XMM-Newton Science Analysis System: User Guide

4.8.6 Use of efluxer

efluxer converts an X-ray EPIC spectrum generated by evselect/xmmselect from the usual counts versus instrument channels space into physical units (i.e. flux density versus energy). The algorithm corrects for the energy redistribution and the effective area of the telescope, for any combination of scientific modes and filters. The output produced as a result of running this task is a FITS file containing the fluxed spectrum, which includes the columns, FLUX, ERROR, ENERGY, ENERGY_BIN. Figure 23 gives two examples to illustrates the results obtained by the use of the efluxer task.

The algorithm used by efluxer inherently degrades the spectral energy resolution with respect to the intrinsic instrumental one. Therefore, users are advised to use the EPIC fluxed spectra to obtain model independent fluxes in broad energy bands or in analysis of continuum shapes or for quick-look analysis and visualisation. Quantitative analysis of narrow-band spectral features or, more generally, any scientific goals requiring the full spectral resolution of the EPIC cameras, should be based on the standard forward-folding approach implemented in, e.g. Xspec[26], SPEX [17] or Sherpa[18], whereby source flux models are convolved with the instrumental response and the convolution compared to the count spectrum.

Figure 23: Examples of the results of the efluxer task for different spectral shapes. The left panel show the fluxed spectra of two sources and the right panel show for these two sources, the comparison with the actual observed counts once the fluxed spectra have been folded with the effective area and the response matrix (solid lines). The top panel shows a featureless spectrum heavily obscured so that most of the "soft" events detected are in practice due to redistribution of higher energy photons. The spectrum in the bottom panel also corresponds to a featureless source, but with no absorption so that the observed spectrum is strongly peaked at low energies. The same flux scale has been set in the top and bottom panels to remark the largely different spectral shapes.

More information on the task efluxer can be found on the online SAS documentation on individual SAS tasks.

Two examples on how to use efluxer are given in section § 4.12.