TITLE: GCN CIRCULAR NUMBER: 30978 SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-211023A DATE: 21/10/24 20:50:39 GMT FROM: Simone Garrappa at DESY <simone.garrappa@desy.de> S. Garrappa (DESY-Zeuthen), S. Buson (Univ. of Wuerzburg) and R. de Menezes (Univ. of Wuerzburg, Univ. of Sao Paulo) on behalf of the Fermi-LAT collaboration: We report an analysis of observations of the vicinity of the high-energy IC211023A neutrino event (GCN 30957) 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 2021-10-23 at 08:31:18.31 UT (T0) with J2000 position RA = 253.30 (+1.05,-1.08) deg, Decl. = -1.72 (+1.16, -1.11) deg (90% PSF containment). One cataloged gamma-ray (>100 MeV) source is located within the 90% IC211023A localization region. This is 4FGL J1653.6-0158 (4FGL-DR2, The Fermi-LAT collaboration 2020, ApJS, 247, 33), identified as PSR J1653-0158 (Nieder et al. 2020 ApJL 202, 46). Based on a preliminary analysis of the LAT data over the timescales of 1-day and 1-month prior to T0, this object is not significantly detected (> 5 sigma). We searched for intermediate (days to years) timescale emission from a new gamma-ray transient source. Preliminary analysis indicates no significant (> 5 sigma) new excess emission (> 100 MeV) at the IC211023A best-fit position. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC211023A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 8.8e-10 ph cm^-2 s^-1 for ~13-years (2008-08-04 to 2021-10-23 UTC), and < 1.6e-8 (< 1.9e-7) 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 S. Garrappa (simone.garrappa at desy.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.