distribution; two peaks at $T_{{\rm max}, 9} \sim 3 - 4$ and at $T_{{\rm max}, 9} \sim 5 - 6$. The former is the detonation wave propagating outward, as also seen in the C-DDT model. The latter one at higher $T_{\rm max}$ is due to the detonation wave propagating inward, near the central region where the fuel still has high densities. The gap between the two peaks corresponds to the (off-center) shell structure of the deflagration products (i.e., neutron-rich Fe-peak elements; Fig. 3).

Deflagration and Electron Captures
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In the densest region in the deflagration stage, electron capture reactions proceed to synthesize neutron-rich Fe-peak elements under NSE conditions. Figure 9 shows the electron fraction ($Y_{\rm e}$) as a function of $\rho_{\rm max}$, for the O-DDT model. The same figure for the other 2D models (not shown) is similar to the O-DDT model. Figure 9 shows that the electron capture becomes important at $\rho_{\rm max} 
\gsim 5 \times 10^{8}$ g cm$^{-3}$, and $Y_{\rm e}$ as low as $0.463$ is realized in the highest density region. Thus, the main product of the highest density region is stable $^{56}$Fe ($Y_{\rm e} \sim 0.464$), followed by $^{54}$Fe ($Y_{\rm e} \sim 0.481$) and $^{58}$Ni ($Y_{\rm 