Left: second-order polynomial fit for region A, represented by the dashed blue line. Middle: the 4C 35.06 radio source as seen by LOFAR, represented by red contours over an inverted grayscale SDSS image of the central region of the Abell 407 cluster. Overlaid in blue are the VLA 4885 MHz image contours. Black circles show the measurement areas in regions A, C, and E. Right: second-order polynomial fit (dashed blue line) for region E. The data points which are upper limits are represented with empty markers and downward pointing arrows. They are not taken into account in the fitting.