ROSAT Guest Observer Facility

Frequently Asked Questions about the ROSAT PSPC

The following questions have been asked often about the ROSAT pspc.

This file will be updated as needed. The dates at the end of the question lines reflect the date of the answer entry.

If you have a question that you think is, or could be, a "Frequently Asked Question", please e-mail it to

The sources for these answers have included the following: G. Hasinger (MPE), J. Schmitt (MPE), R. Fink (GSFC), D. Burrows (PSU), the GSFC GOFers (L. Angelini, K. Arnaud, G. Reichert, E. Schlegel, S. Snowden, and J. Turner), and the SAO GOFers (L. David, F. Harnden, F. Seward, and B. Wilkes).

Select one of the following topics:


  1. How is the background map produced?
  2. Does the background vary?
  3. What are the contributions to the background?
  4. Where can I get more information on the PSPC background?
  5. How has the internal background behaved?

Calibration, Energy

  1. What is the correspondence between the PROS 34-channel spectra and the PI bins?
  2. The initial calibration data apply to PSPCC. Has calibration data been taken for PSPCB?
  3. What is the status of the calibration of the PSPC?
  4. What corrections are applied to the data?
  5. What is the status of the response matrix for the PSPC?
  6. Why do the hardness ratios differ from table to table in the SASS output?
  7. What hardness ratios can be defined?
  8. Is there any sign of rate-dependent gain variations?

Coordinates and Aspect Solutions

  1. How accurate are the coordinates produced by the PSPC processing?
  2. Are there any PROS-related coordinate problems?
  3. What is the conversion from detector coordinates to sky coordinates?
  4. How good are the relative positions?
  5. How good are the aspect solutions believed to be?

Exposure, Exposure Map, Deadtime

  1. How were Steve Snowden's intrument maps over various bandpasses contructed?
  2. How was the SASS .MOI file (the modified instrument map used to contruct the SASS _MEX.FITS exposure map) created?
  3. Why are there instrument maps over different channel ranges? What assumptions go into using maps created from these instrument maps?
  4. Some of the intrument maps cover the channel ranges of other maps. For example, band 10 covers channels 52 to 90, band 4 covers channels 52 to 69, and band 5 covers channels 70 to 90. Is the band 10 instrument jus the same as the average of the band 4 and band 5 instrument maps? If so, why have a map for band 10?
  5. Why is there an instrument map over channels 42 to 201, but not one over channels 20 to 201? Why are there no maps for channels above 201?
  6. If one wanted to use one band for an average representative exposure map, which band should one use?
  7. The livetime in one observation is 13K seconds, but the value in the center of the SASS mean exposure map is only 5K seconds. Does this mean that the SASS exposure map is incorrect?
  8. Would it make sense to add an option to the exposure map program to use the .MOI file to construct an exposure map?
  9. How is the exposure map created? Is deadtime corrected?
  10. Is deadtime corrected for?
  11. What dead times are included in the corrections?
  12. Why is the exposure map blocked?
  13. What gives the exposure map the checkerboard appearance?
  14. How does the spacecraft wobble appear in the exposure map?
  15. What problems are present in the exposure map, or in the times?
  16. How is deadtime calculated?
  17. What is the uncertainty on the flux measurements?
  18. What constitutes a Good Time Interval (OTHER than a jaunt to the local pub)?

Filter, Boron

  1. Does the boron filter affect the data in any way other than blocking unwanted bandpasses?
  2. What effect does this produce on the data?

Housekeeping Information

  1. How can I look at the satellite "housekeeping" information?
  2. How do I know if my observation was wobbled or not?
  3. Is the voltage turned off during SAA?
  4. What else should I notice from the hardcopy housekeeping?
  5. Do the H-V variations convey real gain changes?
  6. What is the status of the gas flow?


  1. What are the two bars visible in the displayed photons?
  2. How is the background image produced?
  3. What are the "ghost images" I've heard about?

Modified Instrument Map

  1. How is the modified instrument map produced?

Point Spread Function

  1. What does the PSF look like?
  2. What do the numbers in the psfil mean?
  3. How does the soft PSF compare with the hard PSF?


  1. What corrections are applied to the individual PSPC events?
  2. What was the problem with the PSPC spatial gain correction, and when was it fixed?


  1. Has the data, or the exposure map, been corrected for vignetting?
  2. What contributes to the vignetting?

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This file was last modified on Monday, 13-Sep-1999 15:47:45 EDT

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