017;Hosseinzadeh et al 2017;Li et al 2019;De et al 2019;Miller et al 2020a).…”