For detailed information and examples of running this tool, refer to the dmappend ahelp file.
Appending a region block may affect the output file GTIs (28 Feb 2011)
When appending a region block from one FITS file to another FITS file, the GTIs from the input file are applied to the output. To avoid this, use a subspace filter to ignore the input GTIs:
unix% dmcopy "evt2_repro.fits[@gti.fits]" evt2_new_gti.fits unix% dmappend "evt2_repro.fits[region][subspace -time]" evt2_new_gti.fits
The output file, evt2_new_gti.fits, will contain the GTIs applied from the file gti.fits. The GTIs (time subspace) of the evt2_repro.fits file are ignored.