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GCN Circular 31257

Subject
Fermi-LAT Gamma-ray Observations of IceCube-211216A
Date
2021-12-18T01:06:44Z (2 years ago)
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 
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.
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