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gtbkg.txt
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NAME
gtbkg - Creates a background spectrum file (PHA1 format).
USAGE
gtbkg phafile outfile scfile expcube expmap irfs srcmdl target
DESCRIPTION
To produce a background spectrum file (PHA1), gtbkg uses as input
several files that are created with other tools: The input spectrum
file (PHA1) by gtbin; The live-time file, by gtltcube; The exposure
map by gtexpmap; The source xml file by ModelEditor.
The exposure map is the same as the one created for the unbinned
likelihood analysis.
The background spectrum file contains total counts based on a gtlike
source model and covers the same energy bands and region-of-interest as
the input PHA1 file. The model will typically contain interstellar and
extragalactic diffuse components as well as nearby point sources.
PARAMETERS
phafile [filename]
Name of input spectrum file (PHA1). This file should be produced with
gtbin (option PHA1). Type "fhelp gtbin" for further explanation.
outfile [filename]
Output spectrum file (PHA1).
scfile [filename]
Spacecraft data file containing information such as the spacecraft
pointing as a function of time. This file could be generated by
gtorbsim for simulated observations (see gtorbsim help for further
explanation) or more commonly it can be obtained from the FSSC
website.
(sctable) [string]
Spacecraft data extension. Default is "SC_DATA".
expcube [filename]
FITS file containing livetime as a function of sky position and
off-axis angle. This file can be generated by gtltcube or obtained
from the FSSC website. See the gtltcube help for further explanation.
Default is "none".
expmap [filename]
Exposure map file used in an unbinned likelihood analysis and created
by gtexpmap. Do not use an exposure map that is appropriate for binned
analysis (i.e. from gtexpcube2). See gtexpmap help for further
explanation. Default is "none".
irfs [string]
Instrument response functions. The instrument response (PSF, effective
area, energy resolution) is currently a function of energy,
inclination angle (the angle between the source and the LAT normal)
and photon category. Since the LAT will usually survey the sky, a
source will be observed at different inclination angles. Each count
will therefore be characterized by a different instrument response
function (IRF). The default value is “CALDB”.
evtype [integer]
The evtype to be used in generating the background data. The
default is INDEF which will use the default in the PHA
file. This can be overridden by entering the desired event
type e.g. 3 for FRONT + BACK events.
srcmdl [filename]
XML file containing the source model definitions. The source model can
be generated by the ModelEditor utility or by following source model
templates. See the ModelEditor help for further explanation. This
model file can be the output of a likelihood fit (either binned or
unbinned) as well.
target [string]
The name of the target source as it appears in the source model
file. Its contribution will be excluded from the background
calculation. If there are no sources to exclude, this field may be
left blank or set to "none" (default).
(chatter) [integer]
This parameter fixes the output verbosity: no screen output (0),
nominal screen output (2), maximum verbosity (4). Default is "2".
(clobber) [boolean]
If true, an existing file of the same name will be overwritten.
Default is "yes".
(debug) [boolean]
Activate debugging mode. Default is "no". When debug is "no", all
exceptions that are not caught and
handled by individual tool-specific code are caught by a top-level
exception handler that displays information about the exception and
then exits. When debug is "yes", such exceptions are not caught by the
top level code. Instead the tool produces a segmentation violation,
which is more useful for debugging. When debugging mode is enabled,
the tool produces more verbose output describing any errors or
exceptions that are encountered.
(gui) [boolean]
Graphical User Interface (GUI) mode is activated if set to "yes".
Default is "no".
(mode) [string]
Mode of automatic parameters: "h" for batch, "ql" for interactive.
Default is "ql".
EXAMPLES
Parameters are passed following the FTOOLs model: They could be passed
answering from a prompt, as a list in a command line, or by editing
the parameter file.
To run gtbkg simply type in the command line:
>gtbkg
This will prompt for parameter values. Not all parameter are prompted:
some of them are "hidden". To change one of the "hidden" parameter,
the user should specify the values in the command line or modify its
mode by editing the parameter file.
For example to prevent overwriting an existing output file, the
following command line as to be typed::
>gtbkg clobber=no
An example of how to run the tool is given below: The file
3C279_3C273_back_filtered_pha1.fits was created using gtbin (option PHA1)
from an original event file. The expMap.fits and the expCube.fits file
were created with gtexpmap and gtltcube respectively. 3C279 is the source
excluded from the background model. The name "3C279" is the same as the one
in the source model file.
> gtbkg
pha file[] 3C279_3C273_back_filtered_pha1.fits
output file[] pha1.fits
Spacecraft file[] spacecraft_data_file.fits
Exposure hypercube file[] expCube.fits
Exposure file[none] expMap.fits
Response functions to use[CALDB] CALDB
Source model file[] src_model.xml
Target source name (excluded from background estimate)[none] 3C279
Excluding source 3C279 from background model.
To run the same example in the command line type:
>gtbkg phafile=3C279_3C273_back_filtered_pha1.fits outfile=pha1.fits \
scfile=spacecraft_data_file.fits expcube=expCube.fits expmap=expMap.fits \
irfs=CALDB srcmdl=src_model.xml target=3C279
SEE ALSO
gtbin
gtltcube
gtexpmap
gtlike
gtorbsim
gtexposure2
ModelEditor