IceCube-231027A

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

On 23-10-27 at 04:16:10.44 UT IceCube detected a track-like event with a high probability of being of astrophysical origin.
The event was selected by the ICECUBE_Astrotrack_GOLD alert stream.
The average astrophysical neutrino purity for Gold alerts is 50%.
This alert has an estimated false alarm rate of 0.1472 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/138487_60138479.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to:

Date: 23-10-27
Time: 04:16:10.44 UT
RA: 267.16 (+3.35/-3.40 deg 90% PSF containment) J2000
Dec: +46.96 (+2.25/-2.88 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.

Seven gamma-ray sources listed in the 4FGL-DR3 Fermi-LAT catalog are located in the 90% containment region. The closest source is 4FGL J1747.9+4704 at RA 266.99, Dec +47.07, 0.16 deg away from the best-fit 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

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-231027A (https://gcn.nasa.gov/circulars/34891
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 ) in a time range of 1000 seconds centered on the alert event time (2023-10-27 04:07:50.440 UTC to 2023-10-27 04:24:30.440 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-231027A. 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-231027A is 1.5e-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 5e+04 GeV. 

A subsequent search was performed including 2 days of data centered on the alert event time (2023-10-26 04:16:10.440 UTC to 2023-10-28 04:16:10.440 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^-2.5 spectrum (E^2 dN/dE at 1 TeV) within the locations spanned by the 90% spatial containment region of IceCube-231027A is 1.8e-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.

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

S. Buson (Uni Wuerzburg), S. Garrappa (Weizmann Institute of Science), C. Bartolini (INFN Bari)  and J. Sinapius (DESY) on behalf of the Fermi-LAT collaboration:
We report an analysis of observations of the vicinity of the IC231027A  high-energy neutrino event (GCN 34891
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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 2023-10-27 at 04:16:10.44 UT (T0) with J2000 position RA =  267.16 (+3.35, -3.40) deg, Decl. = +46.96 (+2.25, -2.88) deg (90% PSF containment).  According to the fourth Fermi LAT source catalog (4FGL-DR4), there are eight 4FGL-DR4 cataloged gamma-ray (>100 MeV; The Fermi-LAT collaboration 2022, ApJS, 260, 53) sources in the 90% IC231027A uncertainty localization region. 
We searched for intermediate (days to years) timescale emission from a new gamma-ray source. Preliminary analysis indicates no significant (> 5 sigma) new excess emission (> 100 MeV) at the IC231027A best-fit position. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC231027A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 7.0e-10 ph cm^-2 s^-1 for ~15-years (2008-08-04 to 2023-10-27 UTC), and < 5.2e-9 (< 1.4e-7) ph cm^-2 s^-1 for a 1-month (1-day) integration time before T0.
The gamma-ray source nearest to the best-fit position of IC231027A is the blazar 4FGL J1747.9+4704 (a.k.a. B3 1746+470, 5BZB J1747+4658), at a 0.16deg separation. Close to the neutrino-event best-fit position, at 0.29deg separation, there is also the unassociated gamma-ray source 4FGL J1749.6+4716. Preliminary analysis indicates that these gamma-ray sources are ongoing a prolonged, enhanced activity state. The year-binned gamma-ray light curves show that they entered the high state in 2021. During the last year, i.e. 1-year integration time before T0, the observed flux (E>100 MeV) of 4FGL J1747.9+4704 is (1.2 +/- 0.3) x 10^-9 photons cm^-2 s^-1 (statistical uncertainty only), more than three times greater than the average flux reported in the 4FGL-DR4; the flux (E>100 MeV) observed for 4FGL J1749.6+4716 during this same period is of (2.3 +/- 0.3) x 10^-8 photons cm^-2 s^-1 (statistical uncertainty only), more than ten times greater than the 4FGL-DR4 average flux. We encourage multiwavelength observations of these sources. 
We performed an analysis of the region selecting only the LAT higher energy events (>1GeV) in order to achieve an improved localisation of the unassociated source 4FGL J1749.6+4716, and obtain as best-fit position RA = 267.3962, Decl. = 47.3276 (0.04 deg 68% containment, 0.07 deg 95% containment). A plausible association is the flat-spectrum radio source B3 1748+473 (GB6 B1748+4720), located 0.01deg away from the best-fit position.
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. Buson (sara.buson at uni-wuerzburg.de <http://uni-wuerzburg.de/>), S. Garrappa (simone.garrappa at weizmann.ac.il <http://weizmann.ac.il/>), J. Sinapius (jonas.sinapius at desy.de <http://desy.de/>), C. Bartolini (chiara.bartolini at ba.infn.it <http://ba.infn.it/>).
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.