Resolving the puzzle of type IIP SN 2016X

Abstract

ABSTRACT The enigmatic type IIP SN 2016X demonstrates the unprecedented asphericity in the nebular Hα line profile, the absence of nebular [O i] emission, and the unusual occultation effect due to the internal dust. The hydrodynamic modelling of the bolometric light curve and expansion velocities suggests that the event is an outcome of the massive star explosion that ejected 28 M$\odot$ with the kinetic energy of 1.7 × 1051 erg and 0.03 M$\odot$ of radioactive 56Ni. We recover the bipolar distribution of 56Ni from the Hα profile via the simulation of the emissivity produced by non-spherical 56Ni ejecta. The conspicuous effect of the dust absorption in the Hα profile rules out the occultation by the dusty sphere or dusty thick disc, but turns out consistent with the thin dusty disc-like structure in the plane perpendicular to the bipolar axis. We speculate that the absence of the nebular [O i] emission might originate from the significant cooling of the oxygen-rich matter mediated by CO and SiO molecules.