Survival of the Fittest: Numerical Modeling of Supernova 2014C

Abstract

Initially classified as a supernova (SN) type Ib, ∼ 100 days after the explosion SN 2014C made a transition to a SN type II, presenting a gradual increase in the Hα emission. This has been interpreted as evidence of interaction between the supernova shock wave and a massive shell previously ejected from the progenitor star. In this paper, we present numerical simulations of the propagation of the SN shock through the progenitor star and its wind, as well as the interaction of the SN ejecta with the massive shell. To determine with high precision the structure and location of the shell, we couple a genetic algorithm to a hydrodynamic and a bremsstrahlung radiation transfer code. We iteratively modify the density stratification and location of the shell by minimizing the variance between X-ray observations and synthetic predictions computed from the numerical model. By assuming spherical symmetry, we found that the shell has a mass of 2.6 M , extends from 1.6 ×10 17 cm to 1.87 × 10 17 cm, implying that it was ejected ∼ 60/(v w /100 km s −1 ) yrs before the SN explosion, and has a density stratification decaying as ∼ r −3 . We found that the product of metallicity by the ionization fraction (due to photo-ionization by the post-shock X-ray emission) is ∼ 0.5. Finally, we predict that, if the density stratification follows the same power-law behaviour, the SN will break out from the shell by mid 2022, i.e. 8.5 years after explosion.

Seven Years of SN 2014C: A Multiwavelength Synthesis of an Extraordinary Supernova

“…Typical orbital velocities if still bound, ∼10 km s −1 , are too small to be directly related to the motion of the fifth Hα Gaussian component or the substructure of the He I λ10830 line, which are of the order of several 100-1000 km s −1 (Section 5.1). The length scale of the orbit is also too small to be related to the CSM density perturbation length determined by Vargas et al (2021) to be ∼10 16 cm. At ∼10 km s −1 , the companion would have moved only ∼2 × 10 14 cm in the 7 yr since explosion, so it would appear essentially to be an unmoving source of Hα.…”

“…Different techniques result in different estimates of the density structure with distributions ranging from constant to declining as ρ ∝ r −3 (Margutti et al 2017;Tinyanont et al 2019;Brethauer et al 2020;Harris & Nugent 2020;Bietenholz et al 2021;Vargas et al 2021). Whatever the origin and morphology of the CSM, it can only have one density profile if it is spherically symmetric.…”

Seven Years of SN 2014C: a Multi-Wavelength Synthesis of an Extraordinary Supernova

“…The ejecta/torus boundary is subject to the instabilities we outlined in §5.3 that Suzuki et al (2019) argue could contribute to irregularities in the light curve that are more distinct for larger disk masses. It would be interesting if the radial length scales of the Kelvin-Helmholz instabilities were comparable to those deduced by Vargas et al (2021).…”

“…Typical orbital velocities if still bound, ∼10 km s −1 , are too small to be directly related to the motion of the fifth Hα Gaussian component or the substructure of the He I λ10830 line that are of order several 100 to 1000 km s −1 ( §5.1). The length scale of the orbit is also too small to be related to the CSM density perturbation length determined by Vargas et al (2021) to be ∼10 16 cm.…”

“…Different techniques result in different estimates of the density structure with distributions ranging from constant to declining as ρ ∝ r −3 (Margutti et al 2017;Harris & Nugent 2020;Tinyanont et al 2019;Brethauer et al 2020;Bietenholz et al 2021;Vargas et al 2021). Whatever the origin and morphology of the CSM, it can only have one density profile if it is spherically-symmetric.…”