GCN Circular 28519

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 
IC200926B neutrino event (GCN 28509
Not found
 
 
) 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 2020-09-26 at 22:35:29.22� 
UT (T0) with J2000 position RA = 184.75 (+3.64, -1.55) deg, Decl. = 
32.93 (+1.15, -0.91) deg 90% PSF containment. No cataloged >100 MeV 
gamma-ray sources (The Fourth Fermi-LAT catalog; The Fermi-LAT 
collaboration 2020, ApJS, 247, 33) are located within the 90% IC200926B 
localization error.

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 IC200926B 
best-fit position. Assuming a power-law spectrum (photon index = 2.0 
fixed) for a point source at the IC200926B best-fit position, the >100 
MeV flux upper limit (95% confidence) is < 1.4e-10 ph cm^-2 s^-1 for 
~12-years (2008-08-04 / 2020-09-26 UTC), < 6.6e-9 (<1e-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.