TITLE:   GCN CIRCULAR
NUMBER:  31953
SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-220425A
DATE:    22/04/26 17:08:51 GMT
FROM:    Sara Buson at GSFC/Fermi  <sara.buson@gmail.com>

S. Buson (Univ. of Wuerzburg), S. Garrappa (DESY-Zeuthen) and G. La Mura (LIP) on behalf of the Fermi-LAT collaboration:

We report an analysis of observations of the vicinity of the high-energy IC220425A neutrino event (GCN 31944) 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 2022-04-25 at 02:44:57.82 UT (T0) with J2000 position RA = 268.24 (+1.98, -1.66) deg, Decl. = -10.73 (+1.71, -1.48) deg (90% PSF containment). One cataloged gamma-ray (>100 MeV) source is located within the 90% IC220425A localization region (4FGL-DR3; arXiv:2201.11184; The Fermi-LAT collaboration 2020, ApJS, 247, 33). This is the gamma-ray source 4FGL J1752.6-1010. Based on a preliminary analysis of the LAT data over the timescales of 1-day and 1-month prior to T0, this object is not significantly detected (> 5 sigma).

4FGL J1752.6-1010 is associated with the flat-spectrum radio object TXS 1749-101 (a.k.a. IVS B1749-101). It has been proposed as promising neutrino emitter candidate by Plavin et al. (2020 ApJ, 894, 101), and tentatively associated with a previously observed EHE IceCube event, i.e. IC181023A (GCN 23375, GCN 23378). The latter was detected by the IceCube Observatory on 2018-10-23 16:37:32.65 UTC (T0) with J2000 position RA = 270.18 (-1.70,+2.00) deg, Decl. = -8.57 (-1.30,+1.25) deg 90% PSF containment. 

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 IC220425A best-fit position. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC220425A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 3.1e-10 ph cm^-2 s^-1 for ~13-years (2008-08-04 to 2022-04-25 UTC), and < 1.3e-8 (< 2.9e-7) ph cm^-2 s^-1 for a 1-month (1-day) integration time before T0.

Outside the neutrino IC220425A 90% PSF containment lies the gamma-ray source 4FGL J1745.4-0753, a.k.a. 3FHL J1745.4-0752 (The Fermi-LAT collaboration 2014, AAS, 223, 256) and TXS 1742-078. TXS 1742-078 is currently undergoing an enhanced optical state (Zhitkov. et al. 2022, GCN 31948). Based on a preliminary analysis of the LAT data over the timescales of 1-day and 1-month prior to T0, this object is not significantly detected (> 5 sigma).

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 desy.de) and S. Buson (sara.buson at 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.