XMM-ATLAS 0.5–2 keV flux vs. eFEDS flux upper limit (3σ–confidence) in the 0.5–2 keV band. Each data point in this plot corresponds to an XMM-ATLAS source detection without a counterpart in the eFEDS source catalogue. For these sources, the 3σ flux upper limits were estimated from the eFEDS observations and are plotted on the vertical axis. The dashed blue line indicates the one-to-one relation. The dotted blue line corresponds to a factor of two in flux relative to the one-to-one relation, i.e. sources with eFEDS 3σ flux upper limits that are twice fainter than the XMM-ATLAS source flux. Sources below this line are highlighted in blue. They were visually inspected to exclude spurious XMM-ATLAS sources and sources close to edge of the FOV. The resulting sample following the visual inspection is listed in Table 5.