========= list of known problems in the ROD for the PSPC ===== 25-Feb-92 ===

This is a list of problems that were found in the past in ROD's for the PSPC.
The correction date indicates whether your tape is likely to contain the
error. The list does not include inconsistencies in the Standard Image and
Source Analysis results. The ordering scheme is the EXSAS file name.

- attitude.tbl - screening          entered:01-Dec-91 corrected:
  The data screening of the delivered data to include only time intervals
  where a good attitude solution is available has been not sufficiently
  stringent in the past. Therefore all data processed after Christmas 1991
  were screened to include only attitude errors of less than 2 arcsec.
  Present knowledge indicates that 1 arcsec may be even more secure. In the 
  April 1992 version of EXSAS the command correct/aspect may be used to
  check and possibly screen the data. 
- attitude.tbl - empty files        entered:01-Dec-91 corrected:15-Dec-91
  In some of the RODs empty attitude files are delivered. Corrected versions
  of the affected RODs have been sent out to the PIs in January 1992.
- eventrates.tbl - wrong_rates      entered:41-Dec-91 corrected:      
  The rate values, as contained in table eventrates.tbl, have interspersed  
  numbers, which are systematically lower than the mean. This is caused
  by an synchronization effect.
  In the present EXSAS Software this may produce a (quite) small 
  underestimation of the deadtime during the affected time intervals. 
  Correction of the bug is underway.
- events.tbl - descriptors         entered:26_Nov-91 corrected:01-Dec-91
  The values of the 2 descriptors RAW_SEL and AMP_SEL are interchanged.
  This may produce difficulties when using the delivered standard images
  in the Maximum Likelihood application. As remedy use the command
  CREATE/SOURCE_DETECT to produce images with complete descriptors.
- events.tbl - descriptor          entered:09-Dec-91 corrected:
  For survey merged photon event tables near to ecliptic pole regions
  the descriptor TIM_SEL may overflow. 
- events.tbl - boresighting        entered:01-Feb-92 corrected:
  If data from one observation were collected at two (or more) distinct 
  periods in time that are e.g. half a year apart (reobservation of targets
  not completed initially) than the boresight error between these periods
  may be as large as 20 arcsec leading to visibly distorted point
  spread functions. We are presently not able to correct this automatically.
  In principle the user has to run source detection on the contiguous time
  intervals separately, compare the source positions, determine the mean
  difference and correct the sky-pixel values in the events.tbl accordingly.
- events.tbl - wrong_times         entered:20-Mar-92 corrected:
  The arrival times of individual events in the file events.tbl are in
  some cases wrong by exactly 1 sec due to an sychronization problem. That
  error can affect the analysis of the timing behaviour of sources when 
  times in the order of seconds or smaller are relevant.
- images - descriptors             entered:25_Nov-91 corrected:01-Dec-91
  The descriptors DET_CEN_X and DET_CEN_Y in some of the image files are
  given in REAL*8 format whereas the EXSAS Users Guide defines them as
  INTEGER*4. 
  We are not aware of any problems (in the EXSAS Software) created by this
  inconsistency. 
- source.tbl - column:DEC          entered:07-Jan-92 corrected:15-Jan-92
  In the file source.tbl all entries in column DEC_2000 with 0 degrees or
  0 seconds have a wrong minus sign in front of the degree part.
- sourceana.tbl - missing          entered:15-Jun-90 corrected:30-Mar-92
  Due to an MIDAS FITS conversion error it was up to now not possible to
  deliver this file on the ROD (the file content is fully contained in the
  Standard Analysis Protocol printout).

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