The accuracy of the rgsproc results depends critically on the accuracy of the coordinates used for the prime source, i.e., the source used to compute corrections for spacecraft attitude variations in the dispersion coordinate (or beta channel).
If you have run previously rgsproc, there will be two sets of coordinates in your source list: PROPOSAL and ONAXIS. The first one gets the position from the target coordinates as given in the proposal and is, by default, the prime source. The second one is calculated from the spacecraft attitude. If you are working with the PPS files, then your source lists are probably longer because, in the PPS, the EPIC sources are added to the RGS source list. Also, in the PPS, the prime source is chosen as the brightest of the EPIC sources within the RGS field of view.
By default the prime source is the only one for which an spectrum is extracted and the only one excluded from the background extraction region.
Care should be taken that the target whose spectrum you are interested in is selected as prime in the source list and that its coordinates are correct.
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Open the source list with e.g. fv:
fv PxxxxxxyyyyR1eeeeSRCLI_0000.FIT
and check that the coordinates of the 'PROPOSAL' source are correct. If this is not the case, please go to the rgsproc, coordinates and masks thread.
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Display the dispersion versus cross dispersion and dispersion
versus energy images and overlay the selected region masks.
evselect table='PxxxxxxyyyyR1eeeeEVENLI0000.FIT:EVENTS' \ imageset='my_spatial.fit' xcolumn='BETA_CORR' ycolumn='XDSP_CORR' evselect table='PxxxxxxyyyyR1eeeeEVENLI0000.FIT:EVENTS' \ imageset='my_pi.fit' xcolumn='BETA_CORR' ycolumn='PI'\ yimagemin=0 yimagemax=3000 \ expression='REGION(PxxxxxxyyyyR1eeeeSRCLI_0000.FIT:RGS1_SRC1_SPATIAL,BETA_CORR,XDSP_CORR)' rgsimplot endispset='my_pi.fit' spatialset='my_spatial.fit' \ srcidlist='1' srclistset='PxxxxxxyyyyR1eeeeSRCLI_0000.FIT' \ device=/xs
The corresponding plots can also be found in the PPS files under the names PxxxxxxyyyyR1eeeeIMAGE_0000.PNG and PxxxxxxyyyyR1eeeeORDIMG0000.PNG, for the spatial and order images with overlaid sources and masks, respectively. Therefore, in case you are directly working with PPS files, you do not need to generate the plots yourself.
In case the plot does not look fine, you may want to select a different source as prime, define new source(s) and/or new source-inclusion and background-exclusion regions. Please refer to the rgsproc, coordinates and masks thread.
It is very important to check that all the sources in the RGS exposures have been correctly identified and that the event-selection regions centered on each source, or extraction masks, are correctly defined. It is also important to check that the region used for background extraction correctly excludes the existing sources.
In common with the other XMM-Newton instruments, RGS observations can be affected by high particle background periods caused by solar activity. The particles are most probably soft protons being focused by the mirrors and gratings. You should check your observations and, if necessary, filter out these periods before extracting any scientific products.
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Create a light curve of the pure background events:
evselect table=PxxxxxxyyyyR1eeeeEVENLI0000.FIT timebinsize=100 \ rateset=my_rgs1_background_lc.fit \ makeratecolumn=yes maketimecolumn=yes \ expression='(CCDNR==9)&&(REGION(PxxxxxxyyyyR1eeeeSRCLI_0000.FIT:RGS1_BACKGROUND,BETA_CORR,XDSP_CORR))' dsplot table=my_rgs1_background_lc.fit x=TIME y=RATE
where timebinsize is the time binning (in seconds) of the light curve and makeratecolumn set to yes is used to create a column RATE (giving count rates in counts/sec per time bin) in the output file. If it was set to no then a COUNTS column would be created instead, with total number of counts per bin.
The first part of the expression in the evselect task indicates that only events in CCD number 9 are selected (it is the one closest to the optical axis of the telescope, therefore the most affected by background flares). The second expression makes use of the background region already generated by rgsregions when called by rgsproc to get rid of genuine target variations.
Check the created light curve as displayed with dsplot for 'flares' with much larger count rates than the average . If such flares are visible, they can be filtered out using good time interval tables.
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If necessary, create a good time interval table:
Good Time Intervals, GTI, are the set of time intervals in which a given scientific product is accumulated. RGS event lists have one GTI extension for each chip generated by rgsproc. These GTI tables define good periods based on the attitude and housekeeping data included on the ODF.
You can construct an extra GTI table for filtering periods of high background out of the event list to be used in conjunction with its internal GTI tables:
tabgtigen table=my_rgs1_background_lc.fit gtiset=my_low_back.fit expression='(RATE<r)'The expression in the tabgtigen task indicates that only periods with count rates less than r counts/sec should be selected. The value of r should be chosen after inspection of the background light curve, typically from 0.1 to 2 counts/sec. -
Re-process the data with rgsproc starting at the
filter stage.
The filter stage needs a combined event list as input. The expected name for this file is PxxxxxxyyyyR1eeeemerged0000.FIT. If you have run rgsproc already, such a file has been created and it is already in your working directory. If you are instead working with the PPS products, the provided filtered event list is still a valid combined event list and can be used as input for rgsproc entrystage=3:filter. You should first copy it to a new file with the appropriate name:
cp PxxxxxxyyyyR1eeeeEVENLI0000.FIT PxxxxxxyyyyR1eeeemerged0000.FITand now you can interactively process the data with:rgsproc entrystage=3:filter auxgtitables=my_low_back.fitor with:rgsfilter mergedset=PxxxxxxyyyyR1eeeemerged0000.FIT \ evlist=PxxxxxxyyyyR1eeeeEVENLI0000.FIT \ auxgtitables=my_low_back.fit rgsproc entrystage=4:spectra
If you were happy with the PPS products, the validity checks were OK, and you did not need to run rgsproc at all, the answer is then NO. You still need to generate response matrices
rgsproc entrystage=4:spectra
With this rgsproc call, only two SAS
tasks are run:
rgsrmfgen
rgsfluxer
that generates the response matrices and the fluxed spectra,
respectively.
