TITLE: GCN CIRCULAR NUMBER: 30872 SUBJECT: IceCube-210922A: Upper limits from a search for additional neutrino events in IceCube DATE: 21/09/23 19:44:12 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-210922A (https://gcn.gsfc.nasa.gov/gcn3/30862.gcn3) in a time range of 2 days centered on the alert event time (2021-09-21 18:17:20.95 UTC to 2021-09-23 18:17:20.95 UTC) during which IceCube was collecting good quality data. Excluding the event that prompted the alert, zero additional track-like events are found in spatial coincidence with the 90% containment region of IceCube-210922A. We accordingly derive a time-integrated muon-neutrino flux upper limit at the alert position of E^2 dN/dE = 3.5 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 2 TeV and 5 PeV. A subsequent search was performed to include the month of data prior to the alert event (2021-08-23 18:17:20.95 UTC to 2021-09-23 18:17:20.95 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 4.1 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>.