IceCube-231202A

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

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. 2023), we observed the localization region of the neutrino event IceCube-231202A (Sommani et. al, GCN 35255
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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- and r-band beginning at 2023-12-08 08:37 UTC, approximately 135.5 hours after event time. We covered 79.8% (6.3 sq deg) of the reported localization region. This estimate accounts for chip gaps. Each exposure was 30s 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 nuztf (Stein et al. 2021, https://github.com/desy-multimessenger/nuztf ).

C. Bartolini (Univ of Trento & INFN Bari), S. Garrappa (Weizmann Institute of Science), S. Buson (Univ of Wuerzburg), J. Sinapius (DESY) and Leonard Pfeiffer (Univ of Wuerzburg) on behalf of the Fermi-LAT collaboration:

We report an analysis of observations of the vicinity of the IC231202A high-energy neutrino event (GCN 35225
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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 2023-12-02 at 17:08:24.09 UT (T0) with J2000 position RA =  139.04 (+1.52, -1.96) deg, Decl. = +0.37 (+1.11, -1.40) deg (90% PSF containment).  According to the fourth Fermi LAT source catalog (4FGL-DR4), there is one 4FGL-DR4 cataloged gamma-ray (>100 MeV; The Fermi-LAT collaboration 2022, ApJS, 260, 53) source, 4FGL J0909.1+0121 (PKS 0906+01), in the 90% IC231202A uncertainty localization region. Based on a preliminary analysis of the LAT data over one month and day timescale prior T0, this object is not significantly detected at gamma rays.

We searched for intermediate (days to years) timescale emission from a new gamma-ray source. Preliminary analysis indicates no significant (> 5 sigma) new excess emission (> 100 MeV) at the IC231202A best-fit position. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC231202A best-fit position, the >100 MeV flux upper limit (95% confidence) is <6.0e-10 ph cm^-2 s^-1 for ~15-years (2008-08-04 to 2023-12-02 UTC), and < 4.3e-9 (<6.1 e-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 region will continue. For this observation the Fermi-LAT contact person is C. Bartolini (chiara.bartolini at ba.infn.it).

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-231202A (https://gcn.nasa.gov/circulars/35255
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 ) in a time range of 1000 seconds centered on the alert event time (2023-12-02 17:00:04.090 UTC to 2023-12-02 17:16:44.090 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-231202A. 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-231202A ranges from 1.4e-01 to 1.5e-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 3e+02 GeV and 2e+05 GeV. 

A subsequent search was performed including 2 days of data centered on the alert event time (2023-12-01 17:08:24.090 UTC to 2023-12-03 17:08:24.090 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-231202A is 1.6e-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.

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

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

On 2023-12-02 at 17:08:24.09 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 4.4035 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/138632_31747601.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to:

Date: 2023-12-02
Time:  17:08:24.09 UT
RA: 139.04 (+1.52, -1.96 deg 90% PSF containment) J2000
Dec: +0.37 (+1.11, -1.40 deg  90% PSF containment) J2000

Deployment of updated software delayed the availability of these results, we apologize for the delay.  We encourage follow-up by ground and space-based instruments to help identify a possible astrophysical source for the candidate neutrino.

One gamma-ray source listed in the 4FGL-DR4 Fermi-LAT catalog is inside the 90% uncertainty region. The source is 4FGL J0909.1+0121, located 2.0 deg away from the best-fit position. The source is also listed in the Fermi 3FHL catalog as 3FHL J0909.1+0121.

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