{"id":"c9d229cf-8257-4051-b3b4-b8687759aed4","arxiv_id":"1908.06122","paper_version":1,"verdict":"ACCEPT","confidence":"MODERATE","novelty_score":4.0,"correctness_risk":"low","formal_verification":"none","parameter_count":3,"one_line_summary":"A search of HAWC data finds no significant very-high-energy gamma-ray counterparts to LIGO/Virgo gravitational wave events, and constrains VHE emission from GW170817.","lead":"HAWC searched for very-high-energy gamma-ray emission from gravitational wave events detected by LIGO and Virgo during the first three observing runs. No significant counterpart was found, and a new upper limit was set on late-time VHE emission from GW170817.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"No significant objection identified: the central null result is robust to plausible errors in the trials factor or background calibration.","rationale":"The reader's verdict (ACCEPT) matches my assessment. I looked specifically for a way the quoted null result could be wrong: a miscalibrated background simulation, an incorrect trials factor, or an unmodeled systematic that creates or hides an excess. None of these is load-bearing because the observed maximum TS=26 is far below what is expected from the large number of trials; any reasonable correction leaves p effectively 1.0. The reader's weakest assumption (background/TS calibration) is a valid caveat for the upper limit and for future searches, but not for this paper's central non-detection. I therefore do not change the verdict. The remaining concerns—aggregate reporting, absence of code/data, and small fractions of localization searched for some O3 events—are real but are standard for a conference proceedings and do not undermine the stated conclusion.","tokens_in":6723,"tokens_out":16380,"duration_ms":183563,"concrete_test":"Ask the collaboration to release the per-event, per-timescale maximum TS values and the null-simulated FAR distributions used in Eq. (2.3). Recompute the post-trial p-value from the full trials factor and re-run the null simulation with the background rate perturbed by ±10%. If the p-value remains 1.0 and the GW170817 95% C.L. flux upper limit shifts by less than ~20%, the central claim is confirmed.","verdict_should_be":"UNCHANGED","load_bearing_attack":"No load-bearing concern found. The paper's central claim is a null result: the largest TS anywhere in the search, 26.0, has post-trial p = 1.0. That conclusion is insensitive to the main candidate uncertainties. The number of effective independent trials is at least millions (HEALPix Nside=512 pixels within the searched solid angle, time-window shifts, eight timescales, and multiple GW events), so the expected number of background fluctuations above TS=26 is far greater than one; even a large error in the trials factor or a ~10% systematic shift in the background rate would not move TS=26 close to significance. The reader's flagged assumption about the null TS distribution therefore does not threaten the non-detection. The genuine limitations are reproducibility-related: no per-event TS table, no public null-simulation code, no systematic error budget on the GW170817 upper limit, and the small covered sky fractions for O3 events (25%, 28%, 4%). These affect the strength and interpretability of the constraints, but not the stated conclusion that no significant VHE counterpart was observed.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper reports a search for very-high-energy (VHE) gamma-ray emission coincident with gravitational-wave (GW) events detected by LIGO/Virgo during O1, O2, and part of O3, using the HAWC observatory. The search is performed on a HEALPix grid over the 95% localization region, with eight time-window widths from 0.3 s to 1000 s, and uses a binned likelihood test statistic. All analyzed events are consistent with background; the maximum test statistic anywhere is TS = 26.0, which corresponds to a post-trial p-value of 1.0. For GW170817, the source was outside the field of view at merger, and an upper limit of 1.5 x 10^-8 erg cm^-2 s^-1 (100 GeV - 1 TeV) is set using the later transit. The paper concludes that no significant VHE counterpart was observed and that HAWC can provide competitive constraints for events in its field of view.","tokens_in":6903,"tokens_out":5320,"duration_ms":50236,"significance":"The result is a null search with no significant excess, which is valuable for constraining VHE emission from compact binary mergers. The paper's strengths are the wide field of view and continuous operation of HAWC, and the explicit post-trial p-value of 1.0 after a large trials correction. However, the quantitative constraints are limited by the small sky coverage for O3 events (25%, 28%, and 4% of localization probability) and the degraded sensitivity for GW170817. The paper does not include systematic uncertainties on the upper limit or full event-by-event results, but these do not affect the central null result, which is robust to plausible errors in the trials factor and background estimation.","major_comments":[],"minor_comments":[{"comment":"The formula for the expected number of false positives should explicitly include the number of gravitational-wave events searched, and the conversion from <n> to a p-value should be stated for the case <n> >= 1 (e.g., p = 1 - exp(-<n>)).","section":"Section 2, Eq. (2.3)"},{"comment":"A table listing all analyzed GW events with the observed maximum TS, location, time window, and searched sky fraction would improve reproducibility and is standard for such searches.","section":"Section 4"},{"comment":"The GW170817 upper limit should be accompanied by an estimate of systematic uncertainties from the background normalization and the assumed spectral index (alpha = -2).","section":"Section 4"},{"comment":"The text contains the typo 'precense' (for 'presence'), and the expansion of ZEBRA should read 'Zenith' instead of 'ZEnith.'","section":"Section 2"},{"comment":"The statement that the search is only weakly dependent on the assumed spectral index is not supported with a reference or figure; a brief justification or citation would help.","section":"Section 2"},{"comment":"The sensitivity curves are compared to Fermi-LAT spectra, but the caption does not state which energy range of the HAWC sensitivity is shown; restating the energy range in the caption would improve clarity.","section":"Section 3, Figures 1 and 2"}],"recommendation":"minor_revision","confidential_remarks":"This is a conference proceedings contribution, and the level of detail is appropriate for that venue. The central null result is robust, but the authors should be encouraged to provide a companion data release or appendix with per-event numbers if the work is expanded to a journal article. The citation pattern and scope are consistent with the journal."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"This is a clean, honest null-result paper from HAWC, and the first time HAWC has reported a systematic search of LIGO/Virgo triggers in O1, O2, and early O3. The method is not new — it is the established HAWC likelihood approach adapted to short timescales — but the specific application is new, and the paper is upfront about what was done.\n\nThe central claim is a non-detection: the largest test statistic anywhere was TS = 26.0, which after trials gives p = 1.0. I agree with the stress-test note that this conclusion is robust. Even if the background rate is off by the quoted ~10%, or the trials factor is miscalculated by a large factor, TS = 26 cannot become significant when the effective number of trials is in the millions. So the reader's weakest assumption — that the null TS distribution is correctly calibrated — does not threaten the main result.\n\nWhat the paper does well: the search window choices are motivated by short-GRB timescales, the sensitivity curves are compared directly to Fermi-LAT measurements of short GRBs, and the GW170817 late-time upper limit, though degraded by the source being at the edge of the field of view, is clearly presented. The description of the automated O3 follow-up is also useful and shows the collaboration is building real multimessenger capability.\n\nThe soft spots are real but not load-bearing. There are no per-event TS tables, no public code or data, and no systematic error budget on the upper limit. The sky localization fractions covered for the three O3 events are small (25%, 28%, 4%), which limits how much these results constrain progenitor models. As a proceedings, this is acceptable; as a full journal paper, it would need those details. None of these gaps change the fact that no significant VHE counterpart was observed.\n\nThe citation pattern looks fine — HAWC's own method papers are cited, as are the relevant GW and GRB references. There is no circularity: the spectral index, EBL model, and time windows are inputs, not fitted outputs.\n\nWho is this for? People working on multimessenger transients, especially those comparing VHE upper limits to short-GRB models, and the HAWC follow-up community. It is worth a serious referee if it is ever submitted as a full paper, but as an ICRC proceedings it already does its job. I would like to see the per-event results and systematics made public in a future archival version. My recommendation: treat it as a legitimate null measurement, cite it if you need a HAWC VHE constraint, and press for the missing details only if it is submitted to a regular journal.","headline":"A robust first null-result search for VHE gamma-ray counterparts of LIGO/Virgo events; the non-detection stands even if the background calibration is off, but the constraints are limited by small sky coverage and missing systematics.","tokens_in":7401,"tokens_out":1520,"would_cite":false,"duration_ms":18783,"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":"HAWC searched for TeV gamma-ray flashes tied to LIGO/Virgo events and found none, a result consistent with background.","keywords":["gravitational waves","gamma-ray bursts","very-high-energy gamma rays","HAWC","multi-messenger astronomy","LIGO/Virgo","transient search","upper limits"],"falsifier":"Take archived HAWC data for the analyzed gravitational-wave events, inject artificial VHE bursts of known flux into the same time windows, and rerun ZEBRA: if the injection recovery fraction differs substantially from the claimed sensitivity at the same test-statistic threshold, the null calibration is wrong. Alternatively, a future binary neutron star merger fully inside HAWC's field of view that is seen in TeV by an independent instrument would directly settle whether the search misses real counterparts.","tokens_in":6544,"feed_emoji":"🔭","tokens_out":4848,"duration_ms":44150,"temperature":0.7,"pith_summary":"This paper asks whether any of the gravitational-wave events detected by LIGO and Virgo in runs O1, O2, and O3 were accompanied by very-high-energy gamma-ray emission in HAWC's sky. The answer it defends is no: after searching eight time windows and all overlapping sky regions, every result is consistent with background, with the largest test statistic giving a trials-corrected p-value of 1.0. The paper also derives an upper limit on late-time TeV emission from GW170817. The point of the exercise is that HAWC's wide field of view and nearly continuous operation let a single instrument check the prompt VHE phase of nearby mergers. A detection would pin down jet physics; an upper limit sharpens what future joint searches must beat.","feed_headline":"No TeV gamma-ray flash accompanies gravitational-wave events","feed_subtitle":"HAWC's wide-field O1-O3 search sees only background; GW170817 gets a new 100 GeV-1 TeV upper limit.","key_machinery":"The load-bearing instrument is HAWC itself plus the internal analysis chain called ZEBRA: a binned likelihood search over a HEALPix grid at Nside = 512, with events binned by the fraction of detector channels hit ($f_{\\mathrm{hit}}$), background estimated by 'direct integration' (convolving a stable local arrival direction probability with the total event rate), and eight logarithmically spaced time windows sliding from $t_0 - 5\\Delta t$ to $t_0 + 10\\Delta t$. The null-hypothesis test-statistic distribution is produced by randomly fluctuating the expected background through the same analysis, which accounts for pixel and time-window correlations; per-timescale false-alarm rates are then combined to yield the trials-corrected p-value. This machinery is what lets a wide-field survey claim either detection or meaningful constraints on prompt TeV emission.","core_discovery":"For every LIGO/Virgo gravitational-wave event with at least partial HAWC sky coverage during O1, O2, and O3, a search over time windows from 0.3 to 1000 seconds and over the sky region containing 95% of the localization probability found no excess above background. The largest test statistic at any location, time, event, or timescale was $TS = 26.0$, corresponding to a p-value of 1.0 after trial correction. For GW170817, whose merger time fell outside HAWC's field of view, HAWC observed the later transit 8.20 to 10.23 hours after coalescence and set an upper limit of $1.5 \\times 10^{-8}\\,\\mathrm{erg\\,cm^{-2}\\,s^{-1}}$ between 100 GeV and 1 TeV. The conclusion is that no very-high-energy gamma-ray counterpart above HAWC's sensitivity was emitted by the analyzed events.","pith_inferences":["One extension the paper leaves implicit: apply the same pipeline to short gamma-ray bursts without gravitational-wave triggers, where larger samples could calibrate the VHE detection rate even if the GW association is absent.","The GW170817 upper limit covers only the later transit, not the prompt phase; interpreting it as a constraint on prompt emission would require an afterglow model, since the prompt emission was outside the field of view.","A sub-second time window below 0.3 seconds could be tried, since Fermi-LAT shows a fraction of short GRB emission concentrated in much shorter intervals than the search's shortest window.","An obvious test, not discussed in the paper: run the same search on fake GW alerts placed at random times and locations; the distribution of maximum test statistics should match the claimed null distribution, validating the false-alarm-rate formula."],"forward_implications":["For nearby binary neutron star and neutron star-black hole mergers inside HAWC's field of view, the search will either detect a VHE counterpart or place an upper limit that constrains prompt-emission models.","Starting in O3, HAWC's automatic follow-up of gravitational-wave alerts can provide a localization to about 0.5 degrees within minutes to an hour, helping other telescopes target the counterpart.","The non-detection across O1-O3 sets a benchmark: any model predicting bright TeV prompt emission for typical LIGO/Virgo events is disfavoured at HAWC's sensitivity.","Continued running increases exposure, so the same pipeline naturally tightens these limits as more gravitational-wave events accumulate."],"supporting_citations":[{"why":"Supplies the direct-integration background estimation method that the search relies on for the cosmic-ray background.","marker":"[17]"},{"why":"Defines the HAWC detector response and the binned likelihood analysis that ZEBRA adapts to short timescales.","marker":"[16]"},{"why":"Provides the extragalactic background light attenuation model used to modify the assumed source spectrum at the distance of each gravitational-wave event.","marker":"[15]"},{"why":"Gives the Fermi-LAT short GRB durations that motivate the eight time windows from 0.3 s to 1000 s and the comparison spectra for sensitivity.","marker":"[20]"},{"why":"Establishes GW170817/GRB170817A as the multi-messenger benchmark that motivates searching for VHE counterparts of compact mergers.","marker":"[7]"},{"why":"Represents the earlier HAWC GRB search whose classical ON/OFF analysis this work improves on with the binned likelihood approach.","marker":"[18]"},{"why":"Shows that the closest GRB, GRB 170817A, had ordinary flux, undercutting the assumption that nearby mergers are necessarily brighter in gamma rays.","marker":"[22]"}],"fun_headline_variants":["HAWC finds no gamma-ray flash with any LIGO/Virgo event","Gravitational waves produce no detectable TeV counterparts","No TeV emission from gravitational-wave events, HAWC reports","HAWC's all-sky hunt: no VHE gamma-ray counterpart to GWs","Binary mergers silent in TeV gamma rays, HAWC search shows"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The background estimate and the simulated null-hypothesis test-statistic distribution are correctly calibrated, including all correlations between nearby pixels and overlapping time windows; if those simulations miss a systematic effect, the reported p-value and upper limit would shift.","fun_headline_variants_meta":{"raw":{"variants":["HAWC finds no gamma-ray flash with any LIGO/Virgo event","Gravitational waves produce no detectable TeV counterparts","No TeV emission from gravitational-wave events, HAWC reports","HAWC's all-sky hunt: no VHE gamma-ray counterpart to GWs","Binary mergers silent in TeV gamma rays, HAWC search shows"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000711,"raw_usage":{"total_tokens":3167,"prompt_tokens":878,"completion_tokens":2289,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":494,"completion_tokens_details":{"reasoning_tokens":2195}},"tokens_in":494,"tokens_out":2289,"duration_ms":14139,"temperature":1.0,"reasoning_tokens":2195,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-14T12:54:09.734337+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Take archived HAWC data for the analyzed gravitational-wave events, inject artificial VHE bursts of known flux into the same time windows, and rerun ZEBRA: if the injection recovery fraction differs substantially from the claimed sensitivity at the same test-statistic threshold, the null calibration is wrong. Alternatively, a future binary neutron star merger fully inside HAWC's field of view that is seen in TeV by an independent instrument would directly settle whether the search misses real counterparts.","supporting_citations":[{"cited_title":"Atkins and et al","cited_arxiv_id":null,"evidence_quote":"Supplies the direct-integration background estimation method that the search relies on for the cosmic-ray background."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Defines the HAWC detector response and the binned likelihood analysis that ZEBRA adapts to short timescales."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Provides the extragalactic background light attenuation model used to modify the assumed source spectrum at the distance of each gravitational-wave event."},{"cited_title":"Ajello and et al","cited_arxiv_id":null,"evidence_quote":"Gives the Fermi-LAT short GRB durations that motivate the eight time windows from 0.3 s to 1000 s and the comparison spectra for sensitivity."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Establishes GW170817/GRB170817A as the multi-messenger benchmark that motivates searching for VHE counterparts of compact mergers."},{"cited_title":"Alfaro and et al","cited_arxiv_id":null,"evidence_quote":"Represents the earlier HAWC GRB search whose classical ON/OFF analysis this work improves on with the binned likelihood approach."},{"cited_title":"Goldstein, P","cited_arxiv_id":null,"evidence_quote":"Shows that the closest GRB, GRB 170817A, had ordinary flux, undercutting the assumption that nearby mergers are necessarily brighter in gamma rays."}],"review_version":1}