{"id":"e5aacb4b-1e82-445e-8fd6-674b75b09a99","arxiv_id":"2507.19625","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":2,"one_line_summary":"ASKAP EMU/POSSUM data yield 6 newly confirmed supernova remnants, 37 new candidates, and updated classifications for 46 previously identified radio candidates in a quarter of the Galactic plane.","lead":"Using new ASKAP radio survey data, this paper compiles a catalogue of supernova remnants and candidate remnants in a quarter of the Milky Way's plane, adding 43 new candidate objects and confirming 14 sources as remnants. The catalogue helps close the gap between the roughly 300 known Galactic supernova remnants and the roughly 1000 that models predict should exist.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"One of the six 'new SNRs' is internally inconsistent: G283.1−0.6 is confirmed only by a two-frequency spectral index that §4.1.1 discredits, and the text itself says the host SNR is uncertain.","rationale":"The paper's most load-bearing assertion is the abstract's 'six new SNRs and 37 new SNR candidates' and the conclusion's 'confirmation of 14 sources as SNRs.' The strongest and most concrete threat to that assertion is internal: G283.1−0.6 is classified as a new SNR despite the paper's own Section 4.1.1 rule that two-frequency spectral indices are not sufficient for confirmation, and despite the text explicitly saying the host SNR is uncertain and that the tabulated flux is for the PWN only. This is not a matter of outside consensus or modeling ambiguity; it is a direct contradiction between the classification scheme and one of the enumerated results. If this one entry is invalid, the 'six new SNRs' count becomes five, and the downstream density estimate in Section 5.2 shifts accordingly. The reader's weakest_assumption focused on the polarization criterion, which is a legitimate and broader concern: five of the six new SNRs rest on the assumption that speckled, >1% peak polarized structures are intrinsic nonthermal emission rather than instrumental leakage or foreground Faraday rotation. That concern is not internally checkable and would require an external null test, so I judge the G283.1−0.6 inconsistency to be the more load-bearing issue. Overall, the catalogue remains valuable and the paper is worth accepting conditionally, but the authors should correct the G283.1−0.6 classification and any count derived from it, and ideally add an explicit audit table showing which of the 14 confirmations use polarization, three-frequency indices, or two-frequency indices.","tokens_in":49194,"tokens_out":5470,"duration_ms":55235,"concrete_test":"Re-run the classification audit by applying Section 3.3 criteria with the Section 4.1.1 restriction that spectral-index confirmations require at least three independent frequencies. For each of the 14 newly confirmed SNRs, tabulate the confirmation method and the number of distinct frequencies used; G283.1−0.6 should be flagged because it has no polarization and only two frequencies. Recompute the six-new-SNR count and the Section 5.2 SNR/kpc² density after reclassifying any flagged sources to strong candidate.","verdict_should_be":"CONDITIONAL","load_bearing_attack":"The central claim of six new SNRs is internally inconsistent. In Section 4.1.1, the authors state that they 'only argue for the confirmation of a source as an SNR based on a steep negative spectral index if we can calculate flux densities for at least three distinct frequencies,' because two-frequency ASKAP+MeerKAT indices are systematically too steep (Table 3). Yet Table 7 lists G283.1−0.6 as a 'New SNR' with Pol = N and a spectral index of −0.55 ± 0.13 derived from only 943 MHz (ASKAP) and 1360 MHz (SMGPS) data. The accompanying Section 4.3.1 text says 'the host SNR is uncertain,' that the tabulated flux is 'for the PWN only,' and that the two-frequency index is expected to be steeper than the true value. Thus at least one of the six listed new SNRs fails the paper's own confirmation criterion. The headline count, the 14 newly confirmed SNRs claim, and the population statistics built on these counts (e.g., the 0.85 SNRs/kpc² density in Section 5.2) are inflated unless G283.1−0.6 is reclassified as a candidate.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper presents a catalogue of Galactic supernova remnants (SNRs) and SNR candidates from the EMU and POSSUM ASKAP surveys, covering a contiguous region of 277.5° ≤ l ≤ 311.7°, |b| ≤ 5.4°, plus an additional field near l ≈ 315.5°–323.0°. It catalogues 44 known SNRs and 46 previously identified radio SNR candidates, confirms eight of those candidates as SNRs, identifies possible radio counterparts for four X-ray and three optical candidates, and claims six newly discovered SNRs and 37 new SNR candidates (43 new sources total). The classification uses ASKAP 943 MHz total-power and polarization images, WISE mid-infrared data, and ancillary radio surveys (SMGPS, SUMSS, GLEAM), with spectral indices and polarization as confirmation tools. The paper also contains completeness statistics (e.g., 0.85 SNRs/kpc² after adding newly confirmed SNRs) and argues that EMU/POSSUM will likely uncover many more remnants, especially at high latitudes.","tokens_in":49445,"tokens_out":9653,"duration_ms":94152,"significance":"If the confirmations hold, this is a valuable contribution: it demonstrates ASKAP's ability to find low-surface-brightness and high-latitude SNRs, validates polarization as a practical confirmation route, and provides a uniformly processed catalogue based on public survey data. The paper is careful in several respects: it explicitly warns that two-frequency ASKAP+MeerKAT spectral indices are systematically too steep (§4.1.1), it states the limitation of MIR-based rejection in dense H II regions (§3.1), and it provides images, flux measurements, and polarization maps for the key sources. The main claims are falsifiable and tied to specific tables and figures. However, the internal inconsistency in the classification of one of the six 'new SNRs' directly affects the headline counts and the population statistics built on them.","major_comments":[{"comment":"The classification of G283.1−0.6 as a 'New SNR' violates the paper's own confirmation criterion. Section 4.1.1 states that two-frequency ASKAP+MeerKAT spectral indices are systematically too steep and that confirmation on the basis of a steep negative spectral index requires flux densities at at least three distinct frequencies. Table 7 lists G283.1−0.6 as a new SNR with Pol = N and a spectral index of −0.55 ± 0.13 derived from only 943 MHz (EMU) and 1360 MHz (SMGPS) data. Section 4.3.1 adds that 'the host SNR is uncertain', that the tabulated flux is 'for the PWN only', and that the two-frequency index is expected to be steeper than the true value. This source therefore meets neither the morphological nor the spectral-index leg of the 'New SNR' definition in §3.3. Please reclassify G283.1−0.6 as a strong candidate and consistently revise all dependent counts: the abstract's 'six new SNRs' and '14 ... confirmed SNRs', the §4.3 statement of '14 newly confirmed SNRs', the §5.2 density estimate (0.85 SNRs/kpc² becomes ~0.84), and the extrapolations in §6.","section":"§4.1.1, Table 7, §4.3.1"},{"comment":"The confirmation of 11 of the 14 sources relies on the polarization criterion of Section 3.1.3: speckled polarized structure with peak percentage polarization >1% is taken as intrinsic nonthermal emission because, the text states, 'This effect cannot be produced instrumentally.' This is a strong, load-bearing claim. The paper does not provide a quantitative validation, for example a demonstration that this criterion does not flag known H II regions or imaging artifacts in the same fields, or a comparison of the RM structure with the known instrumental polarization pattern. Given that some sources show polarized emission with a morphology that differs from the Stokes I shell (e.g., G285.0−3.2), please provide such a check, or explicitly qualify the polarization-based confirmations as resting on a working assumption about instrumental leakage and foreground Faraday effects.","section":"§3.1.3"}],"minor_comments":[{"comment":"The sentence 'they split a couple of our candidates into two separate sources' is ambiguous; please clarify whether the SMGPS list splits sources that the authors treat as single.","section":"§4.2.1"},{"comment":"The section heading 'New SNRs' is confusing because the section also includes previously identified candidates (Table 4); consider renaming it 'Newly Confirmed SNRs'.","section":"§4.3.1"},{"comment":"The description of the Faraday de-rotation method for the PI maps refers only to Ball et al. (2023); a brief statement of the RM range and step size would aid reproducibility.","section":"§2.1"},{"comment":"The statement that the survey 'covers approximately 12% of the Galactic plane by surface area, or 55 kpc²' would benefit from a one-sentence explanation of the projection, since the longitude range alone is only 9.5% of a full circle.","section":"§5.2"},{"comment":"The reference 'Filipovic, M. D.' lacks the accent used elsewhere for the same author; please ensure the spelling is consistent.","section":"Reference list"}],"recommendation":"major_revision","confidential_remarks":"This is a data-rich catalogue paper with public survey data and generally careful presentation. The central issue is the G283.1−0.6 classification, which is internally inconsistent with the paper's own stated criterion on two-frequency spectral indices; this is local and fixable. The polarization criterion is a broader risk but addressable with additional checks. I recommend major revision rather than rejection because the underlying catalogue and imaging are valuable, and the load-bearing problem can be resolved within the manuscript's scope."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Your read is mostly right, and the stress-test note lands. The catalog is a solid piece of work, but the headline count of six new SNRs does not survive contact with the paper's own confirmation rules.\n\nWhat is new: 43 new candidates, updated sizes for four known SNRs, polarization detections for 22 known SNRs, and confirmation of eight previously proposed candidates. The polarization results are genuinely useful, and the paper is honest about the limits of the method. Section 4.1.1 is a real strength: the authors test their two-frequency spectral indices against known SNRs and H II regions, find them systematically too steep, and then mostly refuse to confirm candidates on two points alone. That is the right way to run a catalog.\n\nThe soft spot is exactly where the stress-test points. Table 7 lists G283.1−0.6 as a new SNR. The only quantitative evidence is a −0.55 ± 0.13 index from 943 and 1360 MHz, which Section 4.1.1 says is unreliable. The text itself says 'the host SNR is uncertain' and the tabulated flux is 'for the PWN only.' So by the paper's own standard, this source is a strong PWN candidate, not a confirmed SNR. The other five new SNRs have polarization, so they clear the bar. G283.1−0.6 does not. That means the abstract's 'six new SNRs' should be five, and the '14 newly confirmed' should be 13 unless the authors want to argue the bow-shock morphology plus pulsar association is enough—in which case they should say so explicitly and define the criterion. The population density in Section 5.2 shifts by a negligible amount, so this is not a fatal flaw; it is a counting error that should be fixed in revision.\n\nOther, smaller issues: the polarization peak percentages have no uncertainties, the MIR-absence criterion is acknowledged to be unreliable in dense regions, and the candidate selection is subjective with no quantified completeness. None of these undermines the catalog's value. The data are public, the comparisons to external catalogs are careful, and the caution about weak candidates is genuine.\n\nBottom line: this paper deserves review. It is a useful reference for the SNR and ISM community, and the methodological honesty is notable. The referee should ask for G283.1−0.6 to be reclassified or explicitly justified, and for the counts to be corrected accordingly.","headline":"A genuinely useful SNR catalog whose headline count of six new SNRs is one too many under its own rules.","tokens_in":50100,"tokens_out":3451,"would_cite":true,"duration_ms":36515,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":["98.38.Mz","95.85.Bh"],"model":"deepseek-v4-flash","headline":"This paper argues that ASKAP's EMU/POSSUM surveys confirm 14 supernova remnants — six never before proposed — and adds 37 new candidates across a quarter of the southern Galactic plane.","keywords":["supernova remnants","SNR candidates","radio continuum surveys","linear polarization","Faraday rotation","mid-infrared counterparts","Galactic plane"],"falsifier":"Take full-Stokes follow-up of the eleven remnants confirmed by polarization at a frequency near 5 GHz, where Faraday rotation is much weaker than at 943 MHz. Genuine nonthermal shells should retain their mottled, small-scale polarization structure (the rotation-measure pattern only rescales with $\\lambda^2$), whereas instrumental leakage would be smooth, locked to the total-power morphology, and would not track the frequency change; any source that loses its speckled signature fails the paper's own confirmation criterion, and the same data would supply the extra flux densities needed to check the faintest confirmed remnants for the expected $\\alpha \\approx -0.5$ spectra.","tokens_in":49007,"feed_emoji":"💥","tokens_out":15309,"duration_ms":161966,"temperature":0.7,"pith_summary":"Its load-bearing result is a census: in the surveyed strip of the southern Galactic plane the paper catalogues 44 known remnants and 46 previously proposed candidates, confirms eight of those candidates as genuine remnants, argues that 14 sources in total (six of them never proposed before) should now be confirmed, and adds six new remnants and 37 new candidates of its own. The wider claim is that the long-standing shortfall between the ~300–400 catalogued Galactic remnants and the 1000+ that models predict is largely a population of ordinary, faint shells missed by older surveys, many of them at high Galactic latitude where earlier plane-focused surveys did not look. If the confirmations hold, the remnant-plus-candidate density in this region lands near 2.0 per kpc², close to the density needed for the 1000-remnant lower estimate, and the full EMU/POSSUM plane survey would be expected to turn up over 400 candidates, about 200 of them new. The paper also shows that polarization, not spectral shape, is the practical confirmation tool for these faint sources: 11 of the 14 confirmations rest on it, and polarized structures are found more than twice as often outside the dense plane as inside it.","feed_headline":"ASKAP surveys confirm 14 supernova remnants, add 37 candidates","feed_subtitle":"Faint, high-latitude radio shells missed by older surveys are showing up in polarized light.","key_machinery":"The central tool is the radio–mid-infrared discriminant paired with Faraday-corrected polarization imaging. Because H II regions glow brightly at 12 and 22 µm in WISE while supernova remnants are usually invisible there, a shell-like radio structure lacking a mid-infrared counterpart is selected as a candidate, and evidence of genuine nonthermal emission is then sought in the polarized-intensity maps, produced by de-rotating Stokes Q and U across the 1 MHz channels for each rotation measure and taking the peak of the Faraday depth function. Real synchrotron polarization shows up as a 'speckled' pattern whose rotation measure changes on small scales — a signature the paper argues cannot be fabricated instrumentally — and the requirement of peak percentage polarization above 1% separates it from the roughly 0.2% instrumental leakage floor. Where a source is bright enough, spectral indices from flux densities at 943 MHz (ASKAP), 1360 MHz (MeerKAT), 843 MHz (SUMSS) and 198 MHz (GLEAM) provide a second confirmation route, though the paper shows that two-frequency indices built only from ASKAP and MeerKAT come out systematically too steep and are treated as unreliable.","core_discovery":"The paper claims that combining ASKAP's 943 MHz total-power images with polarization maps built by de-rotating the Stokes Q and U cubes and taking the peak of the Faraday depth function can find and confirm the low-surface-brightness remnants that earlier radio surveys missed. Candidates are first picked out as shell-like radio structures without 12 or 22 µm mid-infrared counterparts, which separates them from H II regions; confirmation then requires either linear polarization with a mottled, small-scale structure and peak percentage polarization above 1%, or a steep negative spectral index near $\\alpha \\approx -0.5$ determined from at least three frequencies. On that basis the authors confirm eight of the 46 previously known radio candidates, present six new remnants and 37 new candidates, and conclude that 14 sources, six of them previously unknown, should now be counted as supernova remnants; they also enlarge four known remnants whose true shells exceed their catalogue sizes, link four X-ray and three optical candidates to radio counterparts, and extrapolate over 400 candidates for the completed survey.","pith_inferences":["If the speckled-polarization test is as reliable as the paper claims, the same test at higher observing frequencies, where Faraday rotation is far weaker, should promote many of the 57 weak candidates to confirmed remnants — a prediction that follows from the paper's logic but is not stated in it.","The systematically too-steep two-frequency spectral indices hint that published spectral-index confirmations of other faint remnants, and some catalogue values, may carry the same missing-flux bias; re-deriving those indices with a third frequency would be a cheap audit of the existing SNR catalogue, which the paper does not propose.","Because the new candidates share the negative-latitude skew of H II regions and track the warp of the outer disk, several 'high-latitude' sources may actually lie inside the warped plane; HI absorption or parallax distances for sources like G289.6+5.8 and G321.3−3.9 would test this directly and would change how the population is compared with Galactic models.","The paper's expectation that some sources are 'radio observable but not radio confirmable' implies the census gap may never close with radio alone; the natural check is whether the unconfirmable weak candidates collectively show a nonthermal component in X-ray or γ-ray surveys, which would decide whether faint shells are being missed or misclassified."],"forward_implications":["If the 14 confirmations hold, the count of securely known remnants in the surveyed strip rises from 44 to 58, and the combined remnant-plus-candidate surface density reaches about 2.0 per kpc², close to the 2.2 per kpc² needed, at the paper's geometry, to reach the 1000-Galactic-remnant lower estimate.","Extrapolating the discovery rate over the full EMU/POSSUM Galactic plane footprint, about five times this area, predicts over 400 SNR candidates, roughly 200 of them new, which the paper says would nearly close the census gap if confirmed.","Polarization, not spectral shape, will be the workhorse for confirming faint candidates: two-frequency spectral indices computed from ASKAP and MeerKAT fluxes come out systematically too steep, so the paper only trusts indices built from three or more frequencies.","Multi-wavelength follow-up now has concrete targets: four X-ray-detected candidates and three optical candidates gain possible radio counterparts, including a radio tail that links the X-ray pulsar wind nebula G284.0−1.8 to its likely host remnant.","Four long-known remnants are bigger than catalogued — G278.9+1.3 spans over 3°, G286.1−1.1 gains a western shell, G291.0+0.1 merges two catalogue entries, and G308.5−1.4 gains a filament — so population statistics built on the old sizes undercount the largest remnants."],"supporting_citations":[{"why":"Supplies the master catalogue of 44 known SNRs with their 1 GHz flux densities, sizes, and spectral indices; every confirmation and update is measured against it.","marker":"Green 2024b"},{"why":"The WISE H II region catalogue that sets the mid-infrared counter-check used to rule out thermal sources.","marker":"Anderson et al. 2014"},{"why":"The SMGPS candidate list that contributes 30 of the previously proposed candidates re-examined and partly confirmed here.","marker":"Anderson et al. 2024"},{"why":"The pilot-field catalogue whose polarized-intensity mapping and polygon flux-integration methods are extended to the full survey.","marker":"Ball et al. 2023"},{"why":"The MeerKAT Galactic plane survey supplying 1360 MHz flux densities for the spectral-index calculations.","marker":"Goedhart et al. 2024"},{"why":"Defines the EMU 943 MHz Stokes I images, resolution, and noise that all detections are drawn from.","marker":"Hopkins et al. 2025"},{"why":"Defines the POSSUM polarization data and the ~0.2% instrumental polarization floor that the >1% polarization criterion must beat.","marker":"Gaensler et al. 2025"},{"why":"The X-ray SNR catalogue from which four candidate counterparts are sought in the radio maps.","marker":"Ferrand & Safi-Harb 2012"},{"why":"Earlier radio survey candidate list providing several candidates (e.g., G319.9−0.7, G320.6−0.9) confirmed here with new data.","marker":"Whiteoak & Green 1996"}],"fun_headline_variants":["ASKAP identifies 6 new supernova remnants and 37 candidates","Polarized radio waves uncover hidden supernova remnants","Askap survey nets 14 remnants, 37 new candidates","Six new supernova remnants plus 37 candidates from ASKAP","Radio survey adds 6 supernova remnants, 37 candidates"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The load-bearing premise is that a mottled, small-scale patch of polarized radio emission peaking above 1% of total power is intrinsic synchrotron radiation from the source rather than telescope leakage or foreground Faraday effects; if that identification fails for any individual source, the corresponding 'new supernova remnant' confirmation loses its quantitative support.","fun_headline_variants_meta":{"raw":{"variants":["ASKAP identifies 6 new supernova remnants and 37 candidates","Polarized radio waves uncover hidden supernova remnants","Askap survey nets 14 remnants, 37 new candidates","Six new supernova remnants plus 37 candidates from ASKAP","Radio survey adds 6 supernova remnants, 37 candidates"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000969,"raw_usage":{"total_tokens":4199,"prompt_tokens":1103,"completion_tokens":3096,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":719,"completion_tokens_details":{"reasoning_tokens":3010}},"tokens_in":719,"tokens_out":3096,"duration_ms":26305,"temperature":1.0,"reasoning_tokens":3010,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-06T14:13:12.596139+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Take full-Stokes follow-up of the eleven remnants confirmed by polarization at a frequency near 5 GHz, where Faraday rotation is much weaker than at 943 MHz. Genuine nonthermal shells should retain their mottled, small-scale polarization structure (the rotation-measure pattern only rescales with $\\lambda^2$), whereas instrumental leakage would be smooth, locked to the total-power morphology, and would not track the frequency change; any source that loses its speckled signature fails the paper's own confirmation criterion, and the same data would supply the extra flux densities needed to check the faintest confirmed remnants for the expected $\\alpha \\approx -0.5$ spectra.","supporting_citations":[],"review_version":1}