2019ApJ...882...68S

The optical and ultraviolet broadband photometric and spectroscopic observations of the Type II supernova (SN) 2016gfy are presented. The V-band light curve (LC) shows a distinct plateau phase with a slope of s₂ ∼ 0.12 mag (100 day)^–1 and a duration of 90 ± 5 days. Detailed analysis of SN 2016gfy provided a mean ⁵⁶Ni mass of 0.033 ± 0.003 M_☉, a progenitor radius of ∼350-700 R_☉, a progenitor mass of ∼12-15 M_☉, and an explosion energy of (0.9-1.4) x 10⁵¹ erg s^–1. The P-Cygni profile of Hα in the early-phase spectra (∼11-21 days) shows a boxy emission. Assuming that this profile arises from the interaction of the SN ejecta with the pre-existing circumstellar material (CSM), it is inferred that the progenitor underwent a recent episode (30-80 yr prior to the explosion) of enhanced mass loss. Numerical modeling suggests that the early LC peak is reproduced better with an existing CSM of 0.15 M_☉ spread out to ∼70 au. A late-plateau bump is seen in the VRI LCs during ∼50-95 days. This bump is explained as a result of the CSM interaction and/or partial mixing of radioactive ⁵⁶Ni in the SN ejecta. Using strong-line diagnostics, a subsolar oxygen abundance is estimated for the supernova H II region (12 + log(O/H) = 8.50 ± 0.11), indicating an average metallicity for the host of an SN II. A star formation rate of ∼8.5 M_☉ yr^–1 is estimated for NGC 2276 using the archival GALEX FUV data.