Non-LTE Synthetic Observables of a Multidimensional Model of Type Ia Supernovae

TL;DR

This study develops a method to produce accurate non-LTE synthetic observables for 2D Type Ia supernova models using 1D calculations, improving agreement with observations and revealing line of sight effects.

Contribution

It introduces a technique to accurately simulate multidimensional supernova observables with 1D non-LTE calculations, overcoming computational challenges.

Findings

1D LTE observables match 2D when bolometric luminosities are equal.

Non-LTE calculations significantly improve agreement with observed supernova features.

Spectral line variations suggest line of sight effects influence supernova classification.

Abstract

Many promising explosion models for the elusive origin of Type Ia supernovae (SNe Ia) ultimately fail to completely reproduce a number of observed properties of these events. One limiting factor for many of these models is the use of the local thermodynamic equilibrium (LTE) assumption in the calculation of their synthetic observables, which has been shown to prevent the accurate prediction of a number of fundamental features of SNe Ia. The inclusion of high-accuracy non-LTE physics, however, increases computational cost and complexity such that multidimensional non-LTE calculations are often unfeasible, which can be problematic for models that are inherently multidimensional. In this work, we conduct radiative transfer calculations using 1D profiles that each correspond with a line of sight from an asymmetric, 2D SN Ia model. We find, in LTE, that the synthetic observables from these calculations efficiently reproduce those from the 2D calculation when an equivalence of bolometric luminosities between the 1D and 2D treatments is enforced. This allows for the accurate calculation of synthetic observables in 1D while still preserving multidimensional effects associated with the model. We leverage this to produce high accuracy observables from 1D non-LTE calculations, showing significantly improved agreement with observation, including a roughly 50% reduction of $B$-band decline rate into congruence with the observed Phillips relation. Additionally, our non-LTE observables show Si II $\lambda$5972 pEWs that are much more similar to observation, while spanning multiple Branch classes, suggesting that some spectral classifications of SNe Ia may arise from line of sight effects.