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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.