IceCube-220501A

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

On 2022-05-01 at 22:50:58.64 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 2.110 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/136588_56014830.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to:

Date: 2022-05-01
Time:  22:50:58.64 UT
RA: 311.57 (+0.82, -1.07 deg  90% PSF containment) J2000
Dec: 18.68 (+1.08, -0.92 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 known gamma-ray sources in the 90% containment region for the event. The nearest source in the 4FGL-DR3 Fermi-LAT catalog is 4FGL J2043.3+1711 (310.84 deg, 17.19 deg J2000, 1.65 deg away from the best-fit neutrino candidate 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

Robert Stein (Caltech), Sven Weimann (Ruhr University Bochum), Simeon Reusch (DESY), Jannis Necker (DESY) and Anna Franckowiak (DESY/Ruhr University Bochum),

On behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations: 

As part of the ZTF neutrino follow up program (Stein et al. 2022),
we observed the localization region of the neutrino event IceCube-220501A (Santander et. al, GCN 31986
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 ) with the Palomar 48-inch telescope, equipped with the 47 square degree ZTF camera (Bellm et al. 2019, Graham et al. 2019). We started observations in the g-band beginning at 2022-05-02 09:39 UTC, approximately 10.8 hours after event time. We covered 87% (2.5 sq deg) of the reported localization region. This estimate accounts for chip gaps. Each exposure was 300s with a typical depth of 21.0 mag. 
 
The images were processed in real-time through the ZTF reduction and image subtraction pipelines at IPAC to search for potential counterparts (Masci et al. 2019). AMPEL (Nordin et al. 2019, Stein et al. 2021) was used to search the alerts database for candidates. We reject stellar sources (Tachibana and Miller 2018) and moving objects, and apply machine learning algorithms (Mahabal et al. 2019).

No candidate counterparts were detected.

ZTF and GROWTH are worldwide collaborations comprising Caltech, USA; IPAC, USA; WIS, Israel; OKC, Sweden; JSI/UMd, USA; DESY, Germany; TANGO, Taiwan; UW Milwaukee, USA; LANL, USA; TCD, Ireland; IN2P3, France.

GROWTH acknowledges generous support of the NSF under PIRE Grant No 1545949.
Alert distribution service provided by DIRAC@UW (Patterson et al. 2019).
Alert database searches are done by AMPEL (Nordin et al. 2019).
Alert filtering is performed with the AMPEL Follow-up Pipeline (Stein et al. 2021).

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

We report an analysis of observations of the vicinity of the high-energy 
IC220501A neutrino event (GCN 31986
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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 2022-05-01 at 22:50:58.64 
UT (T0) with J2000 position RA = 311.57 (+0.82, -1.07) deg, Decl. = 
+18.68 (+1.08, -0.92) deg (90% PSF containment). No cataloged gamma-ray 
(>100 MeV) sources are located within the 90% IC220501A localization 
region (4FGL-DR3; arXiv:2201.11184
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 ; The Fermi-LAT collaboration 2020, 
ApJS, 247, 33).

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 IC220501A 
best-fit position. Assuming a power-law spectrum (photon index = 2.0 
fixed) for a point source at the IC220501A best-fit position, the >100 
MeV flux upper limit (95% confidence) is < 5e-10 ph cm^-2 s^-1 for 
~13-years (2008-08-04 to 2022-05-01 UTC), and < 9e-9 (< 7e-8) 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 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-220501A (https://gcn.gsfc.nasa.gov/gcn3/31986.gcn3
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 ) in a time range of 1000 seconds centered on the alert event time (2022-05-01 22:42:38.635 UTC to 2022-05-01 22:59:18.635 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-220501A. 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-220501A 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 9e+04 GeV.

A subsequent search was performed including 2 days of data centered on the alert event time (2022-04-30 22:50:58.635 UTC to 2022-05-02 22:50:58.635 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-220501A ranges from 1.6e-01 to 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)