Frequency drifts in FRBs due to radius-to-frequency mapping in magnetospheres of neutron stars

Understand

We interpret recent observations of high-to-low frequency drifting features in the spectra of the repeating FRBs as evidence of sharply changing plasma properties in the emission region, presumably the neutron stars magnetospheres.

• The drifts are then FRBs' analogues of radius-to-frequency mapping in pulsars and Solar type-III radio burst (but not in a sense of a particular emission mechanism).
• The drifts rates of $\sim 100$ MHz ms$^{-1}$ at frequencies $\sim$ GHz translate to physical size of $\sim {c \omega}/{\dot{\omega}} \sim$ few $\times 10^8$ cm, matching the hypothesis of the FRB origin in the magnetospheres of neutron stars.
• We suggest that reconnection events result in generation of upward propagating plasma beams that produce radio emission with frequency related to the decreasing local magnetic field and plasma density.