The Corner Problem

There may be an issue concerning an under- or over-estimation of the pn particle background, particularly for relatively short observations (less than $\sim10$ ks of good time). This is primarily due to the poor statistics of the pn corner data as they are both limited in physical extent and they are affected by OOT events.

However, there is a secondary problem; the pn corner data are much more sensitive to SP flares than previously understood. The current pn QPB spectra are thus not as free of SPF emission as they should be. (This is being corrected, but probably will not be available until V22.0.) Thus, oversubtraction of the pn background may occur. Differences between the background subtracted MOS spectra and the background subtracted pn spectrum should be treated with caution, and the MOS spectra should be trusted somewhat more than the pn spectrum.