TITLE: GCN CIRCULAR NUMBER: 33075 SUBJECT: Fermi-LAT gamma-ray observations of IceCube-221210A DATE: 22/12/16 23:09:54 GMT FROM: Simone Garrappa at DESY J. Sinapius (DESY-Zeuthen), S. Buson (Univ. of Wuerzburg) and S. Garrappa (Ruhr Universitaet Bochum) on behalf of the Fermi-LAT collaboration: We report an analysis of observations in the vicinity of the high-energy IC221210A neutrino event (GCN 33040) 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 2022-12-10 at 08:35:11.23 UT (T0) with J2000 position RA = 332.58 (+9.84, -11.77) deg, Decl. = +22.75 (+8.15, -4.13) deg (90% PSF containment). Due to the large uncertainty on the neutrino localization, severalĀ  cataloged gamma-ray (>100 MeV) sources are located within the 90% IC221210A localization region (4FGL-DR3; arXiv:2201.11184; The Fermi-LAT collaboration 2020, ApJS, 247, 33). 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 IC221210A best-fit position. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC221210A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 1.5e-10 ph cm^-2 s^-1 for ~13-years (2008-08-04 to 2022-12-10 UTC), and < 6.6e-9 (< 1.7e-7) ph cm^-2 s^-1 for a 1-month (1-day) integration time before T0. The catalogued source 4FGL J2212.0+2356, associated with the flat-spectrum radio quasar PKS 2209+236, is located 1.25 deg from the best-fit neutrino position. An inspection of the Fermi-LAT data over the 14 years of LAT observations, shows that on timescales of 1-month, the object is a relatively stable and faint gamma-ray emitter. Integrating over a time interval of 1-month prior to T0, the source is significantly detected (> 5 sigma). A preliminary analysis of the data over the past year, indicates that the source is undergoing enhanced activity. It is currently in a fading phase of a flaring episode that started circa September 2022. The peak-activity flux of F = (1.4 +/- 0.2)e-7 ph cm^-2 s^-1, about 10 times the average 4FGL value, is observed between October and November 2022 (see also FAVA light curve https://fermi.gsfc.nasa.gov/ssc/data/access/lat/FAVA/LightCurve.php?ra=333.02&dec=23.93). Three additional sources are significantly detected (> 5 sigma) over a time interval of 1-month prior to T0, with fluxes comparable to their average 4FGL value. 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 J. Sinapius (jonas.sinapius at desy.de), 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.