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A 2-D file-based point-source fitting model.
PTSRC is a file-based model
that may be used in fitting image data, to determine,
e.g., if they are point-like or extended.
This model cannot be used as an instrument model.
FITS formats are allowed for the input model file. The
current implementation requires that the image bins of the data and
the PTSRC2D model file are the same.
Assume that the PSF is provided in a FITS image (file) of
size N_x * N_y. N_x and N_y may be much
larger than the PSF size in pixels. An optimally sized sub-image of
size xsize * ysize can speed up
the computation of model amplitudes.
If xoff = yoff = 0, the sub-image is extracted
from the center of the original image contained in file. The user may
find that changing xoff and/or yoff can
result in his or her being able to extract a smaller optimally sized
sub-image if, say, the PSF is too asymmetric to be fit easily into a
centered rectangle.
If norm is thawed its best-fit value for a point-like
source will be approximately equal to the number of detected counts
from the source.
The parameters xpos and ypos indicate where
the center of the sub-image is to be placed in the data image
that is to be analyzed, i.e., they should be set to the
location of the source centroid. Note that the initial values of the
xpos and ypos are estimated using the input dataset.
PTSRC Parameters
| 1 | file | input FITS file name |
| 2 | xsize | x-width of the subset region of kernel file to use in convolution |
| 3 | ysize | y-width of the subset region of kernel file to use in convolution |
| 4 | xoff | x-direction offset |
| 5 | yoff | y-direction offset |
| 6 | xpos | x-position of the centroid in data image coordinates |
| 7 | ypos | y-position of the centroid in data image coordinates |
| 8 | norm | normalization defined as a sum over the model image |
The example below shows the initial parameter values for the
PTSRC2D model. Note that the default xsize and
ysize values are set to 32. After reading the data file
these parameter can be adjusted to expand the image and include most
of the PSF fraction. Notice after image command indicates the fraction
of PSF included in the sub-image.
sherpa> ptsrc2d[p2]
sherpa> show p2
ptsrc2d[p2] (integrate: on)
Param Type Value Min Max Units
----- ---- ----- --- --- -----
1 file string: "none"
2 xsize frozen 32 1 1024
3 ysize frozen 32 1 1024
4 xoff frozen 0 -512 512
5 yoff frozen 0 -512 512
6 xpos thawed 128.5 0.5 256.5
7 ypos thawed 128.5 0.5 256.5
8 norm thawed 1 0 1000
sherpa> p2.file=psf2.fits
sherpa> show p2
ptsrc2d[p2] (integrate: on)
Param Type Value Min Max Units
----- ---- ----- --- --- -----
1 file string: "psf2.fits"
2 xsize frozen 32 1 1024
3 ysize frozen 32 1 1024
4 xoff frozen 0 -512 512
5 yoff frozen 0 -512 512
6 xpos thawed 128.5 0.5 256.5
7 ypos thawed 128.5 0.5 256.5
8 norm thawed 1 0 1000
sherpa> image p2
NOTE: PSF fraction for (xsize,ysize): FRAC = 0.984733
sherpa> p2.xsize=64
sherpa> p2.ysize=64
sherpa> image p2
- sherpa
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atten,
bbody,
bbodyfreq,
beta1d,
beta2d,
box1d,
box2d,
bpl1d,
const1d,
const2d,
cos,
delta1d,
delta2d,
dered,
devaucouleurs,
edge,
erf,
erfc,
farf,
farf2d,
fpsf,
fpsf1d,
frmf,
gauss1d,
gauss2d,
gridmodel,
hubble,
jdpileup,
linebroad,
lorentz1d,
lorentz2d,
models,
nbeta,
ngauss1d,
poisson,
polynom1d,
polynom2d,
powlaw1d,
ptsrc1d,
rsp,
rsp2d,
schechter,
shexp,
shexp10,
shlog10,
shloge,
sin,
sqrt,
stephi1d,
steplo1d,
tan,
tpsf,
tpsf1d,
usermodel,
xs,
xsabsori,
xsacisabs,
xsapec,
xsbapec,
xsbbody,
xsbbodyrad,
xsbexrav,
xsbexriv,
xsbknpower,
xsbmc,
xsbremss,
xsbvapec,
xsc6mekl,
xsc6pmekl,
xsc6pvmkl,
xsc6vmekl,
xscabs,
xscemekl,
xscevmkl,
xscflow,
xscompbb,
xscompls,
xscompst,
xscomptt,
xsconstant,
xscutoffpl,
xscyclabs,
xsdisk,
xsdiskbb,
xsdiskline,
xsdiskm,
xsdisko,
xsdiskpn,
xsdust,
xsedge,
xsequil,
xsexpabs,
xsexpdec,
xsexpfac,
xsgabs,
xsgaussian,
xsgnei,
xsgrad,
xsgrbm,
xshighecut,
xshrefl,
xslaor,
xslorentz,
xsmeka,
xsmekal,
xsmkcflow,
xsnei,
xsnotch,
xsnpshock,
xsnsa,
xsnteea,
xspcfabs,
xspegpwrlw,
xspexrav,
xspexriv,
xsphabs,
xsplabs,
xsplcabs,
xsposm,
xspowerlaw,
xspshock,
xspwab,
xsraymond,
xsredden,
xsredge,
xsrefsch,
xssedov,
xssmedge,
xsspline,
xssrcut,
xssresc,
xssssice,
xsstep,
xstbabs,
xstbgrain,
xstbvarabs,
xsuvred,
xsvapec,
xsvarabs,
xsvbremss,
xsvequil,
xsvgnei,
xsvmcflow,
xsvmeka,
xsvmekal,
xsvnei,
xsvnpshock,
xsvphabs,
xsvpshock,
xsvraymond,
xsvsedov,
xswabs,
xswndabs,
xsxion,
xszbbody,
xszbremss,
xszedge,
xszgauss,
xszhighect,
xszpcfabs,
xszphabs,
xszpowerlw,
xsztbabs,
xszvarabs,
xszvfeabs,
xszvphabs,
xszwabs,
xszwndabs
- slang
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usermodel
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