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

Abstract

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 56Ni mass model requires ∼0.90 M ⊙ of 56Ni, which is larger than the derived ejecta mass (∼0.10 M ⊙). Alternatively, we use the magnetar plus 56Ni and the fallback plus 56Ni models to fit the LCs of SN 2018gk, finding that the two models can fit the LCs. We favor the magnetar plus 56Ni 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 56Ni mass that can by synthesized by neutrino-powered core-collapse SNe, B = 6.52 × 1014 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 56Ni 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.