GCN Circular 33649
Subject
Fermi-LAT gamma-ray observations of IceCube-230416A
Date
2023-04-18T18:08:48Z (a year ago)
From
Simone Garrappa at DESY <simone.garrappa@desy.de>
J. Sinapius (DESY-Zeuthen), S. Garrappa (Ruhr-Universitaet Bochum) and S. Buson (Univ. of Wuerzburg) on behalf of the Fermi-LAT collaboration:
We report an analysis of observations of the vicinity of the IC230416A high-energy neutrino event (GCN 33633) 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 2023-04-16 at 05:22:26.15 UT (T0) with J2000 position RA = 345.85 (+0.41, -0.63) deg, Decl. = +9.14 (+0.81, -0.76) deg (90% PSF containment). No cataloged gamma-ray (>100 MeV; The Fermi-LAT collaboration 2022, ApJS, 260, 53) sources are located within the 90% IC230416A localization region.
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 IC230416A best-fit position. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC230416A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 1.1e-10 ph cm^-2 s^-1 for ~14-years (2008-08-04 to 2023-04-16 UTC), and < 9.7e-9 (<6.5e-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 region will continue. For these observations the Fermi-LAT contact persons are S. Garrappa (simone.garrappa at ruhr-uni-bochum.de), J. Sinapius (jonas.sinapius 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.