Repeating Fast Radio Bursts from Pulsar-Asteroid Belt Collisions: Frequency Drifting and Polarization

TL;DR

This paper models repeating fast radio bursts as resulting from pulsar-asteroid belt collisions, explaining observed frequency drifting and polarization patterns, and predicts broad frequency bands based on asteroid mass distribution.

Contribution

It introduces a detailed model linking pulsar magnetosphere geometry and asteroid mass distribution to FRB frequency drifting and polarization features.

Findings

Frequency drifting rate index is 25/17.

Asteroids with mass >10^{17} g can power FRBs.

Linear polarization can reach over 30% in weaker FRBs.

Abstract

Fast radio bursts (FRBs) are a new kind of extragalactic radio transients. Some of them show repeating behaviors. Recent observations indicate that a few repeating FRBs (e.g., FRB 121102) present time--frequency downward drifting patterns and nearly 100$\%$ linear polarization. Following the model of \citet{dai 2016} who proposed that repeating FRBs may originate from a slowly-rotating, old-aged pulsar colliding with an asteroid belt around a stellar-mass object, we focus on the prediction of time--frequency drifting and polarization. In this scenario, the frequency drifting is mainly caused by the geometric structure of a pulsar magnetosphere, and the drifting rate--frequency index is found to be $25/17$. On the other hand, by considering the typical differential mass distribution of incident asteroids, we find that an asteroid with mass $m\gtrsim 10^{17}~{\rm g}$ colliding with the pulsar would contribute abundant gravitational energy, which powers an FRB. A broad frequency band of the FRBs would be expected, due to the mass difference of the incident asteroids. In addition, we simulate the linear polarization distribution for the repeating FRBs, and constrain the linear polarization with $\gtrsim$ 30$\%$ for the FRBs with flux of an order of magnitude lower than the maximum flux.