Left: Propagation of emitting elements along a magnetic field line as a functinon time t. The local section of line is projected onto the plane (x,y) orthogonal to the rotation axis. Black crosses on the line represent the edges of the so-called visible segment, which is the section of line where an element emitting in a fixed cone can be seen by an observer located in the direction pointed to by the arrow at the top-right corner. The grey cross represents the characteristic position of the segment. Emitting elements are travelling along the line and are represented by circles. The size of a circle represents the intrinsic intensity of the element, that is its total flux integrated over all directions. Emitting elements are injected on the line with intensities following a sequence of three Gaussian temporal profiles. The colour of an element represents the flux received by the observer from 0 (blue) to maximum (green). We note that each emitting element emits in the forward direction according to a Gaussian angular profile and are therefore also visible when outside of the visible segment (which corresponds to fixed cone) albeit too weakly to be noticeable in this case.
