We present Far Ultraviolet Spectroscopic Explorer ( FUSE ) and X-ray Multi-mirror Mission ( XMM-Newton ) data for the reverse shock of the O-rich supernova remnant ( SNR ) 1E 0102.2–7219 in the Small Magellanic Cloud ( SMC ) .
The FUSE observations cover three regions with significantly different optical [ O iii ] intensities , all associated with the relatively bright part of the X-ray ring .
Emission lines of O vi \lambda \lambda 1032 , 1038 are clearly detected in the FUSE spectra .
By combining this O vi doublet emission with the O vii triplet and O viii Ly \alpha fluxes from the XMM-Newton spectra and assuming a non-equilibrium ionization ( NEI ) model with a single ionization timescale for the spectra , we are able to find a narrow range of temperatures and ionization timescales that are consistent with the respective line ratios .
The increase of the ionization timescale \tau from North ( \tau \approx 0.6 \times 10 ^ { 11 } s cm ^ { -3 } ) to South-East ( \tau \approx 2 \times 10 ^ { 11 } s cm ^ { -3 } ) is indicative of increasing density in the X-ray bright ring , in good agreement with the optical [ O iii ] emission which is strongest in the South-East .
However , if we assume a plane-parallel shock model with a distribution of ionization timescales , the O vi emission appears to be inconsistent with O vii and O viii in X-rays .

We also analyze the total XMM-Newton EPIC-MOS 1/2 spectra for the three regions .
The X-ray spectra are dominated by strong emission lines of O , Ne , and Mg , however , we detect an emission component that accounts for 14 – 25 % of the flux and can be attributed to shocked ISM .
We find that there is no consistent set of values for the temperature and ionization timescale which can explain the observed line ratios for O , Ne , and Mg .
This would be consistent with a structured distribution of the ejecta as the O , Ne , Mg would have interacted with the reverse shock at different times .