SSSBCK (Feb96)               ftools.caltools              SSSBCK (Feb96)



NAME
    sssbck  --  builds the EINSTEIN SSS background PHA files for a given
    source obsn
    
    
USAGE
    phafile (jcgparm) linfexp varfexp bckfile corfile (chatter) (mode)
    
    
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.
    
    
    
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.
    
    
    
PARAMETERS
    
    phafile [character string]
         The user-supplied string for the Einstein SSS PHA filename
    
    (jcgparm=70) [real]
         estimate of the number of 'bad' counts in the PHA file.
    
    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)
    
    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)
    
    bckfile [character string]
         The  name  of  the  output  file  containing  the scaled LINEAR
        background  component.
    
    corfile [character string]
         The name of the output  file  containing  the  scaled  VARIABLE
        background  component.
    
    (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.
    
    (mode = "ql") [character string]
        
    
    
    
    
BUGS
    None known
    
    
    
LOG OF SIGNIFICANT CHANGES
    
    
    
    v2.0.0 (1996 Feb)
            modified for use in conjuction with SSSARF + CALLIB-ised
    
    v1.0.0 (1994 Apr)
            original version (Ron Zellar)
    
    
    
    
PRIMARY AUTHOR
    
    Lorraine Breedon
    HEASARC
    NASA/GFSC
    http://heasarc.gsfc.nasa.gov/cgi-bin/ftoolshelp
    (301) 286-1364