{"id":"fdc27209-29ec-4606-b255-674f964b838b","arxiv_id":"1908.05369","paper_version":1,"verdict":"CONDITIONAL","confidence":"HIGH","novelty_score":4.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":1,"one_line_summary":"VERITAS presents the Matched Runs Method, an archival-run background estimation technique for extended gamma-ray sources, with null-test validation on Segue 1 and Ursa Minor but no Geminga result yet.","lead":"VERITAS describes a new background estimation method, the Matched Runs Method, for very-high-energy gamma-ray sources too extended for standard analysis. The paper validates the method on two source-free dwarf galaxy fields, while the Geminga measurement that motivates it is still in progress.","discovery_kind":"new_method","skeptic_critique":{"model":"deepseek-v4-flash","headline":"MRM is validated only against source-free fields; no test shows it preserves a Geminga-like extended source, and the global Gaussian check is insensitive to localized residuals. The paper itself says Geminga analysis awaits completion of validation.","rationale":"The reader's conditionality is well founded. The paper's abstract and conclusion claim that MRM is a demonstrated technique for estimating the background of the entire field-of-view, based on null results in Segue 1 and Ursa Minor. The decisive gap is that these tests contain no known source, while the method's purpose is to measure a faint, extended source in a field where the source occupies a large fraction of the FOV. A background estimator can produce a null map in an empty field while still being biased in the presence of a source—for instance by over-subtracting extended emission or by not correctly handling the acceptance across a source-filled FOV. The global Gaussian check used in §4 is also weak: it can miss a localized 4–5σ residual that would be exactly what a source search must exclude. The paper itself says in §5 that MRM will be applied to Geminga only after validation tests are completed, which is an explicit acknowledgment that the present validation is incomplete. Therefore the strongest claim should be read as provisional. The reader's CONDITIONAL verdict is the appropriate outcome; no adjustment is needed.","tokens_in":4273,"tokens_out":5979,"duration_ms":67632,"concrete_test":"Run MRM on archival VERITAS data (or Monte Carlo) for a field containing a known extended source—e.g., IC 443 or a simulated Geminga-like source with HAWC's measured 2° morphology and plausible flux—placed in an otherwise blank FOV, using the same matching criteria. Verify the reconstructed excess map has the correct centroid, extension, and flux, and that the significance at the source position scales as expected with exposure. In parallel, for the null fields, compute the distribution of the maximum absolute significance over independent sky bins (or a matched-filter test statistic) rather than only the global μ/σ, to show the map contains no localized residual that could mimic an extended source.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim (abstract: 'MRM has been demonstrated to be an effective technique'; §5: 'capable of estimating the background of the entire field-of-view') is supported only by null tests in two dwarf-spheroidal fields (§4): Segue 1 and Ursa Minor significance distributions are reported as consistent with a standard normal. The intended application, however, is a ~2° extended source (Geminga) filling much of the VERITAS FOV. A source-free field can validate that the MRM background estimate does not create globally biased maps, but it does not test (i) that a real extended source is not partially subtracted by the background/exposure normalization, (ii) that the matching criteria (ΔAz ≤10°, ΔEl ≤10°, ΔT ≤360 days, minimized ΔNCR) remain adequate when the ON field contains a bright extended component, or (iii) that the method recovers the correct flux and morphology. Moreover, the presented statistic—a histogram with μ=0, σ=1—is insensitive to the localized, spatially correlated residuals that a source search cares about; a single 4–5σ blob in a multi-thousand-bin map would barely perturb the global Gaussian shape. The paper itself flags the incompleteness in §5: 'The MRM procedure will be applied to the Geminga data set when the validation tests are completed.' Thus the abstract's 'demonstrated' overstates what the data show.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"This paper presents the Matched Runs Method (MRM), a background estimation technique for VERITAS observations of gamma-ray sources extended on the scale of the camera field of view. The authors describe the method, in which OFF runs are selected from archival data using matching criteria in elevation, azimuth, time, and non-gamma-ray event rate, and present validation tests on two dwarf spheroidal galaxies (Segue 1 and Ursa Minor) showing that significance maps are consistent with a standard normal distribution. The paper also summarizes 93 hours of VERITAS observations of Geminga but states that the MRM analysis awaits completion of validation tests.","tokens_in":4557,"tokens_out":3704,"duration_ms":32046,"significance":"If fully validated, MRM would be a useful addition to IACT background estimation, potentially enabling searches for sources extended on FOV scales without dedicated blank-field observations. The paper's strength is that it describes a concrete, automatable algorithm and provides an empirical null test on archival data. However, the current evidence only demonstrates that MRM produces globally background-like maps in source-free fields; it does not yet establish that the method preserves the signal of an extended source, which is the intended application. The claims in the abstract and conclusion go beyond what the presented tests support.","major_comments":[{"comment":"Section 4 validates MRM only on source-free fields (Segue 1 and Ursa Minor), and Section 5 concludes that the method is 'capable of estimating the background of the entire field-of-view.' This conclusion does not follow from the evidence because a blank-field null test cannot rule out that MRM partially subtracts or distorts a real extended source such as the ~2° Geminga halo. The paper should include a validation with a known or simulated extended source, demonstrating that the source flux and morphology are recovered, before claiming that MRM is demonstrated for the Geminga search.","section":"Section 4 and Section 5"},{"comment":"The global significance distribution check (μ=0, σ=1) is insensitive to localized, spatially correlated residuals. A single 4–5σ excess in a multi-thousand-bin significance map would barely change the global histogram, so this statistic does not validate the method for source searching. The authors should report a quantitative goodness-of-fit test (e.g., a Kolmogorov-Smirnov or Anderson-Darling test with the p-value, or a χ² over the histogram) and an analysis of the distribution of the maximum significance or spatial autocorrelation of residuals.","section":"Section 4, Figures 1b/2b"},{"comment":"The abstract states that MRM 'has been demonstrated to be an effective technique by applying it to archival VERITAS data,' but Section 5 states that 'The MRM procedure will be applied to the Geminga data set when the validation tests are completed.' This internal inconsistency overstates the current status. The claims should be revised to match the evidence: at present, the method has passed null tests, and extended-source validation is still in progress.","section":"Abstract and Section 5"}],"minor_comments":[{"comment":"There is a typo in the abstract: 'spin-down time sca le' should be 'spin-down time scale.'","section":"Abstract"},{"comment":"The definition of ΔNCR in equation (3.1) is unclear: it is written as a sum over 'All Runs,' but the text says the algorithm 'minimizes the ΔNCR to a list of ON and OFF runs.' Please clarify whether this is a sum over pairs of matched ON/OFF runs or a global matching criterion.","section":"Section 3"},{"comment":"The paper title promises a 'Search for Very-High-Energy Emission from Geminga,' but the paper contains no Geminga results; consider changing the title to reflect that this is a methods paper, or adding a short statement that the search will be presented separately.","section":"Title"},{"comment":"Reference [18] cites 'ICRC proceeding 2007' but the arXiv number 1708.07447 corresponds to ICRC 2017; please correct the year.","section":"References"}],"recommendation":"major_revision","confidential_remarks":"This is a conference proceedings rather than a full journal paper, and the central claims are not yet supported by the required validation. The method is plausible, so I recommend major revision rather than rejection; the authors should either add an extended-source validation or substantially temper the claims in the abstract and conclusion."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"MRM is a practical extension of the ON/OFF idea: instead of dedicating new OFF runs, it automatically matches archival runs to the ON pointing using elevation, azimuth, time gap, and a non-gamma-ray rate difference. That is genuinely useful for VERITAS, where the standard ring and reflected-region methods lose power when a source fills the field of view. The automated matching objective is new, and the two null tests on Segue 1 and Ursa Minor are real evidence that the method does not obviously bias empty fields. The maps look featureless, the significance distributions are reported as consistent with a standard normal, and no part of the result is circular: the validation is not fit to the target signal. The prose is clear about the intended application and honest about the fact that Geminga analysis is still pending.\n\nThe soft spot is the gap between what is tested and what is claimed. The abstract says MRM 'has been demonstrated to be an effective technique,' and the conclusion says it is 'capable of estimating the background of the entire field-of-view.' What the paper actually shows is that two source-free dwarf-spheroidal fields analyzed with MRM look consistent with pure background. That does not test the load-bearing case: a bright extended source like Geminga filling much of the field, where background subtraction and exposure normalization could partially absorb the signal. It also does not test whether MRM recovers the correct flux or morphology of a known extended source. The global Gaussian shape is a weak probe, since a localized few-sigma excess in a multi-thousand-bin map would barely move the histogram. And the paper gives no quantitative fit statistics for the null distributions, just an eyeball 'consistent.' The thresholds in the matching algorithm are hand-set, which is fine as a starting point, but there is no study of how sensitive the results are to them.\n\nThese are real limitations, but they are not fatal for what this paper actually is. It is an ICRC proceedings contribution, not a refereed method paper, and its own Section 5 says the procedure will be applied to Geminga only 'when the validation tests are completed.' The abstract simply gets ahead of the evidence. The right fix is to temper the wording and, for the next version, add a known extended source with a mild extension, like IC 443, or an injected-source Monte Carlo, to show that the method preserves signal while subtracting background.\n\nWho should read this? Anyone working on IACT analysis of extended sources, especially within VERITAS, and anyone trying to bridge the Fermi-LAT/HAWC energy gap. It is a credible methodological contribution, not a detection. I would cite it as a reference for the method, and I would send a revised version to a serious referee, because the method is plausible and the energy gap it targets is scientifically important. But the 'demonstrated effective' language should be revised before publication.","headline":"A plausible, honestly framed methods-in-progress paper: the Matched Runs Method is a sensible automated reuse of archival VERITAS runs for extended sources, but the abstract claim that it is 'demonstrated effective' outruns null tests in two empty fields.","tokens_in":5055,"tokens_out":1885,"would_cite":true,"duration_ms":22851,"reading_group":"maybe","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 claims that the Matched Runs Method (MRM) lets VERITAS estimate the gamma-ray background over the entire field of view from archival point-source observations, validated on source-free dwarf spheroidal fields.","keywords":["very-high-energy gamma rays","Geminga pulsar","extended source analysis","background estimation","imaging atmospheric Cherenkov telescope","cosmic-ray positron excess","Matched Runs Method","VERITAS"],"falsifier":"Run MRM on simulated data with an injected extended source matching the HAWC Geminga halo (roughly 2-degree radius with known flux and morphology) and compare the reconstructed sky map to the input; if the significance or surface brightness comes out biased, or the source is smeared or suppressed, the central claim fails. Alternatively, if the MRM analysis of the 93-hour Geminga dataset does not recover the HAWC-detected excess, the method's validity as an estimator for real extended sources is contradicted.","tokens_in":4091,"feed_emoji":"🔭","tokens_out":5114,"duration_ms":48910,"temperature":0.7,"pith_summary":"VERITAS can detect gamma rays from 100 GeV to above 30 TeV, but its standard background estimators need empty patches in the field of view, which fails when a source fills the field. This paper argues that the Matched Runs Method (MRM) cures that by searching archived observations of unrelated point sources for runs whose elevation, azimuth, date, and event rate match the target field, then using those runs to model the background. If MRM works, VERITAS can measure the extended TeV halo around Geminga, filling the energy gap between Fermi-LAT and HAWC and testing whether Geminga still explains the cosmic-ray positron excess. The paper's validation is statistical: MRM maps of the dwarf spheroidals Segue 1 and Ursa Minor show significance distributions consistent with pure noise.","feed_headline":"New background method maps extended gamma-ray sources","feed_subtitle":"A matched-run recipe lets VERITAS see sources as wide as the HAWC Geminga halo.","key_machinery":"The central object is the Matched Runs Method (MRM), a background-estimation algorithm that reuses archival observations of point-like sources as OFF runs for an extended-source ON field. Its matching function minimizes $\\Delta N_{\\rm CR}=\\sum_{\\rm runs}|N_{\\rm CR}^{\\rm ON}-N_{\\rm CR}^{\\rm OFF}|$, the summed difference in non-gamma-like event counts between candidate ON and OFF runs, subject to cuts $\\Delta {\\rm Az}\\le 10^\\circ$, $\\Delta {\\rm El}\\le 10^\\circ$, and $\\Delta T\\le 360$ days. The method then forms the background from ring or wobble-offset regions within those matched OFF fields, so no dedicated blank-field observation is required. The machinery converts the problem of estimating background under an extended source into a database search for geometrically and temporally similar runs.","core_discovery":"The central claim is that a gamma-ray source with spatial extent comparable to the camera field of view can be analyzed with VERITAS by borrowing background from archival runs on point-like sources, instead of taking separate blank-field OFF runs. The Matched Runs Method (MRM) automates the selection of matched runs using four criteria—elevation difference, azimuth difference, time gap, and difference in non-gamma-like event counts—and then uses ring or wobble-offset regions in those OFF observations to model the background across the whole field. Applied to 26 hours of Segue 1 and 5 hours of Ursa Minor, MRM produces sky maps with no excess and significance distributions consistent with a standard normal ($\\mu=0$, $\\sigma=1$), which the paper takes as evidence that the background is correctly estimated everywhere in the field of view. The intended application is the 93-hour Geminga dataset, where MRM would fill the 500 GeV to 1 TeV gap between Fermi-LAT and HAWC and reduce the surface-brightness uncertainties that currently hamper diffusion-model tests.","pith_inferences":["The null-map validation on source-free dwarf spheroidals does not by itself prove that MRM preserves the signal of a real extended source; a natural next test is injecting a simulated Geminga-like halo into a source-free field and checking that the reconstructed flux and morphology match.","If MRM succeeds on Geminga, the same procedure could be applied to other HAWC-detected pulsar halos mentioned in the paper, such as Monogem, to map their energy-dependent morphology at VERITAS's finer angular resolution.","The paper's rationale connects to the debate over radially varying positron diffusion: with sub-degree surface-brightness profiles from MRM, one could test whether the diffusion constant inferred near the pulsar differs from the value outside the halo, which the paper only notes as an unresolved question.","A residual systematic risk is that matched runs from different sky positions could imprint camera-response gradients; the Gaussian significance test would catch large-scale biases but not necessarily small distortions in a faint extended source."],"forward_implications":["If MRM is valid, VERITAS can produce background-modeled sky maps of sources as large as the field of view using archival data, without doubling the observation time.","The method gives a path to measure the Geminga TeV halo across 100 GeV to 30 TeV, bridging the energy gap between Fermi-LAT and HAWC.","MRM enables deep observations of faint extended sources that would be impractical with the ON/OFF technique because of its factor-of-two exposure penalty.","Because matched runs can come from any point-like calibration source such as the Crab or 1ES 0229+200, archival VERITAS data becomes reusable as background for many extended-source analyses."],"supporting_citations":[{"why":"Supplies the standard ring and reflected-region background methods that MRM is designed to replace for extended sources.","marker":"[17]"},{"why":"Provides the dwarf spheroidal observations and standard-analysis null results that serve as the validation dataset for MRM.","marker":"[18]"},{"why":"Reports the HAWC measurement of the Geminga TeV halo and the diffusion constraint that motivates a VERITAS follow-up at lower energies.","marker":"[16]"},{"why":"Establishes the existence of highly extended TeV halos around Geminga and Monogem, defining the source scale MRM must handle.","marker":"[14]"},{"why":"Criticizes the homogeneous-diffusion assumption in the HAWC interpretation, providing the physics reason for wanting better surface-brightness measurements.","marker":"[15]"}],"fun_headline_variants":["VERITAS method bridges TeV gap for Geminga halo","Matched Runs Method enables VERITAS extended-source studies","New background recipe lets VERITAS see wide gamma-ray halos","VERITAS fills energy gap with matched-run background technique","Geminga halo analysis opens with novel VERITAS method"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The method is validated only on fields known to contain no gamma-ray source, where a null significance map shows the background estimate is not grossly biased; the paper does not yet show that MRM correctly reproduces a real, extended source's signal.","fun_headline_variants_meta":{"raw":{"variants":["VERITAS method bridges TeV gap for Geminga halo","Matched Runs Method enables VERITAS extended-source studies","New background recipe lets VERITAS see wide gamma-ray halos","VERITAS fills energy gap with matched-run background technique","Geminga halo analysis opens with novel VERITAS method"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000144,"raw_usage":{"total_tokens":1240,"prompt_tokens":1076,"completion_tokens":164,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":692,"completion_tokens_details":{"reasoning_tokens":79}},"tokens_in":692,"tokens_out":164,"duration_ms":2572,"temperature":1.0,"reasoning_tokens":79,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-14T13:15:49.372178+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Run MRM on simulated data with an injected extended source matching the HAWC Geminga halo (roughly 2-degree radius with known flux and morphology) and compare the reconstructed sky map to the input; if the significance or surface brightness comes out biased, or the source is smeared or suppressed, the central claim fails. Alternatively, if the MRM analysis of the 93-hour Geminga dataset does not recover the HAWC-detected excess, the method's validity as an estimator for real extended sources is contradicted.","supporting_citations":[{"cited_title":"Berge, S","cited_arxiv_id":null,"evidence_quote":"Supplies the standard ring and reflected-region background methods that MRM is designed to replace for extended sources."},{"cited_title":"The VERITAS Dark Matter Program","cited_arxiv_id":"1708.07447","evidence_quote":"Provides the dwarf spheroidal observations and standard-analysis null results that serve as the validation dataset for MRM."},{"cited_title":"U., et al","cited_arxiv_id":null,"evidence_quote":"Reports the HAWC measurement of the Geminga TeV halo and the diffusion constraint that motivates a VERITAS follow-up at lower energies."},{"cited_title":"U., et al","cited_arxiv_id":null,"evidence_quote":"Establishes the existence of highly extended TeV halos around Geminga and Monogem, defining the source scale MRM must handle."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Criticizes the homogeneous-diffusion assumption in the HAWC interpretation, providing the physics reason for wanting better surface-brightness measurements."}],"review_version":1}