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
IC211216A neutrino event (GCN 31241) 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 2021-12-16 07:07:38.13 UTC
(T0) with J2000 position RA = 316.05 (+2.58, -1.95) deg, Decl. = 15.79
(+1.29, -1.63) deg 90% PSF containment. Two cataloged >100 MeV gamma-ray
sources are located within the 90% IC211216A localization error. These
are 4FGL J2100.0+1445 at a distance of roughly 1.5 deg and 4FGL
J2108.5+1434 at a distance of roughly 1.6 deg (The Fourth Fermi-LAT
catalog DR2; The Fermi-LAT collaboration 2020, ApJS, 247, 33). Based on
a preliminary analysis of the LAT data over the 1-month timescale before
T0, these objects are not significantly detected at gamma-rays.
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 (0.1 -
300 GeV) within the IC211216A 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 < 6.3e-10 ph cm^-2 s^-1 for ~13-years (2008-08-04 /
2021-12-16 UTC), < 4.2e-9 (< 2.3e-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 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.