XMM-Newton Science Analysis System


xmmselect (xmmselect-2.67) [xmmsas_20230412_1735-21.0.0]

OGIP spectral products

Unlike the other product categories the generation of spectral products yields more than one output data set, viz.:

• OGIP spectrum for selected source region
• OGIP spectrum for selected background region
• Redistribution Matrix File (RMF) corresponding to source spectrum
• Auxiliary Response File (ARF) corresponding to source spectrum

These are created by the task especget which in turn is a wrapper around rmfgen and arfgen. Please consult the description of those package to learn more about functionality, flow of operations, and limitations. The primary input to especget is an image data set and two spatial selection expressions which need to mark an extraction region around a point source and a source-free background region. These can be generated with xmmselect in a convenient manner:

1. create an image in detector or sky coordinates as described above
2. when the image is displayed in Ds9 mark a normal circular region around the source of interest
3. mark another (not necessarily circular) region that shall comprise only background events. In order that xmmselect can distinguish the source from the background region, the latter must be assigned the Ds9 attribute Background. To do that, double click on the region marker and in the upcoming dialog select “Property” and “Background”. When done the border line style should change from solid to dashed.
   Be sure that no “exclude” regions have been selected.

4. click on OGIP Spectral Products. At this point xmmselect shall read the two regions from Ds9 and perform some basic checks for correctness (e.g. there is exactly one source and one background region). In case this fails informative error messages with suggested corrective actions shall be presented. If the two regions could be successfully read especget is directly called with the necessary inputs unless the option to invoke eregionanalyse on source image is active. In this case there is an additional step which aims at optimizing the position and extent of the source extraction region before it is passed to especget. This is done by running eregionanalyse on the source region. Its primary output is an optimized source region which shall be displayed as a white circle marker on the image. In addition a dialog box with some numerical results from the eregionanalyse run will be shown:
   
   
   
   
   Figure: Dialog with results of source region optimization process
   The dialog gives the option to proceed in three possible ways:
   1. Use optimized region
      The initially user-defined source region will be replaced by the new optimized region
   2. Use initial region
      The optimized region will be erased from the image and execution proceeds with the initially defined region
   3. Start over
      All regions will be deleted from the image - new initial selections for source and background regions must be made
   In the first and second case especget is eventually invoked with the appropriate input.

Please note that the production of an RMF with especget is a computationally intensive task and can take several tens of minutes on a moderately loaded workstation. There is however the option to skip the RMF-generation stage (please consult especget documentation for a description) in which case the task should run to completion within minutes. If it finishes successfully the generated source spectrum shall be shown via dsplot.