Impact of clumping on core-collapse supernova radiation

TL;DR

This study investigates how clumping in supernova ejecta affects the observed radiation, showing that clumping accelerates the photospheric recession, increases luminosity, and causes reddening, with implications for interpreting supernova observations.

Contribution

The paper introduces a velocity-dependent clumping model in supernova ejecta and demonstrates its significant impact on supernova light curves and spectra during the photospheric phase.

Findings

Clumping increases the bolometric luminosity and causes earlier peak brightness.

Clumping leads to faster photospheric recession and spectral reddening.

The model suggests that real supernovae may experience even stronger effects due to unmodeled factors.

Abstract

There is both observational and theoretical evidence that the ejecta of core-collapse supernovae (SNe) are structured. Rather than being smooth and homogeneous, the material is made of over-dense and under-dense regions of distinct composition. Here, we explore the effect of clumping on the SN radiation during the photospheric phase using 1-D non-local thermodynamic equilibrium radiative transfer and an ejecta model arising from a blue-supergiant explosion (yielding a Type II-peculiar SN). Neglecting chemical segregation, we adopt a velocity-dependent volume-filling factor approach that assumes that the clumps are small but does not change the column density along any sightline. We find that clumping boosts the recombination rate in the photospheric layers, leading to a faster recession of the photosphere, an increase in bolometric luminosity, and a reddening of the SN colors through enhanced blanketing. The SN bolometric light curve peaks earlier and transitions faster to the nebular phase. On the rise to maximum, the strongest luminosity contrast between our clumped and smooth models is obtained at the epoch when the photosphere has receded to ejecta layers where the clumping factor is only 0.5 -- this clumping factor may be larger in Nature. Clumping is seen to have a similar influence in a Type II-Plateau SN model. As we neglect both porosity and chemical segregation our models underestimate the true impact of clumping. These results warrant further study of the influence of clumping on the observables of other SN types during the photospheric phase.