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5.3. Memory effects
The band 2 and 4 detectors used in SWS ``remember'' their previous illumination history. Going from low illumination to high illumination, or vice-versa, results in the detectors asymptotically reaching their final value. Currently the only memory effects accounted for in the pipeline are those that affect dark currents.
An example of memory effects can be seen in Figure 4, which shows ERD data from detector 39 (band 4) during a dark current check. The detector takes a few reset intervals to stabilise both on light-dark or dark-light illumination changes.
Figure 4: Example of memory effects
Memory effects can also be seen in up-down scans of bright sources. For sources with fluxes greater than about 1000 Jy memory effects cause the up and down scans to differ in response (and hence flux) by up to 20% in bands 2 and 4.
Memory effects can also change the shape of line profiles. As the grating scans across a strong gaussian line the sensitivity of the detectors change. If this change is large enough it will result in one side of the gaussian having a different shape from the other. As lines are scanned in different directions by the up-down scans, the line will have a different shape in both scans. If the scans are averaged the line will be broader than it actually is. These effects mainly happen in band 4, due to it's larger memory effects.
A. Salama et al.