{"id":"abf0f010-1e54-42d5-bb85-6256f5e8f402","arxiv_id":"2411.11503","paper_version":2,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":5,"one_line_summary":"GRB-linked and ordinary broad-lined type Ic supernovae show statistically indistinguishable expansion velocities and velocity decay rates in the largest such sample to date.","lead":"This paper measured how fast the shredded remains of 74 stellar explosions expand and slow down, comparing the 13 explosions linked to gamma-ray bursts with the 61 that are not. The two groups look statistically the same, so supernova speeds cannot reveal which explosions hid a gamma-ray jet.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The population-equality claim depends on the ordinary Ic-BL sample being representative; its brightness-selected, possibly jet-bearing composition could erase a genuine velocity difference.","rationale":"This is the most load-bearing concern because it attacks the sample-level validity of the central claim. A low-power KS test (n=5-6 GRB-SNe) is a separate problem, but even a well-powered test on a biased sample would not establish a common population. The paper's own Sect. 2.2 identifies the bias, and the paper does not mitigate it. The proposed check uses existing radio/X-ray data to separate ordinary SNe with and without engine evidence; this directly tests whether the null result is due to contamination of the 'ordinary' sample by hidden jets. The p-value discrepancy (0.21 in Sect. 4.2.2 vs 0.39 in Table 3) is a minor internal inconsistency that should be corrected but does not change the conclusion, since both values fail to reject. The reader's CONDITIONAL verdict remains appropriate: the paper is careful and the null result for the sample itself is credible, but the population-level inference should be hedged until the selection bias is either corrected or shown not to matter.","tokens_in":69494,"tokens_out":7905,"duration_ms":86050,"concrete_test":"Compile a sub-sample of ordinary Ic-BL SNe with deep radio/X-ray non-detections that exclude relativistic jets (e.g., Soderberg 2006; Corsi 2016, 2023; Margutti 2014) and a complementary sub-sample with engine evidence. Re-run the Gold-sample KS tests for Fe II and Si II velocities at t0+15 days and for decay indices, comparing the engine-excluded ordinary SNe against the GRB-SNe. If the engine-excluded subset is systematically slower or has steeper indices at p<0.01, the population-equality claim is an artifact of selection rather than physics; if the samples remain indistinguishable, the concern is resolved.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central conclusion that GRB-SNe and ordinary Ic-BL SNe are drawn from one population rests on KS tests that fail to reject the null in a biased sample. Section 2.2 concedes that ordinary Ic-BL SNe come from magnitude-limited surveys (e.g., ZTF BTS m_peak <= 18.5 mag) and that the resulting overabundance of bright SNe may bias the sample toward nickel-rich, polar-viewed events that could harbour jets. Section 2.3 adds that the two discovery channels yield very different redshift ranges (z <~ 0.2 vs z <~ 0.6). If the 'ordinary' sample preferentially includes jet-bearing SNe, a real velocity difference between genuinely jet-free and jet-bearing populations could be masked, producing the Table 6 null results. This would invalidate the headline inference that the two groups share an underlying population. The paper does not quantify or correct for this selection effect, and it includes known engine-driven ordinary SNe (SN2009bb, SN2012ap, PTF12gzk, SN2016coi) in the 'ordinary' group.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The manuscript compiles the largest spectroscopic sample to date of type Ic-BL supernovae with and without associated GRBs: 61 ordinary type Ic-BL SNe and 13 GRB-SNe, comprising 875 spectra. It measures Fe II 5169 Å and Si II 6355 Å expansion velocities using a spline-fitting Monte Carlo method, fits the velocity evolution with power-law (Eq. 1) and broken power-law (Eq. 2) models, and compares the two populations using decay indices and velocities at t0+15 days, restricted to a Gold sample with well-constrained explosion times. The main result is that the two populations show overlapping velocities and statistically indistinguishable decay indices, leading the authors to conclude that GRB-SNe and ordinary Ic-BL SNe are drawn from the same underlying population of events.","tokens_in":69606,"tokens_out":5484,"duration_ms":53355,"significance":"The dataset is the largest of its kind and the methodology is generally careful: the Monte Carlo spline procedure, the Gold/Silver/Bronze quality tiers, the explicit t0-robustness study in Appendix D, and the literature cross-checks in Appendix E are genuine strengths. If the null result survives a treatment of selection effects, it would be an important constraint on jet-ejecta coupling and on the interpretation of Ic-BL SNe as engine-driven events. However, the headline population-equality claim currently rests on small Gold subsamples and on a survey-selected 'ordinary' sample that the manuscript itself acknowledges may be biased toward jet-bearing events. The significance of the central conclusion is therefore conditional on addressing these caveats.","major_comments":[{"comment":"The central population-equality claim is weakened by sample selection. The manuscript notes in Sect. 2.2 that ordinary Ic-BL SNe are drawn from magnitude-limited surveys such as ZTF BTS (m_peak <= 18.5 mag) and that this may bias the sample toward bright, nickel-rich, polar-viewed events that could harbour jets, while Sect. 2.3 notes the very different redshift ranges of the two discovery channels (z <~ 0.2 vs z <~ 0.6). If the 'ordinary' sample preferentially includes jet-bearing SNe, a genuine velocity difference between truly jet-free and jet-bearing populations could be masked, producing the null results in Table 6. The sample also places known engine-driven SNe in the ordinary group (e.g., SN2009bb, SN2012ap, PTF12gzk, SN2016coi). The paper does not quantify or correct for this selection effect, so the abstract conclusion that the two groups are drawn from the same underlying population is stronger than the data currently support.","section":"Sect. 2.2, Sect. 2.3, Tables 3 and 6"},{"comment":"The KS tests use Gold sample sizes of only 5-6 GRB-SNe and 11-13 ordinary Ic-BL SNe. With such small samples, failure to reject the null at the chosen p<0.01 threshold is weak evidence for population equality; p-values of 0.85, 0.39, 0.89, and 0.46 are as consistent with low statistical power as with a genuinely common underlying distribution. A power analysis or a statement of the minimum detectable velocity difference would be needed to support the abstract claim that the two populations are indistinguishable. The manuscript acknowledges the small numbers in passing, but the conclusions do not carry this caveat with sufficient weight.","section":"Tables 3 and 6"},{"comment":"The quantitative statistical comparisons are not model-independent. The 15-day velocities and decay indices used in the KS tests are computed from the same power-law and broken power-law fits that define them, so the two population comparisons inherit the assumptions of the fitted model. In addition, Sect. 5.1 reports a ~12000 km/s difference between the spline-minimum Fe II velocity and the Modjaz et al. template-matching velocity for SN1998bw, illustrating that the Fe II measurements are sensitive to line blending. The raw velocity plots (left panels of Figs. 7 and 8) do show overlap, which is reassuring, but the quantitative p-values alone are not a model-independent demonstration of population equality.","section":"Sect. 4.2, Sect. 4.4, Sect. 5.1"}],"minor_comments":[{"comment":"The sentence 'as a result of these issues, SN2002ap was assigned to the Gold sample' appears to be a typo; the object shown in Fig. 12 and discussed in that paragraph is SN2009bb, not SN2002ap.","section":"Sect. 4.2.2, Fig. 12"},{"comment":"Two different figures are both numbered Figure 25: the Fe II minus Si II velocity difference plot and the literature comparison plot. The latter should be renumbered to avoid confusion.","section":"Sect. 4.6 and Sect. 5.1"},{"comment":"The text states a p-value of 0.21 for the Si II decay-index KS test, while Table 3 lists 0.39 for the same test; the discrepancy should be reconciled.","section":"Sect. 4.2.2, Table 3"},{"comment":"The sentence 'it is certain that these velocities are accurate' appears to be a typo; the surrounding discussion indicates the intended meaning is that the velocities from the Bronze sample are not reliable.","section":"Sect. 4.4.2"},{"comment":"The phrase 'and references therin' should read 'and references therein'.","section":"Sect. 5.4"}],"recommendation":"major_revision","confidential_remarks":"The paper is within scope for A&A and the underlying data compilation and measurement effort are solid. The main concern is that the central claim of population equality is stated more strongly than the evidence supports, given the acknowledged selection biases in the ordinary Ic-BL sample and the small Gold subsamples used for the KS tests. I would encourage the editor to request a revision that either adds a selection-bias analysis (e.g., excluding known engine-driven SNe from the ordinary group, or restricting the comparison to a common redshift/absolute-magnitude range) or substantially softens the population-level conclusion."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"The paper is the real deal on data: 875 spectra, 74 SNe, uniform spline velocities, explicit Gold/Silver/Bronze tiers, a robustness study of t0 uncertainty, and cross-checks against literature velocities. It also makes the first quantitative single/broken power-law comparison between GRB-SNe and ordinary Ic-BL SNe, and the broken-power-law Si II result (always shallow-steep) is genuinely new. The engine-driven SNe (PTF12gzk, SN2016coi) tracking GRB060218-SN2006aj is a nice piece of evidence for a jet/cocoon component.\n\nThe soft spots are the ones flagged in the Pith Report, and they are real, but not all equal. The biggest is selection: the ordinary Ic-BL sample is brightness-selected, the authors say so themselves, and they include known engine-driven SNe (2009bb, 2012ap, PTF12gzk, 2016coi) in the 'ordinary' group. If the ordinary sample is contaminated with jet-bearing SNe, a genuine velocity difference could be erased. That is a genuine threat to the headline 'same underlying population' claim; it is not addressed quantitatively.\n\nThe statistics are also weaker than the prose. The KS tests on 5-6 GRB-SNe have essentially no power; p=0.85 or p=0.39 with n=5 cannot support a positive claim of identical distributions. The 15-day velocities and decay indices come from the same fits, so the two tests are not independent. That said, the raw velocity overlap in Figs. 7-8 does show the central null for the sample itself is not an artifact of the fitting. The circularity concern is therefore real but not fatal.\n\nTwo smaller things. The Fe II velocities depend heavily on the blend method; Appendix 5.1 shows offsets up to ~12000 km/s relative to Modjaz et al. (2016), so the abstract's 'similar velocities' leans on a feature whose absolute scale is method-dependent. And the Si II KS p-value is 0.21 in the text and 0.39 in Table 3; the authors need to reconcile that.\n\nBottom line: the sample-level result is solid and the dataset is a contribution. The population-level claim needs heavy hedging, a power analysis, and a serious discussion of selection effects before it is relied on. This deserves a rigorous refereeing, not a desk rejection, and I would bring it to reading group to talk about how much a null in a biased sample is worth. My vote: accept with major revision, but the authors have to cool the conclusion down to match the statistics.","headline":"The largest, most careful Ic-BL velocity study to date, whose sample-level null result is credible, but whose population-level conclusion outruns the statistics.","tokens_in":70291,"tokens_out":1504,"would_cite":true,"duration_ms":20658,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":["97.60.Bw","98.70.Rz"],"model":"deepseek-v4-flash","headline":"The paper argues that GRB-supernovae and ordinary broad-lined type Ic supernovae have indistinguishable expansion velocities and velocity evolution, so an optical velocity curve cannot reveal whether a jet was launched.","keywords":["type Ic-BL supernovae","gamma-ray bursts","GRB-supernova association","expansion velocity","Fe II absorption","Si II absorption","power-law decay","engine-driven supernovae"],"falsifier":"Build a brightness-unbiased, volume-limited sample of nearby type Ic-BL supernovae with densely sampled pre-peak light curves and late-time radio follow-up, and compare the fifteen-day Fe II velocities of the radio-quiet subclass with those of GRB-supernovae: a statistically significant velocity deficit for the radio-quiet events would overturn the common-population conclusion, whereas continued overlap would confirm it.","tokens_in":2148,"feed_emoji":"💥","tokens_out":3676,"duration_ms":153410,"temperature":0.7,"pith_summary":"This paper asks whether the launch of an ultra-relativistic gamma-ray burst jet leaves a measurable mark on the expanding ejecta of a broad-lined type Ic supernova (a hydrogen-free stellar explosion whose spectral lines are broadened by fast ejecta). Using the largest spectroscopic sample assembled for this question — 875 spectra from 61 ordinary type Ic-BL supernovae and 13 GRB-supernovae — the authors measure the velocities of the Fe II and Si II absorption features and fit the decline of those velocities with power laws. They find that neither the velocities at fifteen days after explosion nor the power-law decay indices differ statistically between the two classes: the median Fe II velocity is about 21,000 km/s in both populations, and Kolmogorov-Smirnov tests on the best-constrained subsample return p-values between 0.39 and 0.89. This contradicts an earlier, smaller study that reported GRB-supernovae expanding about 6,000 km/s faster. If the result stands, optical velocity measurements cannot be used to flag jet-powered explosions, and GRB-supernovae and ordinary type Ic-BL supernovae should be regarded as one underlying population.","feed_headline":"No velocity gap between GRB and ordinary broad-line supernovae","feed_subtitle":"Largest spectral comparison to date finds both classes decelerate identically, so optical speed cannot flag a hidden GRB jet.","key_machinery":"Three pieces of machinery carry the argument. Velocities are measured from the wavelength of minimum flux in the blended Fe II (5169 Å) and Si II (6355 Å) absorption features, located by a cubic spline fit to Savitzky-Golay smoothed spectra, with uncertainties propagated through one thousand Monte-Carlo noise realisations per spectrum. The velocity evolution is then parameterised as a single power law \\$v = a\\,t^{b}\\$ or as a smoothly broken power law with break time \\$t_b\\$, slopes \\$\\alpha_1\\$ and \\$\\alpha_2\\$, and a smoothness parameter \\$s\\$, with MCMC marginalisation of the parameters and an F-test that requires three-$\\sigma$ improvement before a broken law is accepted. Population comparisons are deliberately restricted to the Gold subsample, whose explosion times are known to within three days, so that the fitted slopes and epoch velocities are not corrupted by \\$t_0\\$ uncertainty; the two populations are then compared with two-sample Kolmogorov-Smirnov tests.","core_discovery":"The paper's central claim is that the presence of a GRB jet leaves no imprint on the photospheric expansion of a type Ic-BL supernova. For the Fe II feature, the median gold-sample decay index is \\$-0.27^{+0.04}_{-0.27}\\$ for GRB-supernovae and \\$-0.30^{+0.09}_{-0.25}\\$ for ordinary type Ic-BL supernovae; for Si II the medians are \\$-0.4^{+0.2}_{-0.3}\\$ and \\$-0.6^{+0.3}_{-0.2}\\$. At fifteen days the median Fe II velocity is \\$\\sim 21\\,000\\$ km s\\${}^{-1}\\$ in both populations, and two-sample Kolmogorov-Smirnov tests cannot reject a common parent distribution for the decay indices (Fe II p=0.85, Si II p=0.39) or for the day-15 velocities (Fe II p=0.89, Si II p=0.46). The authors also find that broken power-law evolution is common for Si II and always shallow-steep, while Fe II breaks are mostly steep-shallow, and that the engine-driven supernovae SN2016coi and PTF12gzk follow the same Si II velocity pattern as GRB060218-SN2006aj with a break near eighteen days — a possible sign of a two-component ejecta structure such as a jet or cocoon in some ordinary events. They conclude that neither the velocities nor their evolution can distinguish the classes, and that GRB-supernovae and ordinary type Ic-BL supernovae are likely drawn from the same underlying population of events.","pith_inferences":["If the brightness-limited surveys that found most of the ordinary events preferentially picked up nickel-rich, pole-on explosions, the reported velocity overlap could be a selection effect: a genuinely jet-free subset might still expand more slowly, and the common-population conclusion would then be overstated.","A clean test would split ordinary type Ic-BL supernovae by late-time radio detection: if radio-bright events (hidden jets) show systematically higher velocities than radio-quiet events, the two underlying populations are not actually the same.","The growing Fe II minus Si II velocity difference after roughly day 20 hints that the Fe II 5169 Å minimum is not a clean photospheric tracer once line de-blending sets in, which would add a systematic uncertainty to any cross-class comparison built on this line."],"forward_implications":["Expansion velocity is unusable as a jet discriminator: neither the Fe II nor the Si II velocity at fifteen days separates GRB-supernovae from ordinary type Ic-BL supernovae, so optical spectroscopy alone cannot reveal a hidden jet.","Because the Fe II and Si II decay indices overlap across type Ic, type Ic-BL, and GRB-supernovae, the deceleration rate of the ejecta appears intrinsic to stripped-envelope explosions rather than a signature of jet energy injection.","Broken power-law decline appears in both classes at similar rates, and the resemblance of SN2016coi and PTF12gzk to GRB060218-SN2006aj suggests that some ordinary type Ic-BL supernovae do harbour a second ejecta component, plausibly a jet or a cocoon.","Discriminating jet-bearing from jet-free events will have to rely on late-time radio and X-ray observations rather than on optical velocities, as the paper explicitly concludes."],"supporting_citations":[{"why":"Supplies the earlier, smaller velocity sample (11 GRB-SNe and 10 type Ic-BL SNe) and the reported ~6000 km/s GRB-SN velocity excess that this study re-tests and does not reproduce.","marker":"Modjaz et al. (2016)"},{"why":"Provides the theoretical expectation that jet energy deposition has little effect on supernova spectra and velocities, which the null result aligns with.","marker":"Barnes et al. (2018)"},{"why":"Establishes the smoothing-window and spline-knot-density uncertainty analysis that the velocity measurement pipeline relies on.","marker":"Finneran & Martin-Carrillo (2024)"},{"why":"Origin of the minimum-flux spline fitting method for measuring absorption-feature velocities, adapted here to Fe II and Si II.","marker":"Silverman et al. (2012)"},{"why":"Main spectral archive supplying the type Ic and type Ic-BL spectra and metadata used to build the sample.","marker":"Yaron & Gal-Yam (2012)"},{"why":"Supplies the GRB-supernova list, trigger times, and spectra through the GRBSN webtool.","marker":"Finneran et al. (2025)"},{"why":"Provides comparison properties of ordinary type Ic-BL supernovae (nickel mass, ejecta mass, velocities) and many of the spectra used here.","marker":"Taddia et al. (2019)"},{"why":"Independent velocity measurements of SN1997ef and GRB980425-SN1998bw used to validate the authors' Si II velocities.","marker":"Patat et al. (2001)"}],"fun_headline_variants":["GRB and ordinary supernovae show identical velocity evolution","No velocity difference between GRB and non-GRB supernovae","Optical speeds can't tell GRB from ordinary supernovae","Supernova velocities fail to reveal hidden GRB jets","Broad-line supernovae: GRB or not, same expansion"],"cache_read_input_tokens":72320,"weakest_assumption_plain":"The central result rests on the assumption that the ordinary type Ic-BL supernovae in the sample stand in for genuinely jet-free explosions, even though they were collected by brightness-limited surveys that may favour bright, nickel-rich events seen along the jet direction; if that selection bias is strong, the measured overlap with GRB-supernovae could be an artefact of how the sample was gathered rather than a sign that the two classes are the same.","fun_headline_variants_meta":{"raw":{"variants":["GRB and ordinary supernovae show identical velocity evolution","No velocity difference between GRB and non-GRB supernovae","Optical speeds can't tell GRB from ordinary supernovae","Supernova velocities fail to reveal hidden GRB jets","Broad-line supernovae: GRB or not, same expansion"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000252,"raw_usage":{"total_tokens":1750,"prompt_tokens":1323,"completion_tokens":427,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":939,"completion_tokens_details":{"reasoning_tokens":341}},"tokens_in":939,"tokens_out":427,"duration_ms":4639,"temperature":1.0,"reasoning_tokens":341,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-12T18:27:52.175771+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Build a brightness-unbiased, volume-limited sample of nearby type Ic-BL supernovae with densely sampled pre-peak light curves and late-time radio follow-up, and compare the fifteen-day Fe II velocities of the radio-quiet subclass with those of GRB-supernovae: a statistically significant velocity deficit for the radio-quiet events would overturn the common-population conclusion, whereas continued overlap would confirm it.","supporting_citations":[{"cited_title":"Q., Bianco , F","cited_arxiv_id":null,"evidence_quote":"Supplies the earlier, smaller velocity sample (11 GRB-SNe and 10 type Ic-BL SNe) and the reported ~6000 km/s GRB-SN velocity excess that this study re-tests and does not reproduce."},{"cited_title":"2019, , 621, A71","cited_arxiv_id":null,"evidence_quote":"Provides comparison properties of ordinary type Ic-BL supernovae (nickel mass, ejecta mass, velocities) and many of the spectra used here."},{"cited_title":"2001, , 555, 900","cited_arxiv_id":null,"evidence_quote":"Independent velocity measurements of SN1997ef and GRB980425-SN1998bw used to validate the authors' Si II velocities."}],"review_version":1}