How to choose the source search method in the Science Window analysis

Basically the idea is that you can either let the software look for the excesses in the field or you can tell the software to look for sources from a given catalog. This catalog can be either the one provided by ISDC (CAT_refCat="$ISDC_REF_CAT"), from which you can extract e.g. only the sources that have been detected by ISGRI ("$ISDC_REF_CAT[ISGRI_FLAG>0]"), or a catalog made on your own (see section 9.7 to create a catalog on your own). The number of sources that are detected in an image is important because detecting a source means also removing its ghosts from the images (see section 7.1).

The source search method is defined with the parameters OBS1_SearchMode and OBS1_ToSearch. These parameters allow you the following possibilities:

• OBS1_SearchMode = 0
  This mode was developed for testing purposes and is not recommended for scientific use.
• OBS1_SearchMode = 1
  the software will look for all the sources of the input catalog that are in the field of view (regardless of their detection level, i.e. not using the OBS1_MinCatSouSnr parameter). If the source gives a positive detection, then the relevant results are saved in the isgri_sky_res.fits file, but see also discussion on OBS1_NegModels in Section 8.2.4.
  This mode can be useful in case your Science Window images are noisy and many fake new sources are detected. Searching only the sources from a given catalog will avoid having ghost cleaning for fake sources. This mode can be very time consuming if the observed field is "crowded", such as the Galactic Center region.
• OBS1_SearchMode = 2
  The software will look for the K brightest sources in the field, where K = OBS1_ToSearch.
  They can be either known sources (more significant than OBS1_MinCatSouSnr) or new sources (more significant than OBS1_MinNewSouSnr).
  This mode is useful if you are interested in having a first glance at your field, if you are interested in bright sources only, or if you run your analysis on large data sets. In fact, in these cases you would not like to spend most of your time collecting information on weak sources that are not detected in a single Science Window. The drawback of this method is that these undetected weak sources can produce ghosts in the mosaic image. We recommend you to start the analysis with OBS1_SearchMode = 2 with a high OBS1_ToSearch value (around 50, especially for the Galactic plane or Centre crowded regions), see the sources that are detected and prepare your own catalog of detected sources (see section 9.7). Then launch again the analysis with OBS1_SearchMode = 3 - described below - and give your catalog as input for the analysis (CAT_refCat=usrcat.fits).
  WARNING:

  When using OBS1_SearchMode=2, the position of sources detected in the single science window and associated to catalog sources with ISGRI_FLAG=2 is assigned to the pixel centre, instead of being fixed to the catalog position as it should. This problem is not present with OBS1_SearchMode=1 or 3, since in this case the catalog position is used when no fitting is requested. (see also Sect.11).

• OBS1_SearchMode = 3
  The software will look for all the catalog sources (regardless of their detection level, i.e. not using the OBS1_MinCatSouSnr parameter) plus for K significant excesses more significant than OBS1_MinNewSouSnr, where K = OBS1_ToSearch up to a maximum of K sources. All these sources will be saved in the final isgri_sky_res.fits file if their detection significance is positive, but see also discussion on OBS1_NegModels in Section 8.2.4 . This mode is very efficient in cleaning the ghosts of all the sources in the field of view. It is of course more time consuming since a model is created and deconvolved for each given source.
  We suggest that you should use this mode either with your own catalog (built from the previous run with OBS1_SearchMode = 2, see above) or, if no personalised catalog is available, using the ISDC catalog with only the sources that have been detected by ISGRI ($ISDC_REF_CAT[ISGRI_FLAG>0], see above). Any bright source out of the catalog (new or forgotten!) will be detected as one of the K new sources.