Example of X-ray-detected MBH candidate in SDSS J031743.12+001936.8 at RA, Dec = (49.4296, 0.3269) and ɀ = 0.069, taken from (Baldassare et al. 2018). Left: cutout of the DESI Legacy Imaging Surveys Data Release 10 (Legacy Surveys/D. Lang (Perimeter Institute)), centered at the input position. The white circle highlights the aperture of 30″ used for X-ray products. Contours of the X-ray source are overlayed in red. Center: eRASS:4 image centered at the input optical coordinates. Size and aperture circle correspond to those in the left panel. The positional accuracy of the X-ray centroid is 2″, from the POS_COR quantity (Merloni et al. 2024) of the eRASS:4 catalog. Right: X-ray spectrum of the X-ray source. Black points are source plus background data, empty gray points show the background alone. The power-law continuum model is shown by the dot-dashed red line, while the green line and related light green (dark green) shaded regions are the source plus background model median and 16th-84th (1st–99th) percentiles, respectively. The orange dashed lines shows the background model alone. In the lower panel, the data-model ratio is shown, following the format of the upper panel.