Entering Filters

Xselect supports region, detector, grade, phase and timing filters, pha upper and lower bounds, as well as a general filter on event attributes (ie columns in the event file). 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

xsel > filter detector

xsel > filter grade

xsel > filter column

xsel > filter mkf

xsel > filter hk

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 ds9 format. Region filters for the filter region command can be created graphically via the plot image command, which spawns a ds9 session. However the resultant regions have to be read back into Xselect by hand with the filter region command.

A very important point to note about the region filters is that they must either be in WCS or Physical coordinates. Regions created in Image coordinates will not work correctly if image binning is not 1.

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/FILTER MKF, and the SELECT/FILTER 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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Last modified: Tuesday, 10-Jan-2023 11:03:00 EST