Xselect supports region, phase and timing filters, as well as pha upper and lower bounds. These filters are not immediately applied to the events data, but stored and used in the next run of the extract command.
The filters are entered with the commands
xsel > filter time
xsel > filter region
xsel > filter phase
xsel > filter pha_cutoff
The timing filters can be entered in any of three formats, ASCII, or FITS GTI files, with start and stop columns, and Xronos window format files, with the command FILTER TIME FILE.
Timing filters can also be entered graphically using the FILTER TIME CURSOR command, after a light curve has been made.
Finally, you can enter GTI's by hand in either MJD, SpaceCraft Clock or UT with the commands FILTER TIME MJD, SCC, and UT.
The region filter is in SAOImage format. Region filters for the filter region command can be created graphically via the plot image command, which spawns an SAOIMAGE session. However the resultant regions have to be read back into Xselect by hand with the filter region command.
Another important point to note about the region filters, is that they contain no information about the physical image coordinates, only whatever binning you used in the image from which you made the region. So if you rebin your image, you must scale your region files accordingly before using them again.
At this point, only a lower and upper cutoff for the PHA are allowed.
The phase information is written into a Xronos-format window file (the sort created by the Xronos win command) by the FILTER PHASE command. You enter the epoch and period in days, then you can choose phase windows. Then Xselect will filter the events based on the union of all these phase windows.
You can save this phase information. To read it back into Xselect at a later time, use the FILTER TIME FILE command (which supports Xronos window timing files).
There are a few other filters created within Xselect which are automatically entered into the EXTRACT command. These are the GTI files (in FITS format) created by the SELECT MKF, and the SELECT HK commands, and the GTI files created in the selections made in the PLOT CURVE command.
The filters that have been entered can be listed by the command
xsel > show filter
They can also be cleared by the various CLEAR commands (see clear under the Xselect_Commands subheading)
xsel > clear region
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