Ultra-long Period Magnetars and the Low-Twist Magnetar Model of FRBs

The low-twist magnetospheric magnetar model for FRBs predicts FRBs associated with magnetar short bursts that transpire in particular low charge density states of mature magnetars. This is consistent with the FRB-like burst from SGR 1935+2154 in April 2020 as well as observations that not all short bursts produce radio bursts. Some theoretical and heuristic expectations will be discussed in the context of cosmological FRBs. The possibility of long periodicities associated with prolific repeaters FRB 180916 and FRB 121102 being spin periods and formation channels for such long period magnetars will be detailed, particularly in the recent context of galactic ultralong period magnetar candidates. Finally, I show how trains of FRB could potentially be associated with torsional crustal oscillations and how these could be used to constrain redshifts or the neutron star equation of state.