S. Garrappa (DESY-Zeuthen), S. Buson (Univ. of Wuerzburg) and J.
Sinapius (DESY-Zeuthen) on behalf of the Fermi-LAT collaboration:
We report an analysis of observations of the vicinity of the IC220918A
high-energy neutrino event (GCN 32562) 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 2022-09-18 at 12:46:05.32��
UT (T0) with J2000 position RA = 75.15 (+3.79 , -3.38) deg, Decl. = 3.58
(+3.70 , -3.40) deg (90% PSF containment). Seven cataloged gamma-ray
(>100 MeV) sources are located within the 90% IC220918A localization
region (4FGL-DR3; The Fermi-LAT collaboration 2022, ApJS, 260, 53).
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 IC220918A
best-fit position. Assuming a power-law spectrum (photon index = 2.0
fixed) for a point source at the IC220918A best-fit position, the >100
MeV flux upper limit (95% confidence) is < 5.9e-10 ph cm^-2 s^-1 for
~14-years (2008-08-04 to 2022-09-18 UTC), and < 3.5e-9 (<5.8e-8) ph
cm^-2 s^-1 for a 1-month (1-day) integration time before T0.
Based on a preliminary analysis of the LAT data integrating over the
time interval 1-month prior to T0, the catalogued sources 4FGL
J0509.4+0542�� (associated with the object TXS 0506+056) and 4FGL
J0505.3+0459 (associated with the flat-spectrum radio object PKS
0502+049) are�� significantly detected (> 5 sigma). The observed fluxes
are comparable to the average ones measured in the 4FGL catalog.
Integrating over the time interval�� 1-day prior to T0, 4FGL J0509.4+0542
is detected at a statistical significance of ~4.5 sigma, at a flux level
comparable to the average one measured in the 4FGL catalog.
Within the 90% confidence localization of the neutrino, 3 deg offset
from the best-fit IC220918A position, a new excess of gamma rays, Fermi
J0502.5+0037, 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 > 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 = 75.63 deg, Decl.
= 0.62 deg (99% containment radius = 0.1 deg) with best-fit spectral
parameters, flux = (2.8 +/- 0.9)e-9 ph cm^-2 s^-1, index = 2.2 +/-0.1.
In a preliminary analysis of the LAT data over one month and one day
prior to T0, Fermi J0502.5+0037 is not significantly detected in the LAT
data. All values include the statistical uncertainty only.
A possible counterpart of Fermi J0502.5+0037�� is the radio source PKS
B0500+006, at RA=75.641042 deg, Dec=0.704861 deg (Condon et al. 1998 AJ,
115, 5). This source is located about 0.08 deg from the Fermi
J0502.5+0037 best-fit position, and within the gamma-ray 99% positional
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.