TITLE:   GCN CIRCULAR
NUMBER:  32285
SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-220624A and and detection of a new gamma-ray source, Fermi J1458.0+4119
DATE:    22/06/28 10:12:57 GMT
FROM:    Simone Garrappa at DESY  <simone.garrappa@desy.de>

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

We report an analysis of observations of the vicinity of the high-energy 
IC220624A neutrino event (GCN 32260) 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 2022-06-24 at 16:13:16.41  
UT (T0) with J2000 position RA = +224.12 (+2.23, -1.95) deg, Decl. = 
41.31 (+1.56, -1.56) deg (90% PSF containment). No cataloged gamma-ray 
(>100 MeV) sources are located within the 90% IC220624A localization 
region (4FGL-DR3; arXiv:2201.11184; The Fermi-LAT collaboration 2020, 
ApJS, 247, 33).

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 IC220624A 
best-fit position. Assuming a power-law spectrum (photon index = 2.0 
fixed) for a point source at the IC220624A best-fit position, the >100 
MeV flux upper limit (95% confidence) is < 9.3e-11 ph cm^-2 s^-1 for 
~14-years (2008-08-04 to 2022-06-24 UTC), and < 3.9e-9 (< 5.4e-8) ph 
cm^-2 s^-1 for a 1-month (1-day) integration time before T0.

Within the 90% confidence localization of the neutrino, 0.2 deg offset 
from the best-fit IC220624A position, an excess of gamma rays, Fermi 
J1458.0+4119, was detected in an analysis of the ~14-years integrated 
LAT data (100 MeV - 1 TeV) prior to T0. This putative new source is 
detected at a statistical significance ~4.5 sigma (calculated following 
the prescription adopted in the The Fourth Fermi-LAT catalog, The 
Fermi-LAT collaboration 2020, ApJS, 247, 33). Assuming a power-law 
spectrum, the excess has best-fit localization of RA = 224.52 deg, Decl. 
= 41.32 deg (5 arcmin 68% containment, 10 arcmin 99% containment) with 
best-fit spectral parameters, flux = (5 +/- 2)e-10 ph cm^-2 s^-1, index 
= 1.9 +/- 0.2. In a preliminary analysis of the LAT data over one month 
prior to T0, Fermi J1458.0+4119 is not significantly detected in the LAT 
data. All values include the statistical uncertainty only.

A probable counterpart of Fermi J1458.0+4119 is the high-synchrotron 
peaked blazar WISEA J145820.77+412101.9 (aka 3HSP J145820.8+412102) at 
RA=224.58658 deg, Dec=41.35028 deg, and redshift 0.176463 +/- 0.000027 
(Sloan Digital Sky Survey Data Release 13, 2016 SDSS). It is located 
about 4 arcmin from the Fermi J1458.0+4119 best-fit position, and within 
the gamma-ray 68% positional uncertainty. This source has been proposed 
as a promising very-high-energy candidate emitter (>100 TeV; Arsioli et 
al. 2015, A&A, 579, 34).

Since Fermi normally operates in an all-sky scanning mode, regular 
monitoring of this source 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.