Rosat Status Report #78

[REQUEST@rosat.gsfc.nasa.gov]

			ROSAT Status Report # 78
			       Dec22 1993


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We have received several questions about the PSPC "PI" or "energy"
bands and channels.  Below we summarize pertinent information on this
subject.

PSPC PI bands
-------------
The PSPC detector has 256 channels of pulse height information which are
corrected to Pulse-height Invariant (PI) channels and "down-binned" into 34
channels for SASS spectral analysis (cf. Table 2).  SASS refers to its
various "energy" bands by letter (for hardness ratios), name (common X-ray
astronomy term), and number (for images), as indicated in Table 1:

                      TABLE 1: SASS PI Bands

            band   256-bin   34-bin     name       image
            ----   -------   ------    -------     -----
              A     11- 41    3-10     "soft"        3  
              B     52-201   13-30     "hard"        2  
             A+B    11-235    3-33     "total"       1  
              C     52- 90   13-18        -          -
              D     91-201   19-30        -          -
              -     42- 51   11-12   "carbon edge"   -

These bands and binning schemes were adjusted slightly (both within SASS
and in off-line usage) following the PSPC gain change that was introduced
in October 1992 to correct the "low pulses" problem.  The December 1992
version of the "ROSAT Data Products Guide" reflects these changes (cf. pp.
PSPC 3-1 and PSPC 5c-1), which removed the bottom three PI bins (of the
256-channel scheme, i.e., 8-10) from the soft band and also moved the
boundaries of the "compressed" 34-bin scheme slightly to accommodate this
adjustment.

PSPC PI channels
----------------

The PI-channel binning scheme now in use is given in Table 2.  For spectral
analysis, it is recommended that 34-bin numbers 1, 2, 33, and 34 (#)
be excluded from the fits.
 
                         TABLE 2: SASS PI bins

    34-bin   Energy    256-channels     34-bin    Energy     256-channels
    number  Low - High   included       number   Low - High    included
    ------ ----- -----  ----------      ------  ----- -----   -----------
    # 1 #  0.07 - 0.09   # 7 - 8 #        18    0.84 - 0.91    84 - 90
    # 2 #  0.09 - 0.11   # 9 - 10#        19    0.91 - 0.99    91 - 98
      3    0.11 - 0.14    11 - 13         20    0.99 - 1.07    99 - 106
      4    0.14 - 0.17    14 - 16         21    1.07 - 1.15   107 - 114
      5    0.17 - 0.20    17 - 19         22    1.15 - 1.23   115 - 122
      6    0.20 - 0.24    20 - 23         23    1.23 - 1.32   123 - 131
      7    0.24 - 0.28    24 - 27         24    1.32 - 1.41   132 - 140
      8    0.28 - 0.32    28 - 31         25    1.41 - 1.50   141 - 149
      9    0.32 - 0.37    32 - 36         26    1.50 - 1.60   150 - 159
     10    0.37 - 0.42    37 - 41         27    1.60 - 1.70   160 - 169
     11    0.42 - 0.47    42 - 46         28    1.70 - 1.80   170 - 179
     12    0.47 - 0.52    47 - 51         29    1.80 - 1.91   180 - 190
     13    0.52 - 0.58    52 - 57         30    1.91 - 2.02   191 - 201
     14    0.58 - 0.64    58 - 63         31    2.02 - 2.13   202 - 212
     15    0.64 - 0.70    64 - 69         32    2.13 - 2.24   213 - 223
     16    0.70 - 0.77    70 - 76       # 33 #  2.24 - 2.36 # 224 - 235 #
     17    0.77 - 0.84    77 - 83       # 34 #  2.36 - 2.48 # 236 - 247 #