MCELS images in Hα (left) and [O iii] (right). The images are continuum-subtracted, flux-calibrated, sky-subtracted, and smoothed. The same area of the sky is shown as in the X-ray images in Fig. 2. The contours are taken from the smoothed X-ray broadband image, with 5 contour levels at 18, 28.5, 39, 49.5, and 60 counts/s/deg². The dashed white circle shows the position of the Hα cavity, and the dashed black circle the position of the shell in the [S ii]/Hα image (see Fig. 4).