Here we start with an observed spectrum testdata1:spectrum.tbl of our source. We assume that this spectrum is already corrected by using the correction mode of the projection package (see last example and chapter 4) and begin with setting the context to exsas.
Midas 001> set/context exsasFirst we bin the detector response according to the observed spectrum. We relate the binned detector response matrix to the name of the observed spectrum spectrum_drm instead of using the default.
Midas 002> bin/detector testdata1:spectrum ? spectrum_drm Create binned detector response matrix spectrum_drm.Accordingly we create the parameter file spectrum_grid.par necessary to produce the
values at chosen grid points
(parameter 1: values of column density 
from 0 to 
cm 
in steps of 
cm 
and
parameter 3: values of photon index 
from -8 to 0 in steps of .5)
by entering CREATE/PARFIL FIT with the expert
flag option (parameter file without comments).
We change this file according to the example
and delete all lines,
which have proper defaults.
Any parameter file can be modified also via the
command WRITE/PARFIL.
Midas 003> CREATE/PARFIL fit spectrum_grid ? ? ? expert ! ! --- general key words --- ! FIT ! alternative: COMPARE, CALCULATE FOLD ! folding with detector response INPUT_FILE testdata1:spectrum ! observed X-ray spectrum OUTPUT_FILE spectrum_grid ! 2-D grid of chi-square values CORRECTION_FILE exsas_cal:effarea_pspcc ! corrected effective area RESPONSE_FILE spectrum_drm ! binned detector response matrix ! ! --- power law model, parameters, and red shift --- ! MODEL gamm(1)*powl(2,3,4) ! galactic absorption * power law PARAMETER 1 0.0 15.0 1.0 grid ! nH, units of 10^21 atoms/cm^2 PARAMETER 2 1.E-2 1.E-7 1.E+5 0. free ! flux amplitude at E0 PARAMETER 3 -8.0 0.0 0.5 grid ! photon index gamma PARAMETER 4 1.0 ! reference energy E0 in keV REDSHIFT 0.0 ! red shift z
Figure 6.3:
Contour plot of 
as a function of the galactic
column density 
and the photon index 
for
three confidence levels of 68.3%, 95.4%, and 99.7%
Now we run the command MODEL/SPECTRUM to search for
a 
grid. Since the program runs 
single fits it takes a while to output the results
in the bulk data frame spectrum_grid.bdf.
Midas 004> model/spectrum spectrum_gridWe create a graphic window to make a contour plot of confidence levels by using constant
values of
the `` 
- 
'' parameter grid. Since we don't
want to overload the plot we choose only three of five
possible contour lines corresponding to the first
three default confidence levels of
68.33%, 95.45%, and 99.73%.
If we are satisfied with the result
we send the plot to a proper printer
(see Figure 6.3).
Midas 005> create/graph Midas 006> set/graphic pmode=1 fonts=1 frame=square Midas 007> plot/chi2_contour spectrum_grid 3 ? xlab="nH in atoms/cm2" ylab="Photon index" Midas 008> copy/graphic LASER