🔭 astrophysics

Discovery of 30 Repeating Fast Radio Burst Sources and Uniform Population Statistics of 80 Repeating Sources from CHIME/FRB

This paper reports the discovery of 30 new repeating fast radio burst sources by CHIME/FRB, bringing the total known repeating population to 80, and presents uniform statistical analyses indicating that repeating and one-off FRBs likely belong to a single population with a power-law distribution of burst rates rather than distinct bimodal classes.

Original authors: Amanda M. Cook (Department of Physics, McGill University, Montréal, QC, Canada, Anton Pannekoek Institute for Astronomy, University of Amsterdam, Amsterdam, The Netherlands), Kaitlyn Shin (Cahill CentAmanda M. Cook (Department of Physics, McGill University, Montréal, QC, Canada, Anton Pannekoek Institute for Astronomy, University of Amsterdam, Amsterdam, The Netherlands), Kaitlyn Shin (Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA, USA), Ziggy Pleunis (Anton Pannekoek Institute for Astronomy, University of Amsterdam, Amsterdam, The Netherlands, ASTRON, Netherlands Institute for Radio Astronomy, Dwingeloo, The Netherlands), Maxwell Fine (Department of Physics, McGill University, Montréal, QC, Canada, Trottier Space Institute, McGill University, Montréal, QC, Canada), Naman Jain (Department of Physics, McGill University, Montréal, QC, Canada, Trottier Space Institute, McGill University, Montréal, QC, Canada), Derek Bingham (Department of Statistics and Actuarial Science, Simon Fraser University, Burnaby, BC, Canada), Alice P. Curtin (Department of Physics, McGill University, Montréal, QC, Canada, Anton Pannekoek Institute for Astronomy, University of Amsterdam, Amsterdam, The Netherlands), Gwendolyn Eadie (David A. Dunlap Department of Astronomy and Astrophysics, University of Toronto, Toronto, ON, Canada, Data Sciences Institute, University of Toronto, Toronto, ON, Canada), B. M. Gaensler (Department of Astronomy and Astrophysics, University of California, Santa Cruz, Santa Cruz, CA, USA, David A. Dunlap Department of Astronomy and Astrophysics, University of Toronto, Toronto, ON, Canada), Jason W. T. Hessels (Department of Physics, McGill University, Montréal, QC, Canada, ASTRON, Netherlands Institute for Radio Astronomy, Dwingeloo, The Netherlands), Calvin Leung (Miller Institute for Basic Research, University of California, Berkeley, Berkeley, CA, USA, Department of Astronomy, University of California, Berkeley, Berkeley, CA, USA), Robert Main (Department of Physics, McGill University, Montréal, QC, Canada, Trottier Space Institute, McGill University, Montréal, QC, Canada), Nicole Mulyk (Department of Physics, McGill University, Montréal, QC, Canada, Trottier Space Institute, McGill University, Montréal, QC, Canada), Ayush Pandhi (Department of Physics, McGill University, Montréal, QC, Canada, Trottier Space Institute, McGill University, Montréal, QC, Canada), Paul Scholz (Department of Physics and Astronomy, York University, Toronto, ON, Canada), Seth R. Siegel (SKAO, Science Operations Centre, CSIRO ARRC, Kensington, WA, Australia, Trottier Space Institute, McGill University, Montréal, QC, Canada), David C. Stenning (Department of Statistics and Actuarial Science, Simon Fraser University, Burnaby, BC, Canada), Thomas C. Abbott (Department of Physics, McGill University, Montréal, QC, Canada, Trottier Space Institute, McGill University, Montréal, QC, Canada), Bridget C. Andersen (Department of Astronomy and Astrophysics, University of California, Santa Cruz, Santa Cruz, CA, USA), Mohit Bhardwaj (Department of Space Planetary Astronomical Sciences and Engineering, Indian Institute of Technology Kanpur, Uttar Pradesh, India), Alice Cai (Department of Physics and Astronomy, Northwestern University, Evanston, IL, USA, Center for Interdisciplinary Exploration and Research in Astronomy, Northwestern University, Evanston, IL, USA), Shami Chatterjee (Cornell Center for Astrophysics and Planetary Science, Cornell University, Ithaca, NY, USA), Fengqiu Adam Dong (Department of Physics and Astronomy, York University, Toronto, ON, Canada), Emmanuel Fonseca (Department of Physics and Astronomy, West Virginia University, Morgantown, WV, USA, Center for Gravitational Waves and Cosmology, West Virginia University, Morgantown, WV, USA), Danté M. Hewitt (Anton Pannekoek Institute for Astronomy, University of Amsterdam, Amsterdam, The Netherlands), Ronniy C. Joseph (S&T Netherlands, Delft, The Netherlands), Lordrick Kahinga (Department of Astronomy and Astrophysics, University of California, Santa Cruz, Santa Cruz, CA, USA, Department of Physics, College of Natural and Mathematical Sciences, University of Dodoma, Dodoma, Tanzania), Mattias Lazda (David A. Dunlap Department of Astronomy and Astrophysics, University of Toronto, Toronto, ON, Canada, Dunlap Institute for Astronomy and Astrophysics, University of Toronto, Toronto, ON, Canada), Victoria M. Kaspi (Department of Physics, McGill University, Montréal, QC, Canada, School of Physics and Astronomy, Tel Aviv University, Tel Aviv, Israel), Afrokk Khan (Department of Physics, McGill University, Montréal, QC, Canada, Trottier Space Institute, McGill University, Montréal, QC, Canada), Bikash Kharel (Department of Physics and Astronomy, West Virginia University, Morgantown, WV, USA, Center for Gravitational Waves and Cosmology, West Virginia University, Morgantown, WV, USA), Lluis Mas-Ribas (Department of Astronomy and Astrophysics, University of California, Santa Cruz, Santa Cruz, CA, USA), Kiyoshi W. Masui (MIT Kavli Institute for Astrophysics and Space Research, MIT, Cambridge, MA, USA, Department of Physics, MIT, Cambridge, MA, USA), Kyle McGregor (Department of Physics, McGill University, Montréal, QC, Canada, Trottier Space Institute, McGill University, Montréal, QC, Canada), Daniele Michilli (Laboratoire d'Astrophysique de Marseille, Aix-Marseille Univ., CNRS, CNES, Marseille, France), Ryan Mckinven (Department of Physics, McGill University, Montréal, QC, Canada, Trottier Space Institute, McGill University, Montréal, QC, Canada), Mason Ng (Department of Physics, McGill University, Montréal, QC, Canada, Trottier Space Institute, McGill University, Montréal, QC, Canada), Kenzie Nimmo (Center for Interdisciplinary Exploration and Research in Astronomy, Northwestern University, Evanston, IL, USA), Swarali Shivraj Patil (Department of Physics and Astronomy, West Virginia University, Morgantown, WV, USA, Center for Gravitational Waves and Cosmology, West Virginia University, Morgantown, WV, USA), Aaron B. Pearlman (MIT Kavli Institute for Astrophysics and Space Research, MIT, Cambridge, MA, USA, Trottier Space Institute, McGill University, Montréal, QC, Canada), Mawson W. Sammons (Department of Physics, McGill University, Montréal, QC, Canada, Trottier Space Institute, McGill University, Montréal, QC, Canada), Ketan R. Sand (Department of Physics, McGill University, Montréal, QC, Canada, Trottier Space Institute, McGill University, Montréal, QC, Canada), Aylar Sedaei Oghani (Department of Physics and Astronomy, York University, Toronto, ON, Canada), Vishwangi Shah (Department of Physics, McGill University, Montréal, QC, Canada, Trottier Space Institute, McGill University, Montréal, QC, Canada), Kendrick Smith (Perimeter Institute for Theoretical Physics, Waterloo, ON, Canada), Ingrid Stairs (Department of Physics and Astronomy, University of British Columbia, Vancouver, BC, Canada), Tarik J. Zegmott (Department of Physics, McGill University, Montréal, QC, Canada, Trottier Space Institute, McGill University, Montréal, QC, Canada)

Published 2026-05-12

📖 5 min read🧠 Deep dive

CC BY 4.0

Original authors: Amanda M. Cook (Department of Physics, McGill University, Montréal, QC, Canada, Anton Pannekoek Institute for Astronomy, University of Amsterdam, Amsterdam, The Netherlands), Kaitlyn Shin (Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA, USA), Ziggy Pleunis (Anton Pannekoek Institute for Astronomy, University of Amsterdam, Amsterdam, The Netherlands, ASTRON, Netherlands Institute for Radio Astronomy, Dwingeloo, The Netherlands), Maxwell Fine (Department of Physics, McGill University, Montréal, QC, Canada, Trottier Space Institute, McGill University, Montréal, QC, Canada), Naman Jain (Department of Physics, McGill University, Montréal, QC, Canada, Trottier Space Institute, McGill University, Montréal, QC, Canada), Derek Bingham (Department of Statistics and Actuarial Science, Simon Fraser University, Burnaby, BC, Canada), Alice P. Curtin (Department of Physics, McGill University, Montréal, QC, Canada, Anton Pannekoek Institute for Astronomy, University of Amsterdam, Amsterdam, The Netherlands), Gwendolyn Eadie (David A. Dunlap Department of Astronomy and Astrophysics, University of Toronto, Toronto, ON, Canada, Data Sciences Institute, University of Toronto, Toronto, ON, Canada), B. M. Gaensler (Department of Astronomy and Astrophysics, University of California, Santa Cruz, Santa Cruz, CA, USA, David A. Dunlap Department of Astronomy and Astrophysics, University of Toronto, Toronto, ON, Canada), Jason W. T. Hessels (Department of Physics, McGill University, Montréal, QC, Canada, ASTRON, Netherlands Institute for Radio Astronomy, Dwingeloo, The Netherlands), Calvin Leung (Miller Institute for Basic Research, University of California, Berkeley, Berkeley, CA, USA, Department of Astronomy, University of California, Berkeley, Berkeley, CA, USA), Robert Main (Department of Physics, McGill University, Montréal, QC, Canada, Trottier Space Institute, McGill University, Montréal, QC, Canada), Nicole Mulyk (Department of Physics, McGill University, Montréal, QC, Canada, Trottier Space Institute, McGill University, Montréal, QC, Canada), Ayush Pandhi (Department of Physics, McGill University, Montréal, QC, Canada, Trottier Space Institute, McGill University, Montréal, QC, Canada), Paul Scholz (Department of Physics and Astronomy, York University, Toronto, ON, Canada), Seth R. Siegel (SKAO, Science Operations Centre, CSIRO ARRC, Kensington, WA, Australia, Trottier Space Institute, McGill University, Montréal, QC, Canada), David C. Stenning (Department of Statistics and Actuarial Science, Simon Fraser University, Burnaby, BC, Canada), Thomas C. Abbott (Department of Physics, McGill University, Montréal, QC, Canada, Trottier Space Institute, McGill University, Montréal, QC, Canada), Bridget C. Andersen (Department of Astronomy and Astrophysics, University of California, Santa Cruz, Santa Cruz, CA, USA), Mohit Bhardwaj (Department of Space Planetary Astronomical Sciences and Engineering, Indian Institute of Technology Kanpur, Uttar Pradesh, India), Alice Cai (Department of Physics and Astronomy, Northwestern University, Evanston, IL, USA, Center for Interdisciplinary Exploration and Research in Astronomy, Northwestern University, Evanston, IL, USA), Shami Chatterjee (Cornell Center for Astrophysics and Planetary Science, Cornell University, Ithaca, NY, USA), Fengqiu Adam Dong (Department of Physics and Astronomy, York University, Toronto, ON, Canada), Emmanuel Fonseca (Department of Physics and Astronomy, West Virginia University, Morgantown, WV, USA, Center for Gravitational Waves and Cosmology, West Virginia University, Morgantown, WV, USA), Danté M. Hewitt (Anton Pannekoek Institute for Astronomy, University of Amsterdam, Amsterdam, The Netherlands), Ronniy C. Joseph (S&T Netherlands, Delft, The Netherlands), Lordrick Kahinga (Department of Astronomy and Astrophysics, University of California, Santa Cruz, Santa Cruz, CA, USA, Department of Physics, College of Natural and Mathematical Sciences, University of Dodoma, Dodoma, Tanzania), Mattias Lazda (David A. Dunlap Department of Astronomy and Astrophysics, University of Toronto, Toronto, ON, Canada, Dunlap Institute for Astronomy and Astrophysics, University of Toronto, Toronto, ON, Canada), Victoria M. Kaspi (Department of Physics, McGill University, Montréal, QC, Canada, School of Physics and Astronomy, Tel Aviv University, Tel Aviv, Israel), Afrokk Khan (Department of Physics, McGill University, Montréal, QC, Canada, Trottier Space Institute, McGill University, Montréal, QC, Canada), Bikash Kharel (Department of Physics and Astronomy, West Virginia University, Morgantown, WV, USA, Center for Gravitational Waves and Cosmology, West Virginia University, Morgantown, WV, USA), Lluis Mas-Ribas (Department of Astronomy and Astrophysics, University of California, Santa Cruz, Santa Cruz, CA, USA), Kiyoshi W. Masui (MIT Kavli Institute for Astrophysics and Space Research, MIT, Cambridge, MA, USA, Department of Physics, MIT, Cambridge, MA, USA), Kyle McGregor (Department of Physics, McGill University, Montréal, QC, Canada, Trottier Space Institute, McGill University, Montréal, QC, Canada), Daniele Michilli (Laboratoire d'Astrophysique de Marseille, Aix-Marseille Univ., CNRS, CNES, Marseille, France), Ryan Mckinven (Department of Physics, McGill University, Montréal, QC, Canada, Trottier Space Institute, McGill University, Montréal, QC, Canada), Mason Ng (Department of Physics, McGill University, Montréal, QC, Canada, Trottier Space Institute, McGill University, Montréal, QC, Canada), Kenzie Nimmo (Center for Interdisciplinary Exploration and Research in Astronomy, Northwestern University, Evanston, IL, USA), Swarali Shivraj Patil (Department of Physics and Astronomy, West Virginia University, Morgantown, WV, USA, Center for Gravitational Waves and Cosmology, West Virginia University, Morgantown, WV, USA), Aaron B. Pearlman (MIT Kavli Institute for Astrophysics and Space Research, MIT, Cambridge, MA, USA, Trottier Space Institute, McGill University, Montréal, QC, Canada), Mawson W. Sammons (Department of Physics, McGill University, Montréal, QC, Canada, Trottier Space Institute, McGill University, Montréal, QC, Canada), Ketan R. Sand (Department of Physics, McGill University, Montréal, QC, Canada, Trottier Space Institute, McGill University, Montréal, QC, Canada), Aylar Sedaei Oghani (Department of Physics and Astronomy, York University, Toronto, ON, Canada), Vishwangi Shah (Department of Physics, McGill University, Montréal, QC, Canada, Trottier Space Institute, McGill University, Montréal, QC, Canada), Kendrick Smith (Perimeter Institute for Theoretical Physics, Waterloo, ON, Canada), Ingrid Stairs (Department of Physics and Astronomy, University of British Columbia, Vancouver, BC, Canada), Tarik J. Zegmott (Department of Physics, McGill University, Montréal, QC, Canada, Trottier Space Institute, McGill University, Montréal, QC, Canada)

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine the universe is a vast, dark ocean, and Fast Radio Bursts (FRBs) are like mysterious, bright flashes of lightning appearing out of nowhere. For a long time, astronomers thought these flashes were "one-off" events—like a single firework exploding and then vanishing forever, perhaps signaling a catastrophic event like a star dying.

But then, astronomers realized something strange: some of these flashes keep coming back from the exact same spot. They aren't one-time disasters; they are repeaters.

This paper is a massive census report from the CHIME/FRB telescope, a giant radio dish in Canada that acts like a super-sensitive camera scanning the sky every day. Here is what the team found, explained simply:

1. The Big Discovery: 30 New "Flashers"

The team announced the discovery of 30 new repeating FRB sources. Before this, they had found about 50. Now, they have a total of 80 confirmed repeaters that they found themselves.

Think of it like this: If you were watching a busy city street for five years, you might spot 50 people who wave at you repeatedly. This paper says, "Hey, we just spotted 30 new people waving from the same windows, and now we have a list of 80 total people who wave at us."

2. The "Gold" and "Silver" Lists

Finding these repeaters is tricky. The sky is crowded, and sometimes two different flashes might just happen to look like they are coming from the same place by pure luck (like two people in a crowd wearing the same red hat).

To solve this, the team used a clever statistical test (a "Chance Coincidence Probability" or PCC) to see if a group of flashes is truly from one source or just a lucky accident.

The Gold Sample: These are the 30 new sources they are 100% sure about. They are the "confirmed repeaters."
The Silver Sample: These are 14 other candidates that look very promising but need a little more proof. They are the "probable repeaters."

3. The Mystery of the "One-Offs" vs. Repeaters

For years, scientists debated: Are there two different types of FRBs?

Type A: The "Repeaters" (they come back).
Type B: The "One-Offs" (they flash once and never return, perhaps because they exploded).

The paper asks: Is the universe actually full of two different species of cosmic fireworks, or is it just one species that behaves differently?

The Verdict: The data suggests it's likely just one species.

The "One-Offs" that we see might just be the "Repeaters" that are being very quiet or are too far away for us to catch them a second time yet.
The team found that the "One-Offs" and the "Repeaters" look very similar in almost every way, except for one thing: Repeaters tend to be a bit wider and slower in their signal, while "One-Offs" are sharper and faster.
However, the team argues this difference might just be because our telescope is better at catching the sharp, fast signals. If we could see the slow, wide ones better, we might find that all FRBs actually repeat, but some just repeat so rarely we haven't caught them yet.

4. The "Drifting" Signals

One of the most fascinating findings is that for six of these repeating sources, the signals are changing over time.

Imagine a lighthouse beam that is slowly moving up or down the sky over the course of years.
The team measured the "Dispersion Measure" (a way of counting how much space the signal traveled through). They found that for these six sources, this number is changing linearly (steadily) over years.
This suggests the environment right next to the FRB is evolving. It's like watching a storm cloud slowly drift past a lighthouse, changing how the light looks to us. This gives scientists a unique way to watch the "neighborhood" of these cosmic objects change in real-time.

5. How Often Do They Flash?

The team calculated how often these sources flash.

Some are "hyperactive," flashing dozens of times a day.
Others are "shy," flashing only once every few years.
The distribution of these rates is a smooth curve, not a split. This supports the idea that there aren't two distinct groups (one that repeats and one that doesn't), but rather a single population with a huge variety of activity levels.

The Bottom Line

This paper is a "roll call" of the universe's most mysterious radio signals. It confirms that 80 sources are definitely repeating, and it strongly suggests that all FRBs might actually be repeaters, we just haven't been watching long enough or closely enough to see the quiet ones flash a second time.

The universe isn't necessarily full of two different types of monsters; it's likely just one type of monster that is very good at hiding, with some being chatty and others being incredibly shy.

Technical Summary: Discovery of 30 Repeating Fast Radio Burst Sources and Uniform Population Statistics of 80 Repeating Sources from CHIME/FRB

Problem and Motivation
The nature of Fast Radio Bursts (FRBs) remains elusive, particularly regarding whether the population consists of a single class of sources with varying activity rates or distinct populations of "repeaters" and "one-offs." Prior to this work, the discovery of repeating FRBs ruled out cataclysmic source models for those specific sources, yet the Galactic magnetar SGR 1935+2154 demonstrated that magnetars can produce FRB-like bursts. A central question in the field is whether all FRBs repeat, or if a subset of sources are intrinsically non-repeating. Previous analyses by the CHIME/FRB Collaboration (2023) found no evidence for bimodality in burst rates between repeaters and upper limits from non-repeating sources, but the sample size was limited. This paper addresses the need for a larger, uniform sample to test population models, investigate correlations between source properties, and characterize the evolution of local environments through dispersion measure (DM) variations.

Methodology
The authors utilize the second catalog of bursts (Cat2) detected by the Canadian Hydrogen Intensity Mapping Experiment (CHIME/FRB) backend, covering the period from July 25, 2018, to September 15, 2023. The sample comprises 4,539 bursts meeting specific inclusion criteria (e.g., extragalactic DMs above ISM estimates and expert verification).

Source Identification: A DBSCAN clustering algorithm groups bursts based on Right Ascension (R.A.), Declination (Decl.), and DM. To distinguish true repeaters from chance coincidences, the authors compute the Probability of Chance Coincidence (PCC). Unlike previous iterations (RepCat3), this work employs a hierarchical Bayesian intensity function (A. M. Cook et al. 2026) to model the non-homogeneous Poisson process of CHIME/FRB detections, accounting for exposure, sensitivity, and localization uncertainties.
Significance Thresholds: Sources are categorized into a "gold" sample (confirmed repeaters) and a "silver" sample (candidates). The gold threshold requires a median PCC < 0.5/3641 and the entire 90% credible region of the PCC < 1/3641.
Parameter Estimation: For the gold sample, the authors derive updated source parameters including:
- Localization: Improved via offline baseband beamforming where raw voltage data is available.
- Exposure and Sensitivity: Calculated using Monte Carlo simulations accounting for instrument gain variations and beam response, referenced to a 600 MHz frequency.
- Burst Rates: Scaled to a uniform fluence threshold of 5 Jy ms, assuming a cumulative burst rate power-law index of $\alpha = -1.5$ .
- DM Evolution: For sources with four or more bursts, the authors fit constant and linear models to DM vs. time data, evaluating significance via the Bayesian Information Criterion (BIC) and Monte Carlo simulations to rule out stochastic variations.
Population Analysis: The authors compare the repeating sample to the "one-off" sample using Anderson-Darling tests for DM distributions and Spearman rank correlation tests for source properties. They also re-run the population modeling framework of C. W. James (2023) (J23) to test if a single population with a power-law distribution of repeat rates can explain the observed DMs, declinations, and repeater fractions.

Key Contributions and Results

Discovery of 30 New Repeating Sources: The paper reports 30 newly discovered repeating FRBs, bringing the total number of CHIME/FRB repeaters to 80 (79 discovered by CHIME/FRB). These new sources span extragalactic DMs from 99.4 to 1446.0 pc cm $^{-3}$ and burst rates (scaled to 5 Jy ms) between $10^{-5.7}$ and $10^{-0.5}$ hr $^{-1}$ .
Updated Status of Previous Candidates: Three sources previously classified as "silver" candidates in RepCat3 (FRB 20181201D, FRB 20190905A, FRB 20210323C) are promoted to the gold sample due to additional detections and improved PCC methodology.
DM Variations: The authors identify evidence of monotonic, linear DM variations in four repeaters on year-long timescales (in addition to two previously known cases). The rates of change span $-2.05$ to $+1.02$ pc cm $^{-3}$ yr $^{-1}$ . The authors note that these measurements, derived from lower-resolution total intensity data, may be biased high due to degeneracies with burst morphology (frequency drifting), but the linear trends remain statistically significant.
Population Statistics:
- Repeater Fraction: The observed fraction of sources that repeat is $2.4 \pm 0.4\%$ . This value shows no significant evolution over the duration of the experiment, suggesting the survey has not yet probed the lowest repetition rates of the population.
- Bimodality: There is no substantial evidence for bimodal populations. The distribution of upper limits on repeat rates for "one-offs" is entirely contained within the observed range of repeater burst rates.
- Correlations: No statistically significant correlations were found between burst rate, average duration, fluence, and extragalactic DM.
- DM Discrepancy: A significant discrepancy exists between the DM distributions of repeaters (median $\sim$ 353 pc cm $^{-3}$ ) and one-offs (median $\sim$ 525 pc cm $^{-3}$ ). However, population modeling (J23 framework) suggests this can be explained by a single population where 50–100% of sources repeat, with the discrepancy arising from selection biases (e.g., repeaters having narrower bandwidths and longer durations, making them harder to detect at high DMs).

Significance and Claims
The paper claims that the uniform population statistics of 80 repeaters provide the largest sample of repeating FRBs from a well-characterized, homogeneous survey. The primary significance lies in the lack of evidence for a bimodal population; the data is consistent with a single population of FRBs drawn from a continuum of burst rates, where the apparent "one-offs" are simply sources with low repetition rates or unfavorable viewing geometries.

The authors emphasize that while the observed repeater fraction is low ( $\sim$ 2.4%), this is likely a lower limit due to survey sensitivity and morphological biases against detecting repeater-like bursts. The discovery of linear DM variations in multiple sources offers a unique probe into the evolution of the local environments of FRB sources over years-long timescales. The paper concludes that while phenomenological differences exist between repeaters and one-offs (e.g., bandwidth and duration), these do not necessarily imply distinct progenitor classes, and future surveys with higher sensitivity and better morphological characterization (e.g., CHORD, SKA) are required to definitively resolve the population structure.