TITLE:   GCN CIRCULAR
NUMBER:  33212
SUBJECT: Fermi-LAT gamma-ray observations of IceCube-230122A
DATE:    23/01/23 19:59:55 GMT
FROM:    Simone Garrappa at DESY  <simone.garrappa@desy.de>

S. Garrappa (Ruhr-Universitaet Bochum), 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 IC230122A 
high-energy neutrino event (GCN 33204) 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 2023-01-22 at 03:50:02.00 
UT (T0) with J2000 position RA = 16.79 (+3.17, -2.56) deg, Decl. = +7.78 
(+3.44, -3.26) deg (90% PSF containment). Five cataloged gamma-ray (>100 
MeV; The Fermi-LAT collaboration 2022, ApJS, 260, 53) sources are 
located within the 90% IC230122A localization region. Based on a 
preliminary analysis of the LAT data over the timescales of 1-month 
prior to T0, one of these objects,  the source 4FGL J0100.3+0745 
associated to the BL Lac object GB6 J0100+0745 (at 1.68 deg offset from 
the best-fit neutrino localisation), is detected at ~4 sigma level. The 
flux measured for the source, is however consistent with the average 
value measured in the 4FGL.

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 IC230122A 
best-fit position. Assuming a power-law spectrum (photon index = 2.0 
fixed) for a point source at the IC230122A best-fit position, the >100 
MeV flux upper limit (95% confidence) is < 2.9e-10 ph cm^-2 s^-1 for 
~14-years (2008-08-04 to 2023-01-22 UTC), and < 6.5e-9 (<1.4e-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 region will continue. For these observations the 
Fermi-LAT contact persons are S. Garrappa (simone.garrappa at 
ruhr-uni-bochum.de), J. Sinapius (jonas.sinapius 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.