TITLE: GCN CIRCULAR NUMBER: 39005 SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-241224A DATE: 25/01/21 15:35:18 GMT FROM: Leo Pfeiffer at University of Würzburg <pfeiffer.leo@gmail.com> L. Pfeiffer (Univ. of Wuerzburg), S. Buson (DESY, Univ. of Wuerzburg), C. Bartolini (INFN Bari), S. Garrappa (Weizmann Institute of Science) and J. Sinapius (DESY) and P. M. Veres (Ruhr University Bochum) on behalf of the Fermi-LAT collaboration: We report an analysis of observations of the vicinity of the high-energy IC241224A neutrino event (GCN 38664) 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 2024-12-24 07:10:04.35 UTC (T0) with J2000 position RA = 184.97 (+0.59, -0.52) deg, Decl. = 2.76 (+0.67, -0.67) deg 90% PSF containment (J2000). No cataloged gamma-ray sources are found within the 90% IC241224A localization error (The Fourth Fermi-LAT catalog Data Release 4, The Fermi-LAT collaboration 2023, arXiv:2307.12546). We searched for the existence of intermediate (days to years) timescale emission from a new gamma-ray transient source. Preliminary analysis indicates no significant (>5sigma) new excess emission (> 100 MeV) within the IC241224A 90% confidence localization. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC241224A best-fit position, the >100 MeV flux upper limit (95% confidence) is <1.45e-10 ph cm^-2 s^-1 for ~16-years (2008-08-04 / T0), <9.80e-09(<5.72e-08) ph cm^-2 s^-1 for a 1-month (1-day) integration time before T0. In the analysis of the ~16-years integrated LAT data (100 MeV - 1 TeV), a 4.9 sigma excess of gamma rays, Fermi J1220.3+0200, was detected 0.73 deg offset from the best-fit IC241224A position, outside the 90% confidence localization of the direction of the neutrino. Assuming a power-law spectrum, the best-fit localization is (J2000) RA: 185.09 deg, Dec: 2.04 deg (9.40 arcmin 99% containment, 4.6 arcmin 68% containment). The gamma-ray best-fit spectral parameters are flux = (1.25 +/- 0.65)e-9 ph cm^-2 s^-1 and index = 2.08+/-0.19 (statistical uncertainty only). In a preliminary analysis of the LAT data over 1-day and 1-month prior T0, Fermi J1220.3+0200 is not significantly detected. The statistical significance is calculated following the prescription adopted in the Fourth Fermi-LAT catalog (The Fermi-LAT collaboration 2022, ApJS, 260, 53). The LAT catalogued object 2FGL J1219.7+0201 (The Fermi-LAT collaboration 2011, ApJ, 743, 171) is positionally consistent with Fermi J1220.3+0200 (2.7 arcmin separation). A possible counterpart is the blazar 5BZQJ1220+0203 (PKS 1217+02) at RA= 185.0495 deg, Dec= 2.0617 deg (Massaro et al. 2015 Ap&SS, 357, 1). The blazar is within the 68% positional uncertainty of Fermi J1220.3+0200, located 3 arcmin away from the gamma-ray best-fit position. Since Fermi normally operates in an all-sky scanning mode, regular monitoring of this source will continue. For this source, the Fermi-LAT contact person is L. Pfeiffer (leonard.pfeiffer at stud-mail.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. View this GCN Circular online at https://gcn.nasa.gov/circulars/39005. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...