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Combining RGS1 and RGS2 Spectra

While it is tempting to merge the RGS1 and RGS2 data, or data from different pointings, to provide a single spectrum with a signal-to-noise improvement over either individual spectrum, this is strongly discouraged since it results in data degradation.

The pointings of the two instruments are not identical, resulting in different dispersion angles and wavelength scales. Separate response files are always required for each unit. While it is possible to merge spectra and response files, great care must be taken to account for different exposure times, background subtractions, error propagation, and so on. However, the resulting response will always have inferior resolution to the originals. It is therefore simpler and more accurate to keep data from the two RGS units separate and use both sets to fit one model in tandem. Users who nonetheless wish to merge spectra from RGS1 and RGS2 can do so using the task rgscombine. Information on this task can be found here:
http://xmm.esac.esa.int/sas/10.0.0/doc/rgscombine/index.html


next up previous contents
Next: Approaches to Spectral Fitting Up: Fitting a Spectral Model Previous: Fitting a Spectral Model   Contents
Lynne Valencic 2011-07-26