All subarray datasets.
The 58th subarray frame in both IRAC channels 1 and 2 exhibits a general modulation in the background level of the subframe compared to other frames.
This effect does not appear to have a significant effect on the results of aperture photometry performed using annular background subtraction. While the exact cause of the background variation in this frame is unknown, it has been traced to a problem in the pipeline applying the skydark, due to some periodic variation (or a slight timing difference) when subtracting the detector bias level. It does not appear to have a gain component. To be sure there is no detrimental effect on the reduced data due to this feature, many researchers omit this subframe in their analysis.