{"id":"05de2f3d-a107-4426-a881-edb0ef636feb","arxiv_id":"2412.13166","paper_version":1,"verdict":"CONDITIONAL","confidence":"HIGH","novelty_score":5.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":2,"one_line_summary":"Using archival HST images, the authors identify a moderately reddened red supergiant at the position of SN 2024abfl and infer a 10 to 16 solar mass progenitor.","lead":"Archival Hubble images show a faint red star at the position of supernova 2024abfl before it exploded. The authors argue this star is a red supergiant of 10 to 16 solar masses, adding a new data point for how massive stars end their lives.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The RSG conclusion hinges on an assumed A_F814W≈0.8 from CMD placement; with the NaID-based A_F814W≈0.1, the source is too red for an RSG and the SAGB/ECSN alternative becomes viable, so the 10–16 M⊙ RSG claim is not yet secure.","rationale":"The central premise is that an archival HST source at the SN position is the progenitor and that its colors match a moderately reddened RSG. For the 10–16 M⊙ RSG claim to be secure, the host extinction toward the source must indeed be near A_F814W≈0.8, and no lower-mass evolved star must be able to reproduce the broadband fluxes. The weakest point is the extinction: the CMD-shift method is a classification-by-assumption, because the shift is computed to move the object onto the RSG sequence, while the only spectroscopically grounded estimator (NaID EW) points to a much smaller value. This is not a 1σ parameter error; if A_F814W≈0.1, the source is too red to be an RSG, and the SAGB/ECSN interpretation, which the authors themselves acknowledge in Section 4.3, becomes viable. That would change the central claim from a 10–16 M⊙ RSG to a candidate SAGB/ECSN, a different and arguably more interesting result. The distance uncertainty shifts the luminosity but leaves both classifications possible; post-explosion disappearance would confirm association but not by itself decide RSG versus SAGB. The paper is genuinely careful in Section 5 ('candidate') and in Section 4.3, so the abstract states the conclusion more firmly than the body supports. I agree with the reader's weakest_assumption and with the CONDITIONAL verdict; my analysis does not move that verdict, so I set verdict_should_be to UNCHANGED.","tokens_in":9565,"tokens_out":5816,"duration_ms":55511,"concrete_test":"Fit the source's F814W/F606W photometry and the F225W/F275W upper limits with tabulated model atmospheres for both reddened RSGs and SAGB/ECSN candidates, fixing A_F814W to the NaID-based value (≈0.1) and to the plausible range from the EW scatter. If an SAGB model with log L≈4.3–4.6 and T_eff≈3000–3500 K fits within the photometric errors and predicts F225W/F275W below the observed limits, then the RSG conclusion is not unique and the abstract should be softened; if no such model fits, the extinction-based RSG identification stands. A complementary empirical check is to compare the source's F606W−F814W color under A_F814W≈0.1 with colors of spectroscopically confirmed SAGB/ECSN candidates in nearby galaxies.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The decisive link in the chain is the host-galaxy extinction adopted to place the source on the RSG branch (Section 4.1, Fig. 4). The source is measured at F814W≈25.2 and F606W≈27.2, giving F606W−F814W≈1.9. The RSG interpretation is obtained by shifting the source back along the extinction vector by A_F814W≈0.8 (E(F606W−F814W)≈0.4), an amount derived from the assumption that the object is an RSG on the host CMD's RSG branch. The only independent extinction estimate, from the host NaID doublet EW=0.58 Å, gives A_F814W≈0.1 via Poznanski et al. (2012), and the paper sets it aside 'due to scatter.' If the NaID estimate is closer to the truth, the dereddened color remains ≈1.8, far too red for a normal RSG; Section 4.3 explicitly concedes that in that case a luminous SAGB/ECSN progenitor fits. That alternative is not a minor perturbation: it removes the 10–16 M⊙ RSG conclusion and instead points toward the lower-mass SAGB/ECSN channel, the same debate as for the adjacent SN 2018zd. The paper's own Section 5 calls the source 'a candidate for progenitor of SN 2024abfl,' while the abstract asserts a definite RSG conclusion. Distance uncertainty (12.6–21.7 Mpc) enlarges the luminosity range but is not the central issue; the extinction degeneracy changes the object's classification, not just the mass estimate.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper analyzes archival HST imaging of the site of Type II SN 2024abfl in NGC 2146, detecting a red point source at the SN position in four F814W epochs and two shorter-wavelength epochs. The authors find that the source's brightness and color are consistent with a moderately reddened red supergiant and, using MESA tracks and a distance of 12.6-21.7 Mpc, estimate an initial mass of 10-16 M_sun. They also discuss alternative interpretations, including a luminous SAGB/ECSN progenitor, binary companions, and chance alignment, and use the non-detection of infrared emission to argue for interstellar rather than circumstellar reddening.","tokens_in":9944,"tokens_out":4429,"duration_ms":39311,"significance":"If the RSG interpretation holds, this is a valuable addition to the small sample of directly detected Type II SN progenitors, particularly in a galaxy that also hosted SN 2018zd, allowing a controlled comparison of the RSG and SAGB/ECSN channels. The study makes good use of multi-epoch archival data, and the source's photometric stability over 19 years is clearly documented. The central claim is, however, currently limited by the degeneracy between the assumed host-galaxy extinction and the stellar classification: the RSG solution is obtained by forcing the source onto the RSG branch, and the paper itself concedes that the alternative SAGB interpretation remains viable with the independent NaID-based extinction. With the present data the conclusion is a candidate rather than a secure identification.","major_comments":[{"comment":"The host-galaxy extinction A_F814W ≈ 0.8 is derived by moving the source along the extinction vector until it lands on the RSG branch of the CMD. This procedure presupposes that the source is an RSG, so it cannot independently support the RSG classification. The independent NaID-based estimate (A_F814W ≈ 0.1) is set aside with only a reference to scatter; the paper should either provide a quantitative justification for preferring the CMD-based value or fold both estimates into the analysis.","section":"Section 4.1, Fig. 4"},{"comment":"The paper explicitly concedes that if the NaID-based extinction is adopted, the source color is too red for a normal RSG and a luminous SAGB/ECSN progenitor becomes viable. This is not a minor perturbation: it removes the 10-16 M_sun RSG conclusion and instead points to the lower-mass SAGB/ECSN channel, the same debate as for SN 2018zd. The manuscript should treat this as a live alternative, not a footnote, and state what observations would distinguish the two cases.","section":"Section 4.3"},{"comment":"The abstract states unequivocally that 'the SN 2024abfl had an RSG progenitor with initial mass of 10M⊙-16M⊙', while the Conclusions (Section 5) identify the source as 'a candidate for progenitor' and acknowledge the SAGB possibility. The abstract overstates the certainty of the result and should be brought into line with the body of the paper.","section":"Abstract vs. Section 5"}],"minor_comments":[{"comment":"The header 'photomtry' should be 'photometry'.","section":"Table 1"},{"comment":"The phrase 'Its out of scope of this study' should be 'It is out of the scope of this study'.","section":"Section 3.3"},{"comment":"The sentence 'the F814W brightness of the progenitor translate to' should be 'translates to'.","section":"Section 4.1"},{"comment":"The word 'envelop' should be 'envelope' in both occurrences.","section":"Sections 4.1 and 4.2"},{"comment":"The distance notation '15.6+6.1−3.0 Mpc or D = 12.6−21.7 Mpc' is confusing; please clarify that the range is the full uncertainty interval.","section":"Section 3.3"}],"recommendation":"major_revision","confidential_remarks":"The paper is appropriate for the journal's scope, but the central claim is currently overclaimed in the abstract relative to the body's own caveats. The extinction degeneracy is the key issue; if the authors cannot resolve it with existing data, they should reframe the conclusions as a candidate identification with two viable progenitor scenarios. The multi-epoch HST photometry is a solid contribution and should be preserved."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Dear colleague,\n\nThe paper is a straightforward progenitor search for SN 2024abfl using archival HST images, and the photometry is the best part. Four F814W epochs from 2004 to 2023 plus a couple of marginal F606W/F555W detections give a stable source at the SN position, with clean cutouts and reasonable aperture/background choices. The authors are honest that the body says 'candidate' while the abstract claims a definite RSG progenitor at 10–16 Msun. That gap is the paper's real weakness.\n\nThe RSG interpretation rests on an extinction of A_F814W ~0.8 mag, derived by shifting the source onto the RSG branch of the host CMD. That is a mild circularity—you assume the source is an RSG to get the reddening, then use the reddening to confirm the RSG. The only independent estimate, from the host NaID doublet, gives A_F814W ~0.1. The paper sets it aside because of scatter in the NaID-extinction relation, but if the lower value is closer to the truth the dereddened color is F606W–F814W ~1.8, far too red for a normal RSG. Section 4.3 acknowledges this and says a luminous SAGB/ECSN progenitor would then fit. That is not a trivial alternative; it changes the interpretation from an ordinary 10–16 Msun RSG to a lower-mass electron-capture candidate, the same debate as for SN 2018zd six arcsec away. The distance uncertainty (12.6–21.7 Mpc) only widens the luminosity range; the extinction degeneracy changes the object's classification.\n\nI also note the SN itself is underluminous—never reaching mag 16.5 and showing no clear peak—which the authors flag as possibly peculiar. That makes the SAGB/ECSN scenario worth taking seriously.\n\nWhat the paper does well: the multi-epoch photometry is careful, the source is real and stable, the MESA comparison is explicit, and the caveats are openly discussed. The errors are not hidden. But the abstract overstates what the evidence supports. The conclusion should be that the source is a candidate progenitor, consistent with either a reddened RSG or a luminous SAGB/ECSN progenitor, pending post-explosion disappearance or SN spectral evolution.\n\nI'd send this to a serious referee—the method is established but the specific data point is new and adds to the RSG census and the RSG problem statistics. It needs revision to temper the abstract and to present the extinction ambiguity as a genuine fork, not a nuisance parameter. I would cite the photometry and the candidate source, but not the 10–16 Msun RSG mass as settled. Worth a reading group discussion on how progenitor identifications can hinge on extinction assumptions.\n\nBest,\n[Your name]","headline":"A careful progenitor candidate for SN 2024abfl with solid multi-epoch photometry, but the RSG mass claim hinges on an assumed extinction that the paper's own NaID data contradict; the abstract oversells the conclusion.","tokens_in":10548,"tokens_out":2495,"would_cite":true,"duration_ms":23444,"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":"This paper identifies a red supergiant of about 10 to 16 solar masses as the progenitor of the Type II supernova 2024abfl, based on its pre-explosion appearance in archival Hubble Space Telescope images.","keywords":["core-collapse supernovae","red supergiant progenitors","Type II supernovae","HST archival photometry","stellar evolution tracks","NGC 2146","interstellar extinction","electron-capture supernova candidates"],"falsifier":"After SN 2024abfl fades, a deep HST or JWST image should show that the point source at the explosion site has vanished; if a similarly bright red source remains, the identification as the single progenitor star fails. An improved distance to NGC 2146 could also falsify the mass estimate if it pushes the luminosity outside the 10 to 16 solar mass track range.","tokens_in":9361,"feed_emoji":"💥","tokens_out":4508,"duration_ms":38843,"temperature":0.7,"pith_summary":"This paper identifies the likely progenitor star of SN 2024abfl, a Type II supernova in the galaxy NGC 2146, using archival Hubble Space Telescope images taken between 2004 and 2024. The star appears at the supernova's position, is consistently bright in the red F814W filter near magnitude 25, and is barely detected in shorter-wavelength filters. Placing it on the host galaxy's color-magnitude diagram, the authors argue that its color and brightness match a red supergiant moderately extinguished by dust, with a bolometric luminosity corresponding to an initial mass of about 10 to 16 solar masses. If correct, this adds another direct link between a specific massive star and a core-collapse supernova, at the lower end of the red-supergiant mass range.","feed_headline":"SN 2024abfl's star was a 10–16 solar mass red supergiant","feed_subtitle":"Pre-explosion Hubble images tie the Type II blast to a moderately reddened RSG in NGC 2146.","key_machinery":"The central object is the pre-explosion point source at the supernova location, detected in archival HST data. The argument is carried by comparing its F814W and F606W photometry against a color-magnitude diagram of NGC 2146 built from the same HST frames, using the RSG branch as a reference locus. Extinction is estimated by shifting the source onto this branch, a bolometric correction from Beasor et al. (2024) converts F814W brightness to luminosity, and MESA stellar evolution tracks of 10 to 25 solar mass stars define the expected luminosities at core carbon exhaustion.","core_discovery":"The paper claims that the source at the site of SN 2024abfl is a red supergiant (RSG) progenitor with an initial mass of 10 to 16 solar masses. This is based on four F814W detections at magnitude ~25 together with marginal F606W and F555W detections, which put the source slightly redward and below the RSG branch of NGC 2146's color-magnitude diagram. After applying a total extinction of A_F814W ~ 0.8 mag and a bolometric correction of BC = 0.0, the derived luminosity matches MESA evolution tracks of 10 to 16 solar mass stars at the time of core carbon exhaustion, for the adopted host distance of 12.6 to 21.7 Mpc. The abstract states this as a conclusion, while the body text more cautiously calls the source a candidate for the progenitor of SN 2024abfl.","pith_inferences":["Because the host distance uncertainty (12.6 to 21.7 Mpc) dominates the luminosity error, a precise Cepheid or TRGB distance to NGC 2146 would directly tighten the initial-mass estimate; the paper leaves this as future work.","The alternative low-extinction scenario, in which the source is a luminous super-AGB star that exploded as an electron-capture supernova, would become testable if SN 2024abfl develops electron-capture features in its nebular spectrum; the paper raises this possibility but does not adopt it.","If a binary companion contributed to the pre-explosion flux, the stated initial mass would be an upper limit on the exploding star's mass; only post-explosion deep imaging of the site can settle whether a companion survives.","The paper notes the supernova's unusually low peak brightness; if that persists, SN 2024abfl could be a peculiar object whose connection to a standard RSG progenitor is less straightforward than the photometric match alone suggests."],"forward_implications":["Adds SN 2024abfl to the small sample of Type II supernovae with identified red supergiant progenitors, at the low-mass end of the range.","Supports the standard picture that ordinary Type II supernovae arise from red supergiants, and provides a contrast to the nearby SN 2018zd, an electron-capture supernova candidate in the same host galaxy.","The roughly 25 percent F814W brightening between 2019 and 2023, if real, is a pre-explosion variability signal that could be sought in other RSG progenitors.","If the RSG interpretation holds, the required reddening implies substantial dust along the line of sight in the spiral arm, which could be probed with resolved extinction maps."],"supporting_citations":[{"why":"Provides the adopted host galaxy distance of 15.6+6.1-3.0 Mpc, which the luminosity estimate scales with.","marker":"Callis et al. 2021"},{"why":"Documents SN 2018zd, the nearby electron-capture supernova candidate in the same galaxy, establishing the comparative context for a low-mass SAGB alternative.","marker":"Hiramatsu et al. 2021"},{"why":"Supplies the bolometric correction BC = 0.0 used to convert the F814W magnitude to bolometric luminosity for a red supergiant near core collapse.","marker":"Beasor et al. 2024"},{"why":"Calibration of NaID equivalent width to extinction, used to estimate host reddening and to argue that the extinction is moderate.","marker":"Poznanski et al. 2012"},{"why":"The MESA stellar evolution code used to generate the 10 to 25 solar mass tracks against which the progenitor luminosity is compared.","marker":"Paxton et al. 2011, 2013, 2018"},{"why":"Defines the Red Supergiant Problem and the context for why a 10 to 16 solar mass RSG progenitor is a meaningful addition to the census.","marker":"Smartt 2015"}],"fun_headline_variants":["SN 2024abfl's pre-blast source is a 10-16 solar mass red supergiant","Hubble images tie SN 2024abfl to a red supergiant in NGC 2146","Type II SN 2024abfl traced to a 10-16 Msun red supergiant","RSG progenitor of SN 2024abfl weighs in at 10-16 solar masses"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The source is reddened by about 0.8 magnitudes of dust, a value chosen by moving its color onto the red supergiant branch; if the true extinction is much lower, the source's color no longer fits a red supergiant and a luminous super-AGB star becomes viable.","fun_headline_variants_meta":{"raw":{"variants":["SN 2024abfl's pre-blast source is a 10-16 solar mass red supergiant","Hubble images tie SN 2024abfl to a red supergiant in NGC 2146","Type II SN 2024abfl traced to a 10-16 Msun red supergiant","RSG progenitor of SN 2024abfl weighs in at 10-16 solar masses"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000522,"raw_usage":{"total_tokens":2528,"prompt_tokens":951,"completion_tokens":1577,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":567,"completion_tokens_details":{"reasoning_tokens":1471}},"tokens_in":567,"tokens_out":1577,"duration_ms":12811,"temperature":1.0,"reasoning_tokens":1471,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-11T13:21:31.654794+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"After SN 2024abfl fades, a deep HST or JWST image should show that the point source at the explosion site has vanished; if a similarly bright red source remains, the identification as the single progenitor star fails. An improved distance to NGC 2146 could also falsify the mass estimate if it pushes the luminosity outside the 10 to 16 solar mass track range.","supporting_citations":[],"review_version":1}