Polarisation profile as observed with FAST at a central frequency of 1250 MHz, averaged over a bandwidth of 420 MHz. Top panel: total intensity (black), the linear intensity (red), and circular polarisation (blue) as a function of longitude. The inset shows an enlarged version of the main pulse. Middle panel: low intensity level of the profile across the full rotational period, revealing the existence of an interpulse that is separated from the main pulse by about half a period. Bottom panel: values of the PA of the linear emission as a function of the longitude. An RVM has been fitted to the black PA values. The result is shown as a solid black line, while the dashed line indicates the RVM solution separated by 90 deg.