XMM-Newton at MPE - Data Analysis

Valid for XMMSAS version 5.3.3
This page will describe the control options to use the RGS XMMSAS task for more advanced purposes. When you run rgsproc with all the default setting as we have explained on the RGS complete ODF to scientific data files page the task may not always do all your requirements. On this page we describe the following applications:
I) Select another source or coordinates

II) Change the source selection region (e.g. for extended sources).

III) Handling of two sources in the RGS.

I) Select another source or coordinates:

The default settings of the XMMSAS task rgsproc assume that the object coordinates are those given in the proposal. Therefore the standard source list will contain two position PROPOSAL and ONAXIS. If your source is not on those two positions, or you have a second source on the RGS which spectrum you would like to study, perform the following steps: There are two solutions for this problem: a) run rgsproc with input source coordinates or b) add a new source to the source list file and rerun rgssources, rgsregions, and rgsspectrum again.

If you know already that your source is not on the PROPOSAL or ONAXIS position you can run rgsproc in two ways, either by putting in the coordinated directly on the command line of the task, or by using a source list created by the detection task edetectproc performed for the EPIC PN or MOS instruments. Please have a look at the Source Detection page to see how to perform the source detection. Our first example will use the coordinates given in the command line of the rgsproc task:
    rgsproc withsrc=yes srclabel=SOURCE srcra=113.64958 srcdec=31.88847
In this example the label in the source list file ...SRCLI_0000.FIT is set to SOURCE and the coordinated for the extraction are set to RA=132.10 and DEC=34.95. This will now create a source list file with a third entry labeled SOURCE.

The second option is to use a source list created by the source detection task edetectproc as described on the Source Detection page. As an example we use the source list emllist.ds:
    rgsproc withepicset=true epicset=emllist.ds
In this way the task rgsproc will add all sources with have significant counts in the band between 500 - 2000 eV (ID_BAND=2 in the source detection list) to the output source list. It still only processes the PROPOSAL and ONAXIS positions. To activate the sources in the source list, call the FTOOLS task fv and set in the SRCLIST in the column PROCESS all those sources on True which should be processed and of which you would like to get a spectrum. After this run the XMMSAS task rgsregions (see below). This task will create new region files that will be used by rgsspectrum to extract the source and background spectra.

If you have run rgsproc already, you can still add more sources to the source list later on without running rgsproc again. First of all this will save you lots of time, because rgsproc may take hours with large data sets and second the only things rgsproc would do is the same steps described below, besides creating the event files.

First step is to run the XMMSAS task rgssources. To add new sources there are two ways again, either by given the coordinates directly into the command line or by using a sources list created by the source detection task edetectproc as described on the Source Detection page. Here are examples for both:
    rgssources srclist=P0123710101R1S004SRCLI_0000.FIT \
               addusersource=true label=SOURCE1 \
	       ra=113.64958 dec=31.88847
This will take the already existing source list P0123710101R1S004SRCLI_0000.FIT and adds a new user-defined source with the coordinates ra=113.64958 and dec=31.88847 with the label name SOURCE1 into the source list.
    rgssources srclist=P0123710101R1S004SRCLI_0000.FIT withepicset=true
               epicset=emllist.ds 
In this example the sources of the EPIC source list emllist.ds (created by edetectproc) to the source list file P0123710101R1S004SRCLI_0000.FIT. The sources will be labeled EPIC00001 and so on depending how many sources have been derived from the EPIC source list. After adding (a) new source(s) to the source list you have to choose which sources of the list should be processed. For this purpose edit the extension SRCLIST in the source list. Best way to do this is by using the FTOOLS task fv. Set the logical in the table column PROCESS to T. Next step now is to run the XMMSAS task rgsregions. for normal point sources this is simply:
    rgsregions srclist=P0123710101R1S004SRCLI_0000.FIT
As the default, rgsregions assumes a file called ....EVENLI0000.FIT as the input events file, e.g. as in our example P0123710101R1S004EVENLI0000.FIT. If you have changed the name of the events file, you have to set the parameter evlist=... as well.

Now we are ready to extract the source photons for a spectrum by the task rgsspectrum:
    rgsspectrum evlist=P0123710101R1S004EVENLI0000.FIT \
                srclist=P0123710101R1S004SRCLI_0000.FIT \
		source=3
This will select the photos at the position of source #3 of the source list P0123710101R1S004SRCLI_0000.FIT from the input event file P0123710101R1S004EVENLI0000.FIT. The final source spectrum will be written in a file called P0123710101R1S004SRSPEC1003.FIT with the background spectrum P0123710101R1S004BGSPEC1003.FIT (both in first order).

If you want to check where the region for the selection of the photons are, use the XMMSAS task rgsimplot as described basically on the ODF to science data page. To run rgsimplot in our example you have to use an additional parameter srcidlist, which has to be set to 3:
    rgsimplot device=/CPS srclistset=P0123710101R1S004SRCLI_0000.FIT \
              endispset=image_r1_banana.fits spatialset=image_r1.fits \
	      srcidlist=3 plotfile=R1_plot.ps
Where device defines the output device (in our example it is the postscript file R1_plot.ps).

II) Change the source selection region:

If you have notived from the plot created by rgsimplot that the selected region is not exactly what you wanted you can control this by re-running rgsregions again. Below is an example that shows how to control in the spatial and PI plains:

Plot created by rgsimplot with default values This example shows the spatial (above) and the PI (below) plains. In the spatial plain the source it read out perfectly. However, in the PI plain the selection is a bit off. Below is now shown How to change the selection regions in spatial and PI spaces

The XMMSAS rgsregions has two parameters to control the selection in the spatial space xpsfabove and xpsfbelow. For both parameters the values mean the percentage of the PSF. The default is 90. to move the upper line of the selection region up give a higher number to the parameter xpsfabove. To move the lower line down give a higher value to xpsfbelow. in the example below the upper line will be moved up. In our example this is not necessary for scientific purposes, but it can be for other examples where you for example have an extended source. To control the selection in the PI space use the parameter pdistincl. It specifies the percentage of the pulse-height distribution. Default is 90 again. In order select a larger size in PI space select a higher number. In the example given below, the parameter is set to 96:
     rgsregions srclist=P0123710101R1S004SRCLI_0000.FIT \
                evlist= P0123710101R1S004EVENLI0000.FIT \ 
		pdistincl=96 xpsfabove=99
The result looks like this:

Plot created by rgsimplot with new values As shown in the upper panel, the selection region in the spatial plane has been changed. Also in the lower panel the selection in PI space have been broadened.

III) Handling of two sources in the RGS:

In some cases it can happen that in the RGS field of view two sources are observed, as shown in the example below:

2 sources in the RGS field of view The spatial-dispersion image shows two sources in the field of view of the RGS. The main source is read out directly by the standard rgsproc task.

One problem appears now with having two sources in the field of view: The tasks rgssources and rgsregions do not know about the second source. They assume that everything outside the area of the main source is background. Therefore they would use the second source as background, which of course would produce a wrong source spectrum. A way to check where the RGS tasks define the background region is to create an image by the XMMSAS task evselect and exclude the background regions. The information about the background region is given in the ....SRCLI_0000.FIT file in the extension RGS1_BACKGROUND (for the RGS1 background). As an example:
evselect table= P0123710101R1S004EVENLI0000.FITwithimageset=true \
  xcolumn=BETA_CORR ycolumn=XDSP_CORR \
  expression=".not. region(P0123710101R1S004SRCLI_0000.FIT:RGS1_BACKGROUND)" \
  imageset=image_r1_back.fits
The result is an image as displayed below:

Standard background in the RGS This image shows the source without the background region. Compared to the image above we see that the second source has been defines inside the background area.

How can we now solve this problem? The trick is that you have to add the second source to the source list as described above by using the task rgssources, e.g.:
rgssources srclist=P0123710101R1S004SRCLI_0000.FIT addusersource=true 
           label=SOURCE2 ra=113.64958 dec=31.88847
Next step is to edit the source file P0123710101R1S004SRCLI_0000.FIT by using the ftools task fv. Display the table if the extension SRCLIST. Now set in the columns PROCESS and BKG_EXCLUDE the logical to true. After this step, save the file and re-run rgsregions again. When you now create a new background excluded image by evselectit will give you an image as displayed below:

Background in the RGS considering the second source The image shows now the spatial image without the new background region. As we see the spectrum of the second star remains untouched by the background region.

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