IceCube-260708A
GCN Circular 45171
Subject
IceCube-260708A: Follow-up studies of cosmic-ray origin of high-energy neutrino alert
Date
2026-07-15T20:31:38Z (3 days ago)
From
anna.franckowiak@astro.rub.de
Via
Web form
The IceCube Collaboration (http://icecube.wisc.edu/) reports:
IceCube reported a 2.29 PeV neutrino event (https://gcn.nasa.gov/circulars/45120). We performed follow-up studies based on the timing distribution of hits inside the ice and hits in the IceTop cosmic-ray air-shower array on the surface above the in-ice part of the detector with tools that are not available for realtime selection of events yet. We find that the observed signatures are unlikely to be produced by a high-energy neutrino but instead indicate an origin in multiple muons produced in a cosmic-ray air shower, which is an expected, but rare background.
GCN Circular 45145
Subject
Fermi-LAT Gamma-ray Observations of IceCube-260708A
Date
2026-07-13T11:10:59Z (5 days ago)
From
Leo Pfeiffer at University of Würzburg <pfeiffer.leo@gmail.com>
Via
Web form
L. Pfeiffer (Univ. of Wuerzburg), S. Buson (DESY, Univ. of Wuerzburg), S. Garrappa (Weizmann Institute of Science) and C. Bartolini (INFN Bari) on behalf of the Fermi-LAT collaboration:
We report an analysis of observations of the vicinity of the high-energy IC260708A neutrino event (GCN 45120) 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 2026-07-08 at 17:17:42.55 UTC (T0) with J2000 position RA = 292.81 (+0.48, -0.47) deg, Decl. = -15.17 (+0.44, -0.48) deg 90% PSF containment (J2000). No cataloged gamma-ray sources are found within the 90% IC260708A localization error (FL16Y, The Fermi-LAT 16 Year Source List, The Fermi-LAT collaboration 2026, arXiv:2602.22148).
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 IC260708A 90% confidence localization. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC260708A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 8.0e-10 ph cm^-2 s^-1 for ~18-years (2008-08-04 / T0), <5.7e-08 (<1.4e-07) ph cm^-2 s^-1 for a 1-month (1-day) integration time before T0.
We test the presence of an additional point source at the position of the optical transient AT2026kuv, which is a candidate supernova discovered by GOTO on 2026-04-20 (GCN 45125). The transient is located within the error region of IC260708A at 3.9 arcmin from the neutrino best-fit direction. No significant gamma-ray emission was detected. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the AT2026kuv best-fit position, the >100 MeV flux upper limit (95% confidence) is < 5.8e-08 ph cm^-2 s^-1 for a 1-month integration time before T0.
Since Fermi normally operates in an all-sky scanning mode, regular monitoring of this source will continue. For this analysis, the Fermi-LAT contact person is L. 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.
GCN Circular 45142
Subject
IceCube-260708A: Upper limits from a search for additional neutrino events in IceCube
Date
2026-07-12T18:01:14Z (6 days ago)
From
Alicia Mand at IceCube/UW-Madison <aemand@wisc.edu>
Via
Web form
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-260708A (https://gcn.nasa.gov/circulars/45120) in a time range of 1000 seconds centered on the alert event time (2026-07-08 17:09:22.551 UTC to 2026-07-08 17:26:02.551 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-260708A. 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, ranges from 3.4 to 3.8 GeV cm^-2 within the 90% spatial containment region of IceCube-260708A 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 1e+04 GeV and 2e+06 GeV.
A subsequent search was performed including 2 days of data centered on the alert event time (2026-07-07 17:17:42.551 UTC to 2026-07-09 17:17:42.551 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, ranges from 3.3 to 3.8 GeV cm^-2 within the 90% spatial containment region of IceCube-260708A 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)
GCN Circular 45134
Subject
IceCube-260708A: Observations with the Vera C. Rubin Observatory
Date
2026-07-10T19:24:52Z (8 days ago)
From
Robert David Stein at JSI <rdstein@umd.edu>
Via
Web form
Robert Stein (UMD/NASA GSFC/JSI), Sean MacBride (University of Zürich), Tiago Ribeiro, Lynne Jones, Angelo Fausti, Marina Pavlovic, Kris Mortensen, Jacqueline Seron Navarrete, Carlos Morales, Leanne Guy, Brian Stalder, Bob Blum (NSF-DOE Vera C Rubin Observatory), Erin Howard, Eric Bellm (University of Washington), Igor Andreoni (UNC Chapel Hill), Michael Coughlin (University of Minnesota), Antonella Palmese (Carnegie Mellon), Yousuke Utsumi (National Astronomical Observatory of Japan), Bruno Sanchez (CPPM - IN2P3), and Robert Lupton (Princeton), report on behalf of NSF-DOE Vera C Rubin Observatory:
We observed the localization region of the high-energy neutrino event IceCube-260708A (Zegarelli et. al, GCN 45120) with the 9.6 square degree field of view LSST Camera mounted on the 8.4-m Simonyi Survey Telescope at the Vera C. Rubin Observatory [1].
The neutrino event met the pre-approved trigger criteria for neutrino follow-up with Rubin [2], and observations were conducted following the community-designed plan. The first night of observations consisted of exposures in u (30s), g (4x30s), r (30s) and z (30s). We started observations at 2026-07-10 02:48:12 UTC, approximately 33.5 hours after event time.
These observations achieved the following single-visit median depths:
u: 20.5
g: 22.8 (across four visits)
r: 23.5
z: 22.1
Though the Legacy Survey of Space and Time (LSST) survey has now begun, template images are not yet available for most filters in this region of the sky. For the images acquired on the night of July 9, 2026, approximately 5000 alerts were generated from our z-band observations.
While our automated alert system relies on production-quality templates to function autonomously, we have mobilized a specialized team of Rubin staff to process these images offline using lower quality templates that have been acquired in the region, but do not yet meet the standards for deployment to alert production. Any candidates will be reported to the community via GCN, and reported to TNS.
Observations of the neutrino will continue as part of the community observing plan.
We thank everyone in the Rubin Project and the wider Rubin Science Community who contributed to the success of these observations.
This material is based upon work supported in part by the National Science Foundation through Cooperative Agreements AST-1258333 and AST-2241526 and Cooperative Support Agreements AST-1202910 and 2211468 managed by the Association of Universities for Research in Astronomy (AURA), and the Department of Energy under Contract No. DE-AC02-76SF00515 with the SLAC National Accelerator Laboratory managed by Stanford University. Additional Rubin Observatory funding comes from private donations, grants to universities, and in-kind support from LSST-DA Institutional Members.
[1] Ivezić et al. (2019), https://arxiv.org/abs/0805.2366
[2] Andreoni et al. (2024), https://arxiv.org/abs/2411.04793
GCN Circular 45125
Subject
IceCube-260708A: One candidate from the Zwicky Transient Facility
Date
2026-07-09T16:21:49Z (9 days ago)
From
Robert David Stein at JSI <rdstein@umd.edu>
Via
Web form
Robert Stein (JSI), Tomas Ahumada (Noirlab), Mansi Kasliwal (Caltech), Jesper Sollerman (Stockholm), Cristobal Zilleruelo Cañas (DESY), Jannis Necker (Leiden University), Akshay Eranhalodi (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-260708A (Zegarelli et. al, GCN 45120) 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 2026-07-09 08:12 UTC, approximately 14.9 hours after event time. We covered 23.8% (0.2 sq deg) of the reported localization region at least twice. 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 candidate by our pipeline, lying within the 90.0% localization of the skymap.
+--------------------------------------------------------------------------------+
| ZTF Name | IAU Name | RA (deg) | DEC (deg) | Filter | Mag | MagErr |
+--------------------------------------------------------------------------------+
| ZTF26abfurzw | AT2026kuv | 292.8653948 | -15.1344488 | r | 20.11 | 0.07 |
+--------------------------------------------------------------------------------+
ZTF26abfurzw/AT 2026kuv was discovered by GOTO on 2026-04-20, and reported to TNS. ATLAS forced photometry reveals a lightcurve rising since discovery, later peaking at 17.4 mag at the beginning of May. The source has since slowly faded. The source was detected in our ZTF ToO observations, and the photometry confirms that the source is now very red (g-r = 1) and faded substantially from peak. There were no previous ZTF survey detections, because the source lies in a chip gap for the survey footprint.
The photometric properties (rise, fade, and late-time colour) of AT 2026kuv appear consistent with a supernova. Neutrino emission in a post-peak supernova would be plausible if there were CSM interaction in the source. We encourage spectroscopic observations of this source to confirm its nature, and to search for evidence of CSM interaction.
Further monitoring of this field will continue as part of the ZTF neutrino follow-up program (Stein et al. 2023), and we are planning additional follow-up of AT 2026kuv.
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 ).
GCN Circular 45120
Subject
IceCube-260708A - IceCube observation of a high-energy neutrino candidate track-like event
Date
2026-07-08T23:09:54Z (10 days ago)
From
A. Zegarelli at Ruhr University Bochum <azegarelli@icecube.wisc.edu>
Via
Web form
The IceCube Collaboration (http://icecube.wisc.edu/) reports:
On 26-07-08 at 17:17:42.55 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. Documentation regarding the alert streams and their astrophysical purity can be found here: https://gcn.nasa.gov/missions/icecube.
This alert has an estimated false alarm rate of 0.1472 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/142827_7869742.amon), more sophisticated reconstruction algorithms have been applied offline. Some computational anomalies are observed in the primary offline reconstruction algorithm for this event, so the directional reconstruction results from the alternative offline algorithm are included in this event while these anomalies are investigated. With this alternative algorithm, the direction is refined to:
Date: 26-07-08
Time: 17:17:42.55 UT
RA: 292.81 (+0.48/-0.47 deg 90% PSF containment) J2000
Dec: -15.17 (+0.44/-0.48 deg 90% PSF containment) J2000
As announced in GCN Circular 43419 (https://gcn.nasa.gov/circulars/43419), 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.
No known gamma-ray sources listed in the Fermi LAT 16-year Source List (FL16Y) are located within the 90% uncertainty region of this event.
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