XMM-Newton Users Handbook

3.7.1.2 Non-dispersive spectroscopy: an example

For illustrative purposes, Fig. 114 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 $10^{-12}$ erg cm$^{-2}$ s$^{-1}$ (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. 114 also illustrates the different line spectral resolution that XMM-Newton EPIC and RGS and the Chandra ACIS instruments can achieve.

Figure 114: Top: Comparison of a modelled 30 ks observation of a cluster with a 6 keV thermal plasma spectrum with Chandra ACIS-I (purple line) and XMM-Newton EPIC (pn: black, MOS1: red, MOS2: green). Normalised counts are counts per spectral bin. Bottom: Comparison of the spectral response, for several line triplets at different energies, of XMM-Newton EPIC and RGS and Chandra ACIS instruments. Colour codes are: pn: black; MOS1: red; MOS2: green; RGS1/RGS2: dark/light blue; ACIS LEG/MEG/HEG: purple/green/orange.