Early Observations of the Type Ia Supernova iPTF 16abc: A Case of Interaction with Nearby, Unbound Material and/or Strong Ejecta Mixing

Abstract

Early observations of Type Ia supernovae (SNe Ia) provide a unique probe of their progenitor systems and explosion physics. Here we report the intermediate Palomar Transient Factory (iPTF) discovery of an extraordinarily young SN Ia, iPTF 16abc. By fitting a power law to our early light curve, we infer that first light for the SN, that is, when the SN could have first been detected by our survey, occurred only 0.15 0.07 0.15  days before our first detection. In the ∼24 hr after discovery, iPTF 16abc rose by ∼2 mag, featuring a near-linear rise in flux for 3  days. Early spectra show strong C II absorption, which disappears after ∼7 days. Unlike the extensively observed Type Ia SN 2011fe, the B V 0 -( ) colors of iPTF 16abc are blue and nearly constant in the days after explosion. We show that our early observations of iPTF 16abc cannot be explained by either SN shock breakout and the associated, subsequent cooling or the SN ejecta colliding with a stellar companion. Instead, we argue that the early characteristics of iPTF 16abc, including (i) the rapid, near-linear rise, (ii) the nonevolving blue colors, and (iii) the strong C II absorption, are the result of either ejecta interaction with nearby, unbound material or vigorous mixing of radioactive 56 Ni in the SN ejecta, or a combination of the two. In the next few years, dozens of very young normal SNe Ia will be discovered, and observations similar to those presented here will constrain the white dwarf explosion mechanism.

Constraints on the Physical Properties of SNe Ia from Photometry

“…, of our sample together with the data for several other well-observed SNe Ia: SN 2017cbv(Hosseinzadeh et al 2017), SN 2011fe(Vinkó et al 2012), SN 20112cg, SN 2017fr(Contreras et al 2018), SN 2009ig (Marion et al 2016Foley et al 2012), iPTF16abc(Miller et al 2018), SN 2012ht) and SN 2013dy…”

“…The cause of this dichotomy is still debated (see Section 1). For example, Miller et al (2018) proposed physical models for the progenitor system and the explosion of iPTF16abc. This SN Ia showed blue, nearly constant (B − V ) 0 color starting from t ∼ -10 days, which was thought to be caused by strong 56 Ni-mixing in the ejecta.…”

SN 2019ein: New Insights into the Similarities and Diversity among High-velocity Type Ia Supernovae

“…As an example, the observations of SN 2011fe within one day since the explosion provided a strong constraint (≤ 0.1 − 0.25R ⊙ ; Nugent et al 2011, Goobar et al 2015. In the last decade, there are an increasing number of NV SNe for which similar constraints have been placed (e.g., Bianco et al 2011;Silverman et al 2012b;Zheng et al 2013;Yamanaka et al 2014;Goobar et al 2015;Im et al 2015;Olling et al 2015;Marion et al 2016;Shappee et al 2016;Hosseinzadeh et al 2017;Contreras et al 2018;Holmbo et al 2018;Miller et al 2018;Shappee et al 2018;Dimitriadis et al 2019;Shappee et al 2019). At the same time, diverse nature of the earliest light curve properties has also been noticed.…”

“…The light curves in the early phase are typically well-fit by a single power-law function (e.g., Nugent et al 2011). However, some SNe Ia showing noticeable deviation from this behavior have also been discovered (e.g., Hosseinzadeh et al 2017;Contreras et al 2018;Miller et al 2018), which required a fit by a broken powerlaw function (Zheng et al 2013;Zheng et al 2014). There is also a suggestion that the bright SN 1991T/1999aa-like SNe tend to show the excessive emission in the first few days (e.g., Stritzinger et al 2018;Jiang et al 2018), but it is probably caused by a mechanism other than the companion interaction .…”

ZTF Early Observations of Type Ia Supernovae. I. Properties of the 2018 Sample

“…Early photometry can constrain the radii of the possible companion and the progenitor star (Kasen 2010;Nugent et al 2011;Bloom et al 2012;Goobar et al 2014Goobar et al , 2015. The shape and duration of the rising light curves probe the radial distribution of radioactive 56 Ni in the exploding core, as well as the existence of circumstellar material (Piro & Nakar 2014;Dessart et al 2014;Firth et al 2015;Piro & Morozova 2016;Miller et al 2018).…”