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The Progenitor and Early Evolution of the Type IIb SN 2016gkg

We report initial observations and analysis on the Type IIb SN 2016gkg in the nearby galaxy NGC 613



Tartaglia, L; Fraser, M; Sand, DJ; Valenti, S; Smartt, SJ; McCully, C; Anderson, JP; Arcavi, I; Elias-Rosa, N; Galbany, L; Gal-Yam, A; Haislip, JB; Hosseinzadeh, G; Howell, DA; Inserra, C; Jha, SW; Kankare, E; Lundqvist, P; Maguire, K; Mattila, S; Reichart, D; Smith, KW; Smith, M; Stritzinger, M; Sullivan, M; Taddia, F; Tomasella, L

We report initial observations and analysis on the Type IIb SN 2016gkg in the nearby galaxy NGC 613. SN 2016gkg exhibited a clear double-peaked light curve during its early evolution, as evidenced by our intensive photometric follow-up campaign. SN 2016gkg shows strong similarities with other Type IIb SNe, in particular, with respect to the He i emission features observed in both the optical and near-infrared. SN 2016gkg evolved faster than the prototypical Type IIb SN 1993J, with a decline similar to that of SN 2011dh after the first peak. The analysis of archival Hubble Space Telescope images indicate a pre-explosion source at SN 2016gkg’s position, suggesting a progenitor star with a ~mid-F spectral type and initial mass $15\mbox{–}20$ M ${}_{\odot }$, depending on the distance modulus adopted for NGC 613. Modeling the temperature evolution within $5\,\mathrm{days}$ of explosion, we obtain a progenitor radius of $\sim 48\mbox{–}124$ R ${}_{\odot }$, smaller than that obtained from the analysis of the pre-explosion images ($240\mbox{–}320$ R ${}_{\odot }$).

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