GCN Circular 31258

S. Garrappa (DESY-Zeuthen), S. Buson (Univ. of Wuerzburg) 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 
IC211216B neutrino event (GCN 31249
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 ) 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 2021-12-16 23:41:13.93 UTC 
(T0) with J2000 position RA = 199.34 (+1.66, -1.78) deg, Decl. = 17.04 
(+1.39, -1.36) deg 90% PSF containment. Two cataloged >100 MeV gamma-ray 
sources are located within the 90% IC211216B localization error. No 
cataloged gamma-ray sources are found within the 90% IC211216B 
localization error (The Fourth Fermi-LAT catalog DR2; The Fermi-LAT 
collaboration 2020, ApJS, 247, 33).

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 (0.1 - 
300 GeV) within the IC211216B 90% confidence localization. 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 < 3.6-10 ph cm^-2 s^-1 for ~13-years (2008-08-04 / 
2021-12-16 UTC), < 1.8e-8 (< 1.2e-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.