GCN Circular 27620

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 
IC200421A neutrino event (GCN 27612
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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 2020-04-21 00:35:24.24 UT 
(T0) with J2000 position RA = 87.93 (+3.44, - 2.83) deg, Decl. = 8.23 
(+2.09, -1.84) deg 90% PSF containment. No cataloged >100 MeV gamma-ray 
sources are located within the 90% IC200421A localization error.

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 IC200421A 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 < 2e-9 ph cm^-2 s^-1 for ~11-years (2008-08-04 / 
2020-04-21 UTC), < 8e-9 (< 5e-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 this source the Fermi-LAT 
contact persons are S. Garrappa (simone.garrappa at desy.de 
<http://desy.de/>) and S. Buson (sara.buson at uni-wuerzburg.de 
<http://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.