IceCube-260315A
GCN Circular 44048
Subject
IceCube-260315A: No Candidate Transients from the Zwicky Transient Facility
Date
2026-03-18T18:09:53Z (3 days 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-260315A (Zegarelli et. al, GCN 44017) 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 2026-03-15 07:45 UTC, approximately 5.4 hours after event time. We covered 93.7% (0.7 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.
We do not recover the previously reported candidate counterpart AT 2026fpm (Lipunov et al. 2026, GCN 44023) because it lies outside of the 90% contianment area based on the publicly available probability map of the neutrino event localisation. As the source is also likely a known variable (Fortin et al. 2026, GCN 44026; Feng et al., GCN 44042) it is unlikely to be the neutrino counterpart.
ZTF and GROWTH are worldwide collaborations comprising Caltech, USA; 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 44042
Subject
IceCube-260315A/AT2026fpm: EP-FXT follow-up observation
Date
2026-03-18T04:57:04Z (3 days ago)
Edited On
2026-03-18T13:16:47Z (3 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
J. P. Feng, B. Zhang (USTC), H. N. Yang, Y. Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team:
The Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) performed a follow-up observation of AT2026fpm (Segura et al., GCN 44023) at UTC 2026-03-16T23:31:53 (T0+45.21h) (The IceCube Collaboration, GCN 44017). An X-ray source was detected at R.A. = 176.1586 deg, DEC = -2.6035 deg (J2000) with an uncertainty of 10 arcsec in radius (90% C.L. statistical and systematic) and the flux of 1.1×10^(-13) erg/s/cm^2 in 0.5-10 keV band. The X-ray position is consistent with the optical transient AT2026fpm, which is spatially consistent with a QSO at z=1.389.
Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).
GCN Circular 44036
Subject
Fermi-LAT Gamma-ray Observations of IceCube-260315A
Date
2026-03-17T12:07:57Z (4 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) 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 IC260315A neutrino event (GCN 44017) 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 26-03-15 at 02:19:06.60 UTC (T0) with J2000 position RA = 175.69 (+0.49, -0.46) deg, Decl. = -1.90 (+0.53, -0.51) deg 90% PSF containment (J2000). No cataloged gamma-ray sources are found within the 90% IC260315A 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 IC260315A 90% confidence localization. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC260315A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 2.7e-10 ph cm^-2 s^-1 for ~17-years (2008-08-04 / T0), <1.6e-08 (<5.0e-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 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 44033
Subject
IceCube-260315A: Upper limits from a search for additional neutrino events in IceCube
Date
2026-03-16T17:57:13Z (5 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-260315A (https://gcn.nasa.gov/circulars/44017) in a time range of 1000 seconds centered on the alert event time (2026-03-15 02:10:46.630 UTC to 2026-03-15 02:27:26.630 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-260315A. 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-260315A 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 3e+02 GeV and 2e+05 GeV.
A subsequent search was performed including 2 days of data centered on the alert event time (2026-03-14 02:19:06.630 UTC to 2026-03-16 02:19:06.630 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 1.6e-01 GeV cm^-2 within the 90% spatial containment region of IceCube-260315A 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 44026
Subject
IceCube-260315A: COLIBRÍ optical observations
Date
2026-03-16T13:05:38Z (5 days ago)
From
F. Fortin at IRAP <ffortin.sci.edu@gmail.com>
Via
Web form
IceCube 260315A: COLIBRÍ optical observations
Francis Fortin (IRAP), Leonardo García García (UNAM), Jean-Grégoire Ducoin (CPPM), Jean-Luc Atteia (IRAP), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Edilberto Aguilar-Ruiz (UNAM), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Missimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM) report:
We imaged the field of IceCube 260315A (The IceCube Collaboration, GCN Circ. 44017) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-03-16 06:23:48 to 09:13:24 UTC (from 28 to 30.9 hours after the trigger) and obtained 63 minutes of exposure in the g, r filters, and 126 minutes in the z filter.
The data were reduced, coadded and analyzed with the COLIBRÍ ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction.
We detected the optical counterpart candidate AT 2026fpm reported by Segura et al., GCN Circ. 44023, at a preliminary magnitude of:
g = 19.94 +/- 0.01
r = 19.69 +/- 0.01
z = 19.66 +/- 0.01
The optical counterpart candidate lies on top of a catalogued source in the Legacy Survey with magnitudes of:
g = 21.04
r = 20.59
z = 20.48
However, this LS source is flagged as variable. We also note that it is found in PS1 at a much fainter level. This would indicate that AT 2026 fpm is a known variable source.
We thank the staff of the Observatorio Astronómico Nacional at Sierra de San Pedro Mártir, as well as the technical and engineering teams at CEA, CPPM, IRAP, LAM, OHP, OSU Pytheas, and UNAM.
COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico.
GCN Circular 44023
Subject
IceCube Alert-260315A/AT2026fpm Automatic MASTER optical blue counterpart candidate
Date
2026-03-15T18:39:46Z (6 days ago)
Edited On
2026-03-19T19:18:19Z (2 days ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of Vladimir Lipunov at Lomonosov Moscow State University <lipunov@sai.msu.ru>
Via
email
M.J. Segura, C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio
Astronomico Felix Aguilar (OAFA),
Ya.Kechin, V.Lipunov (Lomonosov MSU), N.Budnev, O.Gress (ISU),
A.Kuznetsov, I.Panchenko, P.Balanutsa, G.Antipov, E.Gorbovskoy, N.Tiurina,
V.Senik, A.Chasovnikov, M.Shilova,V.Topolev, D.Vlasenko, A.Sankovich,
Yu.Tselik (Lomonosov MSU),
D.Svinkin (Ioffe Institute),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
A.Sosnovskij (CrAO),
D.Buckley (SAAO),
R.Rebolo (The Instituto de Astrofisica de Canarias),
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez,
J.Martinez,A.R.Corella, J.Tanori, L. Villalobos, L.H.Rodriguez (INAOE, Guillermo
Haro Astrophysics Observatory)
A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity)
MASTER OT J114437.99-023613.5/AT 2026fpm discovery
MASTER-OAFA robotic telescope [1] located in Argentina (OAFA observatory of San Juan National University) was pointed to the IceCube Alert 260315A (trigger No 46886533,11h 42m 40.32s , -01d 53m 06.0s, R=0.71) errorbox 105 sec after notice time and 224 sec after trigger time at 2026-03-15 02:22:50 UT, with upper limit up to 20.4 mag. The observations began at zenith distance = 45 deg. The sun altitude is -42.8 deg.
The galactic latitude b = 57 deg., longitude l = 272 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=3187113
MASTER-OAFA auto-detection system [4]
discovered OT source at (RA, Dec) = 11h 44m 37.99s -02d 36m 13.5s on 2026-03-15.10943 UT very close to center of neutrino errorbox (GCN Circular #44017).
The OT magnitude in 'CLEAR' filter is 19.2m
(mlim = 20.0).
The OT is seen in 44 images. There is no minor planet at this place.
We have reference image on 2026-02-12.28608 UT with unfiltered mlim=19.9m.
Spectral observations are required.
The discovery and reference images are available at:
http://master.sai.msu.ru/static/OT/114437.99-023613.5.png
[1] Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L
[2] Lipunov et al. 2022, Universe, Vol. 8(5), id.271
[3] Lipunov et a. 2019, ARep, vol.63, 293
[4] Lipunov et al. 2023, Astronomical Robotic Networks and Operative Multichanel
Astrophysics,Lomonosov MSU PRESS, 591pp.
http://www.pereplet.ru/lipunov/625.html#625
GCN Circular 44017
Subject
IceCube-260315A - IceCube observation of a high-energy neutrino candidate track-like event
Date
2026-03-15T11:21:27Z (6 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 26-03-15 at 02:19:06.60 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 3.3512 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/142272_46886533.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to:
Date: 26-03-15
Time: 02:19:06.60 UT
RA: 175.69 (+0.49/-0.46 deg 90% PSF containment) J2000
Dec: -1.90 (+0.53/-0.51 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 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