Differential emission measure (DEM) in the loop and close to its footpoint. The left panel shows an AIA 171 Å snapshot (in a negative scale) with various positions marked (red: near the footpoint; black: away from the footpoint along the loop; blue: background region). In the right panel, DEMs resulting from the background subtracted data are plotted for two positions along the umbral loop. Each curve shown here is the median of DEMs with χ² ≤ 1 that resulted from 300 Monte Carlo iterations. See Sect. 3.2.