IceCube-260805A
GCN Circular 45695
Subject
Fermi-LAT Gamma-ray Observations of IceCube-260805A
Date
2026-09-22T19:59:02Z (2 days ago)
From
Sara Buson at DESY, Univ. of Wurzburg <sara.buson@gmail.com>
Via
Web form
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 IC260805A neutrino event (GCN 45294) 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 2026-08-05 at 14:01:39.70 UTC (T0) with J2000 position RA = 60.47 (+0.91, -0.80) deg, Decl. = 26.07 (+0.54, -0.56) deg 90% PSF containment (J2000). One cataloged >100 MeV gamma-ray source is located within the 90% IC260805A localization error. This is the object FL16Y J0402.5+2615 (FL16Y, The Fermi-LAT 16 Year Source List, The Fermi-LAT collaboration 2026, arXiv:2602.22148).
The FL16Y catalog does not report an associated counterpart at other wavelengths for FL16Y J0402.5+2615. We performed a new analysis of the full ~18yr Fermi-LAT mission data, integrating the period from 2008-08-04 to T0, in the 100 MeV–1 TeV energy range. The best-fit position of FL16Y J0402.5+2615 is (J2000) RA, Dec = 60.83, +25.99 (0.11 deg 68% containment, 0.18 deg 95% containment, 0.22 deg 99% containment). The source 5BZQ J0403+2600 (also known as OF 200), located at (RA, Dec) = (60.7732753, +26.0004174), lies 0.053 deg from the best-fit gamma-ray position, within its 68% localization uncertainty. This positional agreement further supports 5BZQ J0403+2600 as the likely counterpart of the gamma-ray excess, as also reported in the previous Fermi-LAT catalog (4LAC-DR3; The Fourth Catalog of Active Galactic Nuclei Detected by the Fermi Large Area Telescope: Data Release 3, The Fermi-LAT collaboration 2022, DOI: 10.3847/1538-4365/ac9523). Based on a preliminary analysis of the LAT data over the timescales of 1-day and 1-month prior to T0, this object is not significantly detected (> 5 sigma).
5BZQ J0403+2600 is a flat-spectrum radio quasar at z=2.109 (Massaro et al. 2015, Ap&SS, 357, 75; Schmidt 1997, ApJ, 217, 358). The Fermi-LAT spectrum indicates that its gamma-ray emission peaks toward the MeV range, while the source is relatively faint at GeV energies, suggesting that a substantial fraction of its high-energy emission may emerge at lower MeV/X-ray energies. The LAT light curve, integrated over 3-year time bins, shows a mild enhancement in recent years. Given the source's spectral shape, this increase at GeV energies could potentially indicate enhanced activity at lower MeV/X-ray energies. Its X-ray activity over recent years remains largely unconstrained, as only one X-ray observation is available in the archives, obtained by the Neil Gehrels Swift Observatory in 2007. New X-ray observations would help characterize its current activity state and better constrain the high-energy peak of its SED. The source has also been regularly observed at radio wavelengths and is included in the OVRO monitoring program (Richards et al. 2011, ApJS, 194, 29). Recent radio observations could provide useful complementary information on its long-term activity and help assess whether the GeV enhancement is part of a broader multi-wavelength evolution.
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 IC260805A 90% confidence localization. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC260805A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 3.0e-10 ph cm^-2 s^-1 for ~18-years (2008-08-04 / T0), <8.2e-09 (<3.7e-08) 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 analysis, the Fermi-LAT points of contact are L. Pfeiffer (leonard.pfeiffer at uni-wuerzburg.de) and S. Buson (sara.buson 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 45337
Subject
IceCube-260805A: Upper limits from a search for additional neutrino events in IceCube
Date
2026-08-09T23:42:20Z (a month ago)
From
syan079@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-260805A (https://gcn.nasa.gov/circulars/45294)in a time range of 1000 seconds centered on the alert event time (2026-08-05 13:53:19.709 UTC to 2026-08-05 14:09:59.709 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-260805A. 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 1.4e-01 GeV cm^-2 within the 90% spatial containment region of IceCube-260805A 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 7e+04 GeV.
A subsequent search was performed including 2 days of data centered on the alert event time (2026-08-04 14:01:39.709 UTC to 2026-08-06 14:01:39.709 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-260805A 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 45310
Subject
IceCube-260805A: One candidate from the Zwicky Transient Facility
Date
2026-08-07T16:29:17Z (2 months ago)
From
akshay.eranhalodi@desy.de
Via
Web form
Akshay Eranhalodi (DESY), Robert Stein (JSI), Cristobal Zilleruelo Cañas (DESY), 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-260805A (IceCube Collaboration, GCN 45294) 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 2026-08-06 10:23 UTC, approximately 20.4 hours after event time. We covered 65.4% (1.0 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, lying within the 90.0% localization of the skymap.
+--------------------------------------------------------------------------------+
| ZTF Name | IAU Name | RA (deg) | DEC (deg) | Filter | Mag | MagErr |
+--------------------------------------------------------------------------------+
| ZTF26aaskzvj | AT 2026jrc | +60.57411872 | +25.81342036 | g | 20.937 | 0.182 |
+--------------------------------------------------------------------------------+
ZTF26aaskzvj/AT 2026jrc was first detected on 2026-04-15, and is a SN-like transient associated with a nearby galaxy in NED at z=0.0192 (~85 Mpc). The transient is only marginally detected with forced photometry at the neutrino arrival time. The source appears to have peaked 100 days ago at M<-18 in r-band, and is now much fainter at M=-15.4 as of last week.
We encourage spectroscopic follow-up to determine its nature and asses potential high-energy neutrino emission scenarios.
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 45294
Subject
IceCube-260805A - IceCube observation of a high-energy neutrino candidate track-like event
Date
2026-08-06T00:02:49Z (2 months ago)
From
mvelazquez@icecube.wisc.edu
Via
Web form
The IceCube Collaboration (http://icecube.wisc.edu/) reports:
On 26-08-05 at 14:01:39.70 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. 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 1.449 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/142956_64385264.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to:
Date: 26-08-05
Time: 14:01:39.70 UT
RA: 60.47 (+0.91/-0.8 deg 90% PSF containment) J2000
Dec: 26.07 (+0.54/-0.56 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.
One gamma-ray source from the Fermi FL16Y catalog is located within the 90% uncertainty region of this event: FL16Y J0402.5+2615, at RA = 60.647° and Dec = 26.267° (J2000), with an angular separation of 0.254° from the best-fit event position.
We report here sources within the 90% confidence contour available in the multi-order probability map, rather than those selected using the simplified rectangular error-box reported in this Circular.
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