TITLE:   GCN CIRCULAR
NUMBER:  31701
SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-220304A
DATE:    22/03/06 22:17:12 GMT
FROM:    Simone Garrappa at DESY  <simone.garrappa@desy.de>

S. Garrappa (DESY-Zeuthen), 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 high-energy 
IC220304A neutrino event (GCN 31679) with data from the Large Area 
Telescope (LAT), on board the Fermi Gamma-ray Space Telescope. The 
IceCube event was detected on 2022-03-04 17:44:12.21 UTC (T0) with J2000 
position RA = 48.78 (+7.68, -6.24) deg, Decl. = 4.48 (+5.91, -4.96) deg 
90% PSF containment. Several cataloged gamma-ray sources are found 
within the 90% IC220304A localization error (4FGL-DR3; arXiv:2201.11184; 
The Fermi-LAT collaboration 2020, ApJS, 247, 33). Based on a preliminary 
analysis of the LAT data over a 1-day integration time before T0, these 
sources are not significantly detected.

Based on a preliminary analysis of the LAT data over a 1-month 
integration time before T0, two cataloged LAT sources within the 90% 
IC220304A localization error are significantly (>5 sigma) detected. One 
is 4FGL J0313.0+0229, located ~2 deg from the neutrino best-fit 
localization and associated with the blazar of uncertain type TXS 
0310+022. This source is detected with an average monthly flux of�� (1.1 
+/- 0.2)e-7 ph cm^-2 s^-1 and photon index of 2.13 +/- 0.09. This flux 
value is ~20 times the value reported in the 4FGL-DR3, and the photon 
index is significantly smaller than the 4FGL-DR3 value of 2.48 +/- 0.08. 
An inspection of the one-month-binned light curve indicates that 4FGL 
J0313.0+0229 entered an elevated state roughly at the end of 2019 (also 
ATel#13463). The second object is the unidentified source 4FGL 
J0259.0+0552, located ~4.2 deg from the neutrino best-fit localization. 
The current average monthly flux is�� (4 +/- 2)e-8 ph cm^-2 s^-1 (~10 
times the 4FGL flux). The observed photon index of 2.1 +/- 0.2 is 
consistent with the 4FGL-DR3 value of 2.00 +/- 0.05. An inspection of 
the one-month-binned light curve of 4FGL J0259.0+0552 does not indicate 
any remarkable activity during the decade-long Fermi-LAT monitoring.

We searched for the existence of intermediate (day to months) timescale 
emission from a new gamma-ray transient source. Preliminary analysis 
indicates no significant (>5sigma) new excess emission within the 
IC220304A 90% confidence localization. Assuming a power-law spectrum 
(photon index = 2.0 fixed) for a point source at the IC220304A best-fit 
position, the >100 MeV flux upper limit (95% confidence) is < 1.2e-10 ph 
cm^-2 s^-1 for ~13-years (2008-08-04 to 2022-03-04 UTC), <1.2e-8 (< 
1.8e-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 this source 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.