IceCube-200523A

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

On 20/05/23 at 02:30:07.59 UT IceCube detected a track-like event with a moderate probability of being of astrophysical origin. The event was selected by the ICECUBE_Astrotrack_Bronze alert stream.  The average astrophysical neutrino purity for Bronze alerts is 30%. This alert has an estimated false alarm rate of 4.9 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/134116_58596690.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to:

Date: 20/05/23 
Time: 02:30:07.59 UT
RA: 338.64 (+10.77 -6.07 deg 90% PSF containment) J200
Dec: 1.75 (+1.84 -3.54 deg 90% PSF containment) J2000

The larger than usual error region in RA from the offline reconstructions is being investigated.   

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

Ten sources from the Fermi 4FGL catalog are inside the 90% localization region, the closest being 4FGL J2227.9+0036 located at RA 336.98 deg and Dec 0.62 deg (at a distance of 2.01 degrees from the best-fit location).

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

J. Wood (NASA/MSFC) reports on behalf of the Fermi-GBM team:

For the IceCube high-energy neutrino candidate event IceCube-200523A
(GCN 27787
Loading...
 
 ), at the event time Fermi-GBM was observing the reported
neutrino location at:

RA: 338.64 (+10.77 -6.07 deg 90% PSF containment) J2000
Dee: 1.75 (+1.84 -3.54 deg 90% PSF containment) J2000

There was no Fermi-GBM onboard trigger around the event time of the
neutrino candidate. An automated, blind search for short gamma-ray
bursts below the onboard triggering threshold in Fermi-GBM also
identified no counterpart candidates. The GBM targeted search,
the most sensitive, coherent search for GRB-like signals,
was run from +/-30 s around the neutrino candidate time.
From this search, no significant signal was found related
to IceCube-200523A.

We set upper limits on impulsive gamma-ray emission. Using the
representative soft, normal, and hard GRB-like templates described in
arXiv:1612.02395
Loading...
 
 , we set the following 3 sigma flux upper limits over
10-1000 keV (in units of 10^-7 erg/s/cm^2):

Timescale   Soft     Normal   Hard
-------------------------------------------
0.128 s:    6.5      9.5      17.
1.024 s:    2.2      2.9      6.1
8.192 s:    0.9      1.3      1.8

These results are preliminary.

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-200523A (https://gcn.gsfc.nasa.gov/gcn3/27787.gcn3
Loading...
 
 ) in a time
range of 2 days centered on the alert event time (2020-05-22 02:30:07.59 UTC to 2020-05-24 02:30:07.59 UTC) during which IceCube was collecting good quality data. Excluding the
event that prompted the alert, six additional track-like events are found in spatial coincidence
with the 90% containment region of IceCube-200523A. 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 = 4.6 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 5 PeV.

A subsequent search was performed to include the month of data prior to the alert event (2020-04-23 02:30:07.59 UTC to 2020-05-24 02:30:07.59 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
 1.1 x 10^-4 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>.