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Irregularity in Active Fast Radio Burst Repeaters and Magnetar Periodic Radio Pulses: Time, Energy, and Frequency Analyses

Ellen C. C. Lin, Shotaro Yamasaki, Tomotsugu Goto, Tetsuya Hashimoto

Abstract

Fast Radio Bursts (FRBs) are millisecond-duration radio pulses with largely unknown origins, with a subset exhibiting repeating behavior. Magnetars highly magnetized neutron stars and a leading progenitor candidate for FRBs also produce similar but much fainter millisecond radio pulses, suggesting a possible connection between the two phenomena. The irregularity of the time series of repeating FRBs and magnetar pulses may provide insight into the underlying progenitor activity. In this study, we analyze time-series data from three repeating FRB sources (four datasets) and the Galactic magnetar SGR J1935+2154 to investigate potential patterns in burst arrival times, energy fluctuations, and peak-frequency shifts. We quantify the degree of randomness (Pincus Index; PI) and chaos (Largest Lyapunov Exponent; LLE) for these three parameters. We find that waiting times across all repeating FRBs exhibit high PI (high randomness) and low LLE (low chaos), consistent with the behavior of magnetar radio pulses. This similarity suggests that both may share a common triggering mechanism. In contrast, the energy fluctuations of both repeating FRBs and magnetar pulses occupy the same region in PI-LLE phase space but display much larger scatter than the other two domains. We discuss the possibility that beaming effects or strong variability in radio-emission efficiency may explain their distinct behavior in the energy domain.

Irregularity in Active Fast Radio Burst Repeaters and Magnetar Periodic Radio Pulses: Time, Energy, and Frequency Analyses

Abstract

Fast Radio Bursts (FRBs) are millisecond-duration radio pulses with largely unknown origins, with a subset exhibiting repeating behavior. Magnetars highly magnetized neutron stars and a leading progenitor candidate for FRBs also produce similar but much fainter millisecond radio pulses, suggesting a possible connection between the two phenomena. The irregularity of the time series of repeating FRBs and magnetar pulses may provide insight into the underlying progenitor activity. In this study, we analyze time-series data from three repeating FRB sources (four datasets) and the Galactic magnetar SGR J1935+2154 to investigate potential patterns in burst arrival times, energy fluctuations, and peak-frequency shifts. We quantify the degree of randomness (Pincus Index; PI) and chaos (Largest Lyapunov Exponent; LLE) for these three parameters. We find that waiting times across all repeating FRBs exhibit high PI (high randomness) and low LLE (low chaos), consistent with the behavior of magnetar radio pulses. This similarity suggests that both may share a common triggering mechanism. In contrast, the energy fluctuations of both repeating FRBs and magnetar pulses occupy the same region in PI-LLE phase space but display much larger scatter than the other two domains. We discuss the possibility that beaming effects or strong variability in radio-emission efficiency may explain their distinct behavior in the energy domain.

Paper Structure

This paper contains 8 sections, 6 equations, 2 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Data
  3. Burst Irregularity Analysis
  4. Pincus Index
  5. Largest Lyapunov Exponent
  6. Results
  7. Discussion
  8. Conclusions

Figures (2)

  • Figure 1: The ${\rm ApEn}_{\rm max}$ distribution for FRB 20201124A, FRB 20121102, FRB 20220912A, and PRPs from SGR J1935+2154. Kernel density estimates show the distributions of ${\rm ApEn}_{\rm max}$ computed from 100 shuffled realizations of each series. The dashed lines indicate the ${\rm ApEn}_{\rm max}$ values of the original series, with each dashed line matching the color of its corresponding solid line.
  • Figure 2: Chaos–randomness plane: Pincus Index versus Largest Lyapunov Exponent for repeating FRBs and radio pulses, shown for the waiting time (top left), peak frequency (top right), and energy (bottom left) domains. Data points for FRB 20121102A and FRB 20190520B are adapted from Zhang24. The “FRB mean point” represents the average Pincus Index and LLE computed from all FRB datasets analyzed in this work (excluding the two sources from Zhang24). Light grey regions indicate extreme conditions, representing either complete randomness or the absence of chaos.