Symmetry breaking in repeating fast radio bursts

Repeating fast radio bursts (FRB) show temporal symmetry breaking on millisecond time-scales (the 'sad trombone'). On a time-scale of days, the repetitions of FRB 180916B occur at frequency-dependent phases of its 16.3 d period. Some models predict that all such periodic repeating FRB have the same sign of temporal asymmetry, while others predict that sources with both signs are equally abundant. Future observations of other periodically modulated repeating FRB may distinguish among models on this basis.