Lateral expansion of the shock at the locations of the radio sources. (a) Estimated locations of the radio emission on the 3D model of the shock at four different times: 11:05, 11:10, 11:15, and 11:20 UT. The coordinates of the points, which correspond to the radio emission peak intensities within Box 1 (blue) and Box 2 (red) and indicated by the white arrows, can be used to estimate the speed. (b) Distance from the shock centre line of the radio emission sources calculated from the coordinates of the points in a. In the top panel, a second-degree polynomial fit is done to describe the movement. The bottom panel shows the speed calculated as a derivative of the fitted function in the top panel. The blue dashed line indicates a first-degree polynomial fit to the decelerating profile of the radio source in Box 1.