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GCN Circular 34715

Subject
Fermi-LAT gamma-ray observations of IceCube-230914A
Date
2023-09-16T19:38:45Z (6 days ago)
From
Simone Garrappa at DESY <simone.garrappa@desy.de>
Submitted By
email
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 IC230914A  high-energy neutrino event (GCN 34693) 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 2023-09-14 at 05:21:03.71 UT (T0) with J2000 position RA =  163.83 (+2.60, -2.02) deg, Decl. = +31.83 (+1.79, - 2.13) deg (90% PSF containment). There are two Fermi 4FGL-DR4 cataloged  gamma-ray (>100 MeV; The Fermi-LAT collaboration 2022, ApJS, 260, 53; Ballet et al. 2023, arXiv:2307.12546) sources in the 90% IC230914A uncertainty localization region. These are 4FGL J1051.6+3253 associated with the starburst galaxy NGC 3424 and 4FGL J1102.9+3014 associated with the FSRQ B2 1100+30B, at a distance of from the best-fit neutrino localization of 1.3 deg and 2.3 deg, respectively. 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 source. Preliminary analysis indicates no significant (> 5 sigma) new excess emission (> 100 MeV) at the IC230914A best-fit position. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC230914A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 3.9e-10 ph cm^-2 s^-1 for ~15-years (2008-08-04 to 2023-09-14 UTC), and < 3.6e-9 (< 4.2e-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.


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