Over 500 Days in the Life of the Photosphere of the Type Iax Supernova SN 2014dt

Abstract

Type Iax supernovae (SNe Iax) are the largest known class of peculiar white dwarf SNe, distinct from normal Type Ia supernovae (SNe Ia). The unique properties of SNe Iax, especially their strong photospheric lines out to extremely late times, allow us to model their optical spectra and derive the physical parameters of the long-lasting photosphere. We present an extensive spectral timeseries, including 21 new spectra, of SN Iax 2014dt from +11 to +562 days after maximum light. We are able to reproduce the entire timeseries with a self-consistent, nearly unaltered deflagration explosion model from Fink et al. using TARDIS, an open source radiative-transfer code. We find that the photospheric velocity of SN 2014dt slows its evolution between +64 and +148 days, which closely overlaps the phase when we see SN 2014dt diverge from the normal spectral evolution of SNe Ia (+90 to +150 days). The photospheric velocity at these epochs, ∼400–1000 km s−1, may demarcate a boundary within the ejecta below which the physics of SNe Iax and normal SNe Ia differ. Our results suggest that SN 2014dt is consistent with a weak deflagration explosion model that leaves behind a bound remnant and drives an optically thick, quasi-steady-state wind creating the photospheric lines at late times. The data also suggest that this wind may weaken at epochs past +450 days, perhaps indicating a radioactive power source that has decayed away.

SN 2020udy: A New Piece of the Homogeneous Bright Group in the Diverse Iax Subclass

“…The present spectral synthesis covers a longer time, ∼90 days after the maximum. Camacho-Neves et al (2023) showed that radiative transfer codes that assume a blackbodyemitting photosphere can reproduce most of the spectral features and their evolution over years after the explosion because type Iax SNe never show a fully nebular spectrum. At the same time, spectral synthesis is less sensitive to the exact mass fractions of chemical elements at t 30 exp > days than at the earlier epochs.…”

“…The abundance tomography presented in this study is split into two parts: before t 30 exp = days from the date of explosion (hereafter referred to as early epochs), we follow the standard technique for synthesizing a spectral time series (Singh et al 2023), while for the later epochs, a simplified method is adopted similar to that of Camacho-Neves et al (2023). For both phases, the same time of the explosion (t JD 2459116.3 exp =…”