An Example of a Simple XSPEC Session

In the following example, we use XSPEC to simulate a Crab spectrum expected in the HEPC, LEPC, and SIXA detectors, using the response matrices available in the US SXG CF anonymous ftp node. We assume a Crab spectrum with

Note that for the SIXA spectrum, the response matrix is normalized to a maximum effective area of 1.0. XSPEC renormalizes it to the correct value of 1735 in the fakeit command. 

!xspec 16:33:21 16-Jun-95
XSPEC> model wabs powerlaw
 Input parameter value, delta, min, bot, top, and max values for ...
 Mod parameter  1 of component  1 wabs     nH 10^22
    1.000      1.0000E-03      0.          0.      1.0000E+05  1.0000E+06
 0.3
 Mod parameter  2 of component  2 powerlaw PhoIndex
    1.000      1.0000E-02  -3.000      -2.000       9.000       10.00
 2.05
 Mod parameter  3 of component  2 powerlaw norm
    1.000      1.0000E-03      0.          0.      1.0000E+05  1.0000E+06
 10.0
  ---------------------------------------------------------------------------
  mo = wabs[1] (powerlaw[2])
  Model Fit Model   Component     Parameter   Value
  par   par comp
    1    1    1       wabs        nH 10^22  0.300000     +/-      0.
    2    2    2       powerlaw    PhoIndex   2.05000     +/-      0.
    3    3    2       powerlaw    norm       10.0000     +/-      0.
  ---------------------------------------------------------------------------
    3 variable fit parameters
XSPEC> fakeit none
 For fake data, file #  1 needs response file: hepc.rmf
Use counting statistics in creating fake data? (y)
 Input optional fake file prefix (max 12 chars):
 Override default values for file #    1
 Fake data filename (hepc.fak):
 T, A, Bkg, cornorm ( 1.0000 , 1.0000 , 1.0000 , 0. ):
 Net count rate (cts/cm^2/s) for file   1   3114.    +/-   56.43
 Chi-Squared =      111.7     using   128 PHA bins.
 Reduced chi-squared =     0.8934
XSPEC> fakeit none
 For fake data, file #  1 needs response file: lepc.rmf
Use counting statistics in creating fake data? (y)
 Input optional fake file prefix (max 12 chars):
 Override default values for file #    1
 Fake data filename (lepc.fak):
 T, A, Bkg, cornorm ( 1.0000 , 1.0000 , 1.0000 , 0. ):
 Net count rate (cts/cm^2/s) for file   1   8323.    +/-   91.23
 Chi-Squared =      98.38     using   128 PHA bins.
 Reduced chi-squared =     0.7871
XSPEC> fakeit none
 For fake data, file #  1 needs response file: sixa.rmf
Use counting statistics in creating fake data? (y)
 Input optional fake file prefix (max 12 chars):
 Override default values for file #    1
 Fake data filename (sixa.fak):
 T, A, Bkg, cornorm ( 1.0000 , 1.0000 , 1.0000 , 0. ): 1.0,1735.0
 Net count rate (cts/cm^2/s) for file   1   3.697    +/-  4.7748E-02
 Chi-Squared =      756.5     using  1007 PHA bins.
 Reduced chi-squared =     0.7535
XSPEC> quit
For additional examples and a complete description of the XSPEC system, click here.

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Last Updated Nov. 11, 1994