SAS Watchout - 15.0.1 - multipointing mode - XMM-Newton
My observation has been made in EPIC multi-pointing mode, how can I process it correctly ?
In the standard processing of EPIC multi-pointing mode observations the actual position of the source, on the detector, in each pointing step is lost to the SAS. This can result in errors in the calculation of timing corrections and effective areas.
This will be solved in a future version of the SAS. In the meantime, the problem can be solved by taking the following manual steps. To complete step 2 you will need to use SAS version 15.0.1 or later.
- Calculate RA, DEC values for each pointing
After the ODF has been ingested with odfingest and with the SAS_ODF variable still pointing to the directory containing the ODF, execute
This will produce a FITS file called pointings.fit
The POINTATT extension will contain the RA, DEC values that are needed for each pointing step.
- Run attcalc on the event file generated by each pointing setting the reference point to the values calculated in step 1
attcalc eventset=2165_0412601501_EPN_S601_ImagingEvts.ds atthkset=2165_0412601501_AttHk.ds refpointlabel=user nominalra="284.189875" nominaldec="-37.92775"
- Manually change the pointing position keywords in each event file to these values.
This may be done with the 'fv' or 'fmodhead' tools from the ftools package
e.g. for the example in step 2
> fmodhead "2165_0412601501_EPN_S601_ImagingEvts.ds" h.dat > fmodhead "2165_0412601501_EPN_S601_ImagingEvts.ds" h.dat
where h.dat is a local text file that contains the two lines
> cat h.dat RA_PNT 284.189875 DEC_PNT -37.92775
After these steps have been completed the event files may be used to produce time series, images and spectra in the normal way. The products generated from these files will then have the correct attitude and exposure keywords written in the header.