Two gigahertz light curve of 0537-158. Between 1990 and 1993 the variability of the source appears as a sequence of six-month separated ESEs centred at the time of minimum and maximum solar elongation of the source (indicated, respectively, with green and orange arrows). In the upper-right box, as a comparison, a zoom-in on the 2 GHz 1981 event of 0954+658 is shown, which can be considered as the archetype of ESEs.