Status of Realtime Neutrino Alerts in IceCube

Status of Realtime Neutrino Alerts in IceCube Sarah Mancina for the IceCube Collaboration XXI Workshop on Neutrino Telescopes Neutrino Astrophysics Padova, Italy October 2nd, 2025 1 Source: IceCube/NSF Neutrinos in TeV-scale multi-messenger astrophysics (MMA) 2 Gamma Ray Neutrino Cosmic Ray Gamma ray challenges: ●Absorbed by background radiation ●Ambiguous origin: leptonic and hadronic acceleration Cosmic ray challenges: ●Path altered by magnetic fields AGN, TDE, SNR…? Muon Track Angular Resolution: 0.6° Log Energy Resolution: 20% of muon energy at detector entry Atmospheric muons, charged current νμ and ντ (τ → μ + ν’s) Electromagnetic/Hadronic Cascade Angular Resolution: 5°-15° Log Energy Resolution: 15% of neutrino energy Neutral current ν, charged current νe and ντ (τ → e/hadrons + ν’s) Dust layer IceCube detector and event morphologies 3 Digital Optical Module (DOM) Atmospheric background dominates astrophysical signal 4 Atmospheric Muons (south only) 3000 per second Atmospheric Neutrinos ~1 per second Astrophysical Neutrinos ~1 per day Atmospheric Muon Atmospheric Neutrino Astrophysical Neutrino Power-law ϕ ∝ Eγ ~100 TeV Source Location Transient/Flaring Sources + Multimessenger Data Using realtime neutrino alerts to find astrophysical sources 5 IceCube: near 100% uptime and view of full sky Send neutrino targets-of-opportunity to other instruments 6 Filters run on computing system at Pole Events of interest fast tracked to north via Iridium satellites Median latencies: ●South pole processing: 2 s ●Event summary received: 30 s ●Full event received: 40 s Alert stream clients further analyze events using the northern computing systems Communicating events for realtime alerts from the South Pole First example of neutrinos in MMA: TXS 0506+056 7 Fermi-LAT 20 MeV - 300 GeV MAGIC 80-400 GeV DOI: 10.1126/science.aat1378 (2017) high energy neutrino coincided with flare from blazar TXS 0506+056 (3σ significance) Flare observed across electromagnetic spectrum Archival neutrino flare also found by IceCube (also at 3σ) DOI: 10.1126/science.aat2890 Archival neutrino flare The IceCube realtime platform timeline 8 Astropart. Phys., 92, 30 (2017), ApJS 269 25 (2023) Single high-energy event alerts 9 Power-law ϕ ∝ Eγ Neutrino fluxes across decades of energy Rev. Mod. Phys. 92, 45006 (2020) ~100 TeV Events with hundreds of TeV are likely astrophysical neutrinos Alerts report “signalness” or “p-astro”: ratio of expected signal to total signal+background rate ⇒ depends on reconstructed energy and direction and spectral assumption Shared publicly via NASA GCN: - GCN Noticies with quick reconstructions - GCN Circulars with refined reconstructions Work in progress: Provide probability sky maps from the refined reconstructions Conclusions 16 IceCube alerts MMA community of neutrino targets-of-opportunity Realtime platform consists of: ●Single high-energy event alerts ●Neutrino cluster alerts ●Follow-up of external triggers New IceCat-2 with improved directional contours to be available soon GFU-cluster alerts to be public with Neutrino Flarewatch website for source monitoring Follow-up of KM3-230213A in progress, but no correlated alerts from IceCube POS-ICRC2025-1224 Backup 17 GFU Event Sample Properties 18 Gamma-ray Follow-Up (GFU) event sample covers full-sky Harsh energy requirements in southern sky to remove cosmic-ray background Earth absorption effect seen in northern sky for high energy events Time-dependent Likelihood Approach 19 Uniform Time PDF S/B PDF Penalty factor for small time windows Final Test Statistic (TS) Azimuthal term for short time-windows Fitted parameters Example of IACT follow-up: VERITAS and B3 2447+381 IACT can request a more complete report for GFU-cluster alerts IACT analysers look at multiwavelength (MW) data for more evidence of transient activity VERITAS sends ToO to NuSTAR (hard X-ray) for further follow-up 20 DOI: 10.3847/1538-4357/adb30c IceCube GFU-cluster Alerts IACT γ-rays Fermi-LAT γ-rays Swift XRT/NuSTAR x-rays Optical Optical Not a light-curve! Blazar B3 2447+381 Example of IACT follow-up: H.E.S.S. and 1ES 1312-423 GFU-cluster alert from direction of 1ES 1312-423 in 2019 H.E.S.S. 4σ observation can be compared to archival analysis Besides TXS 0506+056, no TeV γ-ray flares identified by follow-ups of neutrino alerts 21 ICRC(2023)1501 H.E.S.S. measurement at time of alert Archival H.E.S.S. measurement 1ES 1312-423 Proposed public alerts distribution 22 False alarm rate calculated by running simulations of 1 year of scrambled data Proposed thresholds: ●σpre = 3.00σ, ~20 bkg alerts per year ●σpre = 3.75σ, ~1 bkg alert per year ●σpre = 4.50σ, ~0.05 bkg alerts per year NASA GCN: Multi-threshold system to provide updates on interesting activity FlareWatch Website: Provide updates on sources without notifications Single example of a simulated source significance curve 23 Injected source: ●5 signal events ●50 day flare duration ●γ = -2 Each point includes data from previous 180 days Not a light curve, adjacent points use overlapping data Significance decays over time as no new signal Best-fit time window Neutrino FlareWatch website - archival alerts page 24 ⭐ Low Threshold (20 bkg per year) ⭐⭐ Medium Threshold (1 bkg per year) ⭐⭐⭐ High Threshold (0.05 bkg per year)