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GCN Circular 33920

Fermi-LAT gamma-ray observations of IceCube-230603A
2023-06-05T20:50:06Z (a year ago)
Simone Garrappa at DESY <>
S. Garrappa (Ruhr-Universitaet Bochum), S. Buson (Univ. of Wuerzburg) and J. Sinapius (DESY-Zeuthen)on behalf of the Fermi-LAT collaboration:

We report an analysis of observations of the vicinity of the IC230603A   high-energy neutrino event (GCN 33911) 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 2023-06-03 at 05:00:47.13 UT (T0) with J2000 position RA =68.20 (+2.62, -3.06) deg, Decl. = +24.21 (+2.08, -2.59) deg (90% PSF containment).  Two cataloged gamma-ray (>100 MeV; The Fermi-LAT collaboration 2022, ApJS, 260, 53) sources are located within the 90% IC230603A localization region. These are 4FGL J0439.2+2151, associated with the blazar candidate of uncertain type IERS B0435+217, and the unassociated source 4FGL J0441.8+2600c. 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 IC230603A best-fit position. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC230603A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 1.8e-10 ph cm^-2 s^-1 for ~14-years (2008-08-04 to 2023-06-03 UTC), and < 9.7e-9 (< 9.5e-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 <>), J. Sinapius (jonas.sinapius <>) and S. Buson (sara.buson <>).

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.

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