Stacked images based on four years of VLBA observations at 15 GHz, 22 GHz, and 43 GHz (Baczko et al. 2019; Lister et al. 2019) restored with a circular beam. The ridge lines are plotted on top (red dots). The contours start at 0.5 times the noise level for 15 GHz, 22 GHz, and 43 GHz, which is derived as the mean rms from the individual images and increases logarithmically by a factor of two (compare Cols. 2 and 5 of Table 2).