Radiative transfer models of two transitional type Ia supernova ( SNe Ia ) have been produced using the abundance stratification technique .
These two objects –designated SN 2007on and SN 2011iv– both exploded in the same galaxy , NGC 1404 , which allows for a direct comparison .
SN 2007on synthesised 0.25 M _ { \odot } of ^ { 56 } Ni and was less luminous than SN 2011iv , which produced 0.31 M _ { \odot } of ^ { 56 } Ni .
SN 2007on had a lower central density ( \rho _ { c } ) and higher explosion energy ( E _ { kin } \sim 1.3 \pm 0.3 \times 10 ^ { 51 } erg ) than SN 2011iv , and it produced less nuclear statistical equilibrium ( NSE ) elements ( 0.06 M _ { \odot } ) .
Whereas , SN 2011iv had a larger \rho _ { c } , which increased the electron capture rate in the lowest velocity regions , and produced 0.35 M _ { \odot } of stable NSE elements .
SN 2011iv had an explosion energy of E _ { kin } \sim 0.9 \pm 0.2 \times 10 ^ { 51 } erg .
Both objects had an ejecta mass consistent with the Chandrasekhar mass ( Ch-mass ) , and their observational properties are well described by predictions from delayed-detonation explosion models .
Within this framework , comparison to the sub-luminous SN 1986G indicates SN 2011iv and SN 1986G have different transition densities ( \rho _ { tr } ) but similar \rho _ { c } .
Whereas , SN 1986G and SN 2007on had a similar \rho _ { tr } but different \rho _ { c } .
Finally , we examine the colour-stretch parameter s _ { BV } vs . L _ { max } relation and determine that the bulk of SNe Ia ( including the sub-luminous ones ) are consistent with Ch-mass delayed-detonation explosions , where the main parameter driving the diversity is \rho _ { tr } .
We also find \rho _ { c } to be driving the second order scatter observed at the faint end of the luminosity-width relationship .