Searches for Gamma-Ray Counterparts of IceCube Neutrino Events in the AGILE Public Data Archive

Searches for Gamma-Ray Counterparts of IceCube Neutrino Events in the AGILE Public Data Archive Elena Gasparri, Rosa Poggiani^, Carlotta Pittori, Fabrizio Lucarelli, Paolo Giommi ^ Department of Physics “E. Fermi”, University of Pisa, INFN Pisa, INAF/IAPS Rome, Italy XXI International Workshop on Neutrino Telescopes, Padova, Italy, September 29 - October 3 2025 High energy astrophysical neutrinos Outline: -Search of AGILE gamma-ray counterparts of IceCube neutrino events -Preliminary results: investigation of a sample of IceCube neutrinos from 2018 to 2020 covering EHE, HESE, GOLD (>2019) events -Search for detections in the AGILE gamma-ray public data archive -Search for associated blazars in the neutrino candidate error region -Estimate relative contribution of LBL/IBL/HBL as neutrino emitters 2 Based on Elena Gasparri’s master thesis, University of Pisa, advisors R. Poggiani, C. Pittori Blazar TXS 0506+056 identified as EM counterpart of IC-170922A neutrino (Aartsen+ 2018) Many works about correlation with blazar catalogs and searches for EM counterparts of neutrino events: Lucarelli+ 2017, 2019: AGILE counterparts of IC-160731A, IC-170321A, IC-170922A Krauss+ 2018: Fermi-LAT 3LAC Aartsen+ 2020: NGC 1068, TXS 0506+056, PKS 1424+240, and GB6 J1542+6129 Abbasi+ 2022: evidence for neutrino emission from the nearby active galaxy NGC 1068 Giommi+ 2020, Franckowiak+ 2020: evidence for blazar connection Plavin+ 2020: radio bright active galaxies as high energy neutrinos source Hovatta+ 2021: association of IceCube neutrinos with OVRO sources Kun+ 2021: neutrinos from temporarily gamma-suppressed blazars (OVRO data) Garrappa+ 2021: Fermi-LAT follow-ups of high energy neutrino alerts (4FGL-DR2) Liodakis+ 2022: extraterrestrial high-energy neutrino counterparts Giommi&Padovani 2021: astrophysical neutrinos and blazars Sahakyan+ 2022: multi-messenger study of PKS 0735+178 Abbasi+ 2023: Fermi-LAT 4LAC-DR2, Radio Fundamental Catalog Abbasi+ 2023: HE neutrinos from the Galactic plane Plavin+ 2023, Suray+ 2023: VLBI blazars and RFC Catalog Bellenghi+ 2023: BZCAT blazars and RFC sources Garrappa+ 2024: Fermi-LAT observations Kouch+ 2024: association with CGRaBS blazars Abbasi+ 2024: association with MOJAVE AGN Abbasi+ 2025: association with millimeter bright blazars ... 3 IceCube •Neutrino detection via Charged Current (CC), Neutral Current (NC) (σ ~ 10-38 cm2 at 1 GeV): •Charged Current (CC) •Neutral Current (NC) Track-like Cascade-like IceCube Collaboration Track-like 4 Δψ < 1° for E > 1 TeV Δψ ~ 10°-15° •EHE (Extremely High Energy event): E = 500 TeV - 10 PeV •HESE (High Energy Starting Event): track-like events with interaction vertex inside detector, E = 100 TeV - 1PeV •GOLD (>2019): signalness > 50% •BRONZE (>2019): signalness > 30% IceCube Alert System (> 2016) δ =declination The AGILE Mission AGILE-GRID: •Silicon Tracker (ST): gamma-ray conversion into e+/epairs, charged particles track reconstruction. Energy range: 30 MeV–50 GeV FOV ~ 2.5 sr Angular resolution ~1.2° for E > 100 MeV (up to 30° off-axis) Sensitivity (10-20)x10-8 ph/cm2/s (depending on sky region, exposure time) •Minicalorimeter (MCAL): measurement of charged particle energy (for estimation of incident photons energy). Also, standalone instrument sensitive in the range 300 keV–100 MeV with a 4π sr acceptance > 800 AGILE references, among them >160 refereed papers, 12 catalogs •Launch: 23/04/2007, 17 years activity •End of scientific operations: 18/01/2024 •Low Equatorial Orbit, 2.5° inclination •Average altitudine: ~ 500 km •Since 2009: "Spinning" observing mode •Revolution period ~ 7 min: 80% sky coverage every day Tavani+ 2008 Tavani+ 2008 Tavani+ 2019 5 6  AGILE - LV3 ( SSDC Analysis tool) Gamma-ray standard AGILE data analysis method for detections and upper limits in light curves: Test statistic (TS) of Maximum Likelihood ratio (ML) used to compare null hypothesis (diffuse background only) with presence of a source. Asymptotic distribution of TS (Wilks’ theorem 1938): ~(½)χ12 Practically: for N>10-20, significance of a detection is the number of standard deviations σ ~ sqrt(TS) (Mattox+ 1996) Analysis Output Bin duration: 2, 4, 7, 28 days, MJD of detection with uncertainty, flux, flux uncertainty, significance. Detection candidate: ML results with sqrt(TS) > 3, light curve, SED data AGILE-GRID data analysis: data reduction software developed by AGILE Team and integrated in an automatic pipeline system at ASI Space Science Data Center (SSDC) SSDC AGILE-LV3 data analysis tool: built on top of command-line version of AGILE-GRID standard software package ( AGILE_SW_6.0_SourceCode/), using official on-line Maximum Likelihood analysis on AGILE LV3 data The IceCube neutrino sample (16 events) (September 2018 – March 2020) *: 50% CL for EHE neutrinos, 90% CL for HESE, GOLD neutrinos **: energy in photoelectrons for HESE neutrinos 7 Sample analized in Elena Gasparri's Master thesis (2022) Identification of candidate counterparts •Analysis of AGILE-LV3 maps around time T0 of neutrino event: time bin 2, 4, 7 and 28 days •Building AGILE light curves centered on neutrino arrival direction and looking for candidate detections with sqrt(TS) > 3: •T0 ± 1 month •T0 ± 1 year •Full-mission •Search with VOU-Blazars (Chang+ 2019) for sources within a radius of 90 arcmin around the reconstructed neutrino direction •Search for multi-frequency observations to build light curves of candidate counterparts and SED for classification 8 Results: EHE neutrinos 2 events out of 3 show a candidate detection within ± 1 year around T0 of neutrino event New candidate counterparts (not previously reported in literature) in bold 9 Results: HESE neutrinos 3 events out of 6 show a candidate detection within ± 1 year around T0 of neutrino event 2AGL associated source Multiple detections in all light curves, only those closest to T0 reported here IC-190730A (GOLD) 16 Ding+ ApJ 881 (2019) 125: multifrequency light curves Kun+ ApJ 911 (2021) 18: gamma-ray minimum, high radio flux at T0 Rodrigues+ ApJ 912 (2021) 54: modelling Britzen+ MNRAS 503 (2021) 3145: ring accelerator? Oikonomou+ JCAP 10 (2021) 082: modelling Blinov, Novikova A&A 694 (2025) 10: connection between repeating patterns of gamma-ray flares in blazars and highenergy neutrino events (also IC-170922A and IC-150926A) IC-190619A (GOLD) T0 = 58653 MJD Closest detection, 4 days bin: ΔT = -0.47 yr MJD Detection= 56785.5 ± 2.0 d Flux = (1.14 ± 0.52)e-6 ph/cm^2/s, sqrt(TS)=3.3 17 90 arcmin search radius IC-190619A (GOLD) 18 Recent paper: Ji and Wang, ApJL 975 (2024) L30: 4FGL J2257.5+0748/PKS 2254+074 (3.2 deg distance) as possible counterpart AGILE detections: -56785.5 +/ -2, flux 1.14e-6, sqrt(TS)=3.3 (W1, W2 decline, low γ-rays) -58485.5 +/- 2, flux 1.18e-6, sqrt(TS)=3.3 (rising flux) VOU-Blazar search, 250 arcmin radius, detects PKS 2254+074 Preliminary results •HBL sub-class favoured compared to IBL, LBL subclass •HESE neutrinos most prolific producers of possible AGILE gamma-ray counterparts 19 Conclusions •16 IceCube neutrino events from 09/2018 to 03/2020, full-mission AGILE-GRID analysis with multi-frequency light curves and SED of candidates found with VOU-Blazars •AGILE-GRID data do not show flaring sources or transients over time scales of the order of days around T0 •8 out of 16 light curves show a significant detection (√ > 3) within T𝑇𝑆 0 ± 1 year: •2 out of 3 EHE neutrinos (IC-180908A, IC-190503A) •3 out of 6 HESE neutrinos (IC-190104A, IC-190221A, IC-190504A) •3 out of 7 GOLD neutrinos (IC-190619A, IC-190922A, IC-191001A) •2 out of 16 light curves: blazars associated to the 2AGL catalog sources: •2AGL J0429-3755 for IC-190504A (HESE) •2AGL J1507+1019 for IC-190730A (GOLD) •For the neutrino event IC-190221A the AGILE-GRID data show a detection above 100 MeV with a post-trial significance of ~3.9 sigma in the time window T0 ± 1 month in a 7-day binning light curve •HBL blazar most favourite class •HESE neutrinos show the largest number of detections in AGILE light curves 20