IceCube-200120A

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

On 20/01/17 at 18:48:18.56 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 0.36 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/133644_43767651.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to:

Date: 20/01/17 
Time: 18:48:18.56 UT
RA:  67.46 (+0.36 -0.43  deg 90% PSF containment) J2000
Dec: -14.63  (+0.32 -0.25  deg 90% PSF containment) J2000

This event had a down-going topology with an extremely large deposited charge in the detector, and was consequently reconstructed with a likely neutrino energy in excess of 6 PeV. We caution that, despite this high energy, there is a known atmospheric muon-bundle background that can produce similar events. The astrophysical signalness of this event is thus 33%, as reported in the initial notice. 

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

There are no 4FGL sources inside the 90% localization region. The closest source is 4FGL J0438.4-1254 located at RA 69.61 deg and dec -12.91 deg (at a distance of 2.71 degrees from the best-fit 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

C. Fletcher (USRA) reports on behalf of the Fermi-GBM Team:

For the IceCube high-energy neutrino candidate event 200120A (GCN 26832
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 ),
the reported position:

RA:  67.46 (+0.36 -0.43  deg 90% PSF containment) J2000
Dec: -14.63  (+0.32 -0.25  deg 90% PSF containment) J2000

was occulted by the Earth for Fermi-GBM from approximately 11.7 minutes
prior until 22.2 minutes after event time. Therefore, the GBM observations
are not constraining for prompt gamma-ray emission.

C. Ferrigno , V. Savchenko (ISDC/UniGE, Switzerland)
J. Rodi (IAPS-Roma, Italy)
A. Coleiro (APC, France)
S. Mereghetti (INAF IASF-Milano, Italy)

on behalf of the INTEGRAL multi-messenger collaboration:
https://www.astro.unige.ch/cdci/integral-multimessenger-collaboration

Using combination of INTEGRAL all-sky detectors (following [1]):
SPI/ACS, IBIS/Veto, and IBIS we have performed a search for a prompt
gamma-ray counterpart of IceCube-200120A (GCN 26832
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 ).

At the time of the event (2020-01-20 18:48:18 UTC, hereafter T0),
INTEGRAL was operating in nominal mode. The peak of the event
localization probability was at an angle of 74 deg with respect to the
spacecraft pointing axis. This orientation implies strongly suppressed
(23% of optimal) response of ISGRI, somewhat suppressed (43% of
optimal) response of IBIS/Veto, and near-optimal (84% of optimal)
response of SPI-ACS.

The background within +/-300 seconds around the event was very stable
(excess variance 1.2).

We have performed a search for any impulsive events in INTEGRAL SPI-
ACS (as described in [2]), IBIS, and IBIS/Veto data.

We do not detect any significant counterparts and estimate a 3-sigma
upper limit on the 75-2000 keV fluence of 2e-07 erg/cm^2 (within the
50% probability containment region of the source localization) for a
burst lasting less than 1 s with a characteristic short GRB spectrum
(an exponentially cut off power law with alpha=-0.5 and Ep=600 keV)
occurring at any time in the interval within 300 s around T0. For a
typical long GRB spectrum (Band function with alpha=-1, beta=-2.5, and
Ep=300 keV), the derived peak flux upper limit is ~1.7e-07 (6.2e-08)
erg/cm^2/s at 1 s (8 s) time scale in 75-2000 keV energy range.

We report for completeness and in order of FAP, all excesses
identified in the search region.�� We find: 8 likely background
excesses:

T-T0 | scale | S/N | flux ( x 1e-06 erg/cm2/s) | FAP
23.1 | 0.9 | 4.1 | 2.96 +/- 0.71 +/- 0.817 | 0.0742
0.792 | 0.05 | 3.4 | 1.09 +/- 0.306 +/- 0.3 | 0.0924
9.17 | 1.3 | 3.2 | 1.87 +/- 0.589 +/- 0.516 | 0.114
-86.2 | 1.95 | 3.8 | 1.79 +/- 0.481 +/- 0.494 | 0.194
217 | 3.5 | 3.7 | 1.34 +/- 0.359 +/- 0.371 | 0.287
101 | 1.4 | 3.7 | 2.1 +/- 0.568 +/- 0.578 | 0.342
27.8 | 0.1 | 4.2 | 0.933 +/- 0.216 +/- 0.257 | 0.704
-41.5 | 0.05 | 4.5 | 1.44 +/- 0.308 +/- 0.396 | 0.86

Note that FAP estimates (especially at timescales above 2s) may be
possibly further affected by enhanced non-stationary local background
noise. This list excludes any excesses for which FAP is close to
unity.

All results quoted are preliminary.

This circular is an official product of the INTEGRAL Multi-Messenger
team.

[1] Savchenko et al. 2017, A&A 603, A46

[2] Savchenko et al. 2012, A&A541A, 122S

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

IceCube has performed a search for additional track-like muon neutrino events arriving
from the direction of IceCube-200120A (https://gcn.gsfc.nasa.gov/gcn3/26832.gcn3
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 ) in a time
range of 2 days centered on the alert event time (2020-01-19 18:48:18.56 UTC to 2020-01-21 18:48:18.56 UTC) during which IceCube was collecting good quality data. Excluding the
event that prompted the alert, zero additional track-like events are found in spatial coincidence
with the 90% containment region of IceCube-200120A. We accordingly derive a time-integrated muon-neutrino flux upper limit at the alert position of E^2 dN/ dE = 1.95 x 10^-4 TeV cm^-2 at 90% CL, under the assumption of an E^-2 power law. 90% of events IceCube would detect from a source at this declination with an E^-2 spectrum are approximately between 50 TeV and 20 PeV.

A subsequent search was performed to include the month of data prior to the alert event (2019-12-21 18:48:18.56 UTC to 2020-01-21 18:48:18.56 UTC). In this case, we report a p-value of 1.0, consistent with no significant excess of track-like events, and a corresponding time-integrated muon-neutrino flux upper limit assuming an E^-2 spectrum (E^2 dN/dE) of
2.60 x 10^-4 TeV cm^-2 at the 90% CL.

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>.

S. Garrappa (DESY-Zeuthen) and S. Buson (Univ. of Wuerzburg) on behalf 
of the Fermi-LAT collaboration:

We report an analysis of observations of the vicinity of the high-energy 
IC200120A neutrino event (GCN 26832
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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 2020-01-20 18:48:18.56 UT 
(T0) with J2000 position RA = 67.46 (+0.36, -0.43) deg, Decl. = -14.63 
(+0.32, -0.25) deg 90% PSF containment. No cataloged >100 MeV gamma-ray 
sources are located within the 90% IC200120A localization error.

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) within the IC200120A 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 < 5e-10 ph cm^-2 s^-1 for ~11-years (2008-08-04 / 
2020-01-20 UTC), < 8e-9 (< 1.4e-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 this source the Fermi-LAT 
contact persons are S. Garrappa (simone.garrappa at desy.de 
<http://desy.de/>) and S. Buson (sara.buson at uni-wuerzburg.de 
<http://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.

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

On 20/01/20 IceCube reported a track-like event with a moderate probability of being of astrophysical origin (https://gcn.gsfc.nasa.gov/gcn/gcn3/26832.gcn3
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 ).   After further study, we now believe this event to likely be due to a highly inclined muon bundle.  Muon bundles are a background arising from down-going cosmic ray air showers and are not from a neutrino of astrophysical origin.

This conclusion is driven by observations with the IceTop surface array portion of IceCube at the time of the alert. The IceTop surface array detects charged particles from cosmic ray induced extensive air showers that occur in the atmosphere above the IceCube detector.  IceTop data is presently not accounted for in the IceCube realtime alert system. A preliminary offline cross check of IceTop data indicate a background origin for this alert.

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