IceCube-211123A

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

On 2021-11-23 at 14:25:22.6 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 2.567 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/135930_15193553.amon, more sophisticated reconstruction algorithms have been applied offline, with the direction refined to:

Date: 2021-11-23 
Time: 14:25:22.6 UT
RA: 265.52 (+3.14 -2.84 deg  90% PSF containment) J2000
Dec: 7.33 (+2.38 -2.48 deg 90% PSF containment) J2000

Both the initial alert and subsequent offline reconstructions were delayed as computing resources were undergoing maintenance. We encourage follow-up by ground and space-based instruments to help identify a possible astrophysical source for the candidate neutrino.

Two gamma-ray sources listed in the 4FGL Fermi-LAT catalog, 4FGL J1736.6+0628 and 4FGL J1734.0+0805, are located within the 90% error region for the event, located 1.6 and 2.1 deg away from the best-fit position, respectively. 

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 IceCube-211123A
(GCN 31110
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 ), at the event time Fermi-GBM was observing the reported
neutrino location at:

RA: 265.52 (+3.14 -2.84 deg  90% PSF containment) J2000
Dec: 7.33 (+2.38 -2.48 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-211123A.

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:   4.7   7.9   20.
1.024 s:   1.8   3.0   6.5
8.192 s:   0.47 0.88 1.6
These results are preliminary.

V. Savchenko, C. Ferrigno (ISDC/UniGE, Switzerland)
S. Mereghetti (INAF IASF-Milano, Italy)
J. Rodi (IAPS-Roma, Italy)
A. Coleiro (APC, France)
on behalf of the INTEGRAL multi-messenger collaboration:
https://www.astro.unige.ch/cdci/integral-multimessenger-collaboration

The INTEGRAL spacecraft has a highly elliptical orbit and the
instruments are not acquiring science data during perigee passage,
every 2.6 days to prevent radiation-induced damages. Unfortunately, at
the time of the IceCube-211123A (2021-11-23 14:25:22) the spacecraft
was preparing to the start the observations after the perigee passage
between the orbits number 2438 and 2439 and no scientific instrument
data are available between 2021-11-23T08:09:55 and
2021-11-23T17:15:45.

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-211123A (https://gcn.gsfc.nasa.gov/gcn3/31110.gcn3
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 ) in a time range of 1000 seconds centered on the alert event time (2021-11-23 14:17:02.600 UTC to 2021-11-23 14:33:42.600 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-211123A. The IceCube sensitivity assuming an E^-2.5 spectrum (E^2 dN/dE at 1 TeV) to neutrino point sources within the locations spanned by the 90% spatial containment region of IceCube-211123A 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 3e+02 GeV and 1e+05 GeV.

A subsequent search was performed including 2 days of data centered on the alert event time (2021-11-22 14:25:22.600 UTC to 2021-11-24 14:25:22.600 UTC). In this case, we report a p-value of 0.10, consistent with no significant excess of track events. The IceCube sensitivity assuming an E^-2.5 spectrum (E^2 dN/dE at 1 TeV) to neutrino point sources within the locations spanned by the 90% spatial containment region of IceCube-211123A ranges from 1.5e-01 to 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)

S. Garrappa (DESY-Zeuthen), S. Buson (Univ. of Wuerzburg) and R. de 
Menezes (Univ. of Wuerzburg, Univ. of Sao Paulo) on behalf of the 
Fermi-LAT collaboration:

We report an analysis of observations of the vicinity of the high-energy 
IC211123A neutrino event (GCN 31110
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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 2021-11-23 at 14:25:22.6 UT 
(T0) with J2000 position RA = 265.52 (+3.14, -2.84) deg, Decl. = 7.33 
(+2.38, -2.48) deg (90% PSF containment). Four cataloged gamma-ray (>100 
MeV) sources are located within the 90% IC211123A localization region 
(4FGL-DR2, The Fermi-LAT collaboration 2020, ApJS, 247, 33). One of 
these, 4FGL J1751.5+0938, associated with the BL Lac object OT 081, is 
also listed in the 3FHL catalog as 3FHL J1751.5+0938 (Ajello et al. 
2017, 232, 18).

We searched for intermediate (days to years) timescale emission from a 
new gamma-ray transient source. Preliminary analysis indicates no 
significant (> 5 sigma) new excess emission (> 100 MeV) at the IC211123A 
best-fit position. Assuming a power-law spectrum (photon index = 2.0 
fixed) for a point source at the IC211123A best-fit position, the >100 
MeV flux upper limit (95% confidence) is < 2.4e-10 ph cm^-2 s^-1 for 
~13-years (2008-08-04 to 2021-11-23 UTC), and < 7.4e-9 (< 8.5e-8) 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.