TITLE: GCN CIRCULAR NUMBER: 33167 SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-Cascade-230109A DATE: 23/01/14 01:15:02 GMT FROM: Simone Garrappa at DESY J. Sinapius (DESY-Zeuthen), S. Buson (Univ. of Wuerzburg), S. Garrappa (Ruhr-Universitaet Bochum) on behalf of the Fermi-LAT collaboration: We report an analysis of observations of the vicinity of the IceCube-Cascade-230109A high-energy neutrino event (https://gcn.gsfc.nasa.gov/notices_amon_icecube_cascade/137527_43987982.amon) 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 2023-01-09 at 11:12:11.29 UT (T0) with J2000 position RA = (174.81 +/- 7.07) deg, Decl. = (45.33 +/- 7.07) deg (90% PSF containment). Several cataloged gamma-ray (>100 MeV) sources are located within the 90% IceCube-Cascade-230109A localization region (4FGL-DR3; The Fermi-LAT collaboration 2022, ApJS, 260, 53). Based on a preliminary analysis of the LAT data over the timescales of 1-day and 1-month prior to T0, one of these objects is significantly detected (> 5 sigma). This source is the FSRQ 4FGL J1146.9+3958 at 5.45 deg from the IC-Cascade-230109A best-fit position.  In a preliminary analysis of LAT data over 30 days before T0, the object is observed at a flux level of (9.38 +/- 1.70) e-8 ph cm^-2 s^-1, consistent with the average value reported in 4FGL-DR3. We searched for intermediate (days to months) timescale emission from a new gamma-ray transient source. Preliminary analysis indicates no significant (> 5 sigma) new excess emission (> 100 MeV) at the IceCube-Cascade-230109A best-fit position. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IceCube-Cascade-230109A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 2.6e-9 (< 5.2e-8) 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 these observations the Fermi-LAT contact persons are J. Sinapius (jonas.sinapius at desy.de), S. Garrappa (simone.garrappa at ruhr-uni-bochum.de) and S. Buson (sara.buson 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.