TITLE: GCN CIRCULAR NUMBER: 31653 SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-220225A DATE: 22/02/26 01:39:33 GMT FROM: Simone Garrappa at DESY S. Garrappa (DESY-Zeuthen), S. Buson (Univ. of Wuerzburg), C. C. Cheung (Naval Research Laboratory) and J. Sinapius (DESY-Zeuthen) on behalf of the Fermi-LAT collaboration: We report an analysis of observations of the vicinity of the high-energy neutrino event IC220225A (GCN 31650) 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 2022-02-25 14:12:00.7 UTC (T0) with J2000 position RA = 34.7 (+3.1, -2.6) deg, Dec = 0.0 (+1.8, -1.5) deg (90% PSF containment). Two cataloged >100 MeV gamma-ray sources are located within the 90% IC220225A localization error (The Fourth Fermi-LAT catalog, 4FGL-DR3; The Fermi-LAT collaboration 2022, arXiv:2201.11184). These are 4FGL J0217.8+0144, located ~1.75 deg from the neutrino best-fit position and associated with the flat-spectrum radio quasar PKS 0215+015 located at z = 1.715 (Foltz & Chaffee 1987, AJ, 93, 529) and 4FGL J0208.5-0046, located ~2.7 deg from the neutrino best-fit position and associated with the BL Lac object PKS 0205-010 with an uncertain SDSS-based redshift (Richards et al. 2004, ApJS, 155, 258; Richards et al. 2009, ApJS, 180, 67). Based on a preliminary analysis of the LAT data over a 1-day and 1-month integration time before T0, 4FGL J0208.5-0046 is not significantly detected at gamma rays. 4FGL J0217.8+0144 has been in an enhanced gamma-ray activity state since mid-2021.  Preliminary analysis of the 1-day interval preceding T0 indicates that the source is in a high state with flux (E>100 MeV) of (3+/-1) x 10^-7 photons cm^-2 s^-1 (integrated before T0, statistical uncertainty only) and power-law index 2.3 +/- 0.3. This flux is more than 7 times greater than the average flux reported in the 4FGL-DR3 catalog. Averaged over the month preceding T0, the flux (E>100 MeV) is (1.6+/-0.2) x 10^-7 photons cm^-2 s^-1 (statistical uncertainty only), more than 3 times greater than the average flux reported in the 4FGL-DR3 catalog, and the power-law index is 2.1 +/- 0.1 . The gamma-ray spectral indices of the flaring state are consistent with the value reported in the latest 4FGL-DR3 catalog (index = 2.21 +/- 0.02). A preliminary light curve can be accessed via the Fermi-LAT Light-Curve Repository at https://fermi.gsfc.nasa.gov/ssc/data/access/lat/LightCurveRepository/source.php?source_name=4FGL_J0217.8+0144. 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) at the the IC220225A best-fit position. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IceCube best-fit position, the >100 MeV flux upper limit (95% confidence) is < 2.5 x 10^-10 ph cm^-2 s^-1 for ~13-years (2008-08-04 / 2022-02-25 UTC), < 1.0x 10^-8 (< 1.1 x 10^-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 region 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). We encourage multifrequency observations of these sources. 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.