GCN Circular 33561

S. Garrappa (Ruhr-Universitaet Bochum), J. Sinapius (DESY-Zeuthen), S. Buson (Univ. of Wuerzburg) and C. C. Cheung (Naval Research Laboratory) on behalf of the Fermi-LAT collaboration:
We report an analysis of observations of the vicinity of the IC230401A  high-energy neutrino event (GCN 33552
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 ) 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 2023-04-01 at 16:14:18.91 UT (T0) with J2000 position RA = 8.17 (+4.26, -2.91) deg, Decl. = +1.94 (+2.44, -1.96) deg (90% PSF containment).  Three cataloged gamma-ray (>100 MeV; The Fermi-LAT collaboration 2022, ApJS, 260, 53) sources are located within the 90% IC230401A  localization region. These are the sources 4FGL J0022.0+0006, 4FGL J0024.7+0349 and 4FGL J0038.1+0012. Based on a preliminary analysis of the LAT data over a month and day timescale prior T0, these objects are not significantly detected at gamma rays. 
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 IC230401A best-fit position. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC230401A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 1.2e-10 ph cm^-2 s^-1 for ~14-years (2008-08-04 to 2023-04-01 UTC), and < 2.5e-8 (<1.2e-7) ph cm^-2 s^-1 for a 1-month (1-day) integration time before T0.
In the analysis of the ~14-years integrated LAT data (100 MeV - 1 TeV), a 4.5 sigma new excess of gamma rays, Fermi J0030.2+0005, was detected 2 deg offset from the best-fit IC230401A  position and within the 90% confidence localization of the direction of the neutrino. Assuming a power-law spectrum, the best-fit localization is (J2000) RA: 7.56 deg, Dec: 0.09 deg (9 arcmin 99% containment, 5 arcmin 68% containment). The gamma-ray best-fit spectral parameters are flux =  (1.7 +/- 0.9)e-9 ph cm^-2 s^-1 and index = 2.3+/-0.2. In a preliminary analysis of the LAT data over 1-day and 1-month prior T0, Fermi J0030.2+0005 is not significantly detected in the LAT data. All values include the statistical uncertainty only. The statistical significance is calculated following the prescription adopted in the 4FGL.
A possible counterpart of Fermi J0030.2+0005 is the blazar object 5BZBJ0030-0000 at RA=7.53283 deg, Dec=-0.002 deg (Massaro et al. 2015 Ap&SS, 357, 1). This source is located about 6 arcmin from the Fermi J0030.2+0005 best-fit position, and within the gamma-ray 99% positional uncertainty.
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 <http://ruhr-uni-bochum.de/>), J. Sinapius (jonas.sinapius 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.