GCN Circular 37833

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-Cascade 241019A (https://gcn.gsfc.nasa.gov/notices_amon_icecube_cascade/139992_18206409.amon) in a time range of 1000 seconds centered on the alert event time (2024-10-19 23:20:39.840 UTC to 2024-10-19 23:37:19.840 UTC) during which IceCube was collecting good quality data. Excluding the event that prompted the alert, one track-like event is found within the 90% containment region of IceCube-Cascade 241019A. We find that this additional event is well described by atmospheric background expectations, with a p-value of 0.05 (which doesn’t account for statistical trials). 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-Cascade 241019A ranges from 1.3e-01 to 7.4e+00 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 3e+02 GeV and 3e+06 GeV. 

A subsequent search was performed including 2 days of data centered on the alert event time (2024-10-18 23:28:59.840 UTC to 2024-10-20 23:28:59.840 UTC). In this search we report a p-value of 0.04, without accounting for statistical trials. This is 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-Cascade 241019A ranges from 1.5e-01 to 7.5e+00 GeV cm^-2 in a 2 day time window. 

The best-fit position for a potential source producing the cascade and the track-like events in the two-day search is RA: 171.4 deg, Dec: -16.6 deg (J2000), with an estimated error radius of 0.5 deg at 90% containment. There are three track-like events which include this best-fit position in their 90% error region, and are also inside of the 90% contour of the cascade event. Properties of these coincident events are shown below.

dt [s]		RA [deg]	Dec [deg]	Angular uncertainty [deg] 
-----------------------------------------------------------------------------------------------------        
415		171.65		-16.09		1.18
21967 		170.90		-16.81		0.71
62271		171.44		-16.72		0.71

where:
dt = Time difference between the track-like event and the cascade event (i.e. T_track - T_cascade) [sec]
Angular uncertainty = Angular uncertainty of track event: the radius of a circle representing 90% CL containment by area.

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)