Description:
<jats:p>We report on observations of SN 1006 with Suzaku. We firmly detected K-shell emission from Fe, for the first time, and found that the Fe ionization state is quite low. The broad-band spectrum extracted from southeast of the remnant was well-fitted with a model consisting of three optically thin thermal non-equilibrium ionization plasmas and a power-law component. Two of the thermal models are highly overabundant in heavy elements, and hence are likely due to ejecta. These components have different ionization parameters, $n_{\rm e}t \sim 1.4\times 10^{10}$cm$^{-3}$s and $n_{\rm e}t \sim 7.7\times 10^8$cm$^{-3}$s; it is the later one that produces Fe-K emission. This suggests that Fe has been heated by reverse shock more recently than the other elements, consistent with a picture where the ejecta are stratified by composition with Fe in the interior. On the other hand, the third thermal component is assumed to be solar abundance, and we associate it with emission from the interstellar medium. The electron temperature ($kT_{\rm e} \sim$0.5keV) is lower than that expected from the shock velocity, which suggests a lack of collisionless electron heating at the forward shock. The extremely low ionization parameter and extreme non-equilibrium state are due to the low density of the ambient medium.</jats:p>