GCN Circular 31479
Subject
Fermi-LAT Gamma-ray Observations of IceCube-220115A and detection of a new gamma-ray source, Fermi J2350.2+2620
Date
2022-01-18T11:40:24Z (3 years ago)
From
Simone Garrappa at DESY <simone.garrappa@desy.de>
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 high-energy
IC220115A neutrino event (GCN 31451) 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 2022-01-15 12:11:39.75 UTC
(T0) with J2000 position RA = 357.45 (+1.75, -1.18) deg, Decl. = 25.28
(+1.03, -0.95) deg 90% PSF containment. No cataloged gamma-ray sources
are found within the 90% IC220115A localization error (The Fourth
Fermi-LAT catalog DR2; The Fermi-LAT collaboration 2020, ApJS, 247, 33).
We searched for the existence of intermediate (months to years)
timescale emission from a new gamma-ray transient source. Preliminary
analysis indicates no significant (>5sigma) new excess emission (> 100
MeV) at the the IC220115A best-fit position. Assuming a power-law
spectrum (photon index = 2.0 fixed) for a point source at the IceCube
best-fit position, the >100 MeV flux upper limit (95% confidence) is <
5.6-10 ph cm^-2 s^-1 for ~13-years (2008-08-04 / 2022-01-15 UTC), <
1.1e-8 (< 5.2e-8) ph cm^-2 s^-1 for a 1-month (1-day) integration time
before T0.
Within the 90% confidence localization of the neutrino, ~1.1 deg offset
from the best-fit IC220115A position, a >4 sigma excess of gamma rays,
Fermi J2350.2+2620 was detected in an analysis of the integrated LAT
data (> 100 MeV) between 2008-08-04 and 2022-01-15. Assuming a power-law
spectrum, the candidate gamma-ray source has best-fit localization
(J2000) RA: 357.564, Dec: 26.343 (0.15 deg 99% containment, 0.07 deg 68%
containment), with best-fit spectral parameters flux = (8 +/- 5)e-10 ph
cm^-2 s^-1 and index = 2.0 +/- 0.2. In a preliminary analysis of the LAT
data over one day and one month prior T0, Fermi J2350.2+2620 is not
significantly detected in the LAT data. All values include the
statistical uncertainty only.
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.