TITLE:   GCN CIRCULAR
NUMBER:  31097
SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-211117A
DATE:    21/11/20 10:52:28 GMT
FROM:    Sara Buson at GSFC/Fermi  <sara.buson@gmail.com>

R. de Menezes (Univ. of Wuerzburg, Univ. of Sao Paulo), S. Garrappa (DESY-Zeuthen) and S. Buson (Univ. of Wuerzburg) on behalf of the Fermi-LAT collaboration:

We report an analysis of observations of the vicinity of the high-energy IC211117A neutrino event (GCN 31093) 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 2021-11-17 at 18:27:03 UT (T0) with J2000 position RA = 225.93 (+0.51,-0.51) deg, Decl. = -0.20 (+0.51, -0.51) deg (90% PSF containment). No cataloged gamma-ray (>100 MeV) source is located within the 90% IC211117A localization region (4FGL-DR2, The Fermi-LAT collaboration 2020, ApJS, 247, 33). 

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 IC211117A best-fit position. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC211117A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 9.5e-10 ph cm^-2 s^-1 for ~13-years (2008-08-04 to 2021-11-17 UTC), and < 4.5e-9 (< 1.26e-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 these observations the Fermi-LAT contact persons are R. de Menzes (raniere.menezes 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.