Although it is possible to carry out an image reconstruction without any prior information, better results will be obtained if the positions of sources known to lie in the FoV are specified beforehand. In any case, source positions have to be provided for spectral extraction.
Source positions are provided through a source_cat.fits file. For a specific analysis, you can either (1) use an existing source_cat.fits, or (2) perform an extraction (cat_extract = CAT_I in the first step of the analysis) from the ISDC reference catalogue. Since the outputs of cat_extract are sometimes hard to predict, it is strongly advisable to run only cat_extract first and to check the result with the ftool ``fv'' before going further in the analysis. If there are sources that should not be taken into the analysis, either set the SEL_FLAG column (one before the last one) to zero, or remove the un-wanted rows. Alternatively, make sure SEL_FLAG is set to one for all sources that should be used in the analysis.
In general, it is difficult to know in advance which of the known sources will actually be detected by INTEGRAL . It is therefore a good practice to make an analysis without specifying any source positions, to look at the results, possibly comparing them with the outputs of cat_extract before evaluating which source positions should be fixed in the analysis.