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GCN Circular 35213

Fermi-LAT gamma-ray observations of IceCube-231125A
2023-11-29T13:33:08Z (8 months ago)
Leonard Pfeiffer at University of Würzburg <>
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L. Pfeiffer (Univ. of Wuerzburg), S. Buson (Univ. of Wuerzburg), S. Garrappa (Weizmann Institute of Science), C. Bartolini (INFN Bari) and J. Sinapius (DESY) on behalf of the Fermi-LAT collaboration:

We report an analysis of observations of the vicinity of the IC231125A high-energy neutrino event (GCN 35194) 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 2023-11-25 at 22:34:56.64 UT (T0) with J2000 position RA = 177.53 (+3.99, -4.03) deg, Decl. = +53.62 (+1.57, -1.64) deg (90% PSF containment). There are two gamma-ray (>100 MeV; 4FGL-DR4, The Fermi-LAT collaboration 2023, arXiv:2307.12546) sources located within the 90% IC231125A localization region. These are:

4FGL J1215.0+5351, associated with the BL LAC GB6 J1215+5349;
4FGL J1208.9+5441, associated with the FSRQ TXS 1206+549

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 IC231125A best-fit position. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC231125A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 1.77e-10 ph cm^-2 s^-1 for ~15-years (2008-08-04 to 2023-11-26 UTC), and < 8.10e-9 (<8.91e-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 person is L. Pfeiffer (leonard.pfeiffer at 

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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