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    Instruments

    IBIS

    Principal investigators

    P. Ubertini
    IAS
    Rome
    Italy

    F. Lebrun
    SAp - CEA Saclay
    France

    G. DiCocco
    ITESRE
    Bologna
    Italy

    IBIS Detector and Mask

    The imager on-board INTEGRAL (IBIS) is giving sharper gamma-ray images than any previous instrument. IBIS 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. The imager examines, simultanesously with the other instruments on INTEGRAL, celestial objects of all classes ranging from the most compact galactic systems to extragalactic objects. 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 spatial resolution is dependent on the number of small sensitive elements of the detector, called pixels (picture elements). IBIS has a detector with a large number of pixels, all physically distinct from one another.

    IBIS Instrument

    The detector uses two parallel planes of pixels located one on top of the other and separated by 90 mm. The top layer (ISGRI) is made of 16 384 cadmium telluride (CdTe) pixels, covering 2600 square centimetres and each measuring 4x4x2 millimetres. This layer detects the low-energy gamma rays. The second layer (PICsIT) consists of 4096 caesium iodide (CsI) pixels, each 9x9x30 millimetres covering 3100 square centimetres. This layer captures high-energy gamma rays.

    The division into two layers allows scientists to track the paths of the photons in 3D, as they scatter and interact with more than one element.

    IBIS Coded Mask

    Events can be categorised and the signal to noise ratio improved by rejecting those which are unlikely to correspond to real (celestial) photons, for example 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 bismuth germanate oxide (BGO) scintillator veto system.

    IBIS was put together by a number of collaborating institutes from around the world:

    • 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)

    Table Showing Predicted Performance

    Parameter

    Value

    Energy range 15 keV - 10 MeV
    Detector area 2600 cm2 (CdTe)
    3100 cm2 (CsI)
    Spectral resolution 8% @ 100 keV
    10% @ 1 MeV
    Field of view 8.3° x 8.0° fully coded
    29.1° x 29.4° zero response
    Angular resolution 12 arcmin FWHM
    Point Source Location Accuracy 30'' @ 100 keV - 50σ source
      3'' @ 100 keV - 5σ source
    5-10'' @ 1 MeV - 5σ source

    Narrow-line sensitivity
     - 3σ  in 106 s, @ 100 keV
     - 3σ  in 106 s, @ 1 MeV


    1.9 x 10-5 phs-1cm-2
    3.8 x 10-4 phs-1cm-2
    Continuum sensitivity 
     - 3σ  in 105 s, @ 100 keV, ∆E = E/2
     - 3σ  in 105 s, @ 1 MeV, ∆E = E/2


    1.9 x 10-5 phs-1cm-2keV-1
    3.8 x 10-5 phs-1cm-2keV-1

    Timing accuracy (3σ ) 61 μs

    Typical Source Location
     - 50σ  source @ 100 keV
     - 5σ  source @ 100 keV


    30''
    3'

    Resources (following EID-A allocation)
    Mass 677 kg (+96 kg for tube)
    Power (sun/eclipse) 240/0 W
    Data rate (solar maximum) 59.8 kbit/s
    Date rate (solar minimum) 56.8 kbit/s

    < Previous article: SPI Next article: JEM-X >

    Last Update: 06 September 2011

    • Shortcut URL
    • http://sci.esa.int/jump.cfm?oid=31175
    • Related Articles
    • Overview
    • SPI
    • IBIS
    • JEM-X
    • OMC
    • IREM
    • Coded Masks
    • TIMM
    • Related Links
    • IBIS at Bologna
    • IBIS at CEA/Saclay
    • IBIS at Rome
    • SPI at CESR, Toulouse
    • SPI at MPE Garching
    • OMC at INTA, Madrid
    • JEM-X at Copenhagen
    • IREM
    • Coded Mask Imaging
    • INTEGRAL Mass Model (TIMM)

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