.help sssbck Feb96 ftools.caltools 
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NAME
sssbck -- builds the EINSTEIN SSS background PHA files for a given source obsn
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USAGE
phafile (jcgparm) linfexp varfexp bckfile corfile (chatter) (mode)
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DESCRIPTION


This task takes a user-defined PHA file from the Solid State Spectrometer
(SSS) onboard the Einstein Observatory, and generates the appropriate two
background PHA files. Each of the o/p files is a scaled version of an input
calibration file, available from anonymous ftp to the HEASARC Calibration 
database (ftp://heasarc.gsfc.nasa.gov/caldb/data/einstein/sss/bcf/). 
The scaling involves : multiplying the background
count rate in each channel by 2 variables (a dimensionless parameter related
to JCG, and a ratio of the source and background exposures); dividing this
result by the source exposure.

  This task therefore takes three files as i/p, all of which must be in 
an OGIP-approved FITS file format (i.e. PHAVERSN = 1992a) : 

(i) an EINSTEIN SSS PHA file for a given source observation. 

(ii) an EINSTEIN SSS Basic Calibration File (type=bcf). This is a .PHA file
containing a component of the SSS background spectrum which is related to
cosmic ray and particle events. This component is independent of energy and is
fairly stable with time (otherwise referred to as the LINEAR component).

(iii) an EINSTEIN SSS Basic Calibration File (type=bcf). This is a .COR file
containing a component of the SSS background spectrum which is of unknown
origin, but at energies >3 keV is variable with time (otherwise referred to as
the VARIABLE component).

(both background calibration data sets were modelled from 10,000 secs of blank
sky observations).

Finally, the source PHA file is updated by writing the names of the two
output background files to the keywords BACKFILE and CORRFILE. Note that
BACKFILE corresponds to the scaled LINEAR component, whilst CORRFILE
corresponds to the scaled VARIABLE component.

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NOTES ON USE

Historically, the 'JCG-parameter' has been used in the analysis of Einstein
SSS to normalise the background calibration data to that expected in the source
observation. This parameter is related to the number of 'bad' counts (total
counts - good counts) in the source PHA file. The details of exactly now the
JCG-parameter should be calculated are currently unavailable. However, in most
cases a value of JCG = 70 appears appropriate. SSSBCK contains a hidden
parameter jcgparm, with a default value of 70, in users users wish to change
this value.

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PARAMETERS
.ls phafile [character string]
 The user-supplied string for the Einstein SSS PHA filename
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.ls (jcgparm=70) [real]
 estimate of the number of 'bad' counts in the PHA file.
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.ls linfexp [character string]
 The user-supplied string for the calibration information to be used for the
 LINEAR component of the background (either caldb or CALDB or pathname of
 calibration file)
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.ls varfexp [character string]
 The user-supplied string for the calibration information to be used for the
 VARIABLE component of the background (either caldb or CALDB or pathname of
 calibration file)
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.ls bckfile [character string]
 The name of the output file containing the scaled LINEAR background 
 component.
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.ls corfile [character string]
 The name of the output file containing the scaled VARIABLE background
 component.
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.ls (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.
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.ls (mode = "ql") [character string]
  
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BUGS
None known

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LOG OF SIGNIFICANT CHANGES


.ls v2.0.0 (1996 Feb)
    modified for use in conjuction with SSSARF + CALLIB-ised
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.ls v1.0.0 (1994 Apr)
    original version (Ron Zellar)
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PRIMARY AUTHOR

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Lorraine Breedon
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HEASARC
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NASA/GFSC
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http://heasarc.gsfc.nasa.gov/cgi-bin/ftoolshelp
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(301) 286-1364
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.endhelp
