AMON: TeV Gamma and Neutrino Coincidence Alerts from HAWC and IceCube subthreshold data

for the IceCube Collaboration); Hugo Alberto Ayala Solares (for the HAWC Collaboration

REVIEW 4 major objections 5 minor 12 references

AMON: TeV Gamma and Neutrino Coincidence Alerts from HAWC and IceCube subthreshold data

T0 review · 4 major / 5 minor · reviewed 2026-08-14 · deepseek-v4-flash

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Pith's one-line read This paper reports that AMON is ready to issue real-time coincidence alerts from HAWC gamma-ray hotspots and IceCube neutrinos, with a median delay of six hours, localization near 0.2 degrees, and a false-alarm rate of one per year.

desk verdict Useful AMON methods proceedings with a clean FAR calibration and an honest null result; the abstract's real-time readiness claim is ahead of the body's future-tense outlook. read the letter →

arxiv 1908.05990 v1 pith:KFZKF7YZ submitted 2019-08-16 astro-ph.HE

Hugo Alberto Ayala Solares (for the HAWC Collaboration , for the IceCube Collaboration) This is my paper · ORCID

classification astro-ph.HE

keywords multimessengerastrophysicsAMONHAWCIceCubegamma-rayneutrinocoincidencefalsealarmratecalibrationsubthresholdtransientsearch

verification ladder T0 review T1 audit T2 compute T3 formal

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The reading

This paper reports that the Astrophysical Multimessenger Observatory Network (AMON) is ready to issue real-time coincidence alerts pairing HAWC TeV gamma-ray hotspots with IceCube astrophysical neutrino events. The goal is to catch transient or variable sources, such as blazars and radio galaxies, that produce both gamma rays and neutrinos, something the recent gravitational-wave and flaring-blazar multimessenger detections suggest should happen more often. To calibrate the alerts, the authors scramble right ascension in two years of archival data and find that a ranking statistic of 7.3 corresponds to one false alarm per year. In the unblinded 1.85 years of livetime, one coincidence exceeds that threshold, consistent with the expected background, and two more sit just below it. If correct, the system would begin sending such alerts to follow-up observatories with a median delay of six hours and angular resolution near 0.2 degrees.

What carries the argument

The machinery is a joint-likelihood ranking statistic built on Fisher's method. For a candidate coincidence, the statistic is $\chi^2_{6+2n_\nu} = -2\ln[p_\lambda p_{\mathrm{HAWC}} p_{\mathrm{cluster}} \prod_i p_{\mathrm{IC},i}]$, where $p_\lambda$ comes from a maximum-likelihood fit for the best overlap position of the HAWC hotspot and IceCube event uncertainties on the sphere, $p_{\mathrm{HAWC}}$ is the probability that the hotspot is a background fluctuation, $p_{\mathrm{cluster}}$ is the probability of seeing the observed number of neutrinos within the HAWC transit time from background, and each $p_{\mathrm{IC},i}$ is the background probability of an IceCube track event. The $\chi^2$ value is converted to a p-value with $6+2n_\nu$ degrees of freedom and then to $\chi'{}^2 = -\log p$, the number used to rank coincidences. The false-alarm-rate curve built from right-ascension-scrambled data converts this ranking into an alert threshold.

What would settle it

Recompute the false-alarm-rate curve using a background ensemble that preserves each detector's real sky-exposure pattern, for example by scrambling event times rather than coordinates, and compare the ranking-statistic value that gives one false alarm per year. If that threshold moves away from 7.3 by more than the statistical uncertainty of the scrambled sample, the alert calibration and its quoted rate are wrong.

Watch

Extended reading notes

Core claim

The central working claim is that a joint-likelihood search combining subthreshold HAWC hotspots and IceCube through-going muon-neutrino track events can be run in real time as an AMON alert stream. The analysis ranks coincidences by Fisher's method, combining a spatial-overlap likelihood and background probabilities for the gamma-ray excess and each neutrino, with degrees of freedom adjusted for the number of neutrinos found inside the HAWC transit window and a 3.5-degree search radius. Scrambling right ascension in the archived two-year dataset yields a false-alarm-rate curve; a ranking statistic of 7.3 corresponds to one alert per year. Unblinding 1.85 years of livetime produces one coincidence at 7.34 and a near-miss at 7.27, matching the background expectation. The paper concludes that the method is ready to broadcast alerts with median six-hour delay, roughly 0.2-degree combined localization, and a public alert threshold set at a one-per-year false alarm rate.

Load-bearing premise

The false-alarm calibration assumes that randomly shuffling the east-west sky positions of the events, while keeping their north-south positions, produces a faithful picture of random coincidences; if either telescope's sky exposure depends on east-west position, the one-per-year alert threshold could be wrong.

Editorial extensions

If this is right

If the system runs as calibrated, AMON will broadcast a HAWC-plus-IceCube coincidence alert with a median delay of six hours, short enough for a full HAWC transit to pass but still timely for deep follow-up by optical, X-ray, and very-high-energy instruments.
Alerts will carry a combined localization of about 0.2 degrees at 1-sigma for a 2D Gaussian, making them suitable for pointed electromagnetic follow-up.
With a one-per-year false alarm rate, essentially every issued alert should be treated as a real multimessenger candidate worth immediate observation.
The single candidate above threshold in 1.85 years of livetime is consistent with the expected background, so the first alerts are a calibrated stream rather than claimed detections.
The same pipeline can be extended to search for sources of ultra-high-energy cosmic rays by combining neutrino alerts with data from additional observatories.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

The paper does not raise the option of requiring multiple neutrinos inside the transit window; doing so with the same ranking statistic would trade alert rate for purity and could be calibrated against the identical scrambled-background ensemble.
If either near-threshold coincidence at ranking 7.34 or 7.27 is later tied to a flaring blazar or radio galaxy, the archival test would retroactively become a multimessenger discovery, because both are consistent with background by the paper's own numbers.
One extension the paper leaves implicit is using the calibrated false-alarm rate as a prior when combining these alerts with gravitational-wave or other multimessenger triggers to prioritize follow-up observations.

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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Desk Editor's Note

read the letter

Read this with an eye to what it actually demonstrates. The novel bit is the AMON joint-likelihood search pairing HAWC hotspot transits with IceCube through-going tracks, using Fisher's method plus a spatial overlap likelihood. That is an incremental extension within AMON, not a new framework, but it is a real combination that has not been published before. The paper does the calibration work properly: 729 years of RA-scrambled data to set the FAR, a pre-defined threshold of 1/yr, then an unblinded search of 1.85 years livetime with one event at 7.34 and a second at 7.27. The authors do not over-interpret; they say the event is consistent with background. Credit where due.

The main soft spot is the abstract/body mismatch. The abstract says AMON is ready to produce real-time alerts with a median six-hour delay, but Sec. 6 says the method "will serve as a base for a real-time search" and "the search would consist of sending alerts." The body contains no online pipeline, no latency measurement, no GCN transmission, no data-quality monitoring. The six-hour number is anticipated, not measured. That is an internal inconsistency, and it is load-bearing for the abstract's strongest claim. The offline analysis is fine; the readiness claim is not.

Other weaknesses are minor but real. There are no uncertainties on the FAR curve, and the comparison of the unblinded ranking distribution with the scrambled expectation (Fig. 2) is only visual; a KS test or a p-value would have made the consistency check quantitative. The RA-scrambling assumption is standard for IceCube point-source analyses, and keeping declination-dependent parameters together mitigates the main worry, but the paper does not show any validation that the scrambled ensemble reproduces the data's null distribution (e.g., by declination band or temporal correlation). I would expect that as a check, not a blocking issue. Also, as a proceedings, the reference list is appropriate, with AMON and detector papers cited; no obvious citation problem.

Who this is for: people building or using multimessenger coincidence frameworks; follow-up network users who need to know what an AMON alert means. It deserves referee time if pushed to a journal, with the explicit request to either demonstrate the online system or soften the abstract. I would not cite it as evidence that real-time alerts are flowing, but I would cite the calibrated FAR method and the null result.

Referee Report

4 major / 5 minor

Summary. The paper reports an AMON joint-likelihood analysis that searches for coincidences between HAWC 'hotspot' gamma-ray excesses observed during a transit and IceCube through-going muon neutrino events. The selection requires temporal overlap with the HAWC transit and an angular separation below 3.5 degrees; a Fisher-style ranking statistic combines the spatial, spectral, and temporal p-values. The false alarm rate is calibrated with right-ascension-scrambled data corresponding to about 729 years, and a threshold ranking statistic of 7.3 gives one false alarm per year. Applied to 1.85 years of archival livetime from 2016-2017, the analysis finds one coincidence with ranking statistic 7.34 and one close to threshold at 7.27. The conclusions describe the method as a basis for a future real-time search, while the abstract states that AMON is ready to produce real-time alerts with a median delay of six hours.

Significance. The analysis addresses a timely and important problem: finding sub-threshold multimessenger coincidences between TeV gamma rays and neutrinos. Its strengths are clear: the false-alarm calibration uses a large scrambled background sample equivalent to 729 years, the ranking statistic combines relevant information through a standard Fisher-type method, and the archival search yields two interesting candidate events whose sky maps are shown. If the claimed real-time alert system were actually operational, this would be a valuable contribution to the multimessenger follow-up ecosystem. However, the body of the paper establishes only an offline archival search, not an operating alert pipeline. The unblinded result is also a weak validation because the threshold is chosen to enforce the false alarm rate rather than used as an independent prediction. With appropriate revisions that scope the claims to the offline analysis and quantify the calibration uncertainties, the method itself is a useful template for subthreshold coincidence searches.

major comments (4)

[Abstract; Section 6] The abstract states 'AMON is ready to produce real-time coincidence alerts' and gives a 'median anticipated delay of six hours,' but Section 6 describes the real-time search only in the future tense: 'This method will serve as a base for a real-time search for multimessenger sources of neutrinos... The search would consist of sending alerts...' The paper presents no running online pipeline, no end-to-end latency measurement, no alert-distribution test through GCN, and no live data-quality monitoring. The six-hour delay is labeled 'anticipated,' not measured. This discrepancy is load-bearing because the title and abstract promise an operational alert system, whereas the analysis demonstrates only an offline archival search. Please either present evidence of the operational system or revise the abstract and conclusions to state that the real-time implementation is planned.
[Section 4, Fig. 1] The false alarm rate curve in Fig. 1 is shown without statistical uncertainties. With about 729 years of scrambled data, the Poisson uncertainty on the FAR at one per year is roughly 4%, but in the high-ranking-statistic tail the effective number of trials is much smaller and the uncertainty is correspondingly larger. Because the alert threshold of 7.3 is derived from this curve, the curve should include confidence bands, and the text should state the number of independent scrambles and how trials are handled. Without this, the one-per-year FAR and the threshold are not fully quantified.
[Section 4] The RA-scrambling procedure assumes that each detector's acceptance is effectively uniform in right ascension. The text says 'The scrambling consisted on randomly permuting the right ascension information of the events. Parameters that are declination dependent were kept together with their respective declination.' If HAWC's transit pattern or IceCube's seasonal or Earth-blocking effects create RA-dependent acceptance, the scrambled background could bias the false alarm rate. Please state explicitly why the RA-uniform assumption holds, and ideally validate the calibration by comparing with an alternative scrambling (for example, a full time-shift or time-randomization).
[Section 5, Fig. 2] The comparison between the unblinded ranking-statistic distribution and the scrambled background in Fig. 2 is only qualitative. The observation of one event above the threshold in 1.85 years is consistent with the calibrated rate of one per year, but because the threshold was chosen to enforce that rate, this single event does not independently validate the analysis or indicate a signal. The paper should include a quantitative goodness-of-fit test for the distribution and should report the expected number of events above threshold for the actual livetime as an explicit check.

minor comments (5)

[Section 1] The Introduction contains a typo: 'The purpose of the this analysis' should read 'The purpose of this analysis.'
[Section 2] The IceCube paragraph says 'The parameters consists of' and should be 'The parameters consist of.' In addition, 'signal acceptance' is listed as an input but is never defined; please define it.
[Section 4] The text refers to the 'Galactic Coordinates Network [10],' but the referenced network is the GRB Coordinates Network (GCN); please correct the name.
[Section 3, Eq. (3.1)] The definition of the ranking statistic should state explicitly the null distributions and the number of degrees of freedom, including the formula for p_cluster, which is described only in words.
[References] Reference [6] is incomplete: 'arXiv:180' does not identify the paper. Please provide the full arXiv identifier or journal reference.

Circularity Check

0 steps flagged · score 0.0 of 10

No significant circularity: the FAR threshold is an operational calibration fixed before unblinding, and the observed candidate is not used to fit any parameter.

full rationale

The paper's derivation chain is not circular. The ranking statistic (Eq. 3.1) combines p-values supplied by HAWC and IceCube; the AMON-internal p_lambda is a likelihood overlap measure, not a fit to the coincidence outcome. The false-alarm-rate curve in Sec. 4 is built from RA-scrambled data and is used only to choose a threshold (7.3) corresponding to 1 event/yr. This threshold is fixed before the unblinding in Sec. 5, so the one candidate at 7.34 and the near-threshold event at 7.27 are not themselves inputs to the calibration; at most they provide a low-statistics consistency check. No fitted physical constant is renamed as a prediction. The references to prior AMON papers ([5], [6]) are descriptive infrastructure citations and carry no load-bearing mathematical content. The abstract's claim that AMON is 'ready to produce real-time coincidence alerts' is not demonstrated by the paper, and Sec. 6 describes the real-time search in future tense; however, that is an internal-support/correctness issue, not a circularity. Therefore no step in the derivation reduces to its own input by construction.

Assumptions & free parameters 3 free parameters · 4 assumptions · 0 invented entities

The central claim rests on chosen thresholds (HAWC significance >2.75 sigma, 3.5 degree matching radius, ranking threshold 7.3) and on background assumptions about RA scrambling, Gaussian spatial uncertainties, and independence of p-values. No new physical entities are introduced.

free parameters (3)

HAWC hotspot significance threshold = >2.75 sigma
Set by the HAWC collaboration to define which hotspots are sent to AMON as sub-threshold events; not derived in this paper.
Angular separation cut = 3.5 degrees
Chosen by hand in Section 3 as the matching radius between HAWC hotspots and IceCube neutrinos.
Ranking statistic alert threshold = 7.3
Selected in Section 4 so that the scrambled-data false alarm rate equals one per year; an operational requirement rather than a fitted physical parameter.

assumptions (4)

standard math Fisher's method requires independent p-values across the combined terms.
Equation 3.1 combines p_lambda, p_HAWC, p_cluster, and per-neutrino p_IC,i as if independent; the paper does not discuss dependence among these quantities.
domain assumption Randomly permuting right ascension while keeping declination-dependent parameters yields a valid background ensemble.
Section 4 uses this scrambling to calibrate the false alarm rate; it assumes RA-independent exposure for both detectors.
domain assumption Spatial uncertainties of HAWC hotspots and IceCube tracks are Gaussian on the sphere.
Equation 3.2 assumes Gaussian distributions on the sphere when computing the spatial overlap likelihood.
domain assumption IceCube and HAWC background p-values are independent under the null hypothesis.
The Fisher combination in Equation 3.1 treats the detector p-values as independent; the paper does not test this.

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Cite this review

Pith. "Pith review of AMON: TeV Gamma and Neutrino Coincidence Alerts from HAWC and IceCube subthreshold data." pith.science (2026). https://pith.science/paper/KFZKF7YZ

@misc{pith2026190805990,
  author       = {Pith},
  title        = {Pith review of: AMON: TeV Gamma and Neutrino Coincidence Alerts from HAWC and IceCube subthreshold data},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/KFZKF7YZ}},
  note         = {Machine review of arXiv:1908.05990}
}

abstract

The era of multimessenger astrophysics has arrived with the simultaneous operation of large cosmic-ray, gamma-ray, neutrino, and gravitational-wave observatories. In just the past two years, an electromagnetic (EM) counterpart was detected for a gravitational wave event, and evidence for an EM counterpart of high energy neutrinos has been identified. These measurements have had a major impact on our view of the non-thermal universe, but understanding cosmic accelerators require a substantial increase in the number of multimessenger observations. The Astrophysical Multimessenger Observatory Network (AMON) is designed for high-statistics searches of sub-threshold transient alerts from gamma-ray and neutrino detectors. Within AMON, we have implemented a joint-likelihood analysis of TeV gamma-ray measurements from the High Altitude Water Cherenkov (HAWC) Observatory and neutrinos from the IceCube Neutrino Observatory. AMON is ready to produce real-time coincidence alerts using HAWC "hotspots" and IceCube astrophysical neutrino events. These alerts will be distributed to AMON follow-up partners with a median anticipated delay of six hours, which corresponds to a full transit in the field of view of HAWC. The alerts will have an angular resolution of ${\sim}0.2^{\circ}$, making them well-suited for deep electromagnetic follow-up observations.

Figures

Figures reproduced from arXiv: 1908.05990 by the authors.

**Figure 2.** Ranking statistics distribution of the analysis. Blue: background expectation obtained [PITH_FULL_IMAGE:figures/full_fig_p005_2.png] view at source ↗

**Figure 3.** Skymaps of the coincidences found with the analysis. The size of the circles correspond [PITH_FULL_IMAGE:figures/full_fig_p005_3.png] view at source ↗

Discussion (0). Continue with ORCID to comment.

Reference graph

Works this paper leans on

12 extracted references · 11 canonical work pages

[1]

write newline

" write newline "" before.all 'output.state := FUNCTION blank.sep after.quote 'output.state := FUNCTION fin.entry output.state after.quoted.block = 'skip 'add.period if write newline FUNCTION new.block output.state before.all = 'skip output.state after.quote = after.quoted.block 'output.state := after.block 'output.state := if if FUNCTION new.sentence out...
[2]

L. S. Collaboration, V. Collaboration, et al., Multi-messenger Observations of a Binary Neutron Star Merger, ApJL, 848, 59, 2017

work page 2017
[3]

IceCube Collaboration, Fermi-LAT, MAGIC, et al., Multimessenger observations of a flaring blazar coincident with high-energy neutrino IceCube-170922A, Science, 361, 8, 2018

work page 2018
[4]

U., et al., Observation of the Crab Nebula with the HAWC Gamma-Ray Observatory, ApJ, 843, 39, 2017

Abeysekara, A. U., et al., Observation of the Crab Nebula with the HAWC Gamma-Ray Observatory, ApJ, 843, 39, 2017

work page 2017
[5]

IceCube Collaboration, M. G. Aartsen et al. , The IceCube Neutrino Observatory: Instrumentation and Online Systems, JINST, 12 , (2017), P03012

work page 2017
[6]

Smith, et al., The Astrophysical Multimessenger Observatory Network (AMON), Astro

M. Smith, et al., The Astrophysical Multimessenger Observatory Network (AMON), Astro. Part. 45, 56, 2013

work page 2013
[7]

H. A. Ayala Solares, et al., The Astrophysical Multimessenger Observatory Network (AMON), arXiv:180, 2018

work page 2018
[8]

and Hooper , D., High-energy gamma rays and neutrinos from nearby radio galaxies , JCAPP, 2017, 12, 2017

Blanco , C. and Hooper , D., High-energy gamma rays and neutrinos from nearby radio galaxies , JCAPP, 2017, 12, 2017

work page 2017

Show all 12 references

[9]

HAWC Collaboration, Extended gamma-ray sources around pulsars constrain the origin of the positron flux at Earth, Science, 358, 911-914 (2017)

2017
[10]

and Oikonomou , F

Murase , K. and Oikonomou , F. and Petropoulou , M, Blazar Flares as an Origin of High-energy Cosmic Neutrinos?, ApJ, 865, 2, 2018

2018
[11]

AMON website http://amon.psu.edu/ http://amon.psu.edu/
[12]

GRB Coordinates Network website https://gcn.gsfc.nasa.gov/ https://gcn.gsfc.nasa.gov/

Pith tools

Reviewed August 14, 2026 · model on record in the stance chip above.

[1] [1]

write newline

" write newline "" before.all 'output.state := FUNCTION blank.sep after.quote 'output.state := FUNCTION fin.entry output.state after.quoted.block = 'skip 'add.period if write newline FUNCTION new.block output.state before.all = 'skip output.state after.quote = after.quoted.block 'output.state := after.block 'output.state := if if FUNCTION new.sentence out...

[2] [2]

L. S. Collaboration, V. Collaboration, et al., Multi-messenger Observations of a Binary Neutron Star Merger, ApJL, 848, 59, 2017

work page 2017

[3] [3]

IceCube Collaboration, Fermi-LAT, MAGIC, et al., Multimessenger observations of a flaring blazar coincident with high-energy neutrino IceCube-170922A, Science, 361, 8, 2018

work page 2018

[4] [4]

U., et al., Observation of the Crab Nebula with the HAWC Gamma-Ray Observatory, ApJ, 843, 39, 2017

Abeysekara, A. U., et al., Observation of the Crab Nebula with the HAWC Gamma-Ray Observatory, ApJ, 843, 39, 2017

work page 2017

[5] [5]

IceCube Collaboration, M. G. Aartsen et al. , The IceCube Neutrino Observatory: Instrumentation and Online Systems, JINST, 12 , (2017), P03012

work page 2017

[6] [6]

Smith, et al., The Astrophysical Multimessenger Observatory Network (AMON), Astro

M. Smith, et al., The Astrophysical Multimessenger Observatory Network (AMON), Astro. Part. 45, 56, 2013

work page 2013

[7] [7]

H. A. Ayala Solares, et al., The Astrophysical Multimessenger Observatory Network (AMON), arXiv:180, 2018

work page 2018

[8] [8]

and Hooper , D., High-energy gamma rays and neutrinos from nearby radio galaxies , JCAPP, 2017, 12, 2017

Blanco , C. and Hooper , D., High-energy gamma rays and neutrinos from nearby radio galaxies , JCAPP, 2017, 12, 2017

work page 2017