IceCube-220115A

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

On 2022-01-15 at 12:11:39.75 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 2.090 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/136170_48281000.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to:

Date: 2022-01-15 
Time:  12:11:39.75 UT
RA: 357.45 (+1.75, -1.18 deg  90% PSF containment) J2000
Dec: 25.28 (+1.03, -0.95 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.

There are no Fermi 4FGL or 3FHL catalog sources in the 90% uncertainty region. The nearest gamma-ray source in either catalog is 4FGL J2354.1+2720 at RA: 358.53 deg, Dec: 27.35 deg (2.28 deg away from the best-fit event position).

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

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 high-energy 
IC220115A neutrino event (GCN 31451
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 ) 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 2022-01-15 12:11:39.75 UTC 
(T0) with J2000 position RA = 357.45 (+1.75, -1.18) deg, Decl. = 25.28 
(+1.03, -0.95) deg 90% PSF containment. No cataloged gamma-ray sources 
are found within the 90% IC220115A localization error (The Fourth 
Fermi-LAT catalog DR2; The Fermi-LAT collaboration 2020, ApJS, 247, 33).

We searched for the existence of intermediate (months to years) 
timescale emission from a new gamma-ray transient source. Preliminary 
analysis indicates no significant (>5sigma) new excess emission (> 100 
MeV) at the the IC220115A best-fit position. Assuming a power-law 
spectrum (photon index = 2.0 fixed) for a point source at the IceCube 
best-fit position, the >100 MeV flux upper limit (95% confidence) is < 
5.6-10 ph cm^-2 s^-1 for ~13-years (2008-08-04 / 2022-01-15 UTC), < 
1.1e-8 (< 5.2e-8) ph cm^-2 s^-1 for a 1-month (1-day) integration time 
before T0.

Within the 90% confidence localization of the neutrino, ~1.1 deg offset 
from the best-fit IC220115A position, a >4 sigma excess of gamma rays, 
Fermi J2350.2+2620 was detected in an analysis of the integrated LAT 
data (> 100 MeV) between 2008-08-04 and 2022-01-15. Assuming a power-law 
spectrum, the candidate gamma-ray source has best-fit localization 
(J2000) RA: 357.564, Dec: 26.343 (0.15 deg 99% containment, 0.07 deg 68% 
containment), with best-fit spectral parameters flux = (8 +/- 5)e-10 ph 
cm^-2 s^-1 and index = 2.0 +/- 0.2. In a preliminary analysis of the LAT 
data over one day and one month prior T0, Fermi J2350.2+2620 is not 
significantly detected in the LAT data. All values include the 
statistical uncertainty only.

Since Fermi normally operates in an all-sky scanning mode, regular 
monitoring of this source 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.

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-220115A (https://gcn.gsfc.nasa.gov/gcn3/31451.gcn3
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 ) in a time range of 1000 seconds centered on the alert event time (2022-01-15 12:03:19.750 UTC to 2022-01-15 12:19:59.750 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-220115A. We find that these data are consistent with atmospheric background expectations, with a p-value of 0.013. 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-220115A is 1.4e-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 8e+04 GeV.

A subsequent search was performed including 2 days of data centered on the alert event time (2022-01-14 12:11:39.750 UTC to 2022-01-16 12:11:39.750 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-220115A is 1.7e-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)