MIPS-Ge data are calibrated using the stimulator flashes (or ''stims'') to track the variation of the short-term response of the detectors; see section 4.1.1 for more information.
The stim flashes are designed to track the responsivity drift of the Ge detectors. Since we measure the stim minus background signal, the calibration most accurately tracks the response to a step function, i.e., the fast response. The stim flash calibration does not completely remove long-term transients for the MIPS-Ge detectors. The effects are most noticeable before the bias change for MIPS-70 (e.g., dark horizontal stripes in bottom of Figure 7.20). The effects are not as noticeable for MIPS-160 due to short time constants for the stressed 160 micron detectors. For point source science, this effect can be removed using a temporal median filter (e.g., for scan data).
For point source science, this effect can be removed using a temporal median filter (see section 8.2). The variation of the drift in the slow response affects the ability to accurately measure the true background level. For point sources, the long-term drifts can be treated as an additive effect (i.e., subtracting off a temporal median). The long-term drifts affect the actual response from the background, suggesting a multiplicative correction may be needed for large extended regions. For large extended sources, we recommended that observers take enough off-source data of the surrounding background so that the total extended source flux can be estimated.
Figure 7.20: Default mosaic from 4 AORs of unfiltered MIPS-70 BCDs. The dark horizontal (in-scan) stripes are fast/slow response variations, and the bright vertical stripes are stim latents.
