IceCube-220928A

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


On 22-09-28 at 12:32:38.30 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 1.99 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/137096_70551815.amon), more 
sophisticated reconstruction algorithms have been applied offline, with 
the direction refined to:


Date: 22-09-28

Time: 12:32:38.30

RA: 207.42 (+1.41 / -2.52 deg�� 90% PSF containment) J2000

Dec: +10.43 (+0.98 / -0.98 deg 90% PSF containment) J2000


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


Two gamma-ray sources listed in the 4FGL-DR2 Fermi-LAT catalog are 
located within the 90% containment of the best-fit candidate neutrino 
position. The sources are 4FGL J1351.3+1115 and 4FGL J1342.6+0944, 
located 0.92 and 1.86 deg away from the best-fit position, respectively.


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

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-220928A (https://gcn.gsfc.nasa.gov/gcn3/32599.gcn3
Loading...
 
 ) in a time range of 1000 seconds centered on the alert event time (2022-09-28 12:24:18.300 UTC to 2022-09-28 12:40:58.300 UTC) during which IceCube was collecting good quality data. Excluding the event that prompted the alert, zero track-like events are found within the 90% containment region of IceCube-220928A. 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-220928A is 1.3e-01 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 2e+02 GeV and 1e+05 GeV.


A subsequent search was performed including 2 days of data centered on the alert event time (2022-09-27 12:32:38.300 UTC to 2022-09-29 12:32:38.300 UTC). In this case, we report a p-value of 1.00, 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-220928A is 1.5e-01 GeV cm^-2 in a 2 day time window.


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>.


[1] IceCube Collaboration, R. Abbasi  et al., ApJ 910 4 (2021)

S. Garrappa (DESY-Zeuthen), S. Buson (Univ. of Wuerzburg) and J. 
Sinapius (DESY-Zeuthen) on behalf of the Fermi-LAT collaboration:

We report an analysis of observations of the vicinity of the IC220928A 
high-energy neutrino event (GCN 32599
Loading...
 
 ) with all-sky survey data from the 
Large Area Telescope (LAT), on board the Fermi Gamma-ray Space 
Telescope. The IceCube event was detected on 2022-09-28 at 12:32:38.30�� 
UT (T0) with J2000 position RA = 207.42 (+1.41 , -2.52) deg, Decl. = 
10.43 (+0.98 , -0.98) deg (90% PSF containment). Three cataloged 
gamma-ray (>100 MeV) sources are located within the 90% IC220928A 
localization region (4FGL-DR3; The Fermi-LAT collaboration 2022, ApJS, 
260, 53). Based on a preliminary analysis of the LAT data over the 
timescales of 1-day and 1-month prior to T0, these objects are not 
significantly detected (> 5 sigma).

We searched for intermediate (days to years) timescale emission from a 
new gamma-ray transient source. Preliminary analysis indicates no 
significant (> 5 sigma) new excess emission (> 100 MeV) at the IC220928A 
best-fit position. Assuming a power-law spectrum (photon index = 2.0 
fixed) for a point source at the IC220928A best-fit position, the >100 
MeV flux upper limit (95% confidence) is < 6.5e-10 ph cm^-2 s^-1 for 
~14-years (2008-08-04 to 2022-09-28 UTC), and < 9e-9 (<1.1e-7) ph cm^-2 
s^-1 for a 1-month (1-day) integration time before T0.

Since Fermi normally operates in an all-sky scanning mode, regular 
monitoring of this region will continue. For these observations the 
Fermi-LAT contact persons are S. Garrappa (simone.garrappa at desy.de) 
and S. Buson (sara.buson at uni-wuerzburg.de).

The Fermi-LAT is a pair conversion telescope designed to cover the 
energy band from 20 MeV to greater than 300 GeV. It is the product of an 
international collaboration between NASA and DOE in the U.S. and many 
scientific institutions across France, Italy, Japan and Sweden.