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gtdiffrsp.txt
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gtdiffrsp.txt
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NAME
gtdiffrsp - Calculates the integral over solid angle of a diffuse source
model convolved with the instrumental response function
USAGE
gtdiffrsp evfile scfile srcmdl irfs
DESCRIPTION
LAT data are modeled using a maximum likelihood method. The unbinned
likelihood function is defined in terms of the expected photon
distribution for a given source model. That distribution is the
convolution of the source model with the instrument response. In
particular, the contribution to the log-likelihood associated with an
individual photon is computed as the integral of the source model with
the instrument response evaluated at the observed photon direction,
energy and arrival time. For point sources, the spatial component is
a delta-function, so this integral is relatively easy to do. However,
for diffuse sources such as the Galactic interstellar component, this
integral is very computationally intensive since it must be performed
over the whole sky (in principle). Therefore, if possible, it is useful
to precompute these quantities in advance. In the likelihood calculations,
it is assumed that the spatial and spectral parts of a source model factor
in such a way that the integral over spatial distribution of a source
can be performed independently of the spectral part and in this case
the integral over the instrument response can be precomputed for each
diffuse model component.
The gtdiffrsp tool will perform these integrations and add the results
as an additional column for each diffuse source into the input event file.
Hereafter, we will refer to these quantities as the "diffuse
responses". If the diffuse responses are not pre-computed using
gtdiffrsp for a given source, gtlike will throw an exception and
report the missing column. The name of each column is a combination
of the name of the diffuse source and the name of the response
function (see the example below). You may use the FTOOL fdelcol
to delete columns if you want to restore the modified file (see the
fdelcol help more information).
You may overwrite the columns produced by gtdiffrsp using the
clobber=yes parameter.
Please be advised that gtdiffrsp is computationally intensive and, depending
on the size of your event file, can take a very long time to run.
PARAMETERS
evfile [filename]
This is the input file containing the event data. If
several events files have to be input, an ASCII file with the complete
list of them should be entered here with an "@" sign before the
name. For example, if the name of that ASCII file is "events", then is
parameter should be entered in this way: evfile=@events.
(evtable) [string]
Event data extension. Default is "EVENTS".
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".
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 by gtlike (see the gtlike help).
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.
(evclsmin) [integer]
This parameter is ignored for data reprocessed after Aug. 1, 2011
(Pass 7 or higher).
Mininum event class ID to include. Each set of IRFs will define a set
of event classes numbered 0 to n, where n+1 is the number of event
classes. These numbers will be ordered such that the more inclusive
classes are numbered lowest. Default is "0".
(evclass) [integer]
Event class selection for pass 8 data: "128" for Source ,
"256" for Clean. Default is "INDEF".
(convert) [boolean]
Parameter to convert header to a new diffrsp format. Default is "no".
(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 gtdiffrsp simply type in the command line:
> gtdiffrsp
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 overwrite the existing output file, the following
command line as to be typed:
> gtdiffrsp clobber=no
An example of how to run the tool is given below:
> gtdiffrsp
Event data file[] ps_filtered.fits
Spacecraft data file[] spacecraft_data_file.fits
Source model file[] src_model.xml
Response functions to use[CALDB] CALDB
That last example could be also run in the command line as follows:
> gtdiffrsp evfile=ps_filtered.fits scfile=spacecraft_data_file.fits \
srcmdl=src_model.xml irfs=CALDB
SEE ALSO
gtlike
gtobssim