4.1 Responsivity transients

Detector transients occur as soon as a change in detector illumination takes place. The resulting relaxation function after the flux step is not easy to model and depends on the flux step, type of detector, flux history, temperature of the detector, etc. PIA contains routines to apply theoretical or semi-empirical drift corrections, but it is to the observer's judgement to use the inter-actively derived fluxes.

The P1 and PHT-S detectors cause the largest responsivity transients causing a photometric bias of more than 100% for large flux steps and short (32 sec) integration times. Typical observations that can be affected at a level higher than 20% accuracy are:

• observations with PHT-S.
• observations with detector P1 and P2.
• multi-filter observations with PHT-P and with relatively short integration times ( sec). Faint targets are more affected because the relaxation time is generally longer.
• PHT32 maps with high dynamic range. For very high dynamic range maps ``ghosts'' of bright point sources have been seen about 1 chopper sweep away from the actual targets.