upper hemisphere of the WD. Due to the lateral expansion in the outer layers of the star, the neutron-rich Fe-peak elements produced by electron captures end up in a characteristic off-center shell-like layer (Fig. 3). The detonation triggers on top of this blob at $\sim$ 1 second. It cannot cross ash regions (Maier & Niemeyer 2006) and has to burn around the ash blob in order to reach the central parts of the WD. Consequently, it initially propagates only outward (at $\sim$ 1.1 second).

At about 1.5 sec after the deflagration ignition, the detonation wave has burned around the ash blob and propagates inward. Since the off-center deflagration did not release much energy, the central parts of the WD are still dense and contain mostly unburned material. This material is converted to Fe-peak (predominantly $^{56}$Ni) by the detonation wave.

Characteristic thermal properties
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To understand the characteristic structure of the ejecta described in §3.2, we examine details of the thermal history of the tracer particles. Figure 6 shows the maximum temperature ($T_{\rm max}$) and density ($\rho_{\rm max}$) for each tracer particle (§3.1) after flame passage. For comparison, the same values for the classical W7 model are also shown. In Figure 