With the help of the spe_pick program, described in the Introduction to the INTEGRAL Data Analysis [1], it is possible to combine the spectra from the different Science Windows. To define the source for which you want to combine the spectra you should either input its Source ID, or the source coordinates. In our case, to combine all the spectra belonging to the given Observation Group of the Crab give the following command
spe_pick group="og_jmx2.fits[1]" instrument="JMX2"\ source="J053432.0+220052" rootname="crab"The rootname argument allows to choose the name of the resulting spectral data files. For example, the above command produces the files
| crab_single_pha2.fits | with all individual spectra of the source, |
| crab_single_arf2.fits | with corresponding individual ARFs, |
| crab_sum_pha.fits | with the combined spectrum, |
| crab_sum_arf.fits | with the ARF for the combined spectrum. |
The resulting spectrum crab_sum_pha.fits can be analysed with XSPEC exactly in the same way as in the case of the individual ScW spectra (see above). The result of such analysis is shown in the right panel of Fig 18. You can check that combining the spectra obtained with/without fixing the source positions results in slightly different spectral fits in XSPEC.
It is also possible to combine the spectra of the Science Windows which belong to different observation groups. This is explained in section 7.4.2.