Analysis of Late--time Light Curves of Type IIb, Ib and Ic Supernovae

TL;DR

This paper analyzes late-time light curves of Type IIb, Ib, and Ic supernovae to better understand their ejecta properties, revealing heterogeneity and proposing a method to estimate effective opacity from observed parameters.

Contribution

It revisits supernova light curve analysis by collecting well-sampled data and introduces a way to determine effective opacity using observable properties.

Findings

Late-time light curves are heterogeneous.

Observed properties can estimate mean opacity.

Effective opacity is smaller than standard estimates.

Abstract

The shape of the light curve peak of radioactive--powered core--collapse "stripped--envelope" supernovae constrains the ejecta mass, nickel mass, and kinetic energy by the brightness and diffusion time for a given opacity and observed expansion velocity. Late--time light curves give constraints on the ejecta mass and energy, given the gamma--ray opacity. Previous work has shown that the principal light curve peaks for SN~IIb with small amounts of hydrogen and for hydrogen/helium--deficient SN~Ib/c are often rather similar near maximum light, suggesting similar ejecta masses and kinetic energies, but that late--time light curves show a wide dispersion, suggesting a dispersion in ejecta masses and kinetic energies. It was also shown that SN~IIb and SN~Ib/c can have very similar late--time light curves, but different ejecta velocities demanding significantly different ejecta masses and kinetic energies. We revisit these topics by collecting and analyzing well--sampled single--band and quasi--bolometric light curves from the literature. We find that the late--time light curves of stripped--envelope core--collapse supernovae are heterogeneous. We also show that the observed properties, the photospheric velocity at peak, the rise time, and the late decay time, can be used to determine the mean opacity appropriate to the peak. The opacity determined in this way is considerably smaller than common estimates. We discuss how the small effective opacity may result from recombination and asymmetries in the ejecta.