October 2025 - vsnet-grb-info - ooruri.kusastro.kyoto-u.ac.jp

[vsnet-grb-info 40434] IceCube Alert 251018.21: Global MASTER-Net observations report
by GCN Circulars 18 Oct '25

18 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42358 SUBJECT: IceCube Alert 251018.21: Global MASTER-Net observations report DATE: 25/10/18 16:39:32 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/42358. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40433] LIGO/Virgo/KAGRA S251018bi: Identification of a GW compact binary merger candidate
by GCN Circulars 18 Oct '25

18 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42357 SUBJECT: LIGO/Virgo/KAGRA S251018bi: Identification of a GW compact binary merger candidate DATE: 25/10/18 16:05:11 GMT FROM: shoki.iwaguchi(a)ligo.org The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S251018bi during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-10-18 15:25:47.021 UTC (GPS time: 1444836365.021). The candidate was found by the Aframe [1], cWB [2], cWB BBH [3], GstLAL [4], MBTA [5], PyCBC Live [6], and SPIIR [7] analysis pipelines. S251018bi is an event of interest because its false alarm rate, as estimated by the online analysis, is 3.2e-10 Hz, or about one in 1e2 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S251018bi The classification of the GW signal, in order of descending probability, is BBH (>99%), Terrestrial (<1%), BNS (<1%), or NSBH (<1%). Assuming the candidate is astrophysical in origin, the probability that at least one of the compact objects is consistent with a neutron star mass (HasNS) is <1%. [8] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [8] Both HasNS and HasRemnant consider the support of several neutron star equations of state for maximum neutron star mass. The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is <1%. The source chirp mass falls with highest probability in the bin (22.0, 44.0) solar masses, assuming the candidate is astrophysical in origin. Two sky maps are available at this time and can be retrieved from the GraceDB event page: * amplfi.multiorder.fits,0, an initial localization generated by AMPLFI [9], distributed via GCN and SCiMMA notices about 23 seconds after the candidate event time. * bayestar.multiorder.fits,0, an initial localization generated by BAYESTAR [10], distributed via GCN and SCiMMA notices about 5 minutes after the candidate event time. The preferred sky map at this time is bayestar.multiorder.fits,0. For the bayestar.multiorder.fits,0 sky map, the 90% credible region is 1463 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 5450 +/- 1489 Mpc (a posteriori mean +/- standard deviation). For further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/. [1] Marx et al. PRD 111, 042010 (2025) doi:10.1103/PhysRevD.111.042010 [2] Klimenko et al. PRD 93, 042004 (2016) doi:10.1103/PhysRevD.93.042004 [3] T. Mishra et al. PRD 105, 083018 (2022) doi:10.1103/PhysRevD.105.083018 [4] Tsukada et al. PRD 108, 043004 (2023) doi:10.1103/PhysRevD.108.043004 and Ewing et al. PRD 109, 042008 (2024) doi:10.1103/PhysRevD.109.042008 [5] Alléné et al. CQG 42, 105009 (2025) doi:10.1088/1361-6382/add234 [6] Dal Canton et al. ApJ 923, 254 (2021) doi:10.3847/1538-4357/ac2f9a [7] Chu et al. PRD 105, 024023 (2022) doi:10.1103/PhysRevD.105.024023 [8] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe [9] Chatterjee et al. MLST 5, 045030 (2024) doi:10.1088/2632-2153/ad8982 [10] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013 View this GCN Circular online at https://gcn.nasa.gov/circulars/42357. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40432] GRB 251016A: Swift-XRT afterglow detection
by GCN Circulars 18 Oct '25

18 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42356 SUBJECT: GRB 251016A: Swift-XRT afterglow detection DATE: 25/10/18 13:49:20 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB), E. Ambrosi (INAF-IASFPA) , S. Lanava (PSU), S. Dichiara (PSU), J.A. Kennea (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of GRB 251016A. We searched for X-ray sources in 3.5 ks of Photon Counting (PC) mode data. The total exposure at the position of the afterglow (see below) is 5.6 ks, obtained between T0+6.6 ks and T0+107.3 ks. Thirty-two uncatalogued X-ray sources are detected, of which one ("Source 1") is fading with >3-sigma significance, and is therefore likely the GRB afterglow. Using 1190 s of PC mode data and 2 UVOT images, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 266.30279, -39.56008 which is equivalent to: RA (J2000): 17h 45m 12.67s Dec(J2000): -39d 33' 36.3" with an uncertainty of 3.2 arcsec (radius, 90% confidence). The light curve can be modelled with a power-law decay with a decay index of alpha=4.53 (+0.08, -3.08). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.4 (+1.0, -0.6). The best-fitting absorption column is 4.8 (+8.8, -0.9) x 10^21 cm^-2, consistent with the Galactic value of 3.9 x 10^21 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 6.4 x 10^-11 (8.0 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 4.8 (+8.8, -0.9) x 10^21 cm^-2 Galactic foreground: 3.9 x 10^21 cm^-2 Excess significance: <1.6 sigma Photon index: 1.4 (+1.0, -0.6) The results of the XRT-team automatic analysis are available at https://www.swift.ac.uk/xrt_products/03000141. The results of the full analysis of the XRT observations are available at https://www.swift.ac.uk/SVOM/SVOM_FIELD00042. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42356. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40431] GRB 251017A: Swift/UVOT Detection
by GCN Circulars 18 Oct '25

18 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42355 SUBJECT: GRB 251017A: Swift/UVOT Detection DATE: 25/10/18 12:06:08 GMT FROM: s.shilling(a)lancaster.ac.uk S. P. R. Shilling (Lancaster U.) and R. Gupta (NASA GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 251017A 98 s after the BAT trigger (Gupta et al., GCN Circ. 42322). A source consistent with the enhanced XRT position (Goad et al., GCN Circ. 42326) is detected in the initial UVOT exposures. Preliminary detections and 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white 121 270 147 20.09 +/- 0.22 v 98 1234 109 >18.8 b 588 5138 83 >19.6 u 333 5126 501 >20.3 w1 712 4921 255 >18.5 w2 811 1384 58 >20.4 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.108 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/42355. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40430] GRB 251016A: Swift/UVOT Detection
by GCN Circulars 18 Oct '25

18 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42354 SUBJECT: GRB 251016A: Swift/UVOT Detection DATE: 25/10/18 12:05:09 GMT FROM: s.shilling(a)lancaster.ac.uk S.P.R. Shilling (Lancaster U.) reports on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 251016A, detected by SVOM/ECLAIRs (Basa et al., GCN Circ. 42308) and Fermi/GBM (Fermi GBM team, GCN Circ. 42309), 6.66 ks after the SVOM/ECLAIRs trigger. A source is detected in the optical by the Swift/UVOT at a position that is consistent with the likely X-ray counterpart detected by the Swift/XRT (Source 1: Evans et al., GCN Circ. 42311). Preliminary detections and upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the images are: Filter T_start(ks) T_stop(ks) Exp(s) Mag u 6.66 12.6 491.7 19.13 +/- 0.26 b 6.91 12.7 296.0 18.70 +/- 0.18 v 7.42 7.67 245.8 17.52 +/- 0.15 w1 12.1 12.4 245.8 >18.93 w2 7.17 7.42 245.8 >19.05 m2 7.68 7.85 168.3 >18.66 The magnitudes reported here are not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/42354. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40429] GRB 251018A: Swift/UVOT Detection
by GCN Circulars 18 Oct '25

18 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42353 SUBJECT: GRB 251018A: Swift/UVOT Detection DATE: 25/10/18 11:57:31 GMT FROM: Paul Kuin at MSSL <npkuin(a)gmail.com> N.P.M. Kuin (MSSL-UCL) and R. Gupta (NASA GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 251018A 84 s after the BAT trigger (Gupta et al., GCN Circ. 42343). A source consistent with the XRT position is detected in the initial UVOT exposures. Preliminary detections using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white 84 128 44 17.98 +/- 0.08 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.101 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/42353. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40428] IceCube-251018A - IceCube observation of a high-energy neutrino candidate track-like event
by GCN Circulars 18 Oct '25

18 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42352 SUBJECT: IceCube-251018A - IceCube observation of a high-energy neutrino candidate track-like event DATE: 25/10/18 11:11:12 GMT FROM: A. Zegarelli at Ruhr University Bochum <azegarelli(a)icecube.wisc.edu> 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+433, 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(a)icecube.wisc.edu View this GCN Circular online at https://gcn.nasa.gov/circulars/42352. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40427] IceCube-251018A - IceCube observation of a high-energy neutrino candidate track-like event
by GCN Circulars 18 Oct '25

18 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42351 SUBJECT: IceCube-251018A - IceCube observation of a high-energy neutrino candidate track-like event DATE: 25/10/18 11:10:28 GMT FROM: A. Zegarelli at Ruhr University Bochum <azegarelli(a)icecube.wisc.edu> 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+433, 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(a)icecube.wisc.edu View this GCN Circular online at https://gcn.nasa.gov/circulars/42351. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40426] GRB 251017A: VLT/MUSE spectroscopic redshift z = 4.327
by GCN Circulars 18 Oct '25

18 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42350 SUBJECT: GRB 251017A: VLT/MUSE spectroscopic redshift z = 4.327 DATE: 25/10/18 10:50:11 GMT FROM: Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo(a)ucd.ie> L. Izzo (INAF/OACn & DARK/NBI), A. Saccardi (CEA/Irfu), M. Garnichey (LUX-Paris Obs.), M. Ferro (INAF-OABr), A. Martin-Carrillo (UCD), D. B. Malesani (DAWN/NBI and Radboud), N. R. Tanvir (U. Leicester), A. L. Thakur (INAF-IAPS), G. Corcoran (UCD), report on behalf of the Stargate collaboration: We observed the optical afterglow (Perez-Garcia et al., GCN 42323; Antier et al., GCN 42325; Goad et al., GCN 42326; Sasada et al., GCN 42329; Lipunov et al., GCN 42330; Fu et al., GCN 42331; Mo et al., GCN 42336; Adami et al., GCN 42339; Xin et al., GCN 42341) of GRB 251017A (Gupta et al., GCN 42322; Woolf et al., GCN 42335), using the ESO VLT UT4 (Yepun) equipped with the MUSE spectrograph. The mid time of our observation was 2025 Oct 18 01:14:28 UT (16.56 hr after the GRB trigger), and consisted of 8 exposures of 700 s each. We extracted a 1D spectrum centered on the afterglow emission, using an aperture radius of 0.6 arcsec. In the reduced spectrum, which covers the wavelength range 4750 - 9330 AA, we detect a clear continuum and a trough due to Lya absorption visible at ~6470 AA. From the identification of several absorption features as due to Si II, Si II*, O I, O I*, CII, C II*, Si IV, C IV, Fe II, Al II, we infer a common redshift of z=4.327 for the GRB. We note that our spectroscopic redshift measurement is consistent with the photometric redshift value provided by Angulo et al. (GCN 42348). We acknowledge expert support from the observing staff in Paranal, in particular Robert de Rosa, Miguel Lopez, Thallis Pessi and Julien Drevon. The analysis of this spectrum was carried out with the help of the zHunter tool (https://doi.org/10.5281/zenodo.15189495). View this GCN Circular online at https://gcn.nasa.gov/circulars/42350. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40425] GRB 251016A: VLT/FORS2 Optical Observation
by GCN Circulars 18 Oct '25

18 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42349 SUBJECT: GRB 251016A: VLT/FORS2 Optical Observation DATE: 25/10/18 09:53:25 GMT FROM: Roberto Ricci at INAF-IRA <ricci(a)ira.inaf.it> Roberto Ricci (U Rome), Niccolo Passaleva ( U Rome) and Eleonora Troja (U Rome) report: We observed the field of the short duration GRB 251016A detected by SVOM/ECLAIRs (Basa et al., GCN 42308), FERMI-GBM (Fermi GBM team, GCN 42309), CALET-GBM (Kawakubo et al., GCN 42321), Glowbug (Woolf et al., GCN 42313) and Astro Sat CZTI (Arya et al., GCN 42327) with the FORS2 imager on the ESO VLT UT1 (Antu). Observations started on Oct 16th, 2025 at 23:45 UT (~9 hours after the SVOM trigger) and were carried out in the I_BESS filter with an average airmass of ~1.3. The GRB lies within a very crowded region at low Galactic latitude. Several optical sources are detected within the localization of Swift/XRT Source #1 (Evans et al., GCN 42311). Objects brighter than 24 AB mag have counterparts in the GAIA DR3 catalogue (Babusiaux et al., 2023), however several fainter (>24 AB mag) sources remain unmatched. Further observations are planned to determine variability. We thank the staff at the VLT for the rapid execution of these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/42349. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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