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###

*rosprf*
- Using the analytical expressions for the point response function

**The point response functions for the ROSAT HRI and PSPC are described
in their respective help files (prfroshri & prfrospspc). rosprf is a
script which builds a model prf by repeating immodel for each
functional part of the PRF. In the following example we build an HRI
prf and subtract it from one of the HRI boresights (type ``help
prfroshri" for a list of available boresights). We commence by
creating a 255 smoothed array, using
**

input xrcal$/rhlmcx1_03.qp[3458:3712,4304:4558]
[the center was chosen based on the coordinates provided in prfroshri]
arg1 2.54 pixels, equivalent to FWHM=3"
out lmcx1_3

**We evaluate this map with tvproj and imcnts, finding 7484 counts in a circle centered on the peak (127,127)
with r=100 pixels. Next we generate the PRF.
**

rosprf
xdim 255
ydim 255
center 127 127
out hriprf
instr hri

**We then measure the ``counts" in the model (circle with radius=100 pixels)
and find a total of 0.98. We thus derive a scaling factor of 7484/0.98=7651
and use imcalc
to perform the subtraction.
**

imcalc,
input hriprf_resid = lmcx1_3_smo.imh - 7651 * hriprf.imh

**The results look crumby since the source is egg shaped and we see that
we are slightly offset. We use imshift to add 1 pixel to each
coordinate of the model, hriprf.imh, effectively moving the PRF to the
NW. This residual also looks crumby.
**

**NB: For best results, we should have smoothed the PRF (with the same
Gaussian used on the map) before subtraction.
**

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**Up:** Source Subtraction
** Previous:** *immodel* - subtracting a
*rsdc@cfa.harvard.edu *

1998-06-10