The X-ray spectrum of the supernova remnant 1E 0102.2-7219

In this letter we present the soft X-ray (5-35 a) spectrum of the supernova remnant (SNR) 1E 0102.2-7219 in the Small Magellanic Cloud, acquired by th e reflection grating spectrometers (RGS) aboard ESA's XMM-Newton. Observato ry. Because the RGS features a large dispersion angle, spatial-spectral con fusion is suppressed even for moderately extended (Delta theta similar to 2 ') sources. Consequently, these data, along with the spectrum of N132d (Beh ar ct al. 2001), provide what are probably the most detailed soft X-ray spe ctrum of entire SNRs. The diagnostic power of performing spectroscopy using groups of emission lines from single ions is demonstrated. In particular, the bright Lyman and helium series lines for light elements (C VI, O VII: O VIII, Ne IX & Ne X) show peculiar ratios, where the values [1s - np] / [1s - (n + 1)p] are systematically weaker than expected for electron impact ex citation close to ionization equilibrium, indicating nonequilibrium ionizin g (NEI) conditions in the source. The well known temperature diagnostics G (Te) = (i + f)/r of helium-like triplets (O VII & NeIX) confirm this sugges tion, with values that; are inconsistent with ionization equilibrium. The t emperatures implied are well above the maximum emission temperature T-m for each ion, and consistent with a purely ionizing plasma. The density diagno stics R(n(e)) = f/i meanwhile, are consistent with the low density limit, a s expected.