GCN Circular 29135

S. Garrappa (DESY-Zeuthen) and S. Buson (Univ. of Wuerzburg) on behalf 
of the Fermi-LAT collaboration:

We report an analysis of observations of the vicinity of the high-energy 
IC201221A neutrino event (GCN 29102
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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 2020-12-21 at 12:36:53.45 
UT (T0) with J2000 position RA = 261.69 (+2.29, -2.50) deg, Decl. = 
41.81 (+1.29, -1.20) deg (90% PSF containment). No cataloged >100 MeV 
gamma-ray source is located within the 90% IC201221A localization region.

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 IC201221A 
best-fit position. Assuming a power-law spectrum (photon index = 2.0 
fixed) for a point source at the IC201221A best-fit position, the >100 
MeV flux upper limit (95% confidence) is < 3.3e-10 ph cm^-2 s^-1 for 
~12-years (2008-08-04 to 2020-12-21 UTC), and < 3.6e-9 (< 4.1e-8) 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.