TITLE:   GCN CIRCULAR
NUMBER:  42352
SUBJECT: IceCube-251018A - IceCube observation of a high-energy neutrino candidate track-like event
DATE:    25/10/18 11:11:12 GMT
FROM:    A. Zegarelli at Ruhr University Bochum <azegarelli@icecube.wisc.edu>

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

On 25-10-18 at 05:05:42.97 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 0.2566 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/141495_22018019.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to:

Date: 25-10-18
Time: 05:05:42.97 UT
RA: 321.11 (+3.09/-2.94 deg 90% PSF containment) J2000
Dec: 41.31 (+2.46/-3.51 deg 90% PSF containment) J2000

Two gamma-ray sources listed in the Fermi 4FGL-DR4 catalog are located within the 90% uncertainty region of the event, both with no clear multi-wavelength counterpart and classification: 4FGL J2118.3+4055 and 4FGL J2120.5+4331, situated 1.3 deg and 2.3 deg away from the best-fit direction of our alert, respectively.

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