Attitude Correction

The two-dimensional off-axis response of the collimator has been derived from slew data of the Crab nebula (Kondo 1988; Turner et al. 1989). From this response, a post facto energy-independent vignetting correction has been calculated and applied to the background subtracted data cubes within the GINGALAC database (these provide a third data cube). Spectra and light curves were extracted from these attitude corrected data cubes for periods when the transmission is <70%. This corresponds to an offset of 0.3° and 0.4° for the X- and Z-directions respectively. However, the inner surfaces of the collimators were found to be reflective in the X-direction, amounting to a few percent below ~6 keV for an offset of ~0.3° from the collimator axis (Turner et al. 1989), which is not corrected for. Data products within the GINGABGD database are not corrected for the response of the collimator.

Both attitude and non-attitude corrected data cubes contain information regarding the satellite pointing position and roll angle as a function of time, thus allowing the user to calculate the appropriate correction for extended and confused sources.

In addition, two plots are available which show the LAC top- and mid-layer count rates versus a number of HK parameters. In particular, the plots within the GINGALAC database show the attitude corrected LAC count rate versus SUD, SOL2, DELTXZ and the transmission. LAC count rate versus SUD and SOL2 can be used to verify that there are no count rate enhancements on the Ginga orbital period (SUD) or due to hard (SUD) and soft (SOL2) particles. The LAC count rate versus DELTXZ can be used to verify that the attitude solution has removed count rate variations due to pointing instability (e.g. during slews at the beginning and end of observations). Satellite pointings away from the source along the X-axis can cause enhancements due to collimator reflection. The plots within the GINGABGD database show the LAC count rate versus SUD, SOL2 and DELTXZ. LAC count rate versus SUD and SOL2 can be used as in the GINGALAC database. LAC count rate versus DELTXZ can be used to identify periods of count rate enhancements due to sources in the Ginga field of view. The user may wish to remove these periods when using the data to model the background either in its own right or for another observation.