hand-on

The Galactic Center

(crowded field and faint sources)

ISGRI

0. Data Selection

Browse the INTEGRAL archive to create the list of Science Windows of Revolution 49 in which an X-ray binary IGR J1630-4751 is in the fully-coded field of view of ISGRI (max 4.5 degrees of-axis). Save a list of several of these Science Windows (e.g. 5, to keep the processing time reasonable) into a file rev49_isgri.txt

Using the list of ScWs create an observation group named rev49_isgri

In this example we will concentrate on the analysis of the faint source
IGR J16320-4751. Browse first the INTEGRAL Source Results page to see what "ready to use" data are available on this source and to select potentially interesting periods of time for analysis of the sources.
Later on you will have a possibility to compare the results of your analysis starting from the raw data with the standartized source results.

1. Image Reconstruction:

Create mosaic image in 5 energy bands with OBS1_PixSpread=0 option
( IBIS_II_E_band_min="19.7 25.0 30.2 40.3 50.3"
IBIS_II_E_band_max="25.0 30.2 40.3 50.3 60.4" ).

By default software is using OBS1_SearchMode = 2, in this mode it looks for K sources,
where K = ToSearch. By default ToSearch=15,but in the crowded field you may want to
increase this number in order to detect faint sources. However, in this case the mosaic images are full of "ghosts"
from the sources not detected in single ScW. To get rid of them change OBS1_SearchMode = 3.

Try to experiment with OBS1_SearchModeparameter (see how "ghosts" of the bright sources appear at the image if you choose OBS1_SearchMode = 2 ).
Analyze your mosaic images with the ds9 tool.
Compare the resulted isgri_mosa_ima.fits with the images of several individual science windows,
paying special attention to IGR J16320-4751. (To ease your life create
a region file from isgri_mosa_res.fits with cat2ds9).

1a. Science window-per-science window analysis.

Note that instead of creating a single observation group for the whole set of science windows you can create separate observation groups for each science window from the list rev49-isgri.txt which you just downloaded. For this you can use the foreach command in the following way

foreach fn ( `cat rev49-isgri.txt` )
setenv REP_BASE_PROD $PWD
echo "$fn"
set fs=`echo "$fn"|cut -c 10-21`
echo "$fs"
echo "$fn">tmp
rm -rf obs/$fs
og_create baseDir="." instrument=ibis idxSwg=tmp ogid=$fs
cd obs/$fs
setenv COMMONLOGFILE +log
setenv COMMONSCRIPT 1
ibis_science_analysis ogDOL="./og_ibis.fits[1]" \
    SWITCH_disablePICsIT=yes \
    startLevel="COR"\
    endLevel="IMA" \
    CAT_refCat="$ISDC_REF_CAT"\
    IBIS_II_ChanNum=2\
    IBIS_II_E_band_min="20 60"\
    IBIS_II_E_band_max="60 200"\
    OBS1_SearchMode=2\
    OBS1_ToSearch=25\
    OBS1_DoPart2=0
cd ../..
rm -rf tmp
end

With the help of another foreach cycle create a list of isgri_sky_ima.fits files from which you want to make the mosaic. Follow the instructions given in the Cookbook and create the mosaic image.

1b. Analysis with the User Catalog:

As you can see faint sources that are clearly seen in the mosaic image are not detected in all individual
science windows. If you want the software to extract the flux from some particular sources independent on its detection level you should create your own catalog with the sources you are interested in and useOBS1_SearchMode = 3 option. In this case software will search for all catalog sources and plus for K significant excesses, where K = ToSearch. To create a catalog create a new file usr_cat.fits with the command
dal_create obj_name=usr_cat.fits template=GNRL-REFR-CAT.tpl

add there the desired number of rows and fill columns SOURCE_ID, NAME, RA_OBJ, DEC_OBJ and ERR_RAD with the information you can find in general catalog. The second option is to copy the general catalog to another file and remove all unnecessary sources.

2. Spectral Analysis:

Extract spectrum of IGR J16320-4751 from the mosaic image using mosaic_spec.

Extract the spectrum of this source using standard spectral extraction procedure. Note that by default the spectra for all sources present in the output catalog ISGRI-SRCL-RES will be produced.
To save time you should carefully define the list of sources for the spectral extraction. To have meaningful results you should include in your analysis all sources brighter or comparable to the source of interest (see instructions in the Spectral extraction section of the IBIS cookbook).

To see the influence of wrong source selection on the resulted spectrum prepare two catalogs - cat_2src.fits with only IGR J16320-4751, and another one cat_full.fits with all sources brighter or comparable to these. Copy the rev49_isgri to rev49_isgri_wrong and launch ibis_science_analysis from BIN_S to SPE level with SCW2_cat_for_extract=cat_full.fitsand SCW2_cat_for_extract=cat_2src.fits respectively. Use spectral binning you have used working with Crab.

To sum up spectra from individulal spectra use spe_pick.

Launch XSPEC and compare the obtained results.