IceCube-230220A

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

On 2023-02-20 at 07:39:10.8 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 2.521 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/137668_51133257.amon), 
attempts to use a more sophisticated algorithm that provides refined 
position and error estimates encountered issues.
Given the topology of the light deposition in the detector, we estimate 
that the initial direction listed below still provides a good 
characterization of the event.

Date: 2023-02-20
Time:  07:39:10.8 UT
RA: 359.33 deg (J2000)
Dec: +3.35 deg (J2000)
Error radius: 0.51 deg (90%, statistical error only)

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-DR3 or 3FHL Fermi-LAT catalogs 
are located within the 90% error radius of the candidate neutrino event.
The nearest source is 4FGL J2359.3+0215, 1.2 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 (Ruhr-Universitaet Bochum), 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 IC230220A 
high-energy neutrino event (GCN 33354
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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 2023-02-20 at 07:39:10.8 UT 
(T0) with J2000 position RA = 359.33 (+0.51, -0.51) deg, Decl. = +3.35 
(+0.51, -0.51) deg (90% PSF containment). No cataloged gamma-ray (>100 
MeV; The Fermi-LAT collaboration 2022, ApJS, 260, 53) sources are 
located within the 90% IC230220A localization region.

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 IC230220A 
best-fit position. Assuming a power-law spectrum (photon index = 2.0 
fixed) for a point source at the IC230220A best-fit position, the >100 
MeV flux upper limit (95% confidence) is < 2.6e-10 ph cm^-2 s^-1 for 
~14-years (2008-08-04 to 2023-02-20 UTC), and < 4.5e-9 (<6.9e-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 region will continue. For these observations the 
Fermi-LAT contact persons are S. Garrappa (simone.garrappa at 
ruhr-uni-bochum.de), J. Sinapius (jonas.sinapius 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.

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-230220A (https://gcn.gsfc.nasa.gov/gcn3/33354.gcn3
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 ) in a time range of 1000 seconds centered on the alert event time (2023-02-20 07:30:50.83 UTC to 2023-02-20 07:47:30.83 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-230220A. The IceCube sensitivity to neutrino point sources with an E^-2.0 spectrum (E^2 dN/dE at 1 TeV) within the locations spanned by the 90% spatial containment region of IceCube-230220A is 2.8e-02 GeV cm^-2 in a 1000 second time window. 90% of events IceCube would detect from a source at this declination with an E^-2.0 spectrum have energies in the approximate energy range between 1e+03 GeV and 4e+06 GeV.


A subsequent search was performed including 2 days of data centered on the alert event time (2023-02-19 07:39:10.83 UTC to 2023-02-21 07:39:10.83 UTC). In this case, we report a p-value of 1.00, consistent with no significant excess of track events. The IceCube sensitivity to neutrino point sources with an E^-2.0 spectrum (E^2 dN/dE at 1 TeV) within the locations spanned by the 90% spatial containment region of IceCube-230220A is 3.1e-02 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.


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