We present a 190 ks observation of the Galactic supernova remnant ( SNR ) G306.3 - 0.9 with Suzaku .
To study ejecta properties of this possible Type Ia SNR , the absolute energy scale at the Fe-K band was calibrated to a level of uncertainty less than 10 eV by a cross-calibration with the Hitomi microcalorimeter using the Perseus cluster spectra .
This enabled us for the first time to accurately determine the ionization state of the Fe K \alpha line of this SNR .
The ionization timescale ( \tau ) of the Fe ejecta was measured to be \log _ { 10 } \tau ( cm ^ { -3 } s ) = 10.24 \pm 0.03 , significantly smaller than previous measurements .
Marginally detected K \alpha lines of Cr and Mn have consistent ionization timescales with Fe .
The global spectrum was well fitted with shocked interstellar matter ( ISM ) and at least two ejecta components with different ionization timescales for Fe and intermediate mass elements ( IME ) such as S and Ar .
One plausible interpretation of the one-order-of-magnitude shorter timescale of Fe than that of IME ( \log _ { 10 } \tau = 11.17 \pm 0.07 ) is a chemically stratified structure of ejecta .
By comparing the X-ray absorption column to the H \emissiontype I distribution decomposed along the line of sight , we refined the distance to be \sim 20 kpc .
The large ISM-to-ejecta shocked mass ratio of \sim 100 and dynamical timescale of \sim 6 kyr place the SNR in the late Sedov phase .
These properties are consistent with a stratified ejecta structure that has survived the mixing processes expected in an evolved supernova remnant .