Statistical and Temporal Analysis of Multi-component Burst-clusters from the Repeating FRB 20190520B

TL;DR

This study analyzes the multi-component burst-clusters of FRB 20190520B using FAST data to investigate whether complex burst morphologies differ spectrally or temporally from single-component bursts. Fluence and spectral properties of multi-component bursts are statistically consistent with the overall burst population, while temporal analyses uncover millisecond-scale quasi-periodic sub-structures in bursts with multiple components. The component-counts follow a power-law indicating scale-free, self-organized criticality behavior, and FRB 20190520B exhibits a relatively low fraction of multi-component clusters (~12%) compared with some other repeaters. No global spin-period is detected, suggesting the observed sub-structures arise from intrinsic magnetospheric processes rather than simple rotational modulation. These results support magnetospheric emission scenarios with SOC-like dynamics and motivate broader, higher-time-resolution, multi-source studies to further constrain FRB progenitors and environments.

Abstract

Fast Radio Bursts (FRBs) are bright, millisecond-duration extragalactic radio transients that probe extreme astrophysical environments. Many FRBs exhibit multi-component structures, which encode information about their emission mechanisms or progenitor systems and thus provide important clues to their origins. In this work, we systematically analyze the burst morphology of FRB 20190520B and compare component distributions across four active FRBs observed with FAST: FRB 20121102A, FRB 20190520B, FRB 20201124A, and FRB 20240114A. We find that multi-component burst-clusters show spectral properties similar to single-peak bursts, and no periodicity is detected in their temporal behavior. The component-count distributions follow a power law, revealing scale-free behavior consistent with self-organized criticality (SOC) processes. Multi-component clusters account for 12-30% of all detected bursts, regardless of source activity, providing new insights into burst-to-burst variability and the physical processes driving FRB emission.

Figures (10)

• Figure 1: The horizontal axis represents the dates, and the vertical axis shows the number of bursts. Different colors are used to distinguish the total burst count, bimodal burst structure, trimodal burst structure, and quadrimodal burst structure.
• Figure 01: Waiting time distribution of four FRBs. The histogram shows the waiting time distribution, with the red line representing the lognormal double-peak fit. The two peaks correspond to the characteristic waiting times, with their values labeled in the upper right corner of the plot. The blue dashed line marks the valley between the peaks, and the valley time is used as a criterion to distinguish whether the events belong to a single burst-cluster.
• Figure 2: Distribution of burst fluences detected from FRB 20190520B. The horizontal axis represents the fluence (Jy$\cdot$ms) , and the vertical axis shows the burst count. The gray bars denote the total distribution of all bursts, while the hatched colored bars highlight bursts that belong to multi-component structures: red for bursts in 2-component clusters, cyan for bursts in 3-component clusters, and purple for bursts in 4-component clusters.
• Figure 02: Two-dimensional dynamic spectra of multi-component burst-clusters from FRB 20190520B. The top row presents a three-component burst-cluster, while the following three rows display nine representative two-component burst-clusters. The three-component burst-cluster is labeled with indices 3-1, 3-2, and 3-3 beneath each panel. The presentation follows the same format as Figure \ref{['fig:burst103']}.
• Figure 3: Distribution of burst center frequencies and bandwidths for FRB 20190520B. The blue hexagons represent all detected bursts, with the color intensity indicating the number of bursts in each bin. Red stars mark bursts that belong to multi-component burst-clusters. The marginal histograms along the top and right axes show the overall distributions of burst center frequency and bandwidth, respectively. The red curve represents the distribution of the multi-component burst-clusters (red stars) in center frequency and bandwidth.