GCN Circular 31557
Subject
Fermi-LAT Gamma-ray Observations of IceCube-220205A
Date
2022-02-07T17:32:29Z (3 years ago)
From
Simone Garrappa at DESY <simone.garrappa@desy.de>
S. Garrappa (DESY-Zeuthen), S. Buson (Univ. of Wuerzburg), C. C. Cheung
(Naval Research Laboratory) 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
IC220205A neutrino event (GCN 31551) 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 2022-02-05 00:22:39.74 UTC
(T0) with J2000 position RA = 216.12 (+2.94, -3.52) deg, Dec = 15.56
(+3.26, -2.65) deg 90% PSF containment. Several cataloged >100 MeV
gamma-ray sources are located within the 90% IC220205A localization
error (The Fourth Fermi-LAT catalog DR3; The Fermi-LAT collaboration
2022, arXiv:2201.11184). Based on a preliminary analysis of the LAT data
over a 1-day integration time before T0, none of them is significantly
detected at gamma rays.
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 IC220205A 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 <
4.0 x 10^-10 ph cm^-2 s^-1 for ~13-years (2008-08-04 / 2022-02-05 UTC),
< 3.7x 10^-9 (< 4.7e-8) ph cm^-2 s^-1 for a 1-month (1-day) integration
time before T0.
Within the 90% confidence localization of the neutrino, ~1.6 deg offset
from the best-fit IC220205A position, an excess of gamma rays, Fermi
J1420.7+1653 was detected in an analysis of the integrated LAT data (>
100 MeV) between 2008-08-04 and 2022-02-05. This putative new source is
detected at a statistical significance of ~5 sigma (calculated following
the prescription adopted in the 4FGL catalog: Abdollahi, et al. 2020,
ApJS, 247, 33).�� Assuming a power-law spectrum, the candidate gamma-ray
source has best-fit localization (J2000) RA = 215.197, Dec = 16.889
(0.16 deg 99% containment radius, 0.08 deg 68% containment radius), with
best-fit spectral parameters flux = (3 +/- 1)e-9 ph cm^-2 s^-1 and index
= 2.4 +/- 0.2. All values include the statistical uncertainty only. In a
preliminary analysis of the LAT data over one day and one month prior
T0, Fermi J1420.7+1653 is not significantly detected in the LAT data.
Among the 4FGL objects located within the 90% confidence localization of
IC220205A, only one object displays significant (> 5 sigma) gamma-ray
emission over one-month integration (2022-01-05 / 2022-02-05 UTC) time
before T0. This is 4FGL J1416.1+1320, located ~3 deg from the neutrino
best-fit position and associated with the flat-spectrum radio source PKS
B1413+135 located at z = 0.247 (Carilli et al. 1992, ApJL 400 L13). The
object entered an enhanced gamma-ray activity state in August 2019
(Angioni et al. 2019, ATel 13049), when the historical peak flux of the
gamma-ray activity was reached with a one-month average flux of (3.3 +/-
0.2) x 10^-7 photons cm^-2 s^-1 (statistical uncertainty only,
integrated between 2019-07-24 and 2019-08-23). The flaring activity at
gamma rays is currently ongoing (Giacchino et al. 2022, ATel 15163), and
the object has been detected at very-high-energy gamma rays (>100 GeV;
Blanch et al. 2022, ATel 15161). Preliminary analysis indicates that the
source is in a high state with a monthly averaged flux (E>100 MeV) of
(1.0+/-0.1) x 10^-7 photons cm^-2 s^-1 (integrated before T0,
statistical uncertainty only), more than 8 times greater than the
average flux reported in the fourth Fermi LAT source catalog (4FGL). The
flaring state is characterised by a hard spectrum with a 1-month
power-law index = 1.95 +/- 0.08, consistent with the value reported in
the latest LAT catalog (index = 2.06 +/- 0.02, 4FGL-DR3). For PKS
B1413+135, a preliminary light curve can be accessed via the Fermi-LAT
Light-Curve Repository (LCR) at
https://fermi.gsfc.nasa.gov/ssc/data/access/lat/LightCurveRepository/source.html?source_name=4FGL_J1416.1+1320.
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). We encourage
multifrequency observations of these sources.
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.