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

@misc{mckinven202620210601a,
  title = {{FRB 20210601A: Extreme Temporal Clustering in a Repeating Fast Radio Burst Source as Evidence for a Hidden Class of Episodic Repeaters}},
  author = {Ryan Mckinven and Amanda M. Cook and Alice P. Curtin and B. M. Gaensler and Jason W. T. Hessels and Naman Jain and Lordrick Kahinga and Victoria M. Kaspi and Charanjot Brar and Tomas Cassanelli and Shami Chatterjee and Fengqiu Adam Dong and Maxwell Fine and Emmanuel Fonseca and Afrokk Khan and Bikash Kharel and Calvin Leung and Robert Main and Kiyoshi W. Masui and Kyle McGregor and Nicole Mulyk and Mason Ng and Kenzie Nimmo and Ayush Pandhi and Aaron B. Pearlman and Ziggy Pleunis and Mawson W. Sammons and Paul Scholz and Kaitlyn Shin and Seth R. Siegel and Kendrick Smith and Ingrid Stairs},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.31365},
  eprint = {2610.31365},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.31365},
}

TY  - UNPB
TI  - FRB 20210601A: Extreme Temporal Clustering in a Repeating Fast Radio Burst Source as Evidence for a Hidden Class of Episodic Repeaters
AU  - Ryan Mckinven
AU  - Amanda M. Cook
AU  - Alice P. Curtin
AU  - B. M. Gaensler
AU  - Jason W. T. Hessels
AU  - Naman Jain
AU  - Lordrick Kahinga
AU  - Victoria M. Kaspi
AU  - Charanjot Brar
AU  - Tomas Cassanelli
AU  - Shami Chatterjee
AU  - Fengqiu Adam Dong
AU  - Maxwell Fine
AU  - Emmanuel Fonseca
AU  - Afrokk Khan
AU  - Bikash Kharel
AU  - Calvin Leung
AU  - Robert Main
AU  - Kiyoshi W. Masui
AU  - Kyle McGregor
AU  - Nicole Mulyk
AU  - Mason Ng
AU  - Kenzie Nimmo
AU  - Ayush Pandhi
AU  - Aaron B. Pearlman
AU  - Ziggy Pleunis
AU  - Mawson W. Sammons
AU  - Paul Scholz
AU  - Kaitlyn Shin
AU  - Seth R. Siegel
AU  - Kendrick Smith
AU  - Ingrid Stairs
PY  - 2026
DA  - 2026/10/22
PB  - arXiv
DO  - 10.48550/arxiv.2610.31365
UR  - https://arxiv.org/abs/2610.31365
AB  - 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 ≳ 2 Jy ms fluences -- yet remained otherwise undetected despite ∼ 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 ≳2.3× higher (≳ 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 (DM_excess ∼ 360 pc cm^−3), Faraday rotation measure (|RM_excess| ∼ 150−170 rad m^−2), and temporal scattering (τ≲ 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 ∼1−4 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.
ER  -