IceCube-220205A

The IceCube Collaboration (http://icecube.wisc.edu/) reports:

On 2022-02-05 at 00:22:39.74 UT IceCube detected a track-like event with a moderate probability of being of astrophysical origin. The event was selected by the ICECUBE_Astrotrack_Bronze alert stream. The average astrophysical neutrino purity for Bronze alerts is 30%. This alert has an estimated false alarm rate of 2.524 events per year due to atmospheric backgrounds. The IceCube detector was in a normal operating state at the time of detection.

Due to a technical issue, the automated GCN notice for this event could not be circulated. More sophisticated reconstruction algorithms have been applied offline, with the direction refined to:

Date: 2022-02-05 
Time:  00:22:39.74 UTC
RA: 216.12 (+2.94, -3.52 deg  90% PSF containment) J2000
Dec: 15.56 (+3.26, -2.65 deg 90% PSF containment) J2000
Initial signal probability: 32.2%
Initial neutrino energy: 109.6 TeV

We encourage follow-up by ground and space-based instruments to help identify a possible astrophysical source for the candidate neutrino.

There are two Fermi 4FGL catalog sources in the 90% uncertainty region: 4FGL J1424.6+1447 and 4FGL J1428.1+1629. The nearest source is 4FGL J1424.6+1447 at RA: 216.17 deg, Dec: 14.78 deg in J2000 coordinates (0.78 deg away from the best-fit event position).

The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc@icecube.wisc.edu

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
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 ) 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
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 ). 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.

The IceCube Collaboration (http://icecube.wisc.edu/) reports:

IceCube has performed a search [1] for additional track-like muon neutrino events arriving from the direction of IceCube-220205A (https://gcn.gsfc.nasa.gov/gcn3/31551.gcn3
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 ) in a time range of 1000 seconds centered on the alert event time (2022-02-05 00:14:19.740 UTC to 2022-02-05 00:30:59.740 UTC) during which IceCube was collecting good quality data. Excluding the event  that prompted the alert, zero track-like events are found within the 90% containment region of IceCube-220205A. The IceCube sensitivity to neutrino point sources with an E^-2.5 spectrum (E^2 dN/dE at 1 TeV) within the locations spanned by the 90% spatial containment region of IceCube-220205A ranges from 1.3e-01 to 1.4e-01 GeV cm^-2 in a 1000 second time window. 90% of events IceCube would detect from a source at this declination with an E^-2.5 spectrum have energies in the approximate energy range between 2e+02 GeV and 1e+05 GeV.

A subsequent search was performed including 2 days of data centered on the alert event time (2022-02-04 00:22:39.740 UTC to 2022-02-06 00:22:39.740 UTC). In this case, we report a p-value of 0.04, consistent with no significant excess of track events. The IceCube sensitivity to neutrino point sources with an E^-2.5 spectrum (E^2 dN/dE at 1 TeV) within the locations spanned by the 90% spatial containment region of IceCube-220205A is 1.6e-01 GeV cm^-2 in a 2 day time window.

The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can
be reached at roc@icecube.wisc.edu<mailto:roc@icecube.wisc.edu>.

[1] IceCube Collaboration, R. Abbasi  et al., ApJ 910 4 (2021)