TITLE:   GCN CIRCULAR
NUMBER:  30038
SUBJECT: IceCube-210516A: Upper limits from a search for additional neutrino events in IceCube
DATE:    21/05/17 17:30:38 GMT
FROM:    Alex Pizzuto at ICECUBE/U of Wisconsin  <pizzuto@wisc.edu>

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-210516A (https://gcn.gsfc.nasa.gov/gcn3/30026.gcn3) in a time
range of 2 days centered on the alert event time (2021-05-15 14:38:20.340 UTC to 2021-05-17 14:38:20.340 UTC) during which IceCube was collecting good quality data. Excluding the
event that prompted the alert, one additional track-like event is found in spatial coincidence
with the 90% containment region of IceCube-210516A. We find that these data are consistent with atmospheric background expectations, with a p-value of 1.0. We accordingly derive a time-integrated muon-neutrino flux upper limit at the alert position of E^2 dN/dE = 3.6 x 10^-5 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 1 TeV and 2 PeV.

A subsequent search was performed to include the month of data prior to the alert event (2021-04-16 14:38:20.340 UTC to 2021-05-17 14:38:20.340 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
4.7 x 10^-5 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>.