Data Selection within Sortac

The program SORTAC allows the selection of data in FRFs, producing data cubes (time, spectral and detector resolution) as output. Initially the data were selected from the FRFs, with full spectral resolution and a time resolution of 16 seconds and 64 seconds for the GINGALAC and GINGABGD databases respectively⁴. Limits were placed on certain HK parameters during the extraction of data, with the LAC count rate above 24 keV (known as Surplus above Upper Discriminator or SUD), the energy that a cosmic-ray requires to penetrate the magnetosphere (Cut-Off Rigidity or COR) and solid state electron monitor count rate (SOL2) all restricted to avoid periods of high particle background (these limits are different for target and background observations; they are listed in table 2). Contamination from X-rays due to the bright Earth was prevented by restricting the angle between the satellite pointing direction and the Earth's horizon (YELEV) to greater than 6 degrees. Occasionally it was necessary to restrict the data with tighter constraints. The constraints actually used are stored for each observation in the database. In addition, DELTXZ (the angle between the satellite pointing direction and the nominal Ginga field of view) has been restricted to angle of and within the GINGALAC and GINGABGD databases respectively. This removes periods when the collimator transmission was less than 60 and 70% for the X- and Z-directions respectively. For solar angles (angle between the satellite pointing direction and the Sun) less than 90 degrees, solar X-rays can penetrate the LAC via the collimator when the satellite is in sunlight. These data were excluded from the database by restricting the observational intervals to those in the Earth's shadow. Whilst this may lead to a large reduction in the useful length of an observation, it does ensure that the data products are free of solar contamination. The minimum acceptable exposure time for any observation was set at 100 seconds and 10³ seconds for the GINGALAC and GINGABGD databases respectively.