# A Physical Basis for the H-band Blue-edge Velocity and Light-Curve Shape Correlation in Context of Type Ia Supernova Explosion Physics

## TL;DR

This paper links the velocity of a specific spectral feature in Type Ia supernovae to their light-curve shape, providing insights into explosion physics and distinguishing between different explosion models.

## Contribution

It introduces a physical interpretation of the $v_{edge}$ velocity and its correlation with light-curve parameters, enhancing understanding of supernova explosion mechanisms.

## Key findings

- $v_{edge}$ correlates with light-curve shape across supernova types.
- Explosion models near the Chandrasekhar limit align with observed $v_{edge}$ values.
- Sub-luminous SN 2015bo suggests diverse explosion scenarios.

## Abstract

Our recent work demonstrates a correlation between the high-velocity blue edge, $v_{edge}$, of the iron-peak Fe/Co/Ni $H$-band emission feature and the optical light curve shape of normal, transitional and sub-luminous type Ia Supernovae (SNe Ia). We explain this correlation in terms of SN Ia physics. $v_{edge}$ corresponds to the sharp transition between the complete and incomplete silicon burning regions in the ejecta. It measures the point in velocity space where the outer $^{56}$Ni mass fraction, $X_{\rm{Ni}}$, falls to the order of 0.03-0.10. For a given $^{56}$Ni mass, $M(^{56}Ni)$, $v_{edge}$ is sensitive to the specific kinetic energy $E_{\rm kin}$($M(^{56}Ni)/M_{WD}$) of the corresponding region. Combining $v_{edge}$ with light curve parameters (i.e., s$_{BV}$, $\Delta m_{15,s}$ in $B$ and $V$) allows us to distinguish between explosion scenarios. The correlation between $v_{edge}$ and light-curve shape is consistent with explosion models near the Chandrasekhar limit. However, the available sub-$M_{Ch}$ WD explosion model based on SN 1999by exhibits velocities which are too large to explain the observations. Finally, the sub-luminous SN 2015bo exhibits signatures of a dynamical merger of two WDs demonstrating diversity among explosion scenarios at the faint end of the SNe Ia population.