IceCube-241006A

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

On 2024-10-06 at 22:38:14.30 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 2.56 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/139939_8268246.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to:

Date: 2024-10-06
Time:  22:38:14.30 UT
RA: 58.36 (+0.94, -0.84 deg 90% PSF containment) J2000
Dec: +8.35 (+0.47, -0.49 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-DR4 or 3FHL catalog sources within the 90% uncertainty region. The nearest gamma-ray source in either catalog is 4FGL J0347.5+0722 at RA: 56.90 deg, Dec: +7.38 deg J2000 (1.74 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

Jannis Necker (DESY), Robert Stein (Caltech), Simeon Reusch (DESY), Sven Weimann (Ruhr University Bochum), and 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-241006A (Zegarelli et. al, GCN 37723
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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 2024-10-08 07:00 UTC, approximately 32.4 hours after event time. We covered 76.0% (1.3 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). We are left with the following high-significance transient candidates by our pipeline, all lying within the 90.0% localization of the skymap.

+--------------------------------------------------------------------------------+
| ZTF Name     | IAU Name  | RA (deg)    | DEC (deg)   | Filter | Mag   | MagErr |
+--------------------------------------------------------------------------------+
| ZTF19accjndb |  -------  | 058.6439041 | +08.5812604 | g      | 20.59 | 0.12    
| ZTF24ablklut |  -------  | 058.2043689 | +08.6628184 | r      | 21.69 | 0.18   |  
+--------------------------------------------------------------------------------+
 

Amongst our candidates, 

ZTF19accjndb was first detected on 2019-09-09, and has a crossmatched detection as WISEA J035434.54+083452.2 at a distance of 0.35". This source is also listed in milliquas (Flesch 2023) as a likely QSO (p=98%). This AGN has been detected previously by ZTF, and does not appear to currently be in an elevated optical state. It had been gradually fading in difference image detections for the past 60 days, and these represent minor fluctations relative to the archival PS1 magnitude of g=18.6 (Chambers et al. 2016). 

ZTF24ablklut was first detected on 2024-10-08. It has a cross-matched detection as WISEA J035249.06+083946.1 at a distance of  0.19". Based on the archival MIR colours of this source (W1-W2=1.0), this object is very likely to be an AGN (Stern et al. 2012). The recent optical detection is very faint in difference imaging, representing a small increase relative to the archival detection in PS1 at r=20.5 (Chambers et al. 2016).

We therefore find no reason to suggest that either ZTF19accjndb/WISEA J035434.54+083452.2 or ZTF24ablklut/WISEA J035249.06+083946.1 are related to the neutrino.

Observations of this field will continue as part of our standard ToO cadence for high-energy neutrinos (Stein et al 2023.).

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 ).

S. Garrappa (Weizmann Institute of Science), C. Bartolini (INFN Bari), S. Buson (DESY, Univ. of Wuerzburg), L. Pfeiffer (Univ. of Wuerzburg), J. Sinapius (DESY) and P. M. Veres (Ruhr University Bochum) on behalf of the Fermi-LAT collaboration:

We report an analysis of observations of the vicinity of the high-energy IC241006A neutrino event (GCN 37723
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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 2024-10-06  22:38:14.30 UTC (T0) with J2000 position RA = 58.36 (+0.94, -0.84) deg, Decl. = +8.35 (+0.47, -0.49) deg 90% PSF containment. No Fermi 4FGL catalog gamma-ray source is located within the 90% IC-240929A localization error (Fourth Fermi-LAT catalog, 4FGL-DR4, The Fermi-LAT collaboration 2023, arXiv:2307.12546
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 ). 

We searched for the existence of intermediate (days to years) timescale emission from a new gamma-ray transient source. Preliminary analysis indicates no significant (>5sigma) new excess emission (>100 MeV) within the IC241006A 90% confidence localization. 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 <1.8e-10 ph cm^-2 s^-1 for ~16-years (2008-08-04 / T0), <8.6e-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 source will continue. For these observations, the Fermi-LAT contact person is S. Garrappa (simone.garrappa at weizmann.ac.il). 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-241006A (https://gcn.nasa.gov/circulars/37723
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 ) in a time range of 1000 seconds centered on the alert event time (2024-10-06 22:29:54.300 UTC to 2024-10-06 22:46:34.300 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-241006A. 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-241006A 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 (2024-10-05 22:38:14.300 UTC to 2024-10-07 22:38:14.300 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-241006A 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.
[1] IceCube Collaboration, R. Abbasi  et al., ApJ 910 4 (2021)