gtselect Help File

Usage: gtselect infile outfile ra dec rad tmin tmax emin emax eventClass

gtselect creates a new FITS file of selected rows from an input event data file based on user-specified cuts that are applied to each row of the input file. This application enables detailed selections to be made on data obtained from the SLAC data server, or generated using
gtobssim, the tool that generates simulated data (see gtobssim help).

The most common selections are those involving time range (minimum and maximum time), and energy range (minimum and maximum energy). For each cut that is applied, Data Subspace (DSS) keywords are written to the EVENTS header of the output FITS file that describe the selection.

This information is used by the likelihood tools and gtrspgen for computing exposure-related information.

evclsmin and evclsmax. For point source analysis, it is recommended that you include events with a high probability of being photons. This cut is performed by selecting diffuse class events with the gtselect tool by including the hidden parameters evclsmin and evclsmax on the command line. For LAT Pass 6 data, diffuse events are specified as event classes 3 and 4. This value may change as LAT data processing develops.

Example: gtselect

Parameters are passed following the FTOOLs model: by answering from a prompt; as a list in a command line; or by editing the parameter file. The command line option facilitates calling gtselect from a script.

To be prompted for gtselect parameter values, simply type in the command line: gtselect

Note: Not all parameters are prompted: some of the parameters are "hidden". If you want to change one of the "hidden" parameters, you should specify its value in the command line. For example, if you do not want to overwrite the existing output file, enter (at the command line):

gtselect clobber=no

An example of how to run the tool is given below:

In this case, quasar 3C279 (centered on Ra=193.98, Dec=-5.82) was simulated using gtobssim (see gtobssim for further explanation) with a photon spectral index of 1.96, an integrated flux of 3.48e-4 m^-2s^-1, until a radius of 20 degrees . The energy for the simulated events ranges between 20 MeV and 200000 MeV. Using gtselect it possible to select the events with energy larger than 100 MeV and within a radius of 20 degrees centered on Ra=193.98, Dec=-5.82 and a time range between 220838400 and 225590400 MET seconds:

The above example can also be run from the command line as follows:

> gtselect infile=3C279_events_0000.fits outfile=3c279_filtered.fits
ra=193.98 dec=-5.82 rad=20 tmin=220838400 tmax=225590400 emin=100
emax=100000 zmax=105

You can also use the defaults in the input file header by using the INDEF syntax:

> gtselect infile=3C279_events_0000.fits outfile=3c279_filtered.fits
ra=INDEF dec=INDEF rad=INDEF tmin=INDEF tmax=INDEF emin=100
emax=100000 zmax=105