FRB progenitor fractions: prompt magnetars versus delayed channels from localized host demographics
Localised samples are growing quickly and population fits are standard, but delay-time distributions and selection effects are poorly constrained, so difficulty is just above the old 40. Application value 10, near the old 11, for FRBs as baryon and IGM probes; leverage 34 near the old 33.
The problem
Fast radio bursts flash for a thousandth of a second from far away. What makes them, and in what shares?
- 1Brief, powerful radio flashes from afar
- 2Galactic magnetar made a burst in 2020
- 3Some hosts are old, some young
- 4Model young and delayed routes
- 5Fit shares to host-galaxy data
The question. Which progenitor channels produce the observed cosmological FRB population, and in what fractions?
- Prompt channel: young magnetars born in core-collapse supernovae of massive stars, so the FRB rate tracks recent star formation.
Path to understanding
foundations → problemThe research entries this problem rests on, in the order to read them. Each links to its explainer.
- Start with
- Step 2
- Step 3
- Radio interferometry and aperture synthesisAlgorithm · host
- Then
- FRB progenitor fractions: prompt magnetars versus delayed channels from localized host demographicsThe problem
State of the art
The Galactic magnetar SGR 1935+2154 produced a bright millisecond radio burst in April 2020 (arXiv:2005.10324). The first CHIME/FRB catalog has 536 bursts (arXiv:2106.04352), and an FRB in a globular cluster of M81 (arXiv:2105.11445) points to a non-prompt channel. The DSA-110 FRB host catalog (arXiv:2307.03344) and subsequent work show a preference for massive star-forming hosts; a repeating FRB in the outskirts of a quiescent galaxy (arXiv:2410.23374, October 2024) shows that delayed channels contribute. The first CHIME/FRB Outriggers host catalog localised 81 bursts to about 2″ × 60″ with CHIME and the KKO outrigger and securely identified 21 new hosts (arXiv:2502.11217, February 2025). The second CHIME/FRB catalog (arXiv:2601.09399, January 2026) has 4,539 bursts from 3,641 sources, including 981 bursts from 83 repeaters, and the full Outrigger array localised FRB 20250316A to 13 pc (arXiv:2506.19006), but no full-array host catalog has been published. Host-population modelling is split: Loudas et al. (51 hosts, arXiv:2502.15566) find that FRBs mostly track star formation but allow up to about 40–50% tracking stellar mass, while Horowicz et al. (arXiv:2504.08038) rule out pure star-formation tracking and find a mix similar to Type Ia supernovae. The population is a mix, but the fractions are not constrained, and no progenitor is identified for the bulk of FRBs.
Realistic applications
The progenitor channel determines whether FRBs trace star formation or old populations, which matters when they are used as probes of the baryon content and intergalactic medium (missing baryons) and for electromagnetic counterparts of mergers. No other application.
What counts as solved
Resolved when population models fitted to a localised sample of at least several hundred bursts (including hosts, offsets and energy function) identify the channel fractions to within about 20%, and a progenitor class is confirmed by a multiwavelength counterpart or persistent source for at least two non-magnetar-flare events.
How it gets verified
ObservationSettled by new measurements or observations.
Needs a localised sample of at least several hundred bursts (hosts, offsets, energy function) from which population models give channel fractions to about 20%, and a multiwavelength counterpart or persistent source confirming a progenitor class for at least two non-magnetar-flare events.
Claims under verification
+ add a claimNo claimed results on the Verification board for this problem yet.
Where the work is
New localizations and host observations are the main need, with population-synthesis modelling.
Bottlenecks
ranked by votes- #1EmpiricalLocalization sample size and host completeness
Hundreds of localised bursts with spectroscopic redshifts are needed, with selection effects from CHIME's sensitivity.
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Connected problems
Progress
- Jan 14, 2026Second CHIME/FRB catalogsource
4,539 bursts from 3,641 sources, including 83 repeaters.
- Feb 16, 2025CHIME Outrigger catalogsource
81 bursts localised to about 2″ × 60″ with the KKO outrigger; 21 new host galaxies.
- Oct 30, 2024FRB in a quiescent galaxysource
A repeating source in the outskirts of an old galaxy.
- May 20, 2020Galactic magnetar burstsource
SGR 1935+2154 emits a bright millisecond radio burst.