IceCube-260115A
GCN Circular 43497
Subject
IceCube-260115A: No Candidate Transients from the Zwicky Transient Facility
Date
2026-01-22T08:15:17Z (a month ago)
From
Jannis Necker at DESY <jannis.necker@desy.de>
Via
Web form
Akshay Eranhalodi (DESY), Robert Stein (JSI), Jannis Necker (Leiden University), 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-260115A (Zegarelli et. al, GCN 43421) 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 2026-01-16 05:53 UTC, approximately 12.3 hours after event time. We covered 99.2% (8.2 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 one transient candidate by our pipeline within the 90.0% localization of the skymap.
+--------------------------------------------------------------------------------+
| ZTF Name | IAU Name | RA (deg) | DEC (deg) | Filter | Mag | MagErr |
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| ZTF26aabnqai | AT2026azb | 145.5760425 | +13.0239392 | r | 21.08 | 0.15 |
+--------------------------------------------------------------------------------+
ZTF26aabnqai was first detected on 2026-01-16 at an apparent magnitude of about 21 mag in r-band. The g-r color is around 0.5 mag. Forced photometry revealed previous detections up to a week earlier with a fading rate of about 0.5 mag per day. The host galaxy has a photometric redshift of 0.23 +/- 0.08 in Legacy Survey. During our latest observatiosn the transient was no longer detectable, consistent with continued fading. This makes the transients too faint for our spectroscopic programs. However, the color, fade time and inferred absolute magnitude are all broadly consistent with a Type Ia supernova. These are not expected to emit high-energy neutrinos and thus we consider ZTF26aabnqai unlikely to be related to IceCube-260115A.
We further identify following quasars without contemporaneous flaring activity. The hosts of ZTF22aaejlfn (SDSS J094112.55+131224.9), ZTF25aadwsdp (SDSS J093659.79+124616.6), ZTF25aadxqgk (SDSS J094449.16+120545.5), and ZTF25aarudkx (SDSS J094755.84+125346.4) are listed in MILLIQUAS (Flesch et al., 2023). ZTF24abwkvpl was first detected on 2024-11-05. Its host, SDSS J093633.62+131948.5, is part of a selection of quasars by SDSS photometry (Richards et al., 2009). The hosts of ZTF25aaedxfb, and ZTF25aadxmes show red, AGN-like WISE colors with W1-W2>0.8 (Stern et al., 2012). ZTF25abttvfc was consistently detected over the last 100 days with varying brightness. ZTF18acqfhyp, ZTF25aadnych, and ZTF25aadoovh were sporadically detected before the neutrino arrival and are likely variable sources at the sensitivity limit.
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 ).
GCN Circular 43443
Subject
Fermi-LAT Gamma-ray Observations of IceCube-260115A
Date
2026-01-18T12:14:23Z (a month ago)
From
Simone Garrappa at Weizmann Institute of Science <simone.garrappa@weizmann.ac.il>
Via
Web form
S. Garrappa (Weizmann Institute of Science), L. Pfeiffer (Univ. of Wuerzburg), S. Buson (DESY, Univ. of Wuerzburg) 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 IC260115A neutrino event (GCN 43421) 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 2026-01-15 at 17:32:35.71 UTC (T0) with J2000 position RA = 145.77 (+2.29, -1.77) deg, Decl. = 12.41 (+1.18, -0.91) deg 90% PSF containment (J2000). No cataloged gamma-ray sources are found within the 90% IC260115A localization error (4FGL-DR4; The Fourth Fermi-LAT catalog Data Release 4, The Fermi-LAT collaboration 2023, arXiv:2307.12546).
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 IC260115A 90% confidence localization. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC260115A best-fit position, the >100 MeV flux upper limit (95% confidence) is <4.3e-10 ph cm^-2 s^-1 for ~17-years (2008-08-04 / T0), <3.8e-09 (<2.9e-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 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.
GCN Circular 43428
Subject
IceCube-260115A: Upper limits from a search for additional neutrino events in IceCube
Date
2026-01-16T21:03:16Z (2 months ago)
From
Yuhua Yao at IceCube/UW-Madison <yyao255@icecube.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-260115A (https://gcn.nasa.gov/circulars/43421) in a time range of 1000 seconds centered on the alert event time (2026-01-15 17:24:15.710 UTC to 2026-01-15 17:40:55.710 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-260115A. 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 1.3e-01 GeV cm^-2 within the 90% spatial containment region of IceCube-260115A 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 (2026-01-14 17:32:35.710 UTC to 2026-01-16 17:32:35.710 UTC). In this case, we report a p-value of 0.19, 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 1.5e-01 to 1.6e-01 GeV cm^-2 within the 90% spatial containment region of IceCube-260115A 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 43421
Subject
IceCube-260115A - IceCube observation of a high-energy neutrino candidate track-like event
Date
2026-01-15T20:05:03Z (2 months ago)
From
A. Zegarelli at Ruhr University Bochum <azegarelli@icecube.wisc.edu>
Via
Web form
The IceCube Collaboration (http://icecube.wisc.edu/) reports:
On 26-01-15 at 17:32:35.71 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 2.0497 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/141917_80302474.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to:
Date: 26-01-15
Time: 17:32:35.71 UT
RA: 145.77 (+2.29/-1.77 deg 90% PSF containment) J2000
Dec: 12.41 (+1.18/-0.91 deg 90% PSF containment) J2000
As announced in GCN Circular 43419 (https://gcn.nasa.gov/circulars/43419), the probability distribution of the true neutrino direction, allowing the extraction of precise 90% containment regions around the best-fit direction, is now available. The corresponding link (for this alert https://roc-2.icecube.wisc.edu/public/alerts/IceCube-260115A_skymap_probdensity_multiorder.fits.gz) is provided through the GCN schema distributed via Kafka.
IceCube GCN notices for high-energy track alerts (Gold and Bronze) are now also distributed via Kafka and can be accessed through the Kafka topic 'gcn.notices.icecube.gold_bronze_track_alerts'.
Further details will be available soon at https://gcn.nasa.gov/missions/icecube.
Please note that the classical GCN stream will be deactivated in the near future.
No known gamma-ray sources listed in the Fermi 4FGL-DR4 or 3FHL catalogs 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