IceCube-211216B

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

On 2021-12-16 at 23:41:13.93 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 2.39 events per year due to atmospheric backgrounds. The IceCube detector was in a normal operating state at the time of detection.

After the initial automated alert (https://gcn.gsfc.nasa.gov/notices_amon_g_b/136057_6147475.amon), more  
sophisticated reconstruction algorithms have been applied offline, with the direction refined to:

Date: 2021-12-16
Time: 23:41:13.93

RA: 199.34 (+1.66/-1.78 deg 90% PSF containment) J2000
Dec: 17.04 (+1.39/-1.36 deg 90% PSF containment) J2000

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

No gamma-ray sources listed in the 4FGL-DR2 Fermi-LAT catalog are located in the 90% containment region. The closest source is 4FGL J1319.5+1404 at RA: 199.90, Dec: 14.07 (3.02 deg from the best-fit event location).

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

J. Wood (NASA/MSFC) reports on behalf of the Fermi-GBM team:

For the IceCube high-energy neutrino candidate event IceCube-211216B
(GCN 31249
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 ), at the event time Fermi-GBM was observing the reported
neutrino location at:

RA: 199.34 (+1.66/-1.78 deg 90% PSF containment) J2000
Dec: 17.04 (+1.39/-1.36 deg 90% PSF containment) J2000

There was no Fermi-GBM onboard trigger around the event time of the
neutrino candidate. An automated, blind search for short gamma-ray bursts
below the onboard triggering threshold in Fermi-GBM also identified no
counterpart candidates.

The GBM targeted search, the most sensitive, coherent search for GRB-like
signals, was run from +/-30 s around the neutrino candidate time.
From this search, no significant signal was found related
to IceCube-211216B.

We set upper limits on impulsive gamma-ray emission. Using the
representative soft, normal, and hard GRB-like templates described in
arXiv:1612.02395
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 , we set the following 3 sigma flux upper limits over
10-1000 keV (in units of 10^-7 erg/s/cm^2):

Timescale   Soft   Normal   Hard
-------------------------------------------
0.128 s:    5.2    8.2      16.
1.024 s:    1.4    2.3      4.7
8.192 s:    0.4    0.7      2.1

These results are preliminary.

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 
IC211216B neutrino event (GCN 31249
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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 2021-12-16 23:41:13.93 UTC 
(T0) with J2000 position RA = 199.34 (+1.66, -1.78) deg, Decl. = 17.04 
(+1.39, -1.36) deg 90% PSF containment. Two cataloged >100 MeV gamma-ray 
sources are located within the 90% IC211216B localization error. No 
cataloged gamma-ray sources are found within the 90% IC211216B 
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 (0.1 - 
300 GeV) within the IC211216B 90% confidence localization. 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 < 3.6-10 ph cm^-2 s^-1 for ~13-years (2008-08-04 / 
2021-12-16 UTC), < 1.8e-8 (< 1.2e-7) ph cm^-2 s^-1 for a 1-month (1-day) 
integration time before T0.

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.

Alexis Coleiro (APC/Universite de Paris) and Damien Dornic (CPPM/CNRS) on behalf of the ANTARES Collaboration.

Using data from the ANTARES detector, we have performed a follow-up analysis of the recently reported event IceCube-211216B (GCN#31249
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  <https://gcn.gsfc.nasa.gov/gcn3/31249.gcn3
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 >). At the time of the alert, the reconstructed origin was -3.7 degrees below the horizon for ANTARES.

No up-going muon neutrino candidate events were recorded within the 90% error box of the IceCube event during a +/- 1h time-window centered on the IceCube event time, and over which the potential source remained visible from [T-60min, T+22min] (68%). This leads to a preliminary 90% confidence level upper limit on the muon-neutrino fluence from a point source of 17 GeV.cm^-2 over the energy range 5 TeV ��� 5 PeV (the range corresponding to 5-95% of the detectable flux) for an E^-2 power-law spectrum, and 40 GeV.cm^-2 (1 TeV - 450 TeV) for an E^-2.5 spectrum.

A search over an extended time window of +/- 1 day has also yielded no detection (40% visibility).

ANTARES <http://antares.in2p3.fr/> is the largest undersea neutrino detector (Mediterranean Sea) and it is primarily sensitive to astrophysical neutrinos in the TeV-PeV energy range. At 10 TeV, the median angular resolution for muon neutrinos is about 0.5 degrees. In the range 1-100 TeV ANTARES has a competitive sensitivity to this position in the sky.

Hugo Ayala (Penn State) reports on behalf of the HAWC
collaboration (http://www.hawc-observatory.org/collaboration):

On 2021/12/16 23:41:13.93 UTC, the IceCube collaboration reported a
track-like very-high-energy event  that has a high probability of
being an astrophysical neutrino, IceCube-211216B. Location is at
RA: 199.34 (+1.66/-1.78 deg  90% PSF containment) J2000
Dec: 17.04 (+1.39/-1.36 deg 90% PSF containment) J2000
(GCN circular 31249
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 ).

We performed two types of analyses for the follow-up. The first is for
a steady source in archival data and the second is a search for a
transient source. We assume a power-law spectrum with an index of -2.3
for both analyses.

Search for a steady source in archival data:
The archival data spans from November 2014 to June 2019. We searched
inside the reported IceCube error region.
The most significant location, with p-value 1.4e-3 (6.3e-2 post-trials),
is at RA 198.19 deg, Dec +116.53 deg (��0.6 deg 68% containment) J2000.
We set a time-integrated 95% CL  upper limit on gamma rays at the
maximum position of:

E^2 dN/dE = 2.13e-13 (E/TeV)^-0.3 TeV.cm^-2.s^-1

Search for a transient source.

Since the event was not in our field of view at the time reported,
we report the combined result for the transits before and after the
IceCube event.

Data acquisition started on 2021/12/15 18:23:07 UTC and ended
2021/12/17 17:15:21 UTC.
The most significant location, with p-value 5.1e-3  (2.2e-1 post-trials),
is at RA 198.28 deg, Dec +17.47 deg (��0.20 deg 68% containment) J2000.
We set a time-integrated 95% CL upper limit at the position of
maximum significance of:

E^2 dN/dE = 9.68e-12 (E/TeV)^-0.3 TeV.cm^-2.s^-1

HAWC is a very-high-energy gamma-ray observatory operating in Central
Mexico at latitude 19 deg. north. Operating day and night with over
95% duty cycle, HAWC has an instantaneous field of view of 2 sr and
surveys 2/3 of the sky every day. It is sensitive to gamma rays from
300 GeV to 100 TeV.