Morphologies of Bright Complex Fast Radio Bursts with CHIME/FRB Voltage Data

TL;DR

This paper reports the discovery and analysis of twelve bright, complex non-repeating FRBs detected by CHIME, revealing diverse morphologies, microstructures, polarization properties, and implications for emission models and classification frameworks.

Contribution

The study introduces a new classification framework for drifting archetypes and provides detailed polarization and microstructure analyses of non-repeating FRBs.

Findings

Diverse drifting behaviors observed, deviating from linear negative drift.

Microstructure features as narrow as 7 microseconds identified.

Wide range of Faraday rotation measures and polarization fractions documented.

Abstract

We present the discovery of twelve thus far non-repeating fast radio burst (FRB) sources, detected by the Canadian Hydrogen Intensity Mapping Experiment (CHIME) telescope. These sources were selected from a database comprising of order $10^3$ CHIME/FRB full-array raw voltage data recordings, based on their exceptionally high brightness and complex morphology. Our study examines the time-frequency characteristics of these bursts, including drifting, microstructure, and periodicities. The events in this sample display a variety of unique drifting phenomenologies that deviate from the linear negative drifting phenomenon seen in many repeating FRBs, and motivate a possible new framework for classifying drifting archetypes. Additionally, we detect microstructure features of duration $\lesssim$ 50 $\mu s$ in seven events, with some as narrow as $\approx$ 7 $\mu s$. We find no evidence of significant periodicities. Furthermore, we report the polarization characteristics of seven events, including their polarization fractions and Faraday rotation measures (RMs). The observed $|\mathrm{RM}|$ values span a wide range of $17.24(2)$ - $328.06(2) \mathrm{~rad~m}^{-2}$, with linear polarization fractions between $0.340(1)$ - $0.946(3)$. The morphological properties of the bursts in our sample appear broadly consistent with predictions from both relativistic shock and magnetospheric models of FRB emission, as well as propagation through discrete ionized plasma structures. We address these models and discuss how they can be tested using our improved understanding of morphological archetypes.