Modelling light curves of bipolar core collapse supernovae from the equatorial plane

TL;DR

This paper models the light curves of bipolar core collapse supernovae, suggesting that jets shape the ejecta and that a significant fraction of CCSNe exhibit bipolar morphology, especially in hydrogen-deficient cases.

Contribution

It introduces a bipolar toy model to fit supernova light curves, linking bipolar morphology to jet-driven explosions and estimating the prevalence of such structures among CCSNe.

Findings

Bipolar ejecta increase maximum luminosity and steepen decline for equatorial observers.

SN 2018gk likely resulted from a jet-driven explosion with energy > neutrino-driven limits.

Approximately 5-15% of CCSNe exhibit pronounced bipolar morphology.

Abstract

We use the two-components bipolar toy model of core collapse supernova (CCSN) ejecta to fit the rapid decline from maximum luminosity in the light curve of the type IIb CCSN SN 2018gk (ASASSN-18am). In this toy model we use a template light curve from a different CCSN that is similar to SN 2018gk, but that has no rapid drop in its light curve. The bipolar morphology that we model with a polar ejecta and an equatorial ejecta increases the maximum luminosity and causes a steeper decline for an equatorial observer, relative to a similar spherical explosion. The total energy and mass of our toy model for SN 2018gk are E=5e51 erg and M=2.7Mo. This explosion energy is more than what a neutrino-driven explosion mechanism can supply, implying that jets exploded SN 2018gk. These energetic jets likely shaped the ejecta to a bipolar morphology, as our toy model requires. We crudely estimate that f=2-5% of all CCSNe show this behavior, most being hydrogen deficient (stripped-envelope) CCSNe, as we observe them from the equatorial plane. We estimate the overall fraction of CCSNe that have a pronounced bipolar morphology to be 5-15% of all CCSNe.