In a couple of papers I've read that it's usual practice to fit early rise of supernova luminosity curve by $t^2$. Let me describe how I see it:
I take the early fast rising part of luminosity curve and then fit them to a curve:
$L = a\cdot\left( t - t_0 \right) ^ 2 + L_0,$
Where $t_0$ is the moment of explosion.
Is this approach right?