# Constraints on Pulsed Emission Model for Repeating FRB 121102

## TL;DR

This paper constrains the properties of a young neutron star model for repeating FRB 121102, showing that certain parameters are tightly limited and predicting a rapid flux decay if the model is correct.

## Contribution

It provides new constraints on neutron star parameters supporting the pulsed emission model for FRB 121102, considering emission geometry and anisotropy effects.

## Key findings

- Neutron star parameters are tightly constrained within small ranges.
- Anisotropy does not significantly affect the allowed parameter space.
- A rapid flux decay is expected if the neutron star model is correct.

## Abstract

Recent localization of the repeating Fast Radio Burst (FRB) 121102 revealed the distance of its host galaxy and luminosities of the bursts. We investigated constraints on the young neutron star (NS) model, that (a) the FRB intrinsic luminosity is supported by the spin-down energy, and (b) the FRB duration is shorter than the NS rotation period. In the case of a circular cone emission geometry, conditions (a) and (b) determine the NS parameters within very small ranges, compared with that from only condition (a) discussed in previous works. Anisotropy of the pulsed emission does not affect the area of the allowed parameter region by virtue of condition (b). The determined parameters are consistent with those independently limited by the properties of the possible persistent radio counterpart and the circumburst environments such as surrounding materials. Since the NS in the allowed parameter region is older than the spin-down timescale, the hypothetical GRP-like model expects a rapid radio flux decay of $\lesssim1$ Jy within a few years as the spin-down luminosity decreases. The continuous monitoring will give a hint of discrimination of the models. If no flux evolution will be seen, we need to consider an alternative model, e.g., the magnetically powered flare.