SN 2018gk Revisited: the Photosphere, the Central Engine, and the Putative Dust

Abstract

We perform a comprehensive study of the physical properties of SN 2018gk, which is a luminous Type IIb supernova (SN). We find that the early-time photospheric velocity varies from a larger value to a smaller one before the photosphere reaches a temperature floor. We generalize the photosphere modulus and fit the multiband light curves (LCs) of SN 2018gk. We find that the ^56 Ni mass model requires ∼0.90 M _⊙ of ^56 Ni, which is larger than the derived ejecta mass (∼0.10 M _⊙ ). Alternatively, we use the magnetar plus ^56 Ni and the fallback plus ^56 Ni models to fit the LCs of SN 2018gk, finding that the two models can fit the LCs. We favor the magnetar plus ^56 Ni model since the parameters are rather reasonable ( M _ej = 1.65 M _⊙ , M _Ni = 0.05 M _⊙ , which is smaller than the upper limit of the ^56 Ni mass that can by synthesized by neutrino-powered core-collapse SNe, B = 6.52 × 10 ^14 G, which is comparable to magnetic fields in luminous and superluminous SNe studied in the literature, and P _0 = 10.42 ms, which is comparable to initial periods for luminous SNe), while the validity of the fallback plus ^56 Ni model depends on the accretion efficiency ( η ). Therefore, we suggest that SN 2018gk might be an SN IIb powered mainly by a central engine. Finally, we confirm the near-IR excesses of the spectral energy distributions of SN 2018gk at some epochs and constrain the physical properties of the putative dust using the blackbody plus dust emission model.

Keywords

• Supernovae
• Type II supernovae
• Magnetars
• Circumstellar dust