TITLE: GCN CIRCULAR NUMBER: 23608 SUBJECT: Fermi LAT Gamma-ray Observations of IceCube-190104A DATE: 19/01/05 01:55:50 GMT FROM: Sara Buson at GSFC/Fermi S. Ciprini (INFN Tor Vergata; ASI Space Science Data Center, Rome) S. Buson (Univ. of Wuerzburg), S. Garrappa (DESY-Zeuthen) on behalf of the Fermi-LAT collaboration: We report an analysis of observations of the vicinity of the very high-energy IC190104A neutrino event (GCN 23605) 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 2019-01-04 08:34:38.23 UTC with J2000 position RA = 357.98 (-2.1,+2.3) deg, Decl. = -26.65 (-2.5,+2.2) deg 90% PSF containment. There are no cataloged >100 MeV gamma-ray sources consistent with the IC180908A localization. The closest known gamma-ray object is 3FGL J2358.3-2853, 2.7 deg from the neutrino best-fit position, and is associated with the blazar PMN J2358 2853 (Ackermann et al. 2015 ApJS 810, 14). We searched for the existence of intermediate (months to years) timescale emission from a new gamma-ray transient source. Preliminary analysis indicates no significant (>5sigma) new excess emission (>100 MeV) within the IC190104A 90% confidence localization. Assuming a power-law spectrum (photon index = 2.2 fixed) for a point source at the IceCube best-fit position, the >100 MeV flux upper limits (95% confidence) are < 2.5e-10 ph cm^-2 s^-1 for ~10.5-years (2008-08-04 / 2019-01-03 UTC) integration time, < 1.1e-9 ph cm^-2 s^-1 for one year (2018-01-03 / 2019-01-03 UTC) integration time, and < 2.9e-8 ph cm^-2 s^-1 for one month (2018-12-04 / 2019-01-03 UTC) integration time before the IceCube IC190104A neutrino detection. Since Fermi normally operates in an all-sky scanning mode, regular monitoring of this source will continue. For this source the Fermi-LAT contact persons are S. Ciprini (stefano.ciprini at ssdc.asi.it), S. Buson (sara.buson at astro.uni-wuerzburg.de) and S. Garrappa (simone.garrappa at desy.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.