TITLE:   GCN CIRCULAR
NUMBER:  31479
SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-220115A and detection of a new gamma-ray source, Fermi J2350.2+2620
DATE:    22/01/18 11:40:24 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 
IC220115A neutrino event (GCN 31451) 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 2022-01-15 12:11:39.75 UTC 
(T0) with J2000 position RA = 357.45 (+1.75, -1.18) deg, Decl. = 25.28 
(+1.03, -0.95) deg 90% PSF containment. No cataloged gamma-ray sources 
are found within the 90% IC220115A localization error (The Fourth 
Fermi-LAT catalog DR2; The Fermi-LAT collaboration 2020, ApJS, 247, 33).

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 (> 100 
MeV) at the the IC220115A best-fit position. 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 < 
5.6-10 ph cm^-2 s^-1 for ~13-years (2008-08-04 / 2022-01-15 UTC), < 
1.1e-8 (< 5.2e-8) ph cm^-2 s^-1 for a 1-month (1-day) integration time 
before T0.

Within the 90% confidence localization of the neutrino, ~1.1 deg offset 
from the best-fit IC220115A position, a >4 sigma excess of gamma rays, 
Fermi J2350.2+2620 was detected in an analysis of the integrated LAT 
data (> 100 MeV) between 2008-08-04 and 2022-01-15. Assuming a power-law 
spectrum, the candidate gamma-ray source has best-fit localization 
(J2000) RA: 357.564, Dec: 26.343 (0.15 deg 99% containment, 0.07 deg 68% 
containment), with best-fit spectral parameters flux = (8 +/- 5)e-10 ph 
cm^-2 s^-1 and index = 2.0 +/- 0.2. In a preliminary analysis of the LAT 
data over one day and one month prior T0, Fermi J2350.2+2620 is not 
significantly detected in the LAT data. All values include the 
statistical uncertainty only.

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.