FRB 20210601A: Extreme Temporal Clustering in a Repeating Fast Radio Burst Source as Evidence for a Hidden Class of Episodic Repeaters

Ryan Mckinven; Amanda M. Cook; Alice P. Curtin; B. M. Gaensler; Jason W. T. Hessels; Naman Jain; Lordrick Kahinga; Victoria M. Kaspi; Charanjot Brar; Tomas Cassanelli; Shami Chatterjee; Fengqiu Adam Dong; Maxwell Fine; Emmanuel Fonseca; Afrokk Khan; Bikash Kharel; Calvin Leung; Robert Main; Kiyoshi W. Masui; Kyle McGregor; Nicole Mulyk; Mason Ng; Kenzie Nimmo; Ayush Pandhi; Aaron B. Pearlman; Ziggy Pleunis; Mawson W. Sammons; Paul Scholz; Kaitlyn Shin; Seth R. Siegel; Kendrick Smith; Ingrid Stairs

arXiv · 2610.31365

FRB 20210601A: Extreme Temporal Clustering in a Repeating Fast Radio Burst Source as Evidence for a Hidden Class of Episodic Repeaters

View original source ↗Read source document ↗Export metadata ↓

Abstract

Population studies of fast radio burst (FRB) repetition typically model sources using a single distribution of steady, time-averaged burst rates, yet individual sources show significant departures from this assumption. Here we present FRB 20210601A, a source discovered by the Canadian Hydrogen Intensity Mapping Experiment FRB project (CHIME/FRB) that represents the most extreme such departure yet identified. The source produced at least nine bursts within a single 106.5 s interval -- the highest instantaneous burst rate yet reported from a repeating FRB source at $\gtrsim 2$ Jy ms fluences -- yet remained otherwise undetected despite $\sim 320$ hr of exposure spanning 7 yr. The active interval occurred while the source was in a side-lobe of the CHIME/FRB digitized beams, implying an instantaneous burst rate $\gtrsim2.3\times$ higher ($\gtrsim$ 21 bursts) at main-lobe sensitivity. The source's intense, brief burst storm flanked by apparent quiescence despite substantial exposure is unique among the CHIME/FRB repeater sample, although its burst morphology, excess dispersion measure ($\rm{DM_{excess}} \sim 360$ pc cm$^{-3}$), Faraday rotation measure ($|\rm{RM_{excess}}| \sim 150-170$ rad m$^{-2}$), and temporal scattering ($τ\lesssim 0.37$ ms at 600 MHz) are otherwise typical. Modeling a population of episodically active repeaters (i.e., short burst storms separated by long recurrence times) and accounting for declination-dependent exposure, we forecast $\sim1-4$ additional source discoveries similar to FRB 20210601A over the next decade of CHIME/FRB operations, corresponding to a CHIME/FRB-detectable population of $9^{+200}_{-8}$ sources (68% credible interval). These results demonstrate that highly episodic repeaters could constitute a selection-biased but detectable component of the FRB population, possibly reflecting distinct magnetospheric states or triggering mechanisms.

Explore related subjects

astro-ph.HE

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

Ryan Mckinven, Amanda M. Cook, Alice P. Curtin, B. M. Gaensler, Jason W. T. Hessels, Naman Jain, Lordrick Kahinga, Victoria M. Kaspi, Charanjot Brar, Tomas Cassanelli, Shami Chatterjee, Fengqiu Adam Dong, Maxwell Fine, Emmanuel Fonseca, Afrokk Khan, Bikash Kharel, Calvin Leung, Robert Main, Kiyoshi W. Masui, Kyle McGregor, Nicole Mulyk, Mason Ng, Kenzie Nimmo, Ayush Pandhi, Aaron B. Pearlman, Ziggy Pleunis, Mawson W. Sammons, Paul Scholz, Kaitlyn Shin, Seth R. Siegel, Kendrick Smith, Ingrid Stairs. 2026-10-22. FRB 20210601A: Extreme Temporal Clustering in a Repeating Fast Radio Burst Source as Evidence for a Hidden Class of Episodic Repeaters. https://arxiv.org/abs/2610.31365

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

No Strong Evidence for Plasma Lensing in FRB 20240114A

FRB 20240114A is an extremely active repeating fast radio burst for which plasma lensing has been proposed to explain its burst-rate variations, spectral evolution, and apparently ``carbon-copy'' burst pairs. Using FAST data and publicly available Parkes observations, we test this interpretation with the predictions of a one-dimensional Gaussian plasma-lens model. Although the burst-rate enhancements may be fitted separately for Parkes and FAST, the corresponding magnification peaks and demagnification troughs between the two datasets are offset from each other, inconsistent with plasma lensing predictions. The enhancement peaks also do not show consistent periodicity, disfavoring a binary plasma lensing origin. The burst bandwidths are not systematically narrower during the proposed lensing interval than in other episodes. Most importantly, the burst energy distribution, which shows an intrinsic turnover peak at low energies, shows no significant shift of the turnover during the magnification interval, providing a model-independent test to the plasma-lensing interpretation. All these suggest that there is no strong evidence in favor of a plasma lensing interpretation to the source. Rather, all the burst property variations are consistent with being caused by the intrinsic variations of the FRB central engine.

astro-ph.HE↗

arXiv2026

Exploring the connection between Fast Radio Bursts and binary neutron star mergers

Fast Radio Bursts (FRBs) are highly energetic radio sources whose duration is of the order of milliseconds. The physical origin of these sources is still unknown. Many models suggest magnetars as possible progenitors of FRBs, and this is supported by the association between FRBs and the Galactic magnetar SGR 1935+2154; other proposed progenitors include binary neutron star (BNS) mergers, that are themselves linked to magnetar formation. In this work we investigate the possible connection between FRBs and BNS mergers, including magnetars that might be produced in such events, by comparing the detection rates inferred from synthetic BNS and associated FRB populations with the rates observed by CHIME. We produce a synthetic catalog of BNS mergers by combining recent theoretically predicted BNS merger rate as a function of redshift and the neutron star mass distribution inferred from measurements of Galactic BNSs. Using this catalog we predict the number of BNS systems ending as magnetars (stable or supramassive neutron star) or black holes (formed promptly or after the collapse of a hypermassive neutron star) for different equations of state. We then simulate for each BNS (and therefore for each magnetar remnant) an associated FRB and estimate how many of them can be potentially detected by CHIME. We find that the rate of BNS mergers and the rate of magnetars produced after BNS represents a non-negligible fraction of the FRBs detected by CHIME, both repeating and non-repeating. Although additional formation channels need to be considered to account for the entire population of FRBs, the existence of a fraction of FRBs that might genuinely be associated to BNS mergers has profound implications in the context of multi- messenger astronomy, supporting the systematic searches of coincident detections of FRBs and GWs from a BNS merger with current and future facilities.

astro-ph.HE↗

arXiv2026

Multiwavelength Classification of Chandra Sources in Omega Centauri

We present a comprehensive study of X-ray sources in the globular cluster NGC 5139 to date. Over 200 Chandra sources are cross-matched to multiwavelength catalogs from HST, JWST, and MeerKAT. We employ a machine-learning classification pipeline (MUWCLASS) for the first time in such a crowded stellar environment and introduce the globular-cluster-specific training dataset, which compiles previously classified sources from 25 Galactic globular clusters. Given the challenges presented by the high-density environment, we compare the MUWCLASS results with traditional classification methods. We confirm counterpart associations suggested in previous works and also identify new confident and candidate associations. We discuss the implications of our classification results in light of models of cluster dynamical evolution and binary formation/destruction.

astro-ph.HE↗