{"id":"c2a448d1-c7b1-4d23-a887-b61d637b1c6c","arxiv_id":"1908.10026","paper_version":2,"verdict":"ACCEPT","confidence":"HIGH","novelty_score":8.0,"correctness_risk":"low","formal_verification":"none","parameter_count":4,"one_line_summary":"FRB 171019, one of the brightest fast radio bursts detected by ASKAP, repeats: two faint bursts were found with the Green Bank Telescope, and the inferred repetition rate versus fluence slope is consistent with FRB 121102.","lead":"Astronomers found two faint repeat radio bursts from FRB 171019, a bright fast radio burst originally seen only once. The repeats are about 590 times fainter than the first burst, showing that bright bursts can come from repeating sources.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"No significant objection identified: the GBT burst source association is the main weak point, but the appended CHIME repeat detection independently supports the repetition claim.","rationale":"The reader's weakest_assumption is the association of the two GBT bursts with FRB 171019, which is indeed the most load-bearing condition for the repetition claim. I agree with that identification. My pass differs only in that footnote 10, treated as in-scope evidence, provides an independent CHIME detection of a repeat burst from this source, which effectively removes the association as a live concern. The internal evidence alone would be moderately strong but not airtight: a 15 arcminute beam contains many sources, and the DM offset is several sigma. However, the CHIME corroboration, if accurate, settles the point. No other step in the paper is load-bearing for the central claim. The rate inference (Eqs. 1-3) is highly uncertain with two bursts and many non-detections, but it is explicitly presented as preliminary and does not affect the existence of repetition. The spectral index and modulation discussion is speculative but clearly flagged. Thus the verdict should remain ACCEPT/UNCHANGED.","tokens_in":12809,"tokens_out":3868,"duration_ms":43099,"concrete_test":"Retrieve ATel 13013 (Patel & CHIME/FRB Collaboration 2019) and verify that the CHIME burst is reported at a position consistent with FRB 171019 and with a dispersion measure matching the ASKAP or GBT values (456-461 pc cm^-3). If those quantities match, the repetition claim has independent external confirmation. If the ATel is not actually a matching detection, re-open the association concern and quantify the probability of two unrelated GBT bursts in the beam with similar DMs.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim is that FRB 171019 repeats. Its most load-bearing assumption is that the two GBT bursts (GBT-1 and GBT-2, Table 2) come from the same source as the ASKAP burst. Internal evidence is coincidence of position within the 15 arcminute GBT beam and DM values (456.1 ± 0.4 and 457 ± 1 pc cm^-3) close to, but not identical with, the ASKAP DM of 461 ± 1 pc cm^-3. The ~4-5 pc cm^-3 offset is statistically significant, and the bursts are faint (0.60 and 0.37 Jy ms), so an unrelated source in the beam could in principle mimic this. However, footnote 10 states that CHIME has recently detected a repeat burst from this source (Patel & CHIME/FRB Collaboration 2019, ATel 13013). If that report is accurate, the repetition claim is independently confirmed and the association concern does not land. I therefore do not raise a substantive objection to the central claim; remaining uncertainties concern rate inference and spectral interpretation, not whether the source repeats.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"This paper reports two repeat bursts from the source of the fast radio burst FRB 171019, which was originally detected by ASKAP at 1.3 GHz with a fluence of 219 Jy ms. The two new bursts were detected with the Green Bank Telescope at 820 MHz with fluences of 0.60 and 0.37 Jy ms, roughly 590 times fainter than the original burst, and with dispersion measures of 456.1 ± 0.4 and 457 ± 1 pc cm^-3, close to but not identical with the ASKAP value of 461 ± 1 pc cm^-3. The bursts were found in a follow-up campaign totaling about 1000 hours that also included ASKAP and Parkes observations from 720 to 2000 MHz. The paper reports that all three bursts show no evidence of scattering, that their widths are broadly similar, that their spectra show strong frequency modulation consistent with either steep spectra or patchy emission, and that a Bayesian fit of the repetition rate as a power-law in fluence and frequency gives a fluence slope consistent with the range seen for FRB 121102. A footnote also notes an independent CHIME detection of a repeat burst from this source.","tokens_in":13040,"tokens_out":14226,"duration_ms":147258,"significance":"If the central claim holds, this is an important result: it demonstrates that at least some FRBs selected from a bright, ostensibly one-off sample repeat at much lower fluence when observed with a more sensitive telescope, and it extends the observed fluence range of a single repeating source by a factor of nearly 600. The paper is careful in several respects: the search pipeline is described in enough detail to be reproduced, the two GBT candidates have signal-to-noise ratios of 15.2 and 7.9 and were vetted by neural-network classification and visual inspection, the scattering analysis is done with Bayesian model comparison, and the DM mismatch between ASKAP and GBT is openly disclosed rather than hidden. The independent CHIME detection cited in footnote 10 substantially mitigates the main source-association risk that would otherwise attach to the 15-arcminute GBT beam and the statistically significant DM offset. The main remaining weakness is statistical: the repetition-rate inference is broad and degenerate, and the wording of the abstract is stronger than the posterior constraints justify.","major_comments":[],"minor_comments":[{"comment":"The statement that the inferred scaling of repetition rate with fluence 'agrees with FRB 121102' is stronger than the data support. The text in Section 3.4 notes that the frequency-dependence index β is inferred to be 'β ≪ −1.5, with the lower prior acceptable,' meaning the posterior for β accumulates at the prior boundary, and Figure 4 shows a strong degeneracy between β and the fluence slope γ. The marginalized range −1.5 ≲ γ ≲ 0 is therefore prior-dominated. Please report the joint γ–β posterior, or present γ conditional on an independently constrained β (for example, using the measured spectral indices in Table 2), and change 'agrees' to 'is consistent with' in the abstract.","section":"Abstract; Section 3.4; Figure 4"},{"comment":"There is an internal inconsistency between Table 2 and note d: the table lists a lower-half-band spectral index for GBT-1 of −0.9 ± 1.8, while note d states that the fit in the frequency range (820, 750 MHz) gives −6.0 ± 2.8. Please clarify which frequency range each number refers to and ensure the table and note agree.","section":"Table 2 and note d"},{"comment":"The phrase 'consistent pulse widths' should be qualified. As tabulated, the measured Gaussian FWHMs are 5.4 ± 0.3 ms for the ASKAP burst and 4.0 ± 0.3 ms for GBT-1, which differ by about 3σ before accounting for DM smearing and time resolution. The authors should state whether the consistency claim refers to intrinsic widths after deconvolution of DM smearing and sampling time, and ideally report those intrinsic widths.","section":"Abstract; Section 3; Table 2"},{"comment":"The sentence 'with 95% confidence is less than <−0.2' contains a doubled inequality; it should read 'less than −0.2' or '< −0.2'.","section":"Section 3.3"},{"comment":"The caption contains a typo: 'The first repeat burst is found in be observation dated 2018 July 20' should read 'in the observation dated 2018 July 20.'","section":"Figure 1 caption"},{"comment":"The phrase 'with the lower prior acceptable' is unclear. If the posterior distribution for β reaches the lower boundary of the uniform prior at −10, that should be stated explicitly, because it is important for interpreting the implications of the fit.","section":"Section 3.4"},{"comment":"The independent CHIME detection of a repeat burst from this source is important supporting evidence for the central claim. It should be mentioned in the main text in Section 3 or 4 rather than only in a footnote, and the authors should state explicitly whether the CHIME burst is included in the repetition-rate analysis or only cited as external confirmation.","section":"Discussion, footnote 10"}],"recommendation":"minor_revision","confidential_remarks":"The paper's core detection claim is convincing and is independently supported by the cited CHIME detection. The main revisions I request are local: tempering the abstract's rate-scaling claim, reconciling the Table 2 spectral-index values, and clarifying the pulse-width consistency statement. I do not see a load-bearing error that would justify rejection, and the source-association concern is adequately addressed by footnote 10. The paper is a good fit for the journal's Letters format."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Two things to know. First, this is the first repeat-burst detection from FRB 171019, one of the brightest one-offs in the ASKAP sample, and the fluence gap (a factor of ~590) is the largest yet seen from a repeating source. Second, the claim is solid — not just because the two GBT bursts have consistent DMs and fall within the beam, but because footnote 10 notes a CHIME repeat detection, which independently confirms that the source repeats. The stress-test concern about source association is real but does not land, given that independent confirmation.\n\nWhat is new is the detection itself and the repetition-rate versus fluence inference for this particular source. The methodology is standard: a Poisson likelihood across the ASKAP, Parkes, and GBT surveys, with uniform priors on the power-law indices. The paper is also honest about the DM discrepancy (456.1 and 457 pc cm^-3 at GBT versus 461 at ASKAP), reports scattering upper limits, and shows the spectral modulation clearly. The conclusion that the burst-intensity slope is consistent with FRB 121102 is a useful data point for the question of whether most FRBs repeat.\n\nSoft spots, in proportion. The repetition-rate parameters R0, gamma, and beta are weakly constrained; the posteriors in Figure 4 are broad and degenerate. That is not a flaw in the analysis, but the abstract should not imply a tight measurement. The spectral indices (alpha ~ -8 to -13) come from forced power-law fits, and the paper itself concedes that patchy emission could explain the band-limited behavior. Calling these steep spectra is an over-interpretation, though they do hedge. Minor: no data release, and the modulation index m^2 is quoted without uncertainties. The DM offset between telescopes is given a plausible but untested explanation; it is the weakest link in the association, but the CHIME detection means it is no longer load-bearing.\n\nWho should read this: anyone working on FRB repetition rates, the one-off/repeater dichotomy, or follow-up observing strategies. It is a solid observational Letter that deserves a serious referee. I would send it out. My only editorial request would be to move the CHIME confirmation out of the footnote and into the main text, and to ask for the data behind Figure 4 to be made available.","headline":"Solid first repeats from a bright ASKAP FRB; the central claim survives, and the CHIME confirmation in the footnote takes the edge off the source-association worry.","tokens_in":13595,"tokens_out":1838,"would_cite":true,"duration_ms":20672,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"The bright fast radio burst FRB 171019 repeats, with bursts 590 times fainter than the original flash.","keywords":["fast radio bursts","FRB 171019","repeating FRB","Green Bank Telescope","ASKAP","dispersion measure","burst fluence distribution","radio transients"],"falsifier":"If future interferometric localization of a burst from this sky position places it outside the 10-arcminute ASKAP error box, or shows a clearly different dispersion measure, then the GBT bursts are a different source and the repetition claim is wrong.","tokens_in":12655,"feed_emoji":"📡","tokens_out":11943,"duration_ms":107131,"temperature":0.7,"pith_summary":"This paper reports that FRB 171019, one of the brightest fast radio bursts found in the ASKAP fly's-eye survey, is a repeating source. Two additional bursts from the same sky position were detected with the Green Bank Telescope at 820 MHz, with fluences (time-integrated radio energy per unit area) about 590 times smaller than the original burst. The bursts are similar in width to the first one and show no scattering, but they are visible only in the lower half of the observed band, suggesting either very steep spectra or patchy, band-limited emission. These two detections were the only ones found in roughly 1000 hours of follow-up with ASKAP, Parkes, and the Green Bank Telescope, and the inferred relationship between burst rate and fluence agrees with the known repeater FRB 121102. If correct, the result means that at least some FRBs drawn from bright, apparently one-off samples will show repetitions when followed with more sensitive, lower-frequency telescopes.","feed_headline":"FRB 171019 repeats, 590 times fainter than its first flash","feed_subtitle":"Two faint GBT bursts prove a bright 'one-off' FRB repeats when watched closely","key_machinery":"The load-bearing object is the pair of 820 MHz bursts detected by the Green Bank Telescope, because they are what turns FRB 171019 from a one-off event into a repeating source. The quantitative machinery is a Bayesian Poisson likelihood built on a cumulative burst rate $R(>S,\\nu)=R_0\\,(S/S_0(\\nu))^{\\gamma}$ with $S_0(\\nu)=S_0(\\nu/\\nu_0)^{\\beta}$; each survey contributes an expected count $\\lambda_i = T_i R(>S_i,\\nu_i)$ set by its exposure time and fluence sensitivity. Comparing the two GBT detections with the non-detections at ASKAP, Parkes, and GBT L-band yields posteriors on the fluence slope $\\gamma$ and the spectral dependence $\\beta$, and the consistency of $\\gamma$ with the value measured for FRB 121102 is what links this source to the broader repeating population.","core_discovery":"The paper's central claim is that the source of FRB 171019 is a repeating fast radio burst. Two bursts appeared in Green Bank Telescope observations at 820 MHz on 2018 July 20 and 2019 June 9, with fluences of $0.60\\pm0.04$ and $0.37\\pm0.05$ Jy ms, about 590 times fainter than the $219\\pm5$ Jy ms ASKAP burst. All three bursts are free of measurable scattering, have consistent widths, and are detected only in the lower half of their respective bands; their spectra fit steep power laws (spectral indices between roughly $-13$ and $-8$) or, alternatively, patchy band-limited emission. The repeats have apparent dispersion measures a few pc cm$^{-3}$ below the original burst, which the authors attribute either to genuine DM variation, to non-dispersive timing effects, or to different plasma volumes being probed. From the two detections and the surrounding non-detections, the inferred slope of the cumulative burst rate versus fluence is $-1.5\\lesssim\\gamma\\lesssim0$, matching FRB 121102. The authors conclude that at least some FRBs selected from bright samples will repeat when followed up with more sensitive telescopes, and they caution against over-interpreting the steep-spectrum explanation because few physical mechanisms produce such steep spectra.","pith_inferences":["Beyond the paper: this detection shifts the prior on the ASKAP sample, suggesting that the lack of repeats in ASKAP's self-follow-up reflects its fluence threshold rather than a genuinely non-repeating population.","Beyond the paper: the apparent dispersion-measure offset between the GBT bursts and the ASKAP burst, if real, could be a probe of time-variable plasma along the line of sight; simultaneous multi-frequency observations of future bursts would test whether the offset is frequency-dependent.","Beyond the paper: if the steep-spectrum or patchy interpretation holds, the next repeat from this source should be detected more readily with low-frequency instruments below 800 MHz, and its absence at higher frequencies would be expected rather than surprising.","Beyond the paper: the absence of scattering in all three bursts suggests a relatively clean sightline, which may allow the source's environment to be studied through dispersion and rotation measures without scattering contamination."],"forward_implications":["At least some FRBs discovered as bright, apparently one-off events belong to the repeating population; sensitivity and observing frequency, not source type, determined whether repetition was seen.","The fluences of bursts from a single source span a factor of about 590, and inferred luminosities span nearly three orders of magnitude, so emission models must allow a wide range of burst energies from the same engine.","The agreement of the burst-rate-versus-fluence slope with FRB 121102 supports a common, possibly power-law, energy distribution for repeating FRBs.","If the bursts' steep or patchy spectra are typical, repeating sources will be increasingly detectable toward lower radio frequencies; high-frequency searches may systematically miss repetitions.","The paper notes that CHIME has since detected another repeat from this source, providing independent corroboration of its repeating nature."],"supporting_citations":[{"why":"It reports the discovery of FRB 171019 in the ASKAP fly's-eye survey and supplies the burst's fluence, dispersion measure, and arcminute localization that the follow-up campaign targets.","marker":"Shannon et al. 2018"},{"why":"It provides the multi-beam localization technique that places FRB 171019 within the Green Bank Telescope beam, making the follow-up feasible.","marker":"Bannister et al. 2017"},{"why":"It establishes FRB 121102 as the first repeating fast radio burst, the comparison source for repetition properties.","marker":"Spitler et al. 2016"},{"why":"It supplies the burst-rate-versus-fluence distribution of FRB 121102 against which the inferred gamma for FRB 171019 is compared.","marker":"Law et al. 2017"},{"why":"It gives the ASKAP population's spectral index distribution, the reference for evaluating the steep spectra of these bursts.","marker":"Macquart et al. 2019"},{"why":"It reports eight new repeating FRB sources, providing the broader repeater population context and fluence-range comparisons.","marker":"CHIME/FRB Collaboration et al. 2019c"},{"why":"It provides the sample of FRB 121102 bursts used to compare pulse widths, spectral variability, and repetition behavior.","marker":"Hessels et al. 2019"},{"why":"It localizes a one-off ASKAP FRB to a massive host galaxy, contrasting with FRB 121102's dwarf host and motivating the question of multiple source populations.","marker":"Bannister et al. 2019a"}],"fun_headline_variants":["Bright FRB 171019 repeats, 590 times fainter than its first flash","Faint repeats from a bright FRB: a one-off becomes a repeater","A bright FRB source shows faint repeat bursts on close inspection","One of the brightest FRBs turns out to repeat faintly","FRB 171019's faint repeats reveal a bright source that repeats"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The two GBT bursts come from the same source as the original ASKAP burst; if the slightly different measured dispersion and the broad telescope beam hide a different, unrelated source, the repetition claim falls apart.","fun_headline_variants_meta":{"raw":{"variants":["Bright FRB 171019 repeats, 590 times fainter than its first flash","Faint repeats from a bright FRB: a one-off becomes a repeater","A bright FRB source shows faint repeat bursts on close inspection","One of the brightest FRBs turns out to repeat faintly","FRB 171019's faint repeats reveal a bright source that repeats"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000933,"raw_usage":{"total_tokens":4040,"prompt_tokens":1041,"completion_tokens":2999,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":657,"completion_tokens_details":{"reasoning_tokens":2901}},"tokens_in":657,"tokens_out":2999,"duration_ms":22268,"temperature":1.0,"reasoning_tokens":2901,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-14T10:55:14.655776+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"If future interferometric localization of a burst from this sky position places it outside the 10-arcminute ASKAP error box, or shows a clearly different dispersion measure, then the GBT bursts are a different source and the repetition claim is wrong.","supporting_citations":[{"cited_title":"M., Macquart, J","cited_arxiv_id":null,"evidence_quote":"It reports the discovery of FRB 171019 in the ASKAP fly's-eye survey and supplies the burst's fluence, dispersion measure, and arcminute localization that the follow-up campaign targets."},{"cited_title":"W., Shannon, R","cited_arxiv_id":null,"evidence_quote":"It provides the multi-beam localization technique that places FRB 171019 within the Green Bank Telescope beam, making the follow-up feasible."},{"cited_title":"J., Abruzzo, M","cited_arxiv_id":null,"evidence_quote":"It supplies the burst-rate-versus-fluence distribution of FRB 121102 against which the inferred gamma for FRB 171019 is compared."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"It provides the sample of FRB 121102 bursts used to compare pulse widths, spectral variability, and repetition behavior."}],"review_version":1}