TITLE: GCN CIRCULAR NUMBER: 45058 SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-260622A DATE: 26/06/30 23:04:48 GMT FROM: Simone Garrappa at Weizmann Institute of Science <simone.garrappa@weizmann.ac.il> S. Garrappa (Weizmann Institute of Science), L. Pfeiffer (Univ. of Wuerzburg), S. Buson (DESY, Univ. of Wuerzburg), J. Valverde (Marquette University) and C. Bartolini (University of Trento, INFN Bari) on behalf of the Fermi-LAT collaboration: We report an analysis of observations of the vicinity of the high-energy IC260622A neutrino event (GCN 45018) with all-sky survey data from the Large Area Telescope (LAT), on board the Fermi Gamma-ray Space Telescope. The IceCube event was detected on 2026-06-22 at 15:41:54.81 UTC (T0) with J2000 position RA = 173.36 (+0.5, -0.52) deg, Decl. = 1.34 (+0.58, -0.58) deg, 90% PSF containment. No cataloged >100 MeV gamma-ray sources are located within the 90% IC260622A localization error (4FGL-DR4; The Fourth Fermi-LAT catalog Data Release 4, The Fermi-LAT collaboration 2023, arXiv:2307.12546). In the preliminary list of the upcoming 5FGL catalog (FL16Y, Ballet et al. 2026), we find the gamma-ray source FL16Y 1134.2+0051 within the neutrino 90% PSF containment, at 0.53 deg from the best-fit neutrino position. From a preliminary analysis of Fermi-LAT data integrated on 1 month before T0, the source is significantly detected (> 5 sigma) in gamma-rays. The source is detected with a flux F = (1 +/- 0.3)e-7 ph cm^-2 s^-1 and best-fit power-law index 2.9 +/- 0.2, statistical errors only. A tentative counterpart to FL16Y 1134.2+0051 is the flat-spectrum radio source CRATES J1133+0058 (Healey et al. 2007, ApJS 171 1 61), ~9 arcmin from the Fermi-LAT best-fit localization and within its 68% error. We note that the localization region of IceCube-260622A is very close to the ecliptic; therefore the aforementioned results could be partially contaminated by the emission from the Moon. Time intervals with the Sun in the region of interest have been excluded from the analysis. We searched for the existence of intermediate (days to years) timescale emission from a new gamma-ray transient source. Preliminary analysis indicates no significant (>5sigma) new excess emission (> 100 MeV) within the IC260622A 90% confidence localization. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC260622A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 2.2e-10 ph cm^-2 s^-1 for ~18-years (2008-08-04 / T0), <1.2e-08 (<8.4e-07) ph cm^-2 s^-1 for a 1-month (1-day) integration time before T0. Since Fermi normally operates in an all-sky scanning mode, regular monitoring of this source will continue. For this source the Fermi-LAT contact person is Simone Garrappa (simone.garrappa at weizmann.ac.il). The Fermi LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden. View this GCN Circular online at https://gcn.nasa.gov/circulars/45058. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...