Imager IBIS

Principal Investigator:

Pietro Ubertini, IAS Rome Italy

Co-Principal Investigators:

Francois Lebrun, CE-Saclay, France

Guido DiCocco, ITESRE Bologna, Italy

with collaborating scientific institutes in Italy (IAS Rome, ITESRE Bologna, IFCAI Palermo), France (CEA Saclay), Norway (U Bergen), Germany (U Tuebingen), Spain (U Valencia), USA (NASA/MSFC Huntsville), Poland (Space Research Centre, Warsaw), UK (U Southampton).
The Imager IBIS (Imager on Board the Integral Satellite) provides diagnostic capabilities of fine imaging (12 arcmin FWHM), source identification and spectral sensitivity to both continuum and broad lines over a broad (15 keV - 10 MeV) energy range. A tungsten coded-aperture mask (located at 3.2 m above the detection plane) is optimised for high angular resolution. As diffraction is negligible at gamma-ray wavelengths, the angular resolution obtainable with a coded mask telescope is limited by the spatial resolution of the detector array. The Imager design takes advantage of this by utilising a detector with a large number of spatially resolved pixels, implemented as physically distinct elements. The detector uses two planes, one 2600 cm^2 front layer of CdTe pixels, each (4x4x2) mm (width x depth x height), and a 3000 cm^2 layer of CsI pixels, each (9x9x30) mm. The CdTe array (ISGRI) and the CsI array (PICsIT) are separated by 90 mm. The detector provides the wide energy range and high sensitivity continuum spectroscopy required for Integral. The division into two layers allows the paths of the photons to be tracked in 3D, as they scatter and interact with more than one element. Events can be categorised and the signal to noise ratio improved by rejecting those which are unlikely to correspond to real (celestial) photons, e.g. towards the high end of the energy range. The aperture is restricted by a lead shielding tube and shielded in all other directions by an active BGO scintillator veto system.
Further details of the current design can be accessed here:

Overall design (Cut-away view of detector assembly and shield (hopper), mask at 3.2m above focal plane not shown.)
Imager inside the payload module
Coded mask
Detector assembly STM
Mask and detector assembly viewed from the top (3D)
Various IBIS models (STM, EM, FM)
IBIS qualification model (QM) during testing at Laben/Torino
ISGRI modular detection unit (QM), 2048 pixels, 1/8 of total detection area
PICSIT modular detection unit (QM), 512 pixels, 1/8 of total detection area

ISGRI image (2048 pixels or 1/8 of the detection plane) can be viewed here.

ISGRI FM image (July 2001) (16384 pixels, full detection plane). A text (courtesy Francois Lebrun/CE-Saclay) explaining the ISGRI FM image can be found here.

ISGRI FM integrated in detector unit (October 2001)
The IBIS FM detector unit at Laben (October 2001) (I)
The IBIS FM detector unit at Laben (October 2001) (II)
The PICSIT FM integrated in detector unit (with heater layer on top of the detector pixels) (October 2001)
The IBIS detector unit (FM) during calibration at Laben (November 2001) (I)
The IBIS detector unit (FM) during calibration at Laben (November 2001) (II)
ISGRI FM calibration detector image (Co57)
PICSIT FM calibration detector image (Y88)
Continuum sensitivity (3, 10**6 s, E = E, ISGRI = solid line, PICSIT = dashed line, AO-1)
Continuum sensitivity (IBIS Observer's Manual, Issue 2 (AO-2) p.30)
Continuum sensitivities (JEM-X, IBIS, SPI, 3, 10**6 s, Nov. 2000, AO-1)
Continuum sensitivities (comparison with other instruments, August 2003)
Line sensitivity (3, 10**6 s, ISGRI = solid line, PICIST = dashed line, AO-1)
Line sensitivity (IBIS Observer's Manual, Issue 2 (AO-2), p.30)

Key performance parameters of the IBIS Imager

Imager IBIS WWW home page IAS Rome, Italy
Imager IBIS WWW in Bologna TeSRE Bologna, Italy

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