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 heasarc.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

CATEGORY

Oct95 ftools.rosat