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

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 (LC) shape of normal, transitional and subluminous 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 ⁵⁶Ni mass fraction, X _Ni, falls to the order of 0.03-0.10. For a given ⁵⁶Ni mass, M(⁵⁶Ni), v _edge is sensitive to the specific kinetic energy E _kin(M(⁵⁶Ni)/M _WD) of the corresponding region. Combining v _edge with LC parameters (i.e., s _BV, 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 that are too large to explain the observations. Finally, the subluminous 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.