# On the Time-Frequency Downward Drifting of Repeating Fast Radio Bursts

## TL;DR

This paper presents a geometrical model explaining the downward drifting frequency pattern observed in repeating fast radio bursts, linking it to neutron star magnetosphere dynamics and two specific generation scenarios.

## Contribution

It introduces a unified geometrical framework to interpret downward drifting in FRBs within the context of neutron star magnetospheres and proposes explanations for different FRB generation mechanisms.

## Key findings

- The model successfully explains the downward frequency drift in FRBs.
- It links drift patterns to the geometry of neutron star magnetic field lines.
- Provides a unified explanation for different FRB generation scenarios.

## Abstract

The newly discovered second repeating fast radio burst (FRB) source, FRB 180814.J0422+73, was reported to exhibit a time-frequency downward drifting pattern, which is also seen in the first repeater FRB 121102. We propose a generic geometrical model to account for the observed downward drifting of sub-pulse frequency, within the framework of coherent curvature radiation by bunches of electrons or positrons in the magnetosphere of a neutron star. A sudden trigger event excites these coherent bunches of charged particles, which stream outwards along open field lines. As the field lines sweep across the line of sight, the bunches seen later have traveled farther into the less curved part of the magnetic field lines, thus emitting at lower frequencies. We use this model to explain the time-frequency downward drifting in two FRB generation scenarios, the transient pulsar-like sparking from the inner gap region of a slowly rotating neutron star, and the externally-triggered magnetosphere reconfiguration known as the "cosmic comb".