IceCube-251018A
GCN Circular 42371
Subject
Fermi-LAT gamma-ray observations of IceCube-251018A
Date
2025-10-19T23:49:18Z (2 days 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 (Univ. of Trento & INFN Bari) on behalf of the Fermi-LAT collaboration:
We report an analysis of observations of the vicinity of the IC251018A high-energy neutrino event (GCN 42351) 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 25-10-18 at 05:05:42.97 UT (T0) with J2000 position RA = 321.11 (+3.09/-2.94) deg, Decl. = +41.31 (+2.46/-3.51) deg (90% PSF containment). There are three catalogued gamma-ray sources (4FGL-DR4; The Fourth Fermi-LAT catalog Data Release 4, The Fermi-LAT collaboration 2023, arXiv:2307.12546) located within the 90% IC251018A localization region. These are:
4FGL J2118.3+4055: unassociated,at 1.2 deg distance from the best-fit neutrino position;
4FGL J2120.5+4331: unassociated, at 2.3 deg distance from the best-fit neutrino position;
4FGL J2136.5+4259: associated with the blazar of uncertain type TXS 2134+428, at 2.8 deg from the best-fit neutrino position;
Based on a preliminary analysis of the LAT data over the timescale of one day and one month prior T0, these objects are not significantly detected at gamma-rays.
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) at the IC251018A bestfit position. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC251018A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 8.4 e-10 ph cm^-2 s^-1 for ~17-years (2008-08-04 / T0), < 7.4e-09 (<5.9e-08) ph cm^-2 s^-1 for a 1-month (1-day) integration time before T0.
In the analysis of the ~17-years integrated LAT data (100 MeV - 1 TeV), a 5 sigma new excess of gamma rays, Fermi J2125.8+3940 was detected 1.65 deg offset from the best-fit IC251018A position and within the 90% confidence localization of the direction of the neutrino. Assuming a power-law spectrum, the best-fit localization is (J2000) RA = 321.46 deg, Dec = +39.69 deg (6 arcmin 99% containment, 3 arcmin 68% containment). The gamma-ray best-fit spectral parameters are flux = (8 +/- 3)e-10 ph cm^-2 s^-1 and index = 1.84+/-0.12. In a preliminary analysis of the LAT data over 1-day and 1-month prior T0, Fermi J2125.8+3940 is not significantly detected in the LAT data. All values include the statistical uncertainty only. The statistical significance is calculated following the prescription adopted in the 4FGL (Abdollahi et al. 2020, ApJS, 247, 33).
Since Fermi normally operates in an all-sky scanning mode, regular monitoring of this region will continue. For these observations 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 42369
Subject
IceCube-251018A: Upper limits from a search for additional neutrino events in IceCube
Date
2025-10-19T18:45:31Z (2 days 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-251018A (https://gcn.nasa.gov/circulars/42352) in a time range of 1000 seconds centered on the alert event time (2025-10-18 04:57:22.970 UTC to 2025-10-18 05:14:02.970 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-251018A. 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-251018A 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 6e+04 GeV.
A subsequent search was performed including 2 days of data centered on the alert event time (2025-10-17 05:05:42.970 UTC to 2025-10-19 05:05:42.970 UTC). In this case, we report a p-value of 0.02, 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 1.7e-01 to 1.8e-01 GeV cm^-2 within the 90% spatial containment region of IceCube-251018A 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 42367
Subject
IceCube-251018A: DDOTI Optical Upper Limit
Date
2025-10-19T07:31:09Z (3 days ago)
From
Rosa Leticia Becerra Godínez at Instituto de Astronomía, UNAM <rbecerra@astro.unam.mx>
Via
Web form
Rosa L. Becerra (UNAM), Alan M. Watson (UNAM), Camila Angulo Valdez (UNAM), Sahil Atri (U Roma), Nat Butler (ASU), Simone Dichiara (Penn State University), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Océlotl López (UNAM), Margarita Pereyra (UNAM) and Eleonora Troja (U Roma) report:
We observe the field of the IceCube-251018A (gold) event (IceCube Collaboration, GCN Circ. 42352) with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on the Sierra of San Pedro Martir (http://ddoti.astroscu.unam.mx) on the night of 2025-10-19 UTC.
DDOTI observed from 03:00 UTC to 06:18 UTC (from T+21.9 h to T+25.2 h after the trigger) with a total exposure of 96 min, covering the total error region reported by IceCube (IceCube Collaboration, GCN Circ 42352).
Comparing our observations to the USNO-B1 and PanSTARRS PS1 DR2, we detect no uncatalogued sources within the observed field to a 10-sigma limiting AB magnitude of:
w > 20.6.
Further observations are planned to assess variability.
This value is not corrected for the Galactic extinction.
We thank the staff of the Observatorio Astronómico Nacional on the Sierra of San Pedro Mártir.
GCN Circular 42358
Subject
IceCube-251018A: Global MASTER-Net observations report
Date
2025-10-18T16:39:32Z (3 days ago)
Edited On
2025-10-20T16:44:29Z (a day 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
V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko,
G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU),
O.Gress, N.Budnev (ISU),
C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
A.Sosnovskij (CrAO),
A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity),
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, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory)
MASTER-Kislovodsk robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the IceCube Alert 251018.21 (trigger No 22018019,21h 25m 13.92s , +39d 11m 09.6s, R=2.69) errorbox 39638 sec after notice time and 39688 sec after trigger time at 2025-10-18 16:07:11 UT, with upper limit up to 18.9 mag. The observations began at zenith distance = 8 deg. The sun altitude is -19.7 deg.
The galactic latitude b = -8 deg., longitude l = 86 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=3017315
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
22029 | 2025-10-18 11:12:21 | MASTER- | (21h 25m 26.91s , +38d 32m 19.1s) | C | 60 | 18.7 | Coadd
22142 | 2025-10-18 11:14:15 | MASTER- | (21h 34m 49.32s , +38d 32m 13.7s) | C | 60 | 18.4 | Coadd
22136 | 2025-10-18 11:14:33 | MASTER- | (21h 24m 42.35s , +40d 38m 41.0s) | C | 10 | 18.2 |
22149 | 2025-10-18 11:14:47 | MASTER- | (21h 24m 42.32s , +40d 38m 40.6s) | C | 10 | 18.3 |
22163 | 2025-10-18 11:15:00 | MASTER- | (21h 24m 42.33s , +40d 38m 40.8s) | C | 10 | 18.3 |
22176 | 2025-10-18 11:15:13 | MASTER- | (21h 24m 42.36s , +40d 38m 40.0s) | C | 10 | 18.3 |
22189 | 2025-10-18 11:15:27 | MASTER- | (21h 24m 42.37s , +40d 38m 39.1s) | C | 10 | 18.3 |
22203 | 2025-10-18 11:15:40 | MASTER- | (21h 24m 42.39s , +40d 38m 39.0s) | C | 10 | 18.3 |
22216 | 2025-10-18 11:15:54 | MASTER- | (21h 24m 42.42s , +40d 38m 38.2s) | C | 10 | 18.3 |
22230 | 2025-10-18 11:16:07 | MASTER- | (21h 24m 42.40s , +40d 38m 37.6s) | C | 10 | 18.2 |
22244 | 2025-10-18 11:16:21 | MASTER- | (21h 24m 42.40s , +40d 38m 37.0s) | C | 10 | 18.2 |
22266 | 2025-10-18 11:16:43 | MASTER- | (21h 24m 42.40s , +40d 38m 36.1s) | C | 10 | 18.4 |
22280 | 2025-10-18 11:16:58 | MASTER- | (21h 24m 42.41s , +40d 38m 35.3s) | C | 10 | 18.4 |
22294 | 2025-10-18 11:17:11 | MASTER- | (21h 24m 42.40s , +40d 38m 34.7s) | C | 10 | 18.4 |
22307 | 2025-10-18 11:17:25 | MASTER- | (21h 24m 42.46s , +40d 38m 34.3s) | C | 10 | 18.3 |
22324 | 2025-10-18 11:17:38 | MASTER- | (21h 24m 42.44s , +40d 38m 34.3s) | C | 15 | 18.7 |
22342 | 2025-10-18 11:17:57 | MASTER- | (21h 24m 42.43s , +40d 38m 32.8s) | C | 15 | 18.7 |
22361 | 2025-10-18 11:18:16 | MASTER- | (21h 24m 42.47s , +40d 38m 32.7s) | C | 15 | 18.7 |
22380 | 2025-10-18 11:18:34 | MASTER- | (21h 24m 42.47s , +40d 38m 31.2s) | C | 15 | 18.7 |
22398 | 2025-10-18 11:18:52 | MASTER- | (21h 24m 42.73s , +40d 38m 28.8s) | C | 15 | 17.7 |
22417 | 2025-10-18 11:19:11 | MASTER- | (21h 24m 42.65s , +40d 38m 27.9s) | C | 15 | 17.4 |
22987 | 2025-10-18 11:28:20 | MASTER- | (21h 31m 15.12s , +40d 24m 56.9s) | C | 60 | 19.3 | Coadd
23065 | 2025-10-18 11:29:38 | MASTER- | (21h 20m 28.77s , +36d 38m 22.6s) | C | 60 | 19.3 | Coadd
23238 | 2025-10-18 11:32:30 | MASTER- | (21h 24m 47.36s , +40d 38m 33.7s) | C | 60 | 19.4 | Coadd
23395 | 2025-10-18 11:35:08 | MASTER- | (21h 24m 39.85s , +40d 38m 56.5s) | C | 60 | 19.6 | Coadd
23440 | 2025-10-18 11:35:53 | MASTER- | (21h 26m 55.46s , +34d 43m 11.4s) | C | 60 | 19.6 |
23514 | 2025-10-18 11:37:06 | MASTER- | (21h 24m 38.44s , +40d 36m 49.8s) | C | 60 | 19.6 |
23586 | 2025-10-18 11:38:19 | MASTER- | (21h 31m 14.78s , +40d 24m 32.2s) | C | 60 | 19.6 |
23659 | 2025-10-18 11:39:32 | MASTER- | (21h 20m 28.45s , +36d 37m 54.8s) | C | 60 | 19.4 |
23810 | 2025-10-18 11:42:03 | MASTER- | (21h 24m 45.36s , +40d 38m 28.6s) | C | 60 | 19.6 |
23959 | 2025-10-18 11:44:31 | MASTER- | (21h 24m 41.51s , +40d 38m 32.1s) | C | 60 | 19.6 |
24033 | 2025-10-18 11:45:46 | MASTER- | (21h 39m 37.95s , +36d 37m 01.8s) | C | 60 | 19.9 |
24113 | 2025-10-18 11:47:06 | MASTER- | (21h 26m 55.34s , +34d 43m 32.1s) | C | 60 | 19.6 |
24186 | 2025-10-18 11:48:19 | MASTER- | (21h 24m 38.56s , +40d 37m 23.4s) | C | 60 | 19.6 |
24261 | 2025-10-18 11:49:34 | MASTER- | (21h 31m 08.05s , +40d 25m 50.0s) | C | 60 | 19.6 |
24335 | 2025-10-18 11:50:47 | MASTER- | (21h 20m 31.98s , +36d 36m 32.3s) | C | 60 | 19.4 |
24673 | 2025-10-18 11:56:25 | MASTER- | (21h 38m 44.90s , +37d 40m 08.5s) | C | 60 | 19.7 |
24746 | 2025-10-18 11:57:39 | MASTER- | (21h 26m 06.59s , +35d 44m 31.8s) | C | 60 | 19.6 |
24911 | 2025-10-18 12:00:24 | MASTER- | (21h 30m 14.16s , +41d 26m 28.4s) | C | 60 | 19.5 |
24992 | 2025-10-18 12:01:44 | MASTER- | (21h 19m 42.75s , +37d 38m 24.3s) | C | 60 | 19.5 |
25296 | 2025-10-18 12:06:48 | MASTER- | (21h 38m 47.62s , +37d 39m 00.3s) | C | 60 | 19.9 |
25372 | 2025-10-18 12:08:04 | MASTER- | (21h 26m 09.90s , +35d 45m 43.2s) | C | 60 | 19.7 |
25618 | 2025-10-18 12:12:11 | MASTER- | (21h 30m 14.23s , +41d 26m 02.8s) | C | 60 | 19.5 |
25692 | 2025-10-18 12:13:25 | MASTER- | (21h 19m 42.14s , +37d 37m 52.9s) | C | 60 | 19.5 |
25916 | 2025-10-18 12:17:08 | MASTER- | (21h 38m 41.75s , +37d 38m 43.9s) | C | 60 | 19.9 |
25989 | 2025-10-18 12:18:21 | MASTER- | (21h 26m 04.07s , +35d 45m 22.4s) | C | 60 | 19.6 |
26238 | 2025-10-18 12:22:30 | MASTER- | (21h 30m 15.89s , +41d 26m 02.0s) | C | 60 | 19.6 |
26312 | 2025-10-18 12:23:45 | MASTER- | (21h 19m 42.33s , +37d 38m 56.0s) | C | 60 | 19.5 |
26642 | 2025-10-18 12:29:15 | MASTER- | (21h 38m 40.69s , +37d 39m 18.2s) | C | 60 | 20.0 |
26716 | 2025-10-18 12:30:28 | MASTER- | (21h 26m 03.39s , +35d 42m 50.9s) | C | 60 | 19.6 |
27298 | 2025-10-18 12:40:11 | MASTER- | (21h 38m 41.77s , +37d 38m 45.3s) | C | 60 | 19.9 |
39779 | 2025-10-18 16:07:11 | MASTER-Kislovodsk | (21h 23m 12.87s , +39d 31m 52.3s) | C | 180 | 18.3 |
39959 | 2025-10-18 16:07:11 | MASTER-Kislovodsk | (21h 23m 12.87s , +39d 31m 52.2s) | C | 540 | 18.6 | Coadd
39779 | 2025-10-18 16:07:11 | MASTER-Kislovodsk | (21h 28m 59.97s , +39d 09m 35.7s) | C | 180 | 18.7 |
39919 | 2025-10-18 16:10:31 | MASTER-Kislovodsk | (21h 29m 03.89s , +41d 25m 46.0s) | C | 60 | 17.5 |
39919 | 2025-10-18 16:10:31 | MASTER-Kislovodsk | (21h 35m 00.82s , +41d 03m 22.0s) | C | 60 | 18.1 |
40059 | 2025-10-18 16:11:51 | MASTER-Kislovodsk | (21h 23m 12.96s , +39d 29m 49.4s) | C | 180 | 18.2 |
40059 | 2025-10-18 16:11:51 | MASTER-Kislovodsk | (21h 29m 00.21s , +39d 07m 33.0s) | C | 180 | 18.6 |
40199 | 2025-10-18 16:15:11 | MASTER-Kislovodsk | (21h 32m 40.41s , +39d 30m 38.4s) | C | 60 | 17.3 |
40199 | 2025-10-18 16:15:11 | MASTER-Kislovodsk | (21h 38m 27.62s , +39d 08m 21.8s) | C | 60 | 17.9 |
40339 | 2025-10-18 16:16:31 | MASTER-Kislovodsk | (21h 23m 15.28s , +39d 31m 25.2s) | C | 180 | 18.2 |
40339 | 2025-10-18 16:16:31 | MASTER-Kislovodsk | (21h 29m 02.86s , +39d 09m 10.0s) | C | 180 | 18.5 |
40706 | 2025-10-18 16:23:38 | MASTER-Kislovodsk | (21h 28m 41.27s , +41d 26m 54.8s) | C | 60 | 17.8 |
40706 | 2025-10-18 16:23:39 | MASTER-Kislovodsk | (21h 34m 56.99s , +41d 04m 17.1s) | C | 60 | 18.4 |
40846 | 2025-10-18 16:24:59 | MASTER-Kislovodsk | (21h 22m 51.36s , +39d 31m 08.1s) | C | 180 | 18.3 |
40846 | 2025-10-18 16:24:59 | MASTER-Kislovodsk | (21h 28m 56.82s , +39d 08m 19.4s) | C | 180 | 18.7 |
40986 | 2025-10-18 16:28:18 | MASTER-Kislovodsk | (21h 32m 12.06s , +39d 32m 51.9s) | C | 60 | 17.7 |
40986 | 2025-10-18 16:28:18 | MASTER-Kislovodsk | (21h 38m 17.80s , +39d 09m 55.3s) | C | 60 | 18.2 |
41126 | 2025-10-18 16:29:38 | MASTER-Kislovodsk | (21h 22m 59.40s , +39d 31m 04.5s) | C | 180 | 18.6 |
41126 | 2025-10-18 16:29:38 | MASTER-Kislovodsk | (21h 29m 05.14s , +39d 07m 57.1s) | C | 180 | 18.9 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
GCN Circular 42352
Subject
IceCube-251018A - IceCube observation of a high-energy neutrino candidate track-like event
Date
2025-10-18T11:11:12Z (3 days ago)
Edited On
2025-10-20T02:27:41Z (2 days ago)
From
A. Zegarelli at Ruhr University Bochum <azegarelli@icecube.wisc.edu>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of A. Zegarelli at Ruhr University Bochum <azegarelli@icecube.wisc.edu>
Via
Web form
The IceCube Collaboration (http://icecube.wisc.edu/) reports:
On 25-10-18 at 05:05:42.97 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.
The average astrophysical neutrino purity for Gold alerts is 50%.
This alert has an estimated false alarm rate of 0.2566 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/141495_22018019.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to:
Date: 25-10-18
Time: 05:05:42.97 UT
RA: 321.11 (+3.09/-2.94 deg 90% PSF containment) J2000
Dec: 41.31 (+2.46/-3.51 deg 90% PSF containment) J2000
Two gamma-ray sources listed in the Fermi 4FGL-DR4 catalog are located within the 90% uncertainty region of the event, both with no clear multi-wavelength counterpart and classification: 4FGL J2118.3+4055 and 4FGL J2120.5+4331, situated 1.3 deg and 2.3 deg away from the best-fit direction of our alert, respectively.
We encourage follow-up observations by both ground- and space-based instruments to help identify a possible astrophysical counterpart to the candidate neutrino.
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
GCN Circular 42351
Subject
IceCube-251018A - IceCube observation of a high-energy neutrino candidate track-like event (duplicate submission)
Date
2025-10-18T11:10:28Z (3 days ago)
Edited On
2025-10-20T02:29:51Z (2 days ago)
From
A. Zegarelli at Ruhr University Bochum <azegarelli@icecube.wisc.edu>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov>
Via
Web form
This is a duplicate submission of GCN 42352.