GCN Circular 31947
Subject
Fermi-LAT Gamma-ray Observations of IceCube-220424A
Event
Date
2022-04-25T07:55:40Z (4 years ago)
From
Sara Buson at GSFC/Fermi <sara.buson@gmail.com>
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 IC220424A neutrino event (GCN 31942) 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 2022-04-24 at 01:06:24.06 UT (T0) with J2000 position RA = 346.11 (+1.26, -1.33) deg, Decl. = +8.91 (+0.95, -1.01) deg (90% PSF containment). One cataloged gamma-ray (>100 MeV) source is located within the 90% IC220424A localization region (4FGL-DR3; arXiv:2201.11184; The Fermi-LAT collaboration 2020, ApJS, 247, 33). This is the unassociated gamma-ray source 4FGL J2306.6+0940.
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 IC220424A best-fit position. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC220424A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 1.5e-10 ph cm^-2 s^-1 for ~13-years (2008-08-04 to 2022-04-24 UTC), and < 5.1e-9 (< 4.1e-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. Garrappa (simone.garrappa at desy.de <http://desy.de/>) and S. Buson (sara.buson at uni-wuerzburg.de <http://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.