# Growing evidence that SNe Iax are not a one-parameter family: the case of PS1-12bwh

## TL;DR

This paper presents detailed observations and modeling of two SNe Iax, revealing that differences in their early spectra are due to variations in high-velocity ejecta, challenging the idea of a one-parameter family.

## Contribution

It demonstrates that SNe Iax exhibit diversity in high-velocity ejecta, indicating they are not a simple one-parameter family, through combined observational and radiative transfer analysis.

## Key findings

- Early spectra differences are due to ejecta density variations.
- Post-maximum spectra are nearly identical despite early differences.
- High-velocity ejecta variations explain spectroscopic diversity.

## Abstract

In this study, we present observations of a type Iax supernova, PS1-12bwh, discovered during the Pan-STARRS1 3$\pi$-survey. Our analysis was driven by previously unseen pre-maximum, spectroscopic heterogeneity. While the light curve and post-maximum spectra of PS1-12bwh are virtually identical to those of the well-studied type Iax supernova, SN 2005hk, the $-$2 day spectrum of PS1-12bwh does not resemble SN 2005hk at a comparable epoch; instead, we found it to match a spectrum of SN 2005hk taken over a week earlier ($-$12 day). We are able to rule out the cause as being incorrect phasing, and argue that it is not consistent with orientation effects predicted by existing explosion simulations. To investigate the potential source of this difference, we performed radiative transfer modelling of both supernovae. We found that the pre-maximum spectrum of PS1-12bwh is well matched by a synthetic spectrum generated from a model with a lower density in the high velocity ($\gtrsim$6000 km~s$^{-1}$) ejecta than SN 2005hk. The observed differences between SN 2005hk and PS1-12bwh may therefore be attributed primarily to differences in the high velocity ejecta alone, while comparable densities for the lower velocity ejecta would explain the nearly identical post-maximum spectra. These two supernovae further highlight the diversity within the SNe Iax class, as well as the challenges in spectroscopically identifying and phasing these objects, especially at early epochs.