GCN Circular 30895

S. Garrappa (DESY-Zeuthen), S. Buson (Univ. of Wuerzburg) and R. de 
Menezes (Univ. of Sao Paulo, Univ. of Wuerzburg) on behalf of the 
Fermi-LAT collaboration:

We report an analysis of observations of the vicinity of the high-energy 
IC210926A neutrino event 
(<https://gcn.gsfc.nasa.gov/notices_amon_icecube_cascade/135747_58376130.amon>) 
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 
2021-09-26 at 05:26:10.94 UT (T0) with J2000 position RA = 249.4993 deg, 
Decl. = -35.7347 deg (centered at an error region with 10.18��� radius, 
90% PSF containment). Several cataloged gamma-ray (>100 MeV) sources are 
located within the 90% IC210926A localization region (4FGL-DR2, The 
Fermi-LAT collaboration 2020, ApJS, 247, 33).

We searched for intermediate (days to month) timescale emission from a 
new gamma-ray transient source. Preliminary analysis indicates no 
significant (> 5 sigma) new excess emission (> 100 MeV) at the IC210926A 
best-fit position. Assuming a power-law spectrum (photon index = 2.0 
fixed) for a point source at the IC210926A best-fit position, the >100 
MeV flux upper limit (95% confidence) is < 6.3e-9 (< 5.6e-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.