SIGMA - GRANAT

The SIGMA modes of observation
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Several modes of observation can be used with the telescope:

* 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.