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Creates a simulated 1-D dataset.
sherpa> FAKEIT [#]
# specifies the number of the dataset to be simulated (default dataset
number is 1).
The FAKEIT command creates a simulated 1- or 2-D dataset.
It cannot be successfully issued without first:
- defining a SOURCE model
stack; and
- defining a grid over which to evaluate the model stack.
The user may define the grid in one of three ways:
- reading in a dataset (in which case, the faked data will replace the
read-in amplitudes);
- specifying a DATASPACE;
or
- defining an instrument stack that contains a response matrix file
(RMF), from which a dataspace may be inferred; note that an instrument
stack be defined automatically if PHA data are input, and the PHA data file
header keywords RESPFILE and/or ANCRFILE
point to existing files.
If one defines a dataspace and plans to use XSPEC models,
then one must use the HISTOGRAM modifier to the
DATASPACE command,
since XSPEC models expect the dataset
to be binned. Otherwise, the simulated data set may be either
binned or unbinned.
Other, optional information may be input before FAKEIT
is run.
- A background dataset (see the command
BACK)
or a background model stack
(BACKGROUND).
If PHA data are input, a background dataset will be automatically input
if the header keyword BACKFILE points to an existing file.
- Values for the FAKEIT parameters TIME
and BACKSCALE. If PHA data are input,
TIME and BACKSCALE will have default settings
corresponding to the values of
the header keywords EXPTIME and BACKSCAL.
These may of course be changed; see below.
Values of the FAKEIT parameters may be set as follows:
sherpa> FAKEIT TIME = <time>
sherpa> FAKEIT BACKSCALE = <backscale>
where <time> is in seconds,
<backscale> is a dimensionless number.
Background data and/or models are treated as follows in
FAKEIT:
-
If a background model stack is defined, it is evaluated on the
source data grid, and the resulting background amplitudes are added to the
source amplitudes (taking into account differences in exposure time
and backscale). Faked data are then sampled given the sum.
If background data exist, they are not altered. If the source dataset
was background-subtracted prior to the command FAKEIT being
issued, it will not be background-subtracted afterwards.
-
If no background model stack is defined, and the data are
background-subtacted, then the source model stack is evaluated
directly, and the new, faked data are background-subtracted. Note that
subsequently issuing an
UNSUBTRACT
command in CIAO 3.0 is unwise, because as an artifact of the algorithm
the unsubtracted data will not be integer counts data.
-
If no background model stack is defined, and the data are not
background-subtacted, then the source model stack is evaluated
directly, and the (properly scaled) background data are added to
the faked data.
FAKEIT creates a new dataset
and keeps it in memory (the Sherpa number assigned to
this dataset is
specified with # in the FAKEIT command).
This new dataset may then be treated as though it were a dataset that
the user had read from a file (e.g., it may be plotted using the
LPLOT DATA [#] command; it may be used in a fit,
etc.).
Note that if the user has previously read a dataset,
it will be overwritten with the new dataset created by
FAKEIT.
Note that in CIAO 3.0, there is no facility for faking background spectra
(i.e., there is no BFAKEIT command).
Simulate a dataset, with an instrument model:
sherpa> RSP[instrumentA](data/example2.rmf,data/example2.arf)
The inferred file type is ARF. If this is not what you want, please
specify the type explicitly in the data command.
sherpa> INSTRUMENT = instrumentA
The above commands define an instrument model named instrumentA,
using the RMF and ARF files data/example2.rmf and
data/example2.arf respectively.
Next, a background data file is input:
sherpa> BACK data/example2_bkg.pha
The inferred file type is PHA. If this is not what you want, please
specify the type explicitly in the data command.
The FAKEIT parameters are then set:
sherpa> FAKEIT TIME = 33483.2
sherpa> FAKEIT BACKSCALE = 0.0441895
sherpa> SHOW FAKEIT
Fakeit exposure time: 33483.2 seconds.
Fakeit backscale: 0.0441895
And, a simple source model expression is defined:
sherpa> PARAMPROMPT OFF
Model parameter prompting is off
sherpa> SOURCE = POW[modela]
sherpa> modela.gamma=2
sherpa> modela.ampl.min=0.000001
sherpa> modela.ampl=0.0003
sherpa> modela.ref=1
Finally, a simulated dataset is created:
sherpa> FAKEIT
FAKEIT: The current background data have been added to the faked spectrum.
This simulated dataset may be plotted, and written as PHA and ASCII files:
sherpa> LPLOT DATA
sherpa> WRITE DATA sim1.pha PHA
Write X-Axis: Energy (keV) Y-Axis: Counts
sherpa> WRITE DATA sim1.dat ASCII
Write X-Axis: Energy (keV) Y-Axis: Flux (Counts/sec/keV)
Simulate a dataset, utilizing a previously input PHA file:
sherpa> ERASE ALL
sherpa> DATA data/example2.pha
The inferred file type is PHA. If this is not what you want, please
specify the type explicitly in the data command.
WARNING: using systematic errors specified in the PHA file.
RMF is being input from:
<directory_path>/example.rmf
ARF is being input from:
<directory_path>/example.arf
Background data are being input from:
<directory_path>/example_bkg.pha
sherpa> SHOW
Optimization Method: Levenberg-Marquardt
Statistic: Chi-Squared Gehrels
-----------------
Input data files:
-----------------
Data 1: example2.pha pha.
Total Size: 95 bins (or pixels)
Dimensions: 1
Total counts (or values): 1688
Exposure: 33483.25 sec
Count rate: 0.050 cts/sec
Backscal: 0.044189
Background 1: /data/simteste/Testing/sherpaTest/data/example2_bkg.pha pha.
Total Size: 512 bins (or pixels)
Dimensions: 1
Total counts (or values): 2220
Exposure: 108675.66 sec
Count rate: 0.020 cts/sec
Backscal: 0.044189
The data are NOT background subtracted.
------------------------------
Defined analysis model stacks:
------------------------------
instrument source 1 = AutoReadResponse
instrument back 1 = AutoReadResponse
------------------------------------
Defined instrument model components:
------------------------------------
rsp1d[AutoReadResponse]
Param Type Value Min Max Units
----- ---- ----- --- --- -----
1 rmf string: "/data/simteste/Testing/sherpaTest/data/example2.rmf"
2 arf string: "/data/simteste/Testing/sherpaTest/data/example2.arf"
sherpa> SHOW FAKEIT
Fakeit exposure time: 33483.2 seconds.
Fakeit backscale: 0.0441895
After inputting a PHA dataset, the SHOW command confirms
that an instrument model
has been automatically defined using RMF and ARF files.
Also, a background data
file has been automatically read. The SHOW FAKEIT command confirms
that the input data file contained the
exposure time, backscale, and areascale keywords pertinent to
the observation. Next, a source model expression is defined, and then a
simulated dataset is created and written:
sherpa> PARAMPROMPT OFF
Model parameter prompting is off
sherpa> SOURCE = POW[modelA]
sherpa> modelA.gamma=2
sherpa> modelA.ampl.min=0.000001
sherpa> modelA.ampl=0.0003
sherpa> modelA.ref=1
sherpa> FAKEIT
FAKEIT: The current background data have been added to the faked spectrum.
sherpa> WRITE DATA simA.pha PHA
Write X-Axis: Energy (keV) Y-Axis: Counts
Simulate a second dataset:
sherpa> RSP[instrumentB](data/example2.rmf,data/example2.arf)
The inferred file type is ARF. If this is not what you want, please
specify the type explicitly in the data command.
sherpa> INSTRUMENT 2 = instrumentB
sherpa> BACK 2 data/example2_bkg.pha
The inferred file type is PHA. If this is not what you want, please
specify the type explicitly in the data command.
sherpa> FAKEIT 2 TIME = 66966.4
sherpa> FAKEIT 2 BACKSCALE = 0.0441895
sherpa> SOURCE 2 = POW[modelB]
sherpa> modelB.gamma=2
sherpa> modelB.ampl.min=0.000001
sherpa> modelB.ampl=0.0003
sherpa> modelB.ref=1
sherpa> FAKEIT 2
FAKEIT: The current background data have been added to the faked spectrum.
sherpa> LPLOT 2 DATA 1 DATA 2
sherpa> WRITE DATA 2 fakeit3.pha PHA
Write X-Axis: Energy (keV) Y-Axis: Counts
These commands define a second instrument model, input a background
data file for dataset number 2, set the FAKEIT parameters for
dataset number 2, and define a second source model. The command
FAKEIT 2 then creates simulated dataset number 2. Both
simulated datasets are then plotted, and the second dataset
is written to the data file fakeit3.pha.
Simulate a dataset, without an instrument model:
sherpa> ERASE ALL
sherpa> PARAMPROMPT OFF
Model parameter prompting is off
sherpa> SOURCE = POW[modela]
sherpa> DATASPACE (1:1000:2)
sherpa> FAKEIT TIME = 33483.2
sherpa> FAKEIT BACKSCALE = 0.0441895
sherpa> SHOW FAKEIT
Fakeit exposure time: 33483.2 seconds.
Fakeit backscale: 0.0441895
sherpa> modela.gamma=2
sherpa> modela.ampl.min=0.000001
sherpa> modela.ampl=0.0003
sherpa> modela.ref=1
sherpa> FAKEIT
sherpa> LPLOT DATA
Instead of defining an instrument model, the DATASPACE
command is used
to define the appropriate grid over which to calculate the model values.
Fake a 2-D image:
sherpa> DATASPACE (1:256:1,1:256:1)
sherpa> PARAMPROMPT OFF
sherpa> INSTRUMENT = FPSF2D[p]
sherpa> p.file = psf.fits
sherpa> SOURCE = GAUSS2D[g]
sherpa> g.xpos = 128
sherpa> g.ypos = 128
sherpa> g.ampl = 100
sherpa> g.fwhm = 25
sherpa> FAKEIT
- chandra
-
guide
- sherpa
-
autoest,
back,
berrors,
bsyserrors,
coord,
data,
dataspace,
feffile,
group,
guess,
is_subtracted,
load,
load_arf,
load_ascii,
load_back_from,
load_backset,
load_dataset,
load_fitsbin,
load_image,
load_inst,
load_inst_from,
load_pha,
load_pha2,
load_rmf,
read,
set_analysis,
set_axes,
set_backscale,
set_coord,
set_data,
set_exptime,
set_subtract,
set_weights,
setback,
setdata,
subtract,
ungroup,
unsubtract,
use
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