The SIGMA modes of observation

• The spectral-imaging mode is the most frequently used mode of observation. The average acquisition time for a session is 24 hours. The following data are recorded simultaneously :
  • Fine images with 1.6 arc-minute resolution (248 x 232 pixels) in four consecutive programmable energy bands.

  • Spectral images (124 x 116 pixels) through the entire energy domain in 95 energy bands varying logarithmically in width.

  • A spectral analysis for all the photons detected in the position detector.

  • Slow variability data : the photon count is recorded every four seconds in the four same consecutive programmable energy bands as the fine images.

  • Attitude of the telescope every four seconds.

  • When a burst trigger is sent :
    • Images of bursts are made by the detector.

    • A temporal and spectral analysis can be made of the bursts by anticoïncidence counters placed around the telescope.

• During the variability-imaging mode, the spectral images in the 95 energy bands are replaced by 48 consecutive time images obtained in a programmable energy band.

• The photon-photon mode is measuring the position and the energy of all the photons which enter the detector area. Each 63rd photon is dated in milliseconds.

• In the fast-variability mode, the energy and date in milliseconds of each photon detected is calculated without spatial information.

Data transmission

SIGMA data are downlinked about every 24 hours to the ground station in Evpatoria in Crimea during the part of the orbit during which the payload operates.

Every month, a French scientist team is present to receive data from SIGMA and do operational data control. Then SIGMA data are taken back in France to be processed and analysed.

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