We present a study of the peculiar Type Ia supernova 2001ay ( SN 2001ay ) .
The defining features of its peculiarity are : high velocity , broad lines , and a fast rising light curve , combined with the slowest known rate of decline .
It is one magnitude dimmer than would be predicted from its observed \Delta m _ { 15 } , and shows broad spectral features .
We base our analysis on detailed calculations for the explosion , light curves , and spectra .
We demonstrate that consistency is key for both validating the models and probing the underlying physics .
We show that this SN can be understood within the physics underlying the \Delta m _ { 15 } relation , and in the framework of pulsating delayed detonation models originating from a Chandrasekhar mass , M _ { \mathrm { Ch } } , white dwarf , but with a progenitor core composed of 80 % carbon .
We suggest a possible scenario for stellar evolution which leads to such a progenitor .
We show that the unusual light curve decline can be understood with the same physics as has been used to understand the \Delta m _ { 15 } –relation for normal SNe Ia .
The decline relation can be explained by a combination of the temperature dependence of the opacity and excess or deficit of the peak luminosity , \alpha , measured relative to the instantaneous rate of radiative decay energy generation .
What differentiates SN 2001ay from normal SNe Ia is a higher explosion energy which leads to a shift of the ^ { 56 } { \mathrm { Ni } } distribution towards higher velocity and \alpha < 1 .
This result is responsible for the fast rise and slow decline .
We define a class of SN 2001ay-like SNe Ia , which will show an anti-Phillips relation .