In front of the MOS detectors Reflection Grating Arrays (RGA) exist. The RGA splits some of the photons into RGS. However it also produces some reflected structures, called RGA spikes, detected on MOSs, which can be seen when there is a very bright source(s) in the field of view.
Unfortunately no quantative study has been made about the RGA spikes, such as the surface brightness and intensity or position of bright sources. However, it is known that the RGA spikes appear across the whole MOS, rather than a single chip like the OOT events, and it is parallel to the X-axes of chip 1 or the Y-axes of the other chips.
Although we do not know the quantative nature of the RGA spikes, the pixels which show significant pile-ups are likely to cause significant RGA spikes. Hence, this task creates, if forrgaspike=`yes', a mask image, which represents the RGA spike streaks caused by heavily piled-up pixels.
If there is a too bright source, the same argument as discussed in subsection 3.1.1 applies.