For instance, one glint has been seen 1.5 degrees from the center of a scan map as a result of a very bright source - a source of >1500 Jy created a diffuse ghost of 12 Jy. When a bright source is at or just off the edge of the array, there are linear glints that appear in the frame.
Redundancy (e.g., additional dithered frames) and median-combining frames can reduce some of these effects.
Figure 7.16: Very rare glint - fake ~12 Jy source seen ~1.5 degrees from ~1500 Jy source.
7.1.8 Apparent zero-level offset
Occasionally, there is a zero-level offset in a single BCD frame, e.g., the whole frame appears brighter than others; see Figure 7.17. This is not entirely understood, and may be due to a bright cosmic ray. If you see this in your data, you can correct it with an additive offset to that frame, or you can use background matching in MOPEX if there is sufficient overlap with adjacent BCDs.
Figure 7.17: Example of single frame with zero-level offset. No background matching was performed in creating this mosaic.