[Paper Review] Connecting repeating and non-repeating fast radio bursts via their energy distributions

Franz Kirsten, O. S. Ould-Boukattine+12 more|arXiv (Cornell University)|Jun 27, 2023

Pulsars and Gravitational Waves Research4 citations

TL;DR

This study analyzes the energy distribution of 46 high-energy bursts from the hyperactive repeating fast radio burst source FRB 20201124A, detected over 2,000 hours using four 25–32 m radio telescopes. It finds that the high-energy burst distribution closely resembles that of apparently non-repeating FRBs, suggesting that non-repeaters may simply be the rarest bursts from repeating sources, implying a common physical origin for both populations.

ABSTRACT

Fast radio bursts (FRBs) are extremely energetic, millisecond-duration radio flashes that reach Earth from extragalactic distances. Broadly speaking, FRBs can be classified as repeating or (apparently) non-repeating. It is still unclear, however, whether the two types share a common physical origin, differing only in their activity rate. Here we report on an unprecedented observing campaign that targeted one hyperactive repeating source, FRB 20201124A, for more than $2000~\mathrm{hr}$ using four $25-32\mathrm{-m}$ class radio telescopes. In total, we detect $46$ high-energy bursts, many more than one would expect given previous observations of lower-energy bursts using larger radio telescopes. We find a high-energy burst distribution that resembles that of the non-repeating FRB population, suggesting that apparently non-repeating FRB sources may simply be the rarest bursts from repeating sources. We also discuss how FRB 20201124A contributes strongly to the all-sky FRB rate and how similar sources would be observable even at very high redshift.

Motivation & Objective

• To investigate whether repeating and non-repeating fast radio bursts (FRBs) share a common physical origin by comparing their energy distributions.
• To probe the high-energy tail of the burst population using a hyperactive repeating source, FRB 20201124A, which enables detection of rare, energetic events.
• To test the hypothesis that apparent non-repeaters are simply the least active sources in a repeating population, rather than physically distinct objects.
• To assess the contribution of hyperactive sources like FRB 20201124A to the all-sky FRB rate and their detectability at high redshift.

Proposed method

• Conducted a 2,000+ hour observing campaign using four 25–32 m radio telescopes to monitor FRB 20201124A, a hyperactive repeating source.
• Measured burst fluence and spectral energy density (Eν = E/ν) using a fiducial bandwidth of 300 MHz to standardize comparisons across FRB populations.
• Applied a power-law model R(>Eν) ∝ Eν^γ to fit the cumulative burst spectral energy distribution, with γ as the key parameter for comparison.
• Used dispersion measure (DM) measurements from ten bright, multi-component bursts to confirm source distance and consistency of emission properties.
• Calculated expected burst numbers across P-, L-, and C-bands using detection thresholds and observed integration time to assess sensitivity and completeness.
• Compared the derived energy distribution of FRB 20201124A with published energy distributions of non-repeating FRBs to assess similarity in spectral slope γ.

Experimental results

Research questions

• RQ1 Do the energy distributions of repeating and non-repeating FRBs show statistical similarity, suggesting a common physical origin?
• RQ2 Is the high-energy tail of the repeating FRB population consistent with the energy distribution of apparently non-repeating FRBs?
• RQ3 Can the rarity of non-repeating FRBs be explained by the low detection probability of the most energetic bursts from repeating sources?
• RQ4 To what extent does FRB 20201124A contribute to the all-sky FRB rate, and how detectable are similar sources at high redshift?
• RQ5 Does the observed spectral energy distribution of FRB 20201124A, particularly at high Eν, show a power-law slope γ consistent with non-repeating FRBs?

Key findings

• FRB 20201124A produced 46 high-energy bursts over 2,000+ hours of observation, significantly more than expected from previous surveys with larger telescopes.
• The spectral energy distribution of FRB 20201124A, with a power-law slope γ ≈ -1.5 to -0.6, closely matches the flatter energy distribution observed in apparently non-repeating FRBs.
• The high-energy tail of the repeating source's burst distribution is consistent with the energy distribution of non-repeating FRBs, suggesting that non-repeaters may be the rarest bursts from repeating sources.
• FRB 20201124A contributes significantly to the all-sky FRB rate, with an estimated 1.5–3.2 bursts per day detectable in the 300 MHz bandwidth.
• The source remains detectable at high redshift (z ≈ 0.098), and similar hyperactive sources could be observable even at z > 1, extending the cosmological reach of FRB surveys.
• Dispersion measures from ten bright bursts were consistent across the campaign, with values between 410.4 and 411.9 pc cm⁻³, supporting a stable distance of z = 0.098.