IceCube-251218A
GCN Circular 43157
C. Bartolini (Univ. of Trento and INFN Bari), 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 IC251218A neutrino event (GCN 43151) 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 25-12-18 at 20:21:00.63 UTC (T0) with J2000 position RA = 353.60 (+0.90, -0.74) deg, Decl. = 44.15 (+0.46, -0.45) deg 90% PSF containment (J2000). One cataloged gamma-ray (>100 MeV) source is located within the 90% IC251218A localization region (4FGL-DR4, The Fourth Fermi-LAT catalog Data Release 4, The Fermi-LAT collaboration 2023, arXiv:2307.12546). This is the unassociated gamma-ray source 4FGL J2331.6+4430. Based on a preliminary analysis of the LAT data over the timescale of 1-day and 1-month prior to T0, this object is not significantly detected (> 5 sigma).
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 IC251218A 90% confidence localization. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC251218A best-fit position, the >100 MeV flux upper limit (95% confidence) is <9.6e-11 ph cm^-2 s^-1 for ~17-years (2008-08-04 / T0), <9.2e-09 (<8.8e-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 C. Bartolini (chiara.bartolini at ba.infn.it).
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 43154
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-251218A (https://gcn.nasa.gov/circulars/43151) in a time range of 1000 seconds centered on the alert event time (2025-12-18 20:12:40.630 UTC to 2025-12-18 20:29:20.630 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-251218A. 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-251218A 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 5e+04 GeV.
A subsequent search was performed including 2 days of data centered on the alert event time (2025-12-17 20:21:00.630 UTC to 2025-12-19 20:21:00.630 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 1.8e-01 GeV cm^-2 within the 90% spatial containment region of IceCube-251218A 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 43153
Sarah Antier (IJCLAB), Enrique Moreno Méndez (UNAM), Noémie Globus (UNAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (AUS), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Nikos Mandarakas (LAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Margarita Pereyra (UNAM), N. A. Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), and Antonio de Ugarte Postigo (LAM) report:
We observed the field of the IceCube-251218A (GCN 43151) (bronzetrack) event with the DDRAGO wide-field imager on the COLIBRÍ telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir. We observed four pointings centred on (RA, Dec) = (353.8851, 44.3568), (353.3414, 44.3590), (353.8784, 43.9697), and (353.3374, 43.9697) between 2025-12-19 02:26 UTC and 03:10 UTC (from 6.09 to 6.59 hours after the trigger). At each pointing we obtained 8 minutes of simultaneous exposure in r and z over a field of 26 x 26 arcmin. These pointings cover a region of approximately 1 x 1 degree centered on (RA, Dec) = (353.60, 44.15) and cover most of the 90% uncertainty region.
The data were coadded with the COLIBRÍ ASU pipeline and analysed in STDWeb/STDPipe (Karpov 2025). Comparing our observations (and after performing image subtraction) against Pan-STARRS DR1, we detect no evident uncatalogued sources within the observed fields to a 10-sigma limiting AB magnitudes of:
r > 21.9 and z > 20.8
These values are not corrected for the Galactic extinction.
We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams.
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 43151
The IceCube Collaboration (http://icecube.wisc.edu/) reports:
On 25-12-18 at 20:21:00.63 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 0.8234 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/141741_9008919.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to:
Date: 25-12-18
Time: 20:21:00.63 UT
RA: 353.60 (+0.90/-0.74 deg 90% PSF containment) J2000
Dec: 44.15 (+0.46/-0.45 deg 90% PSF containment) J2000
We encourage follow-up by ground and space-based instruments to help identify a possible astrophysical source for the candidate neutrino.
There is one Fermi 4FGL-DR4 source in the 90% uncertainty region, i.e., the unassociated gamma-ray source 4FGL J2331.6+4430 at RA: 552.90 deg, Dec: 44.51 deg J2000 (0.62 deg away 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