TITLE:   GCN CIRCULAR
NUMBER:  31768
SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-220317A
DATE:    22/03/18 22:00:09 GMT
FROM:    Sara Buson at GSFC/Fermi  <sara.buson@gmail.com>

S. Buson (Univ. of Wuerzburg) and S. Garrappa (DESY-Zeuthen) on behalf of the Fermi-LAT collaboration:

We report an analysis of observations of the vicinity of the high-energy IC-220317A neutrino event (GCN 31762) 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 2022-03-17 at 02:32:17.68 UT (T0) with J2000 position RA = 155.74 (+2.23, -1.74) deg, Decl. = 11.19 (+1.00, -1.39) deg (90% PSF containment). One cataloged gamma-ray (>100 MeV) source is located within the 90% IC-220317A localization region. This is 4FGL J1018.9+1043  (4FGL-DR3; arXiv:2201.11184; The Fermi-LAT collaboration 2020, ApJS, 247, 33), associated with the blazar of uncertain type WISEA J101857.98+103625.5. Based on a preliminary analysis of the LAT data over the timescales of 1-day and 1-month prior to T0, this object is not significantly detected (> 5 sigma).

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 IC-220317A best-fit position. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC-220317A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 2.0e-10 ph cm^-2 s^-1 for ~13-years (2008-08-04 to 2022-03-17 UTC), and < 2.2e-8 (< 9.6e-8) 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 these observations the Fermi-LAT contact persons are S. Buson (sara.buson at uni-wuerzburg.de) and S. Garrappa (simone.garrappa at desy.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.