GCN Circular 35887
Subject
Fermi-LAT gamma-ray observations of IceCube-240229A
Date
2024-03-06T13:18:35Z (2 months ago)
From
Simone Garrappa at DESY <simone.garrappa@desy.de>
Via
email
S. Garrappa (Weizmann Institute of Science), C. Bartolini (INFN Bari), S. Buson (DESY; Univ. of Wuerzburg), L. Pfeiffer (Univ. of Wuerzburg) and J. Sinapius (DESY) on behalf of the Fermi-LAT collaboration:
We report an analysis of observations of the vicinity of the IC240229A high-energy neutrino event (GCN 35841) 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 2024-02-29 at 15:48:21.52 UT (T0) with J2000 position RA = 72.25 (+1.28, -1.26) deg, Decl. = +15.79 (+1.08, -0.92) deg (90% PSF containment). Two catalogued gamma-ray (>100 MeV; The Fermi-LAT collaboration 2022, ApJS, 260, 53) sources are located within the 90% IC240229A localization region. These are the unassociated sources 4FGL J0445.7+1535 and 4FGL J0444.4+1621, located at 0.81 and 1.24 deg from the best-fit neutrino position, respectively. Based on a preliminary analysis of the LAT data over the timescales of 1-month and 1-day prior to T0, these objects are not significantly detected (> 5 sigma).
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 IC240229A best-fit position. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC240229A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 7.3e-10 ph cm^-2 s^-1 for ~15-years (2008-08-04 to 2024-02-29 UTC), and < 8.6e-9 (<8.5e-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 is S. Garrappa (simone.garrappa at weizmann.ac.il).
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.