Contextual maps of AR 12108 and the region of interest taken from the SDO/HMI and AIA observations. a) SDO/HMI line-of-sight magnetogram saturated at ±750 G. b) SDO/AIA 1600 Å channel image mainly showing the chromosphere. Panels c) and d) display AIA 171 Å and 193 Å maps. The intensities in panels c) and d) are in logarithmic scale. The white solid and dashed rectangles in panels a) and c) indicate the regions of IRIS slit-jaw and raster scan observations, respectively. In all the panels we identify the regions of interest with isolated umbral coronal loops in red. One such loop is traced with a white dotted curve in panels c). A zoom into the region indicated by the red rectangle is shown in Fig. 2. North is up.