Overview

In this Section, we give an overview of the analysis of IBIS data.

Each photon detected by IBIS is analyzed with the on-board electronics and tagged with the arrival time, type (ISGRI , PICsIT, Compton etc.), energy, position etc. according to the operation mode (i.e., photon-by-photon, standard, calibration etc.). These data are then sent to ground in telemetry (TM) packets.

During Pre-Processing the TM packet information is deciphered and rewritten into a set of FITS files (RAW data). Then, the local on-board time is converted into the common on-board time (OBT) and the House Keeping (HK) parameters into physical units (PRP data).

These steps are done at ISDC and results stored into the available archive of data. In the Appendix A and B, you will respectively find the description of the raw and prepared data and also the description of the instrument characteristic files that are used in the Scientific Analysis.

INTEGRAL data are organized into the so-called Science Windows (see Introduction to the INTEGRAL Data Analysis [1] for more explanations). During the scientific analysis, all the Science Windows belonging to the same observation are grouped together to form the ``Observation Group''.

Figure  shows in details the different steps performed by the scientific analysis script, ibis_science_analysis. This high-level script consists of four smaller ones: ibis_scw1_analysis, ibis_obs1_analysis, ibis_scw2_analysis and ibis_obs2_analysis. ibis_scw1_analysis and ibis_scw2_analysis work on a Science Window basis while ibis_obs1_analysis and ibis_obs2_analysis work on the Observation Group basis. Each subscript performs the tasks shown in Figure , explained in more details in the text below.

Figure: Science Analysis Overview

• The first script ibis_scw1_analysis performs the following tasks:

  COR - Data Correction
  
  Tags noisy pixels, corrects energy of the photons for rise time and temporal variations of the gain, transforms channels to energy. See Section for more details.

  GTI - Good Time Handling
  
  Generates, selects, and merges Good Time Intervals (GTI) to produce a unique GTI that is then used by the software to select good events. See Section for more details.

  DEAD - Dead Time Calculation
  
  Calculates the total dead time during which the incoming photons may be lost due to the processing of the previous events. Also veto strobe signals generated by BGO (Bismuth Germanate) shield, calibration source and Compton events are taken into account. See Section for more details.

  BIN_I - Event Binning for Imaging
  
  Sorts data into energy bins. For each energy range, the intensity shadowgram and a corresponding efficiency map are created. See Section for more details.

  BKG_I - Background Correction
  
  Creates rebinned maps for background and absorption of support mask (see Section ) corrections. Corrects for efficiency and subtracts background. See Section for more details.

  After these steps the high-level analysis is performed.
  

• The second script ibis_obs1_analysis takes the whole Observation Group previously created as input and performs the following tasks:

  CAT_I - Catalog Source Selection for Imaging
  
  Selects from the given catalog a list of sources in the Field of View matching the criteria defined by script parameters, and creates an output list with location and expected flux values of the selected sources. See Section for more details.

  IMA - ISGRI and PICsIT (staring) Image Reconstruction
  
  In the case of ISGRI, shadowgrams are deconvolved, source search is performed in the single images as well as in the mosaic (combination of different images) and a list of detected sources is created.

  If INTEGRAL was stable during the whole period of interest, then, at your request, all PICsIT shadowgrams are combined into one and then are deconvolved into a single image. See Section for more details.
  

• The third script ibis_scw2_analysis again works Science Window by Science Window and performs the following tasks:

  IMA2 - PICsIT Image Reconstruction
  
  PICsIT shadowgram deconvolution is done at this step, creating a separate image for each science window. See Section for more details. Nothing is done at this step for ISGRI.

  BIN_S - Event Binning for Spectra
  
  Creates rebinned maps for background and absorption of support mask (see Section ) corrections. Sorts data into energy bins. For each energy range the shadowgram and a corresponding efficiency shadowgram is created. See Sections , for more details.

  SPE - ISGRI spectra extraction
  
  For each source of interest,one PIF is produced. ISGRI spectral extraction is done for all catalog sources with the use of these PIFs. See Section for more details.

  LCR - PICsIT Detector Light Curve Creation and ISGRI source lightcurve extraction
  
  At this step, PICsIT Detector light curves are built from the spectral timing data. For all sources from the input ISGRI catalog light curves are extracted. See Section for more details.
  

• The fourth script ibis_obs2_analysis again works in the whole Observation Group previously created, and performs a single task for PICsIT data:

  CLEAN - Last step
  
  At this step PICsIT mosaic is created. See Section for more details.

Revision 3 (rev_3) of the INTEGRAL Archive is the default data format and the older Revision 2 (rev_2) archive is no more available. Rev_3 data have been regenerated starting from INTEGRAL telemetry, including an optimal time correlation and the data selection and calibrations used in OSA9. Even if the data correction step (COR), as well as the instrumental GTI and deadtime handling (DEAD) steps have already been performed at science window level, the energy reconstruction has become inaccurate. To fully exploit OSA11 improvements, it is mandatory to rerun the analysis from COR step included, as new algorithms and calibration files are available.

The resulting OSA count rates in scientific products are corrected for the off-axis transparency of the mask supporting structure.