Upper panels (context images of AR 11836): full disk (left) and cut-out (middle) HMI magnetogram and corresponding AIA 171 Å image (right). Lower panels: zoom of HMI continuum image on the area marked by the red box in the upper panel, with the IRIS slit marked at x = 0 (left), and the corresponding spectra in the Si iv 1403 Å window averaged over 1 min (right panel). All data were taken on 2013 Sep. 2, 17:14 UT. Regions where the slit crosses the penumbra (PU) and umbra (U) are marked. The central part of the umbra, where the Si iv and O iv lines show satellites, is indicated in red. In the northern part, where the satellites are strongest, the centre of this region is labelled C and used as the reference point of the satellite feature in this report. The prominent upflow, labelled T, is due to a short-lived transient.