GCN Circular 33075
Subject
Fermi-LAT gamma-ray observations of IceCube-221210A
Date
2022-12-16T23:09:54Z (2 years ago)
From
Simone Garrappa at DESY <simone.garrappa@desy.de>
J. Sinapius (DESY-Zeuthen), S. Buson (Univ. of Wuerzburg) and S.
Garrappa (Ruhr Universitaet Bochum) on behalf of the Fermi-LAT
collaboration:
We report an analysis of observations in the vicinity of the high-energy
IC221210A neutrino event (GCN 33040) 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 2022-12-10 at 08:35:11.23
UT (T0) with J2000 position RA = 332.58 (+9.84, -11.77) deg, Decl. =
+22.75 (+8.15, -4.13) deg (90% PSF containment). Due to the large
uncertainty on the neutrino localization, several�� cataloged gamma-ray
(>100 MeV) sources are located within the 90% IC221210A 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 IC221210A
best-fit position. Assuming a power-law spectrum (photon index = 2.0
fixed) for a point source at the IC221210A best-fit position, the >100
MeV flux upper limit (95% confidence) is < 1.5e-10 ph cm^-2 s^-1 for
~13-years (2008-08-04 to 2022-12-10 UTC), and < 6.6e-9 (< 1.7e-7) ph
cm^-2 s^-1 for a 1-month (1-day) integration time before T0.
The catalogued source 4FGL J2212.0+2356, associated with the
flat-spectrum radio quasar PKS 2209+236, is located 1.25 deg from the
best-fit neutrino position. An inspection of the Fermi-LAT data over the
14 years of LAT observations, shows that on timescales of 1-month, the
object is a relatively stable and faint gamma-ray emitter. Integrating
over a time interval of 1-month prior to T0, the source is significantly
detected (> 5 sigma). A preliminary analysis of the data over the past
year, indicates that the source is undergoing enhanced activity. It is
currently in a fading phase of a flaring episode that started circa
September 2022. The peak-activity flux of F = (1.4 +/- 0.2)e-7 ph cm^-2
s^-1, about 10 times the average 4FGL value, is observed between October
and November 2022 (see also FAVA light curve
https://fermi.gsfc.nasa.gov/ssc/data/access/lat/FAVA/LightCurve.php?ra=333.02&dec=23.93).
Three additional sources are significantly detected (> 5 sigma) over a
time interval of 1-month prior to T0, with fluxes comparable to their
average 4FGL value.
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 J. Sinapius (jonas.sinapius at desy.de),
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.