IceCube-260610A

L. Pfeiffer (Univ. of Wuerzburg), S. Buson (DESY, Univ. of Wuerzburg) and S. Garrappa (Weizmann Institute of Science) on behalf of the Fermi-LAT collaboration:

We report an analysis of observations of the vicinity of the high-energy IC260610A neutrino event (GCN 44899
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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 26-06-10 at 20:02:41.03 UTC (T0) with J2000 position RA = 309.20 (+2.04, -2.06) deg, Decl. = 37.22 (+0.96/-0.93) deg 90% PSF containment. Two cataloged >100 MeV gamma-ray source are located within the 90% IC260610A localization error, at a distance of roughly 0.77 and 1.45 deg (4FGL-DR4; The Fourth Fermi-LAT catalog Data Release 4, The Fermi-LAT collaboration 2023, arXiv:2307.12546
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 ). These are the objects:

4FGL J2035.0+3632 associated with PSR J2034+3632. Based on a preliminary analysis of the LAT data over the timescale of 1-day and 1-month, this object is not significantly detected at gamma-rays.

4FGL J2030.0+3641 associated with PSR J2030+3641. Based on a preliminary analysis of the LAT data over the timescale of 1-day, this object is not significantly detected at gamma-rays. On a 1-month integration timescale prior to T0, it is detected significantly but the flux is in agreement with the average flux of the source reported in 4FGL-DR4. We conclude that the source is not in high state.

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 IC260610A 90% confidence localization. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC260610A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 2.7e-9 ph cm^-2 s^-1 for ~18-years (2008-08-04 / T0), <1.2e-08 (<2.6e-07) 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 this source the Fermi-LAT contact person is Leonard Pfeiffer (leonard.pfeiffer 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-260610A (https://gcn.nasa.gov/circulars/44899
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 ) in a time range of 1000 seconds centered on the alert event time (2026-06-10 19:54:21.035 UTC to 2026-06-10 20:11:01.035 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-260610A. We report a p-value of 1.00 in this time window.  IceCube’s sensitivity to neutrino point sources with an E^-2.5 spectrum, expressed as E^2 dN/dE evaluated at 1 TeV, is 1.5e-01 GeV cm^-2 within the 90% spatial containment region of IceCube-260610A 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 6e+04 GeV. 

A subsequent search was performed including 2 days of data centered on the alert event time (2026-06-09 20:02:41.035 UTC to 2026-06-11 20:02:41.035 UTC). In this case, we report a p-value of 1.00, consistent with no significant excess of track events. IceCube’s sensitivity to neutrino point sources with an E^-2.5 spectrum, expressed as E^2 dN/dE evaluated at 1 TeV, is 1.7e-01 GeV cm^-2 within the 90% spatial containment region of IceCube-260610A 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)

Jannis Necker (Leiden University), Akshay Eranhalodi (DESY), Robert Stein (JSI), Cristobal Zilleruelo Cañas (DESY), and Anna Franckowiak (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-260610A (IceCube Collaboration 2026, GCN 44899
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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 2026-06-11 06:12 UTC, approximately 10.2 hours after event time. We covered 95.9% (4.6 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/IPAC, USA; University of Maryland, USA; University of California, Berkeley, USA; Cornell University, USA; Drexel University, USA; University of North Carolina at Chapel Hill, USA; Institute of Science and Technology, Austria; National Central University, Taiwan; OKC, Sweden; DZA, Germany.

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 ).

G. J. Yang, Q. Y. Wu and Y. Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team:

EP-FXT conducted a follow-up observation of IceCube-260610A (GCN 44899
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 ), a Gold-track neutrino event. The observation began at 2026-06-10T21:56:33, approximately 1.9 hours after the neutrino trigger, with a total exposure of 7.9 ks.

Within the neutrino localization uncertainty region, none of the detected X-ray sources exhibited significant variability compared with their historical fluxes or upper limits. The properties of the detected sources, excluding those clearly associated with stars, are summarized below.

Name | RA | Dec | Flux (erg /cm^2 /s) | Flux error (erg /cm^2 /s) | SNR
EPF_J203646.2+370943 | 309.1926 | 37.1612 | 6.52e-14 | 1.71e-14 | 5.14
EPF_J203731.0+370929 | 309.3791 | 37.1577 | 5.66e-14 | 1.99e-14 | 4.72
EPF_J203711.7+370245 | 309.2994 | 37.0434 | 1.05e-13 | 2.00e-14 | 8.60
EPF_J203710.6+370109 | 309.2940 | 37.0191 | 5.46e-14 | 1.38e-14 | 6.10
EPF_J203748.1+370629 | 309.4505 | 37.1080 | 5.80e-14 | 1.54e-14 | 5.06
EPF_J203709.1+365818 | 309.2880 | 36.9716 | 6.02e-14 | 1.65e-14 | 4.40
EPF_J203803.5+371737 | 309.5105 | 37.2954 | 9.50e-14 | 2.40e-14 | 5.00
EPF_J203717.9+365622 | 309.3246 | 36.9393 | 5.75e-14 | 1.67e-14 | 4.24
EPF_J203730.0+373440 | 309.3750 | 37.5779 | 1.36e-13 | 5.01e-14 | 4.84
EPF_J203737.9+365019 | 309.4045 | 36.8384 | 7.51e-14 | 2.50e-14 | 4.75
EPF_J203835.0+364342 | 309.6481 | 36.7285 | 2.01e-13 | 4.98e-14 | 6.20
EPF_J203601.0+363247 | 309.0040 | 36.5464 | 2.38e-13 | 8.65e-14 | 3.60

We note that EPF_J203835.0+364342 is associated with a CV named ASASSN -16ix.

Additional follow-up observations are planned.

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

On 26-06-10 at 20:02:41.03 UT IceCube detected a track-like event with a high probability of being of astrophysical origin. 
The event was selected by the ICECUBE_Astrotrack_GOLD alert stream.
The average astrophysical neutrino purity for Gold alerts is 50%.
Given the path through the IceCube detector (track traversing only a limited instrumented volume), the detector does not observe the full energy deposition as well as it would for a track crossing a larger portion of the array. This leads to some uncertainty in the p_astro value, circulated via GCN notice.  Regardless, this track remains a strong candidate for an astrophysical neutrino event.
This alert has an estimated false alarm rate of 0.1495 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/142709_10606089.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to:

Date: 26-06-10
Time: 20:02:41.03 UT
RA: 309.20 (+2.04/-2.06 deg 90% PSF containment) J2000
Dec: 37.22 (+0.96/-0.93 deg 90% PSF containment) J2000

As announced in GCN Circular 43419
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  (https://gcn.nasa.gov/circulars/43419
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 ), IceCube alert notices for high-energy track alerts are now also streamed via Kafka.
IceCube Gold/Bronze track alerts are available on the Kafka topic 'gcn.notices.icecube.gold_bronze_track_alerts'.
The probability distribution of the true neutrino direction, allowing the extraction of precise 90% containment regions around the best-fit direction, is now available for revised reconstruction of high-energy track alerts.
The corresponding sky map is distributed as a FITS file and follows the explicit naming convention IceCube-YYMMDDX, where YYMMDD indicates the date of the event and X is a letter distinguishing multiple alerts on the same day. The download link is provided through the GCN schema distributed via Kafka.
Detailed documentation describing the alert distribution, schemas, and probability maps is available at: https://gcn.nasa.gov/missions/icecube.

Two gamma-ray sources from the Fermi 4FGL-DR4 catalog are located within the 90% uncertainty region of this event. The closest source is 4FGL J2035.0+3632 (PSR J2034+3632), at RA = 308.7571° and Dec = 36.5371° (J2000), with an angular separation of 0.77° from the best-fit event position. The second-closest source is 4FGL J2030.0+3641 (PSR J2030+3641), at RA = 307.5086° and Dec = 36.6872° (J2000), with an angular separation of 1.45° 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