By default the slew processing does not include any filtering for periods of high background. Such a filtering would lead to blank regions in the slew images. It is has been seen that strong background flares lead to a section of the slew being relatively bright. At first sight, this is indistinguishable from a slew image of a large Supernova remnant (SNR). Usually photon energies can be used to make the distinction. High background usually leads to an excess at high energies (2 keV) whereas SNR are usually brightest at energies below 2 keV.
In high background regions, source search algorithms will tend to find a large number of spurious sources.