# Type Ia SN 2019ein: New Insights into the Similarities and diversities among High-Velocity SNe Ia

## TL;DR

This study provides detailed optical observations and spectral analysis of SN 2019ein, revealing its classification as a high-velocity Type Ia supernova with unique spectral evolution and structural properties, offering insights into explosion mechanisms.

## Contribution

It offers new spectral synthesis modeling results and compares the structure of HV and NV SNe Ia, highlighting differences in burning layers and spectral evolution.

## Key findings

- SN 2019ein belongs to the HV and Broad Line groups with rapid light curve decline.
- The Si II velocity decreases rapidly, correlating with light curve decline rate.
- Outer layers are consistent with delayed detonation models, differing from NV SNe like 2011fe.

## Abstract

We present optical observations of type Ia supernova (SN) 2019ein, starting at 2 days after the estimated explosion date. The spectra and the light curves show that SN 2019ein belongs to the High-Velocity (HV) and Bload Line groups with relatively rapid decline in the light curves (Delta m15(B) = 1.36 +- 0.02 mag) and the short rise time (15.37 +- 0.55 days). The Si II 6355 velocity, associated with a photospheric component but not with a detached high-velocity feature, reached ~ 20,000 km s-1 at 12 days before the B-band maximum. The line velocity however decreased very rapidly and smoothly toward the maximum light, where it was ~ 13,000 km s-1 as relatively low among HV SNe. This indicates that the speed of the spectral evolution of HV SNe Ia is correlated not only to the velocity at the maximum light, but also to the light curve decline rate like the case for Normal-Velocity (NV) SNe Ia. Spectral synthesis modeling shows that the outermost layer at > 17,000 km s-1 is well described by the O-Ne-C burning layer extending to at least 25,000 km s-1, and there is no unburnt carbon below 30,000 km s-1; these properties are largely consistent with the delayed detonation scenario, and are shared with the prototypical HV SN 2002bo despite the large difference in Delta m15(B). This structure is strikingly different from that derived for the well-studied NV SN 2011fe. We suggest that the relation between the mass of 56Ni (or Delta m15) and the extent of the O-Ne-C burning layer provides an important constraint on the explosion mechanism(s) of HV and NV SNe.