XMM-Newton Science Analysis System


emchain (emchain-11.20) [xmmsas_20190531_1155-18.0.0]

Customisation

Many options allow to run emchain on a subset of the data, restart from previous output, change the options of constituent tasks.

• The exposures, instruments and ccds parameters allow to run emchain on a subset of the data files (select an explicit list of exposures, instruments or CCDs).

• If addvigweight=Y, then evigweight is called to add a WEIGHT column to the events list (for extended source analysis).

• All individual steps in emchain except emframes may be skipped (withbadpix, withemevents, withattcalc, withemenergy, runevlistcomb, applyccdgti, makeflaregti). The whole loop over CCDs may be skipped if runccdloop=N (the only available functionalities are then those of Fig 1).

• If runevlistcomb=N, the merged event files are not built and the output is the collection of individual event and frame files. For example, the event files are called eventnn.out.mos, where nn is the same as CCDNR of the merged file (10*node+ccd). To avoid overwriting the files of one exposure with the next, they are renamed eventnn.out.MkEEEE where k is 1 or 2 and EEEE is EXPIDSTR (exposure number including S or U). They are not renamed if only one exposure is processed. Note that all the files must be renamed manually back to *.out.mos to allow restarting emchain from them (startfromodf=N).

• If randomize does not contain the letter P, emevents is run with randomizeposition=N. If randomize does not contain the letter T, emevents is run with randomizetime=N. If randomize does not contain the letter E, emenergy is run with randomizeenergy=N.

• Parameters may be passed to constituent tasks. The syntax is 'taskname:paramname=soandso', where 'paramname' is the parameter name for task 'taskname'. This will be passed as 'paramname=soandso' when calling 'taskname'.
  For example, 'emenergy:useccfdarkframe=Y' allows using the CCF dark frame for the CCD background correction (this corrects for variations at the pixel scale, whereas the E$_4$ data allows to correct for variations on scales larger than 5 pixels).
  This syntax does not allow to specify different parameter values on different occurrences of 'taskname' within emchain. The additional parameter will be passed on all occasions.
  Parameters specified in that way supersede possible settings of the same parameters by emchain itself.

• For calibration purposes (offsets' evolution), or checking optical loading, it can be useful to look at the background (base level) of a CCD. If writeccdbackground=Y, then emchain writes one file per CCD and per exposure, containing the CCD background (as determined by emenergy). This is similar to passing backgroundset to emenergy, but allows to save all such files under a different name.

• emchain normally ignores data obtained with CCD read-out gain set to low (/10). This behaviour may be overridden by setting processlowgain=Y. Low gain data is then treated as if it was normal data, and included in the merged events file in output, in addition to normal data. Its PI will still be wrong, and the flare screening mechanism will not work normally (because there are very few events at energy more than 100 keV even during flares).

• If fulloutput=Y, all columns originally present in the events files (in the ODF) are preserved in the output file (this about doubles the size of the file).

• If intermediate files from a previous call to emchain still exist (for example eventnn.in.mos files), emchain may use them as a starting point instead of the ODF (startfromodf=N).