threshold well above the background level.

The threshold necessary to separate two blended sources varies according to the background, the distance between the sources, and the size of the sources themselves, which, for unresolved sources, is determined only by the PSF profile. This step has been performed by @horner08 on the [vtpdetect]{} direct output. They ran [vtpdetect]{} five times on each X-ray image using different thresholds of surface brightness, and then selected the best threshold for each field by visually inspecting the source photon distribution for each threshold value. This procedure is reliable but time-consuming, especially for a large survey that spans a wide range of exposure times and therefore surface brightness thresholds. As previously anticipated, a major improvement of our new software consists in including the auto-deblending procedure in the algorithm.

As a first step, to flag blended sources, we created a number of source maps[^5] by running FOF with thresholds corresponding to different photon densities, starting from the lowest (corresponding to the background level, map with index $j=1$) to the highest value present in the photon density image, distributed on a logarithmic scale. Clearly, the source regions defined in the map $j=1 $ will be larger than the 