Summary

We presented relationships between the ACIS-XRCF spot size and PRF shape as a function of energy, off-axis angle, and degree of pileup (fluence), and we compared these relationships to the SAOSAC+ACIS model as implemented in MARX. We arrived at the following conclusions.

• The SAOSAC+MARX model FWHM and EER(70%) are within a few percent of XRCF Al-K on-axis data, and are within one standard deviation of the scatter in these quantities imparted by ACIS pixelation.
• The off-axis model spot is slightly smaller than the XRCF spot at all energies and off-axis angles, but the modeled growth of the spot with increasing off-axis angle agrees with the data to within the measurement errors.
• The current MARX-ACIS model cannot reproduce observed XRCF pileup spectra for any reasonable range of model parameters. This limits the current ACIS model's utility for modeling Chandra science spectra. The new MIT model will soon be implemented into MARX and this issue will be revisited.
• The ACIS model itself is apparently the limiting factor in our ability to model the on-orbit performance of Chandra.
• We have prepared a web site containing data and detailed analyses for most of the in-focus, XRCF Phase H ACIS tests. The data and information contained at this site are intended for detailed comparisons to the telescope model and on-orbit calibration data, and to aid in software development. http://asc.harvard.edu/cal/Links/Acis/acis/Cal_prods/psf/psf.html

• Install new MIT ACIS model currently being used to generate ACIS response matrices into MARX, and repeat raytrace simulations for a larger sample of tests. The new model, with a presumably improved gate structure and more realistic quantum efficiency, should provide a better understanding of pixelation effects and hopefully a more robust pileup treatment
• Produce backside chip simulations when model becomes available
• Continue efforts to calibrate MARX as an analysis tool

  We are indebted to Diab Jerius for providing the SAOSAC rays used in this analysis, and for implementing the finite source size model into SAOSAC. We thank Dick Edgar, Terry Gaetz, Mike Wise, and Kester Allen for their help and advice.

  
  

    

  Figure 23: Energy, BND flux, framesize, frametime, and pileup fractions for all on-axis XRCF tests used in our analysis of the ACIS PRF.

  
  

  
  

   

  Figure 24: Energy, BND flux, framesize, frametime, and pileup fractions for all off-axis XRCF tests used in our analysis of the ACIS PRF.

  Questions about any part of the CXC calibration website should be emailed to

  cxccal@cfa.harvard.edu.

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  Next: About this document ... Up: Abstract Previous: Model Comparison to Off-Axis
  Alexandria Ware
  1999-03-29