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

Abstract

In this paper, we perform a comprehensive study for the physical properties of SN 2018gk which is a luminous type IIb supernova (SN). We find that the early-time photospheric velocity vary from a larger value to a smaller value before the photosphere reach a temperature floor. We generalize the photosphere modulus and fit the multi-band light curves (LCs) of SN 2018gk. We find that the $^{56}$Ni mass model require $\sim0.90$ M$_\odot$ of $^{56}$Ni which is larger than the derived ejecta mass ($\sim0.10$ M$_\odot$). 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 since the parameters are rather reasonable ($M_{\rm ej} =1.65$ M$_\odot$, $M_{\rm Ni}=0.05$ M$_\odot$ which is smaller than the upper limit of the value of the $^{56}$Ni mass can by synthesized by the neutrino-powered core collapse SNe $B=6.52\times10^{14}$ G which is comparable to those of luminous and superluminous SNe studied in the literature, and $P_0=10.42$ ms which is comparable to those of luminous SNe), while the validity of the fallback plus $^{56}$Ni model depends on the accretion efficiency ($\eta$). Therefore, we suggest that SN 2018gk might be a SN IIb mainly powered by a central engine. Finally, we confirm the NIR excesses of the spectral energy distributions (SEDs) of SN 2018gk at some epochs and constrain the physical properties of the putative dust using the blackbody plus dust emission model.