XMM-Newton Users Handbook

3.4.4.3 RGS spectral resolution for extended sources

The RGS spectral resolution depends on the angular extent of the observed source. For extended sources, emission lines are broadened according to the relation

$$\Delta\lambda({\rm ext}) = 0.138~~\theta({\rm ext})/{\rm m}$$ (2)

where $\Delta\lambda$(ext) is the resolution in Å in case of an extended source, for the spectral order m and a source extent of $\theta$(ext), in arcmin. This illustrates that, for a source extent of order 1$^\prime$, RGS still clearly outperforms EPIC in terms of spectral resolution. This is demonstrated for example by the observed spectra of a moderately extended source like 1E 0102.2-7219. This target is a supernova remnant in the Small Magellanic Cloud with an angular extent of 2$^\prime$. The first and second order spectra of 1E 0102.2-7219 are shown in Figs. 91, 92 and 93.