For illustrative purposes, Fig. 117 shows a comparison of an XMM-Newton EPIC and a Chandra ACIS-I observation of a cluster with a 6 keV thermal plasma spectrum, 0.3 solar metallicity, a redshift of 0.3 and an X-ray flux in the 0.1-10 keV band of erg cm s (thus a fairly luminous system). Such a comparison gives a good feel for the capabilities of both instruments for performing studies of faint objects. We simulated the response of the Chandra ACIS front-illuminated CCD imaging instrument, using the response matrices supplied for the guest observer proposal submission. With a 30 ksec observation, ACIS is able to measure the temperature of the cluster to about 10% accuracy (assuming only poissonian noise and neglecting systematic effects). Following the same procedure, i.e., up-to-date detector response matrices, input spectrum and observing time, the combined response of the 3 EPIC focal plane cameras on XMM-Newton allows a 2.5% accuracy on the estimated cluster temperature (neglecting systematic effects).
The bottom panel of Fig. 117 also illustrates the different line spectral resolution that XMM-Newton EPIC and RGS and the Chandra ACIS instruments can achieve.