This allows the entry of timing selections. There are three entry methods for timing filters, by the mouse cursor (FILTER TIME CURSOR), from a file (FILTER TIME FILE), or by the keyboard (FILTER TIME UT, SCC, MJD).
FILTER TIME FILE supports three formats : ascii and fits GTI, and the Xronos window format. They can be used in any combinations, and the GTI forms allow multiple files. Xselect automatically senses the file type, so there is no need to specify this.
FILTER TIME CURSOR requires that a light curve has been made. You will be provided with instructions when you give the command on how to use the mode...
The other three commands (UT, SCC and MJD) are for entering the timing filters from the keyboard. The command names specify the timing system : Universal Time, Modified Julian Days, or SpaceCraft Clock. If a light curve has been made, then these commands will put up the curve, and you will see your selections as you enter them. Start and stop times must be separated by a comma. The UT should be given in form yyyy-mm-ddThh:mm:ss.sss. These GTI's are then written to FITS files, which can be saved for later use with the SAVE TIME KEYBOARD command.
These timing filters are not immediately applied to the data, but rather stored for use in the next run of the extract command.
Some care must be taken in combining timing files. The way it is done is the following: The intervals within each file are ORed together, then all the separate input files are ANDed together to make up the resultant GTI file.
Consequently, if you wish to OR two ascii or fits GTI files, you have to put them together into one file. There is no requirement that they be time ordered, so for ascii files this is as simple as cat'ing the files. For FITS files the fmerge task will do the trick, or if you want to be fancier, the mgtime task. Xselect does not do this for you however.
To see that the extract comand has done what you expected, you can use the show goodtime command after you run extract to see the resultant GTI's.
xsel > filter time file <file list>
To enter two ascii files (ascii1.flt, and ascii2.flt), and two fits files (fits1.flt and fits2.flt) you would say:
xsel > filter time file "ascii1.flt ascii2.flt fits1.flt fits2.flt"
To remove the file ascii1.flt, you can say
xsel > filter time file "-ascii1.flt"
Though CLEAR TIME FILE is more straightforward.
The list of files can be put in a file, say time.lis, one on a line, and entered via
xsel > filter time file "@time.lis"
The quotes are required (see the XPI magic subheading).
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