Oscillation of the loop. Panels a) and b) show the intensity and Doppler shift of the Fe xiii line synthesised from the coronal model as a function of time and space along the slit. The location of the slit is indicated in Fig. 2 and the range of Doppler shifts is from −15 km s^-1 to + 15 km s^-1, just as in Fig. 2. The black boxes in these space-time plots indicate the position of the loop with the clearest oscillation pattern. Panel c) shows the Doppler shift of the loop as a function of time. Here the Doppler shifts are averaged along the slit across the loop, i.e. along y within the black box in panel b). The red line shows the fit by a damped sinusoidal function as defined in Eq. (3). See Sect. 3.3.