PCSASSCOR (Oct95)             ftools.rosat             PCSASSCOR (Oct95)

NAME
    pcsasscor -- Corrects PI channel in Events file
    
    
USAGE
    pcsasscor infile outfile
    
    
DESCRIPTION
    
    This  tool operates on  Rev0, or RDF PSPC events file. The tool also
    operates on any German  PSPC events file  converted  to  RDF  format
    using  the  'gevt2rdf'  ftool. The PI column in all events files are
    currently incorrect, in the sense that there  is  an  error  in  all
    versions of the SASS spatial gain correction.
    
    This  tool  recalculates  the  PI  column  from the PHA and position
    information, a new events file is written out with the  same  format
    as  the  original,  but  with  the  PI  column  replaced  by the new
    corrected values of PI. This tool allows correction  of  the  events
    files without the need for reprocessing of the data with SASS.
    
    (Later  versions of this program will eventually correct the PI data
    for temporal deviations).
    
    
    EVENT CORRECTION :
    
    A detailed description of the  calibration  corrections  applied  to
    individual PSPC events is available in the HEASARC memo
    
    /caldb/docs/rosat/cal_ros_95_010/cal_ros_95_010.tex
    
    available  in  latex  and  post script format from the anonymous ftp
    account at legacy.gsfc.nasa.gov
    
    The aforementioned memo is essentially a copy of  the  original  MPE
    memo  TN-ROS-ME-ZA00/027  (Hasinger  \&  Snowden, 1990), but updated
    and expanded to refer to the FITS versions of the calibration  files
    available  from  the  HEASARC and to detail the corrected algorithms
    as performed by PCSASSCOR.
    
    In summary, the calibration corrections performed on PSPC events  in
    the  SASS  processing  include corrections for electronic variations
    (detailed  characteristics   of   the   anode   amplifier   chains), 
    electric-field  variations  due  to the (slight) variable spacing of
    the  anode  wires,  and  long-term  temporal  gain  variation.   The 
    corrections  are  performed  using event arrival position, time, and
    pulse height. The PHA to PI corrections are performed in SASS within
    the CT module.
    
    
    THE ORIGIN OF THE ERROR :
    
    Detailed  analysis  of  the  PSPC  in-flight  aluminum  K  (1487 eV)
    calibration-source data showed that the corrections, as  they  stand
    in  SASS,  have  an  error in the spatial gain correction. The error
    produces spurious fluctuations in PI channels across the image.  For
    more detail on the problem, see
    
    http://heasarc.gsfc.nasa.gov/docs/heasarc/caldb/docs/summary/
    cal_ros_95_003_summary.html
    
    The  spatial  gain  correction should remove the gain variations due
    to the variable  distance  of  the  anode  wires  and  the  relative
    position  of  the  events  with respect to the anode wires. The SASS
    DCORG subroutine applies the spatial gain correction to  the  events
    data.  That  subroutine uses corrections based on ground calibration
    data from the gain_kor3_b SASS calibration file.  An  error  in  the
    implementation  of the original ground calibration files within SASS
    has lead to a mis-correction which produces spurious  variations  in
    PI  channel  across  the  detector. To correct this error, PCSASSCOR
    recalculates the PI column from the PHA column,  using  the  Y-based
    spatial correction instead of the X-based correction.
    
    The  electronically  corrected coordinate information is required to
    convert  PHA  channels  to  PI.  As  the  electronically   corrected 
    coordinates  are  an  intermediate  coordinate  system, they are not
    stored in the Rev0 or RDF events file.  This  version  of  PCSASSCOR
    calculates  electronically  corrected  positions  starting from DETX
    and DETY and undoing the field and window corrections.  In  the  RDF
    case  the RAWX and RAWY coordinates are available, and one can avoid
    the  minor  approximations  that  undoing  the  field   and   window 
    correction  entails,  by  simply  applying  the  electronic position
    correction to RAWY. This enhancement will be available in  the  next
    release of this tool.
    
    
    THE CALIBRATION FILES REQUIRED FOR THE TASK
    
    The  default  setting  for  the  input calibration files is 'CALDB',
    this  facility  can  only  be  used  by  beta-test  sites   of   the 
    calibration  database  access  software.  Most  users  will  need to
    obtain  a  set  of  calibration  files  via   anonymous   ftp   from 
    heasarc.gsfc.nasa.gov. The datasets are located in the directory:
    
             /caldb/data/rosat/pspc/bcf/sass_ct
    
    and have the names/descriptions as follows:
    
    
    adc_bins.fits     - PSPC ADC non-linearity correction
    
    alkhist_v1_b.fits - PSPCB Gain hist from Prescott fits to Al-K obs (v1.0)
    
    alkhist_v1_c.fits - PSPCC Gain hist from Prescott fits to Al-K obs (v1.0)
    
    gain_kor3_b.fits  - PSPCB Spatial Gain Correction: Pos-dep terms (v1.0)
    
    gain_kor3_c.fits  - PSPCC Spatial Gain Correction: Pos-dep terms (v1.0)
    
    gnampl_new.fits   - PSPC Spatial Gain Correction: Energy-dep term (v1.0)
    
    scal3.fits        - PSPC Window Correction: Energy-dep correction term
    
    tabx_093_b.fits   - PSPCB Window Correction: X-axis term
    
    tabx_093_c.fits   - PSPCC Window Correction: X-axis term
    
    taby_093_b.fits   - PSPCB Window Correction: Y-axis term
    
    taby_093_c.fits   - PSPCC Window Correction: Y-axis term
    
    Some  files  are  valid  for  both  PSPC instruments, and hence have
    'PSPC' as the instrument keyword.
    
    Note: Correct use of this  task  requires  that  the  ymapfile  used
    should  be  either  taby_093_b.fits  or  taby_093_c.fits, use of the
    tabx files will result in a  reproduction  of  the  error  currently
    occurring in SASS.
    
    EXAMPLE:
    
    An example of the pcsasscor parameter file might be:
    
    
    infile = rp700332.fits      Please enter EVENTS filename
    
    (gtifile = %match)           Please enter gtifile name
    
    outfile =                    Please enter output filename
    
    endepfile = scal3.fits       Please enter energy dependent correction file
    
    ymapfile = taby_093_b.fits   Please enter golden disk file
    
    adcfile = adc_bins.fits      Please enter adc binfile
    
    spgfile = gnampl_new.fits    Please enter E-dep spatial gain correction file
    
    spgkfile = gain_kor3_b.fits  Enter pos-dep spatial gain correction file
    
    alkfile = alkhist_v1_b.fits  Enter alk history file
    
    (chatter = 9)                Please enter chatter flag
    
    (clobber = no)               Overwrite output file if it already exists ?
    
    (mode = ql)               Mode
    
    REMINDER:
    
    If  your  observation  was  made before Jan 25  1991 then you should
    use  PSPCC   calibration  files,  after   that   date,   use   PSPCB 
    calibration  files  (the  observation date is stored as the DATE-OBS
    keyword.
    
    
    
    
WARNINGS ON USAGE
    
    Note: Correct use of this  task  requires  that  the  ymapfile  used
    should  be  either  taby_093_b.fits  or  taby_093_c.fits, use of the
    tabx files will result in a  reproduction  of  the  error  currently
    occurring in SASS.
    
    
    
    
    
    
SUPPORTED FITS FILE FORMATS
    
       Currently  only  the  following  OGIP  standards are supported by
    this task
    
    
    For the input events file :
    
    RDF EXTNAME = 'STDEVT'
    
    US REV0 EXTNAME='EVENTS'  
    
    HDUCLAS1='EVENTS'
    
    HDUCLAS2='ACCEPTED'
    
    
    For the Calibration files :
    
    File conatining the energy dependent Ga term -
    
    HDUCLAS1='RESPONSE'
    
    HDUCLAS2='WC_E'
    
    File containing the electronic correction
    
    HDUCLAS1='IMAGE'
    
    File containing the energy dependent spatial correction
    
    HDUCLAS1='RESPONSE'
    
    HDUCLAS2='SGC_E'
    
    File containing the position dependent spatial correction
    
    HDUCLAS1='RESPONSE'
    
    HDUCLAS2='SGC_POS'
    
    File containing the temporal gain correction
    
    HDUCLAS1='RESPONSE'
    
    HDUCLAS2='DET_GAIN'
    
    For further details see OGIP calibration memo CAL/ROS/95-010
    
    
    
PARAMETERS
    
    infile [character string]
         The name of the Events file
    
    outfile [character string]
         The name of the output file.
    
    (endepfile) [character string]
         The name of the energy dependent correction file
    
    (ymapfile) [character string]
         The name of the golden disk file
    
    (adcfile) [character string]
         The name of the adc bin correction file
    
    (spgfile) [character string]
         The name of the energy dependent spatial gain correction file
    
    (spgkfile) [character string]
         The name of the position dependent spatial correction file
    
    (clobber = no) [boolean]
         Overwrite output file, if it already exists ?
    
    (chatter=9) [Integer]
         Flag to indicate how chatty the task is at execution.  A  value
        of  9  is  the   default,  with  lower/higher  values  producing 
        quieter/verbose output  respectively.
    
    
    
    
BUGS
    None known
    
    
    
LOG OF SIGNIFICANT CHANGES
    
    
    v1.0.0 (1995 Oct)
            Beta-test version
    
    
    
PRIMARY AUTHOR
    
    Rehana Yusaf
    HEASARC
    NASA/GFSC
    http://heasarc.gsfc.nasa.gov/cgi-bin/ftoolshelp
    (301) 286-6115