Rays and Events

The first step in the simulation is to pass SAOSAC rays (generated and supplied for each XRCF test by Diab Jerius of the Mission Support Team) through the MARX package, which propagates them to the appropriate ACIS focus via two special parameters that configure MARX for XRCF use (supplied by Michael Wise): SourceDistance = 537.583 and DetOffsetX = -194.872. These parameters serve to inform MARX that the source is at a finite distance and that ACIS is not at the default focus used by the rays. These supplied values were not adjusted in this analysis.

The virtual photons generated in this process were then allowed to interact with the CCD via the acis_sim program. Before we compare the simulated CCD output to the XRCF data, a useful aside is to compare the rays incident upon the CCD to the set of events generated by the interaction of those rays with the CCD. This illustrates the degradation of the PSF by convolving it with the quantized detector picture elements.

Figure 6.13 shows the SAOSAC rays configured to match the geometry of the XRCF for test H-IAI-CR-1.001. In order to facilitate comparison between the rays and the simulated CCD events, Figure 6.14 and Figure 6.15 show the rays grouped into 1X1 pixel bins beside the CCD simulator output. Because Al K$\alpha$ photons often produce single-pixel events, the simulated output very closely resembles the binned rays. This is not to be expected at higher energies, where split events are more prevalent. The ``lego'' plots (Figure 6.15) better illustrate the PSF broadening due to pixelization.
 
 

Figure 6.13:  The left-hand panel shows a scatter plot of
the rays for test H-IAI-CR-1.001.  The right-hand panel shows the same
rayfile, displayed as a surface and binned arbitrarily at 0.2 pixels.

Figure 6.14:  The left-hand panel shows an image of
the rays for test H-IAI-CR-1.001, grouped in 1X1  pixel bins.
The right-hand panel shows the simulated CCD events binned similarly.

 

Figure 6.15:  The left-hand panel shows a 2-dimensional histogram (``lego plot'') of the rays for test H-IAI-CR-1.001, grouped in 1X1 pixel bins.  The right-hand panel shows the simulated CCD events binned similarly.