Fast radio bursts (FRBs) are intense bursts of radio emission lasting milliseconds and showcasing characteristic dispersion sweep of radio pulsars. The physical nature of these bursts is yet unknown, and astronomers consider a variety of explanations ranging from synchrotron maser emission from young magnetars in supernova remnants to cosmic string cusps. FRB 121102 is the first repeating fast radio burst detected and one of the most extensively studied FRB sources. It exhibits complex burst morphology, sub-burst downward frequency drifts, and also complex pulse phenomenology. FRB 121102 is also one of only two FRBs reported to be spatially associated with persistent...