Left: radial velocity from the explosion centre after 8000 yr of our fiducial model based on the XMM-Newton data (upper panel). Supersonic Mach numbers after 8000 yr for our fiducial model based on the XMM-Newton data (lower panel). Right: radial velocity from the explosion centre after 11 000 yr of our fiducial model based the Chandra data (upper panel). Supersonic Mach numbers after 11 000 yr for our fiducial model based on the Chandra data (lower panel). Regions with Mach numbers less than 1 are not displayed, hence they appear white. The position of the SN explosion is marked with a black star and the position of the AXP with a magenta star.