GCN Circular 45145
Subject
Fermi-LAT Gamma-ray Observations of IceCube-260708A
Event
Date
2026-07-13T11:10:59Z (3 days ago)
From
Leo Pfeiffer at University of Würzburg <pfeiffer.leo@gmail.com>
Via
Web form
L. Pfeiffer (Univ. of Wuerzburg), S. Buson (DESY, Univ. of Wuerzburg), S. Garrappa (Weizmann Institute of Science) and C. Bartolini (INFN Bari) on behalf of the Fermi-LAT collaboration:
We report an analysis of observations of the vicinity of the high-energy IC260708A neutrino event (GCN 45120) 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 2026-07-08 at 17:17:42.55 UTC (T0) with J2000 position RA = 292.81 (+0.48, -0.47) deg, Decl. = -15.17 (+0.44, -0.48) deg 90% PSF containment (J2000). No cataloged gamma-ray sources are found within the 90% IC260708A localization error (FL16Y, The Fermi-LAT 16 Year Source List, The Fermi-LAT collaboration 2026, arXiv:2602.22148).
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 IC260708A 90% confidence localization. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC260708A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 8.0e-10 ph cm^-2 s^-1 for ~18-years (2008-08-04 / T0), <5.7e-08 (<1.4e-07) ph cm^-2 s^-1 for a 1-month (1-day) integration time before T0.
We test the presence of an additional point source at the position of the optical transient AT2026kuv, which is a candidate supernova discovered by GOTO on 2026-04-20 (GCN 45125). The transient is located within the error region of IC260708A at 3.9 arcmin from the neutrino best-fit direction. No significant gamma-ray emission was detected. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the AT2026kuv best-fit position, the >100 MeV flux upper limit (95% confidence) is < 5.8e-08 ph cm^-2 s^-1 for a 1-month integration time before T0.
Since Fermi normally operates in an all-sky scanning mode, regular monitoring of this source will continue. For this analysis, the Fermi-LAT contact person is L. Pfeiffer (leonard.pfeiffer at uni-wuerzburg.de).
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.