S. Garrappa (Weizmann Institute of Science), C. Bartolini (INFN Bari), S. Buson (Uni Wuerzburg) and J. Sinapius (DESY) on behalf of the Fermi-LAT collaboration:
We report an analysis of observations of the vicinity of the IC230725A high-energy neutrino event (GCN 34261) 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 2023-07-25 at 21:30:51.06 UT (T0) with J2000 position RA = 327.04 (+2.27, -2.03) deg, Decl. = 12.33 (+1.80, -1.36) deg (90% PSF containment). There is one Fermi 4FGL-DR3 cataloged gamma-ray (>100 MeV; The Fermi-LAT collaboration 2022, ApJS, 260, 53) source in the 90% IC230725A uncertainty localization region. This is 4FGL J2150.8+1118 associated with the BL Lac object NVSS J215051+111915, located at 1.2 deg from the IC230725A position. Based on a preliminary analysis of the LAT data over a month and day timescale prior T0, this object is not significantly detected at gamma rays.
We searched for intermediate (days to years) timescale emission from a new gamma-ray source. Preliminary analysis indicates no significant (> 5 sigma) new excess emission (> 100 MeV) at the IC230725A best-fit position. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC230725A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 3.5e-10 ph cm^-2 s^-1 for ~15-years (2008-08-04 to 2023-07-25 UTC), and < 5.3e-9 (< 7.3e-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 weizmann.ac.il), C. Bartolini (chiara.bartolini at ba.infn.it), S. Buson (sara.buson at uni-wuerzburg.de) and J. Sinapius (jonas.sinapius 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.