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

[vsnet-grb-info 40552] EP251023a: Mondy optical observations
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42468 SUBJECT: EP251023a: Mondy optical observations DATE: 25/10/27 09:21:37 GMT FROM: Alina Volnova at IKI RAS <alinusss(a)gmail.com> A. Volnova (IKI), A. Pozanenko (IKI) , N. Pankov (HSE, IKI), E. Klunko (ISTP) report on behalf of IKI-GRB-FuN: We observed the field of the EP transient EP251023a (Wu et al., GCN 42388) in the R-filter with the AZT-33IK 1.5m telescope of the Sayan Solar Observatory (Mondy). We observed the field on Oct. 23 and 25, 2025, taking several frames with 120 s exposures. The optical couterpart detected by GOTO (Wortley et al., GCN 42387) and also observed by Li et al., GCN 42389; Liu et al., GCN 42391; Mandarakas et al., GCN 42400; Lipunov et al., GCN 42405; Selezneva et al., GCN 42406; Mohan et al., GCN 42411; Rakotondrainibe et al., GCN 42420; Rajabov et al., 42422, is clearly detected in the stacked frame of the first epoch and is not detected in that of the second one. The preliminary photometry is the following: Date UT start t-T0 Exp. Filter OT Err. UL (mid,days) (n*s) (3sigma) 2025-10-23 20:15:41 0.75316 20*120 R 20.64 0.12 22.0 2025-10-25 20:07:45 2.75807 35*120 R n/d n/d 22.7 The photometry is based on several nearby PS1 stars (R-magnitudes Lupton's transformation) and is not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/42468. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40551] GRB 251025C: CALET Gamma-Ray Burst Monitor detection
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42467 SUBJECT: GRB 251025C: CALET Gamma-Ray Burst Monitor detection DATE: 25/10/27 05:49:55 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University <kawakubo(a)phys.aoyama.ac.jp> S. Torii (Waseda U), A. Yoshida, T. Sakamoto, S. Sugita, Y. Kawakubo (AGU), K. Yamaoka (Nagoya U), S. Nakahira (JAXA), Y. Asaoka (ICRR), Y. Akaike, K. Kobayashi (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U), N. Cannady (GSFC/UMBC), M. L. Cherry (LSU), S. Ricciarini (U of Florence), P. S. Marrocchesi (U of Siena), and the CALET collaboration: The long GRB 251025C (Fermi GBM Final Real-time Localization: Fermi GBM team, GCN Circ. 42449) triggered the CALET Gamma-ray Burst Monitor (CGBM) at 23:08:37.27 UTC on 25 October 2025 (https://cgbm.calet.jp/cgbm_trigger/flight/1445468431/index.html) The burst signal was seen by all CGBM detectors. The burst light curve shows a multi-peaked structure that starts at T+2.9 sec, peaks at T+3.5 sec, and ends at T+46.7 sec. The T90 and T50 durations measured by the SGM data are 38.6 +/- 2.6 sec and 15.1 +/- 1.4 sec (40-1000 keV), respectively. The ground-processed light curve is available at https://cgbm.calet.jp/cgbm_trigger/ground/1445468431/ The CALET data used in this analysis are provided by the Waseda CALET Operation Center located at Waseda University. View this GCN Circular online at https://gcn.nasa.gov/circulars/42467. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40550] GRB 251025B: MAO/AZT-22 optical observations
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42466 SUBJECT: GRB 251025B: MAO/AZT-22 optical observations DATE: 25/10/27 03:45:44 GMT FROM: Yodgor Rajabov at UBAI <rajabov(a)astrin.uz> Y. Rajabov, B.Abidkhanov, O. Burkhonov, S. Ehgamberdiev, Y. Tillayev (UBAI), A. Shaymanov (Maidanak Observatory/UBAI) report on behalf of UBAI team. We observed the field of the GRB 251025B (Hussein et al., GCN 42437) with the 1.5-m at Maidanak Observatory telescope AZT-22 equipped with the 4kx4k CCD SNUCAM camera (Im et al., 2010). The OT (Wu et al., GCN 42438; Gress et al., GCN 42439; Wu et al., GCN 42440; Beardmore et al., GCN 42445; Mohan et al., GCN 42447; Hernández Funget al., GCN 42450; Pereyra et al., GCN 42452; Li et al., GCN 42453; Mo et al., GCN 42459; Rakotondrainibe et al., GCN 42460) is clearly detected in the individual and stacked frames. Preliminary photometry is as follows: Date UTstart Exptime t-T0 Filter OT Err. UL Site/Telescope (nxs) (mid, days) 2025-10-26 19:09:36 6x300 1.19827 R 20.75 0.03 23.10 MAO/AZT-22 All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained in Johnson Cousins filters were calibrated using the Gaia DR3 Synphot catalog. The data has not corrected for the Galactic extinction. Maidanak astronomical observatory (MAO) is an observational facility of the Ulugh Beg Astronomical Institute (UBAI), Uzbekistan Academy of Sciences (http://maidanak.uz/) View this GCN Circular online at https://gcn.nasa.gov/circulars/42466. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40549] LIGO/Virgo/KAGRA S251026bn: Updated Sky localization
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42465 SUBJECT: LIGO/Virgo/KAGRA S251026bn: Updated Sky localization DATE: 25/10/27 02:40:22 GMT FROM: lucy.thomas(a)ligo.org The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We have conducted further analysis of the LIGO Hanford Observatory (H1) and LIGO Livingston Observatory (L1) data around the time of the compact binary merger (CBC) candidate S251026bn (GCN Circular 42462). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby.multiorder.fits,0, distributed via GCN and SCiMMA notices, is available for retrieval from the GraceDB event page: https://gracedb.ligo.org/superevents/S251026bn For the Bilby.multiorder.fits,0 sky map, the 90% credible region is 744 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1202 +/- 347 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] Ashton et al. ApJS 241, 27 (2019) doi:10.3847/1538-4365/ab06fc and Morisaki et al. PRD 108, 123040 (2023) doi:10.1103/PhysRevD.108.123040 View this GCN Circular online at https://gcn.nasa.gov/circulars/42465. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40548] Fermi GRB 251026B: Global MASTER-Net observations report
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42464 SUBJECT: Fermi GRB 251026B: Global MASTER-Net observations report DATE: 25/10/27 01:31:39 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 Fermi GRB 251026B ( Fermi GBM team, GCN 42455) errorbox 59309 sec after notice time and 62633 sec after trigger time at 2025-10-27 00:42:47 UT, with upper limit up to 18.4 mag. The observations began at zenith distance = 68 deg. The sun altitude is -32.5 deg. The galactic latitude b = 20 deg., longitude l = 239 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3023975 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 62664 | 2025-10-27 00:42:47 | MASTER-Kislovodsk | (08h 46m 04.47s , -11d 51m 14.2s) | C | 60 | 17.9 | 62664 | 2025-10-27 00:42:47 | MASTER-Kislovodsk | (08h 50m 15.56s , -12d 14m 29.7s) | C | 60 | 18.3 | 63317 | 2025-10-27 00:53:40 | MASTER-Kislovodsk | (08h 46m 04.23s , -11d 50m 49.0s) | C | 60 | 17.8 | 63317 | 2025-10-27 00:53:40 | MASTER-Kislovodsk | (08h 50m 17.20s , -12d 14m 14.5s) | C | 60 | 18.1 | 63959 | 2025-10-27 01:04:22 | MASTER-Kislovodsk | (08h 46m 02.23s , -11d 50m 25.1s) | C | 60 | 18.2 | 63959 | 2025-10-27 01:04:22 | MASTER-Kislovodsk | (08h 50m 16.29s , -12d 13m 53.6s) | C | 60 | 18.4 | 64626 | 2025-10-27 01:15:29 | MASTER-Kislovodsk | (08h 46m 09.08s , -11d 49m 58.6s) | C | 60 | 18.2 | 64626 | 2025-10-27 01:15:29 | MASTER-Kislovodsk | (08h 50m 18.58s , -12d 13m 27.0s) | C | 60 | 18.4 | 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/42464. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40547] Fermi GRB 251025C: Global MASTER-Net observations report
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42463 SUBJECT: Fermi GRB 251025C: Global MASTER-Net observations report DATE: 25/10/27 01:31:01 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 Fermi GRB 251025C ( Fermi GBM team, GCN 42449) errorbox 1 days 5134 sec after notice time and 1 days 5165 sec after trigger time at 2025-10-27 00:34:45 UT, with upper limit up to 18.6 mag. The observations began at zenith distance = 53 deg. The sun altitude is -33.9 deg. The galactic latitude b = 58 deg., longitude l = 147 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3023716 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 91596 | 2025-10-27 00:34:45 | MASTER-Kislovodsk | (11h 18m 11.77s , +54d 29m 42.9s) | C | 60 | 18.3 | 91596 | 2025-10-27 00:34:45 | MASTER-Kislovodsk | (11h 25m 08.42s , +54d 06m 43.1s) | C | 60 | 18.5 | 91675 | 2025-10-27 00:36:05 | MASTER-Kislovodsk | (11h 31m 25.80s , +55d 59m 16.1s) | C | 60 | 18.3 | 91675 | 2025-10-27 00:36:05 | MASTER-Kislovodsk | (11h 24m 10.23s , +56d 22m 21.0s) | C | 60 | 18.1 | 91755 | 2025-10-27 00:37:25 | MASTER-Kislovodsk | (11h 20m 02.72s , +52d 12m 24.9s) | C | 60 | 18.6 | 91755 | 2025-10-27 00:37:25 | MASTER-Kislovodsk | (11h 13m 24.71s , +52d 35m 17.4s) | C | 60 | 18.6 | 91835 | 2025-10-27 00:38:45 | MASTER-Kislovodsk | (11h 44m 17.61s , +54d 29m 12.9s) | C | 60 | 18.1 | 91835 | 2025-10-27 00:38:45 | MASTER-Kislovodsk | (11h 51m 11.39s , +54d 06m 05.0s) | C | 60 | 18.3 | 91916 | 2025-10-27 00:40:05 | MASTER-Kislovodsk | (11h 38m 20.05s , +52d 33m 52.5s) | C | 60 | 18.1 | 91996 | 2025-10-27 00:41:25 | MASTER-Kislovodsk | (11h 31m 44.37s , +58d 17m 35.7s) | C | 60 | 18.1 | 91996 | 2025-10-27 00:41:25 | MASTER-Kislovodsk | (11h 39m 22.93s , +57d 54m 25.4s) | C | 60 | 18.3 | 92236 | 2025-10-27 00:45:26 | MASTER-Kislovodsk | (11h 18m 07.62s , +54d 29m 57.0s) | C | 60 | 18.3 | 92236 | 2025-10-27 00:45:26 | MASTER-Kislovodsk | (11h 25m 08.02s , +54d 06m 32.4s) | C | 60 | 18.3 | 92316 | 2025-10-27 00:46:46 | MASTER-Kislovodsk | (11h 24m 08.47s , +56d 22m 38.2s) | C | 60 | 18.1 | 92316 | 2025-10-27 00:46:46 | MASTER-Kislovodsk | (11h 31m 24.36s , +55d 59m 08.8s) | C | 60 | 18.3 | 92396 | 2025-10-27 00:48:06 | MASTER-Kislovodsk | (11h 13m 23.20s , +52d 35m 54.1s) | C | 60 | 18.6 | 92396 | 2025-10-27 00:48:06 | MASTER-Kislovodsk | (11h 20m 01.70s , +52d 12m 36.7s) | C | 60 | 18.6 | 92476 | 2025-10-27 00:49:26 | MASTER-Kislovodsk | (11h 44m 17.35s , +54d 29m 36.7s) | C | 60 | 18.0 | 92476 | 2025-10-27 00:49:26 | MASTER-Kislovodsk | (11h 51m 11.53s , +54d 06m 03.7s) | C | 60 | 18.2 | 92556 | 2025-10-27 00:50:46 | MASTER-Kislovodsk | (11h 38m 19.67s , +52d 34m 11.0s) | C | 60 | 18.2 | 92644 | 2025-10-27 00:52:13 | MASTER-Kislovodsk | (11h 31m 43.71s , +58d 18m 05.9s) | C | 60 | 18.1 | 92644 | 2025-10-27 00:52:13 | MASTER-Kislovodsk | (11h 39m 22.66s , +57d 54m 30.1s) | C | 60 | 18.3 | 92890 | 2025-10-27 00:56:20 | MASTER-Kislovodsk | (11h 18m 04.46s , +54d 30m 35.0s) | C | 60 | 18.3 | 92890 | 2025-10-27 00:56:20 | MASTER-Kislovodsk | (11h 25m 08.64s , +54d 07m 10.4s) | C | 60 | 18.3 | 92970 | 2025-10-27 00:57:40 | MASTER-Kislovodsk | (11h 24m 09.70s , +56d 23m 16.5s) | C | 60 | 18.1 | 92970 | 2025-10-27 00:57:40 | MASTER-Kislovodsk | (11h 31m 27.23s , +55d 59m 48.2s) | C | 60 | 18.1 | 93050 | 2025-10-27 00:58:59 | MASTER-Kislovodsk | (11h 13m 21.24s , +52d 36m 14.7s) | C | 60 | 18.5 | 93050 | 2025-10-27 00:58:59 | MASTER-Kislovodsk | (11h 20m 01.17s , +52d 12m 57.7s) | C | 60 | 18.4 | 93129 | 2025-10-27 01:00:19 | MASTER-Kislovodsk | (11h 44m 15.91s , +54d 29m 56.6s) | C | 60 | 18.1 | 93129 | 2025-10-27 01:00:19 | MASTER-Kislovodsk | (11h 51m 11.44s , +54d 06m 23.7s) | C | 60 | 18.2 | 93210 | 2025-10-27 01:01:40 | MASTER-Kislovodsk | (11h 38m 18.17s , +52d 35m 14.3s) | C | 60 | 18.1 | 93290 | 2025-10-27 01:02:59 | MASTER-Kislovodsk | (11h 31m 44.06s , +58d 18m 37.3s) | C | 60 | 18.2 | 93290 | 2025-10-27 01:02:59 | MASTER-Kislovodsk | (11h 39m 24.39s , +57d 55m 02.7s) | C | 60 | 18.3 | 93533 | 2025-10-27 01:07:03 | MASTER-Kislovodsk | (11h 18m 02.58s , +54d 31m 12.2s) | C | 60 | 18.2 | 93533 | 2025-10-27 01:07:03 | MASTER-Kislovodsk | (11h 25m 08.82s , +54d 07m 52.0s) | C | 60 | 18.3 | 93613 | 2025-10-27 01:08:23 | MASTER-Kislovodsk | (11h 24m 07.26s , +56d 23m 53.1s) | C | 60 | 18.1 | 93613 | 2025-10-27 01:08:23 | MASTER-Kislovodsk | (11h 31m 26.30s , +56d 00m 29.1s) | C | 60 | 18.3 | 93693 | 2025-10-27 01:09:43 | MASTER-Kislovodsk | (11h 13m 21.14s , +52d 37m 05.7s) | C | 60 | 18.6 | 93693 | 2025-10-27 01:09:43 | MASTER-Kislovodsk | (11h 20m 02.47s , +52d 13m 53.0s) | C | 60 | 18.6 | 93793 | 2025-10-27 01:11:23 | MASTER-Kislovodsk | (11h 44m 13.86s , +54d 30m 52.5s) | C | 60 | 18.1 | 93793 | 2025-10-27 01:11:23 | MASTER-Kislovodsk | (11h 51m 10.90s , +54d 07m 24.6s) | C | 60 | 18.1 | 93879 | 2025-10-27 01:12:49 | MASTER-Kislovodsk | (11h 38m 18.19s , +52d 35m 51.5s) | C | 60 | 18.1 | 93959 | 2025-10-27 01:14:09 | MASTER-Kislovodsk | (11h 31m 42.25s , +58d 19m 32.6s) | C | 60 | 18.1 | 93959 | 2025-10-27 01:14:09 | MASTER-Kislovodsk | (11h 39m 23.62s , +57d 56m 04.3s) | C | 60 | 18.4 | 94399 | 2025-10-27 01:21:29 | MASTER-Kislovodsk | (11h 17m 59.49s , +54d 30m 58.7s) | C | 60 | 18.4 | 94399 | 2025-10-27 01:21:29 | MASTER-Kislovodsk | (11h 25m 03.05s , +54d 07m 53.1s) | C | 60 | 18.3 | 94478 | 2025-10-27 01:22:48 | MASTER-Kislovodsk | (11h 24m 10.99s , +56d 25m 08.0s) | C | 60 | 18.2 | 94478 | 2025-10-27 01:22:48 | MASTER-Kislovodsk | (11h 31m 32.09s , +56d 01m 57.7s) | C | 60 | 18.3 | 94558 | 2025-10-27 01:24:08 | MASTER-Kislovodsk | (11h 13m 15.55s , +52d 39m 26.4s) | C | 60 | 18.6 | 94558 | 2025-10-27 01:24:08 | MASTER-Kislovodsk | (11h 19m 58.90s , +52d 16m 26.6s) | C | 60 | 18.5 | 94640 | 2025-10-27 01:25:30 | MASTER-Kislovodsk | (11h 44m 14.15s , +54d 30m 13.3s) | C | 60 | 18.1 | 94640 | 2025-10-27 01:25:30 | MASTER-Kislovodsk | (11h 51m 12.53s , +54d 06m 56.7s) | C | 60 | 18.4 | 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/42463. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40546] LIGO/Virgo/KAGRA S251026bn: Identification of a GW compact binary merger candidate
by GCN Circulars 26 Oct '25

26 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42462 SUBJECT: LIGO/Virgo/KAGRA S251026bn: Identification of a GW compact binary merger candidate DATE: 25/10/26 22:11:15 GMT FROM: joan-rene.merou(a)ligo.org The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S251026bn during real-time processing of data from LIGO Hanford Observatory (H1) and LIGO Livingston Observatory (L1) at 2025-10-26 21:16:05.296 UTC (GPS time: 1445548583.296). 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. S251026bn is an event of interest because its false alarm rate, as estimated by the online analysis, is 4.8e-12 Hz, or about one in 1e4 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S251026bn The classification of the GW signal, in order of descending probability, is BBH (>99%), Terrestrial (<1%), NSBH (<1%), or BNS (<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 8%. The source chirp mass falls with highest probability in the bin (5.5, 11.0) 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: * bayestar.multiorder.fits,0, an initial localization generated by BAYESTAR [9], distributed via GCN and SCiMMA notices about 29 seconds after the candidate event time. * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [9], 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,1. For the bayestar.multiorder.fits,1 sky map, the 90% credible region is 956 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1254 +/- 349 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] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013 View this GCN Circular online at https://gcn.nasa.gov/circulars/42462. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40545] GRB 251026A: Swift-XRT observations
by GCN Circulars 26 Oct '25

26 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42461 SUBJECT: GRB 251026A: Swift-XRT observations DATE: 25/10/26 21:42:15 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P.A. Evans (U. Leicester), J.A. Kennea (PSU), E. Ambrosi (INAF-IASFPA) , A.P. Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB), R. Brivio (INAF-OAB), D.N. Burrows (PSU), S. Campana (INAF-OAB), M. Capalbi (INAF-OAR), A. D'Ai (INAF-IASFPA), P. D'Avanzo (INAF-OAB), V. D'Elia (SSDC & INAF-OAR), S. Dichiara (PSU), M. Ferro (INAF-OAB), A. Melandri (INAF-OAR), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), M. Perri (SSDC & INAF-OAR), C. Salvaggio (INAF-OAB), T. Sbarrato (INAF-OAB), B. Sbarufatti (INAF-OAB), M.A. Williams (PSU) report on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the SVOM/ECLAIRs-detected source GRB 251026A (SVOM burst-id sb25102605), collecting 1.7 ks of Photon Counting (PC) mode data between T0+5.8 ks and T0+12 ks after the trigger. We have detected 2 sources. These have been automatically classified as follows: * 0 likely counterparts * 0 candidate counterparts * 2 uncatalogued X-ray sources * 0 known X-ray sources We note that neither source is consistent with the SVOM/MXT position given in GCN Circ. 42454. Uncatalogued X-ray sources -------------------------- Source 1 (SWIFT J044944.9+514605): ================================== RA (J2000.0): 72.4374 = 04 49 44.98 Dec (J2000.0): +51.7683 = +51 46 05.9 Error: 5.1 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 5.8 arcmin from the SVOM/ECLAIRs position. Mean rate: 0.0123 +/- 0.0033 ct s^-1 Mean flux: (4.6 +/- 1.2)e-13 erg cm^-2 s^-1 Peak rate: 0.0123 +/- 0.0033 ct s^-1 Peak flux: (4.6 +/- 1.2)e-13 erg cm^-2 s^-1 ECF: 3.75e-11 erg cm^-2 ct^-1 assuming NH=1.57e+22 cm^-2, gamma=2.98 determined from a spectral fit. XMM UL: 3.5e-12 erg cm^-2 s^-1, (0.3-10 keV) so the source is not above this 3-sigma upper limit. There is no evidence for fading. A SIMBAD object `NVSS J044945+514603' is 7.5" away. There are 2 2MASS objects within the source's 3-sigma error radius. Source 2 (SWIFT J045052.5+515630): ================================== RA (J2000.0): 72.7189 = 04 50 52.54 Dec (J2000.0): +51.9418 = +51 56 30.5 Error: 9.7 (arcsec, radius, 90% confidence). Detect flag: REASONABLE Distance: 9.6 arcmin from the SVOM/ECLAIRs position. Mean rate: (4.0 [+2.6, -1.8])e-3 ct s^-1 Mean flux: (1.74 [+1.10, -0.78])e-13 erg cm^-2 s^-1 Peak rate: (4.0 [+2.6, -1.8])e-3 ct s^-1 Peak flux: (1.74 [+1.10, -0.78])e-13 erg cm^-2 s^-1 XMM UL: 2.3e-12 erg cm^-2 s^-1, (0.3-10 keV) so the source is not above this 3-sigma upper limit. There is no evidence for fading. A SIMBAD object `NVSS J045052+515630' is 3.9" away. There are 6 2MASS objects within the source's 3-sigma error radius. All fluxes are 0.3-10 keV, observed. For all flux conversions and comparisons with catalogues and upper limits from other missions, we assumed a power-law spectrum with NH=3x10^20 cm^-2 and photon index (Gamma)=1.7 unless otherwise stated. The results of the XRT-team automatic analysis of the XRT observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/SVOM/SVOM_FIELD00045. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42461. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40544] GRB 251026A: Swift-XRT observations
by GCN Circulars 26 Oct '25

26 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42461 SUBJECT: GRB 251026A: Swift-XRT observations DATE: 25/10/26 21:42:15 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P.A. Evans (U. Leicester), J.A. Kennea (PSU), E. Ambrosi (INAF-IASFPA) , A.P. Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB), R. Brivio (INAF-OAB), D.N. Burrows (PSU), S. Campana (INAF-OAB), M. Capalbi (INAF-OAR), A. D'Ai (INAF-IASFPA), P. D'Avanzo (INAF-OAB), V. D'Elia (SSDC & INAF-OAR), S. Dichiara (PSU), M. Ferro (INAF-OAB), A. Melandri (INAF-OAR), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), M. Perri (SSDC & INAF-OAR), C. Salvaggio (INAF-OAB), T. Sbarrato (INAF-OAB), B. Sbarufatti (INAF-OAB), M.A. Williams (PSU) report on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the SVOM/ECLAIRs-detected source GRB 251026A (SVOM burst-id sb25102605), collecting 1.7 ks of Photon Counting (PC) mode data between T0+5.8 ks and T0+12 ks after the trigger. We have detected 2 sources. These have been automatically classified as follows: * 0 likely counterparts * 0 candidate counterparts * 2 uncatalogued X-ray sources * 0 known X-ray sources We note that neither source is consistent with the SVOM/MXT position given in GCN Circ. 42454. Uncatalogued X-ray sources -------------------------- Source 1 (SWIFT J044944.9+514605): ================================== RA (J2000.0): 72.4374 = 04 49 44.98 Dec (J2000.0): +51.7683 = +51 46 05.9 Error: 5.1 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 5.8 arcmin from the SVOM/ECLAIRs position. Mean rate: 0.0123 +/- 0.0033 ct s^-1 Mean flux: (4.6 +/- 1.2)e-13 erg cm^-2 s^-1 Peak rate: 0.0123 +/- 0.0033 ct s^-1 Peak flux: (4.6 +/- 1.2)e-13 erg cm^-2 s^-1 ECF: 3.75e-11 erg cm^-2 ct^-1 assuming NH=1.57e+22 cm^-2, gamma=2.98 determined from a spectral fit. XMM UL: 3.5e-12 erg cm^-2 s^-1, (0.3-10 keV) so the source is not above this 3-sigma upper limit. There is no evidence for fading. A SIMBAD object `NVSS J044945+514603' is 7.5" away. There are 2 2MASS objects within the source's 3-sigma error radius. Source 2 (SWIFT J045052.5+515630): ================================== RA (J2000.0): 72.7189 = 04 50 52.54 Dec (J2000.0): +51.9418 = +51 56 30.5 Error: 9.7 (arcsec, radius, 90% confidence). Detect flag: REASONABLE Distance: 9.6 arcmin from the SVOM/ECLAIRs position. Mean rate: (4.0 [+2.6, -1.8])e-3 ct s^-1 Mean flux: (1.74 [+1.10, -0.78])e-13 erg cm^-2 s^-1 Peak rate: (4.0 [+2.6, -1.8])e-3 ct s^-1 Peak flux: (1.74 [+1.10, -0.78])e-13 erg cm^-2 s^-1 XMM UL: 2.3e-12 erg cm^-2 s^-1, (0.3-10 keV) so the source is not above this 3-sigma upper limit. There is no evidence for fading. A SIMBAD object `NVSS J045052+515630' is 3.9" away. There are 6 2MASS objects within the source's 3-sigma error radius. All fluxes are 0.3-10 keV, observed. For all flux conversions and comparisons with catalogues and upper limits from other missions, we assumed a power-law spectrum with NH=3x10^20 cm^-2 and photon index (Gamma)=1.7 unless otherwise stated. The results of the XRT-team automatic analysis of the XRT observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/SVOM/SVOM_FIELD00045. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42461. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40543] GRB 251025B: OHP/T193 optical detection
by GCN Circulars 26 Oct '25

26 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42460 SUBJECT: GRB 251025B: OHP/T193 optical detection DATE: 25/10/26 21:20:15 GMT FROM: Christophe Adami at LAM <christophe.adami(a)lam.fr> N.A. Rakotondrainibe (LAM), C. Adami (LAM/Pytheas/AMU), E. Le Floc'h (CEA/Irfu), S. basa (UAR Pytheas) report on behalf of the MISTRAL GRB collaboration We carried out observations of the GRB 251025B (Hussein et al., GCN 42437) optical and NIR afterglow (Wu et al., GCN 42438; Gress et al., GCN 42439; Wu et al., GCN 42440; Beardmore et al., GCN 42445; Mohan et al., GCN 42447; Hernández Funget al., GCN 42450; Pereyra et al., GCN 42452; Li et al., GCN 42453; Mo et al., GCN 42459) using the T193cm telescope at Observatoire de Haute-Provence (France) equipped with the MISTRAL spectro-imager. We obtained 1 exposure of 3 min and 5 exposures of 12 min in the r-band at a midtime of 2025-10-26 20:11:53 UT corresponding to T-T0 = 29.8 hours. The afterglow is well detected in r’ and we measured the following preliminary magnitude: r’ = 20.93+/-0.07 mag (AB) The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the magnitudes are not corrected for Galactic extinction. We used the STDWeb/STDPipe tools (Karpov 2025). We acknowledge the excellent support from the Observatoire de Haute-Provence and in particular Jean Balcaen and the SOPHIE observer Guillaume Hebrard. View this GCN Circular online at https://gcn.nasa.gov/circulars/42460. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40542] GRB 251025B: SVOM/VT optical observations with VHF data
by GCN Circulars 26 Oct '25

26 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42440 SUBJECT: GRB 251025B: SVOM/VT optical observations with VHF data DATE: 25/10/25 16:47:24 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> C. Wu., L.P. Xin, H.L. Li, Y. L. Qiu (NAOC), J. T. Palmerio (CEA), S. Hussein (IJCLab), M. Brunet (IRAP) report on behalf of the SVOM team. SVOM/VT performed an automatic slew on the burst triggered by SVOM/ECLAIRs (Hussein et al., GCN 42437). SVOM/VT began observing the field automatically at 2025-10-25T14:30:18 UTC, 373 seconds after the T0, with the slew of the platform triggered on-board, in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. We confirm the clear detection of the source reported by Wu et al.(GCN 42438) and Gress et al.(GCN 42439) in both the VT_B and VT_R bands with the downlinked VHF data. The AB magnitudes were derived as follows: -------------------------------------------- (T-T0)_mid exptime band mag 523 sec 300 sec VT_R 18.61 +/-0.01 523 sec 300 sec VT_B 19.15 +/-0.02 We note that the color of VT_B - VT_R ~ 0.5 mag may indicate a low-to-medium redshift event, following the analysis of Wang et al. (2020, RAA). Additional follow-up observations are encouraged. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/42440. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40541] GRB 251025B: J-band detection with WINTER
by GCN Circulars 26 Oct '25

26 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42459 SUBJECT: GRB 251025B: J-band detection with WINTER DATE: 25/10/26 17:17:21 GMT FROM: Geoffrey Mo at Caltech / Carnegie Observatories <gmo(a)mit.edu> Geoffrey Mo (Caltech/Carnegie), Benjamin Schneider (LAM), Tomas Ahumada (Caltech), Viraj Karambelkar (Columbia), Robert Stein (UMD), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report: We observed the field of GRB 251025B (Hussein et al., GCN 42437; Beardmore et al., GCN 42445) in the near-infrared J band with the Palomar 1-m telescope, equipped with the 1.2-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024). Observations began at 2025-10-26T04:48:17 UTC in the J band (~14.4 hours after the GRB trigger), consisting of 15 x 120 s exposures. The images were processed using the WINTER data reduction pipeline implemented with mirar (https://github.com/winter-telescope/mirar, https://doi.org/10.5281/zenodo.13352565) We detect a clear source at the optical counterpart location (Wu et al., GCN 42438; Gress et al., GCN 42439; Wu et al., GCN 42440; Mohan et al., GCN 42447; Hernández Fung et al., GCN 42450; Pereyra et al., GCN 42452; Li et al., GCN 42453), likely during its rebrightening phase, with magnitude J ~ 20.0 mag (AB). WINTER (Wide-field INfrared Transient ExploreR) is a partnership between MIT and Caltech, housed at Palomar Observatory, and funded by NSF MRI, NSF AAG, the David and Lucile Packard Foundation, and the MIT Kavli Institute for Astrophysics and Space Research. View this GCN Circular online at https://gcn.nasa.gov/circulars/42459. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40540] GRB 251026A: SVOM/C-GFT upper limit
by GCN Circulars 26 Oct '25

26 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42458 SUBJECT: GRB 251026A: SVOM/C-GFT upper limit DATE: 25/10/26 14:04:34 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Chao WU (NAOC), Zhe Kang (CHO), Liping Xin(NAOC), Xuhui Han(NAOC), Pinpin Zhang (NAOC), Xiaomeng Lu (NAOC), Zhenwei Li (CHO), You Lv (CHO), Ruosong Zhang (NAOC), Yujie Xiao(NAOC), Yulei Qiu(NAOC), Jing Wang (NAOC), Jinsong Deng(NAOC), Lei Huang(NAOC), Jianyan Wei (NAOC), J.X Cao (GXU), X. Tian (GXU) report on behalf of the SVOM/C-GFT team: We observed the field of GRB 251026A (sb25102605) detected by SVOM/ECLAIRs (Cao et al., GCN 42454) with LATIOS on SVOM/C-GFT. Observations started at 2025-10-26T10:31:43 UTC, ~2.07 hr after the trig-ger. A series of g, r, and i band images were obtained. No credible candidate was detected within the error box provided by SVOM/MXT (Cao et al., GCN 42454) in our stacked images. The corresponding three sigma upper limit is, mag_i=19.65 at the midpoint of the observations, T₀ + 2.15 hr. The photometry was calibrated against nearby Pan-STARRS1 stars and no correction for Galactic dust extinction was applied. This result is consistent with Postigo et al. (GCN 42456). We thank the observation assistants Bowen Li and Hongxu Xuan at Jilin observatory for their excellent support. The Chinese Ground Follow-up Telescope (C-GFT) for the SVOM mission is located at Jilin Station, Changchun Observatory, National Astronomical Observatories, CAS. It features two instruments: (1) CATCH at the Cassegrain focus with a 21 arcsec x 21 arcsec FOV for simultaneous g/r/i-band imaging, and (2) LATIOS, a 4k x 4k CMOS camera at the prime focus with a 1.28 deg x 1.28 deg FOV that images in g, r, and i bands via filter switching. View this GCN Circular online at https://gcn.nasa.gov/circulars/42458. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40539] IceCube-251025A: DDOTI Optical Upper Limit
by GCN Circulars 26 Oct '25

26 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42457 SUBJECT: IceCube-251025A: DDOTI Optical Upper Limit DATE: 25/10/26 13:42:49 GMT FROM: Rosa Leticia Becerra Godínez at Instituto de Astronomía, UNAM <rbecerra(a)astro.unam.mx> Rosa L. Becerra (UNAM), Alan M. Watson (UNAM), Camila Angulo Valdez (UNAM), 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-251025A (bronze) event (IceCube Collaboration, GCN Circ. 42436) 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 2025-10-26 UTC. DDOTI observed from 10:41 UTC to 12:41 UTC (T+20.9 h to T+22.9 h after the trigger), with a total exposure time of 24 minutes, covering the entire error region reported by IceCube (IceCube Collaboration, GCN Circ. 42436). These observations were interleaved with other scientific programs. Comparing our observations to the USNO-B1 and PanSTARRS PS1 DR2 catalogues, we detect no uncatalogued sources within the observed field to a 10-sigma limiting AB magnitude of: w > 20.0. 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/42457. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40538] GRB 251026A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
by GCN Circulars 26 Oct '25

26 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42456 SUBJECT: GRB 251026A: SVOM/COLIBRÍ (FM-GFT) optical upper limit DATE: 25/10/26 11:16:33 GMT FROM: Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo(a)gmail.com> Antonio de Ugarte Postigo (LAM), Margarita Pereyra (UNAM), Jean-Grégoire Ducoin (CPPM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Fredd Alvarez (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), J.X Cao (GXU), X. Tian (GXU): We imaged the field of the SVOM GRB 251026A (Cao et al., GCN Circ. 42454) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-10-26 08:49:51 to 09:08:59 UTC (from 22.5 to 41.6 minutes after the trigger) and obtained 16x60 seconds of exposure in the r and z filters. The data were reduced and coadded with the COLIBRÍ pipeline and analyzed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1/SkyMapper catalog, is in the AB system, and is not corrected for Galactic extinction. In the stacked image, we do not detect any new source within the MXT source position (Cao et al., GCN Circ. 42454) down to the following 5-sigma limit: r > 23.0 mag z > 21.6 mag Further observations are ongoing. 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/42456. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40537] GRB 251026A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
by GCN Circulars 26 Oct '25

26 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42456 SUBJECT: GRB 251026A: SVOM/COLIBRÍ (FM-GFT) optical upper limit DATE: 25/10/26 11:16:33 GMT FROM: Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo(a)gmail.com> Antonio de Ugarte Postigo (LAM), Margarita Pereyra (UNAM), Jean-Grégoire Ducoin (CPPM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Fredd Alvarez (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), J.X Cao (GXU), X. Tian (GXU): We imaged the field of the SVOM GRB 251026A (Cao et al., GCN Circ. 42454) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-10-26 08:49:51 to 09:08:59 UTC (from 22.5 to 41.6 minutes after the trigger) and obtained 16x60 seconds of exposure in the r and z filters. The data were reduced and coadded with the COLIBRÍ pipeline and analyzed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1/SkyMapper catalog, is in the AB system, and is not corrected for Galactic extinction. In the stacked image, we do not detect any new source within the MXT source position (Cao et al., GCN Circ. 42454) down to the following 5-sigma limit: r > 23.0 mag z > 21.6 mag Further observations are ongoing. 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/42456. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40536] GRB 251026A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
by GCN Circulars 26 Oct '25

26 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42456 SUBJECT: GRB 251026A: SVOM/COLIBRÍ (FM-GFT) optical upper limit DATE: 25/10/26 11:16:33 GMT FROM: Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo(a)gmail.com> Antonio de Ugarte Postigo (LAM), Margarita Pereyra (UNAM), Jean-Grégoire Ducoin (CPPM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Fredd Alvarez (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), J.X Cao (GXU), X. Tian (GXU): We imaged the field of the SVOM GRB 251026A (Cao et al., GCN Circ. 42454) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-10-26 08:49:51 to 09:08:59 UTC (from 22.5 to 41.6 minutes after the trigger) and obtained 16x60 seconds of exposure in the r and z filters. The data were reduced and coadded with the COLIBRÍ pipeline and analyzed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1/SkyMapper catalog, is in the AB system, and is not corrected for Galactic extinction. In the stacked image, we do not detect any new source within the MXT source position (Cao et al., GCN Circ. 42454) down to the following 5-sigma limit: r > 23.0 mag z > 21.6 mag Further observations are ongoing. 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/42456. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40535] GRB 251026B: Fermi GBM Final Localization
by GCN Circulars 26 Oct '25

26 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42455 SUBJECT: GRB 251026B: Fermi GBM Final Localization DATE: 25/10/26 09:48:27 GMT FROM: Marianna Dafčíková at Masaryk University <500025(a)mail.muni.cz> The Fermi GBM team reports the detection of a likely SHORT GRB "At 07:18:53.33 UT on 26 October 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251026B (trigger 783155938/251026305). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 132.32, Dec = -12.21 (J2000 degrees, equivalent to J2000 8h 49m, -12d 12'), with a statistical uncertainty of 8.04 degrees. The angle from the Fermi LAT boresight is 19 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251026305/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251026305/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251026305/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/42455. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40534] GRB 251026A: SVOM detection of a long burst
by GCN Circulars 26 Oct '25

26 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42454 SUBJECT: GRB 251026A: SVOM detection of a long burst DATE: 25/10/26 09:04:48 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> J.X Cao (GXU), X. Tian (GXU), J-L. Atteia (IRAP), W.J Xie (NAOC), F. Lacreu (IAP), M. Moita (CEA), report on behalf of the SVOM mission team: At 2025-10-26T08:27:22 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 251026A (SVOM burst-id sb25102605). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was detected both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT), which produced a sequence of 11 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 11.73 in the [8-120] keV energy band over a time window of 81.92 seconds starting at 2025-10-26T08:26:46. The localization of the best alert is R.A., Dec. 72.5819, 51.8058 degrees (J2000) with a 90% confidence level (C.L.) radius of 6.86 arcmin (including systematic error of 2 arcmin added in quadrature). SVOM slewed to the burst. SVOM/MXT began observing the field at 2025-10-26T08:31:19 UTC, 237 seconds after T0. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec. 72.707, 51.776 degrees: R.A. (J2000) = 04h50m49s Dec. (J2000) = 51d46m32s with a 90% C.L. radius of 65 arcseconds. This location is 5.17 arcminutes from the ECLAIRs onboard position. This position may be improved as more data is received. VT began observing the field after the slew. The analysis of the data will be published in a future circular. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE. The Burst Advocate (BA) on shift for this alert is Jiaxin Cao: cjx(a)st.gxu.edu.cn. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/42454. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40533] GRB 251025B: SVOM/VT optical bump
by GCN Circulars 26 Oct '25

26 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42453 SUBJECT: GRB 251025B: SVOM/VT optical bump DATE: 25/10/26 04:30:16 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H.L. Li, L.P. Xin, Y.L. Qiu, C. Wu, Y.N. Ma, Z.H. Yao, X.H. Han, J. Wang, H.B. Cai, W.J. Xie, Y. Xu, J.R. Xu, P.P. Zhang, Y.J. Xiao, J.S. Deng, J.Y. Wei (NAOC), J. Palmerio (CEA), J.X. Cao, X. Tian (GXU), S. Hussein (IJCLab), M. Brunet (IRAP) report on behalf of the SVOM team. SVOM performed an automatic slew on the burst GRB 251025B triggered by SVOM/ECLAIRs (Julakanti et al., GCN 42437) in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. The observation began at 2025-10-25T14:26:52, i.e., 167 sec post trigger. The optical counterpart (Wu et al., GCN 42438, 42440; Budnev et al., GCN 42439; Mohan et al., GCN 42447; Fung et al., GCN 42450) consistent with the location of Swfit-XRT (Beardmore et al., GCN 42445) was clearly detected in both VT channels. The brightness was decaying with a slope of -0.7 before 3000 sec post trigger, followed by a bump with the peak of VT_R~19.59+/-0.05 mag and VT_B~19.95+/-0.05 mag at the mid time of 5.24 hours post trigger. Our photometry was estimated in AB magnitude, and not corrected for Galactic extinction. More follow-up for this burst is encouraged. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/42453. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40532] GRB 251025B: SVOM/COLIBRÍ (FM-GFT) strong rebrightening of the optical counterpart
by GCN Circulars 26 Oct '25

26 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42452 SUBJECT: GRB 251025B: SVOM/COLIBRÍ (FM-GFT) strong rebrightening of the optical counterpart DATE: 25/10/26 04:18:33 GMT FROM: Margarita Pereyra Talamantes at IA-UNAM Ensenada <mpereyra(a)astro.unam.mx> Margarita Pereyra (UNAM), Antonio de Ugarte Postigo (LAM), Benjamin Schneider (LAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (NYUAD), Camila Angulo (UNAM), Sarah Antier (IJCLAB), 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), Noémie Globus (UNAM), Diego López-Cámara (UNAM), Kin Ocelotl López (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), and S. Hussein (IJCLab) report: We imaged the field of the SVOM GRB 251025B (Hussein et al., GCN Circ. 42437) using the DDRAGO two-channel wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-10-26 02:54 to 03:17 (12.51 to 12.89 hours after the trigger) and obtained 6, 5, 5, and 16 minutes exposure in the the g, r, i, and z filters. The images were analyzed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS catalog, is in the AB system, and is not corrected for Galactic extinction. We detect the optical counterpart (Wu et al., GCN Circ. 42438; Gress et al., GCN Circ. 42439; Wu et al., GCN Circ. 42440; Beardmore et al., GCN Circ. 42445; Mohan et al., GCN Circ. 42447; Hernández Funget al., GCN Circ. 42450) with preliminary magnitudes of: g = 20.58 +/- 0.03 r = 20.20 +/- 0.03 i = 19.90 +/- 0.04 z = 19.79 +/- 0.04 We note that the afterglow appears to be brighter in r in our observations at about 12 hours than it was in the observations of Mohan et al. (GCN Circ. 42447) at about 2 hours, suggesting a very strong rebrightening. We further note a possible host galaxy candidate at the afterglow position in the Legacy Survey with r ≈ 23.3 and a photometric redshift if z ≈ 0.98 +/- 0.19. This is consistent with the detection in g. Further observations and analysis are ongoing. 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/42452. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40531] GRB 251023A: SVOM/GRM observation
by GCN Circulars 26 Oct '25

26 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42451 SUBJECT: GRB 251023A: SVOM/GRM observation DATE: 25/10/26 03:54:05 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> SVOM/GRM team: Chen-Wei Wang, Zheng-Hang Yu, Wen-Jun Tan, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Feliu Lacreu (IAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by a burst GRB 251023A (SVOM trigger reference: sb25102301) at 2025-10-23T05:57:44.000 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN#42385) and Glowbug (R. Woolf, GCN#42408). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multiple peaks with a T90 of 63.5 +19.5/-5.5 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb251023A.png In addition, the position of this burst, as determined by Fermi/GBM (RA= 39.87, DEC= -6.53, GCN#42385), is located at about 51 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. With this localization, the time-averaged spectrum from T0-2 to T0+70 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.45 +0.25/-0.26 and the cutoff energy, parameterized as Epeak, is 143 +26/-19 keV. The event fluence (10-1000 keV) in this time interval is (5.47 +0.55/-0.56)E-6 erg/cm^2. The localization of GRB 251023A in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb251023A_amati.png The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM point of contact for this burst is: Chen-Wei Wang (IHEP)(cwwang(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/42451. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40530] GRB 251025B: ULL-ASTRO-MASTER optical counterpart detection with IAC80 telescope at Teide Observatory
by GCN Circulars 26 Oct '25

26 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42450 SUBJECT: GRB 251025B: ULL-ASTRO-MASTER optical counterpart detection with IAC80 telescope at Teide Observatory DATE: 25/10/26 03:31:47 GMT FROM: Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf(a)iac.es> J. Hernández Fung, P.G. Berdayes, M. Contreras, B. Gandolfi, L. Juliá-Maroto, A. Schenone-Zanuzzi, E. Urquijo-Rodríguez, J. Basurto Merino, A. Caballero-Almagro, A. Cerón, F. Díaz-Segado, T. Ferrer-Laviña, V. Ghiraldo, E. Lekaroz-Urriza, M. Manzano García, E. Mejía-Martínez, J. Prieto Polo, M. Pulido-Torres, M. Quintana-Ansaldo, A. Selezneva, T. Tundidor Rodríguez (all ULL), M. Abdul-Masih (IAC and ULL), and I. Pérez-Fournon (IAC and ULL). Following the detection of GRB 251025B (sb25102502) by SVOM (Hussein et al., GCN circ. 42437), we observed the field with the IAC80 telescope equipped with the CAMELOT2 camera at Teide Observatory (Tenerife, Canary Islands, Spain). The observation, a single exposure of 300 sec in the SDSS g' filter, started on 2025-10-26 at 00:50:31 UT, about 10.44 hours after the SVOM trigger. The optical counterpart detected by Wu et al. (GCN circ. 42438), Gress et al. (GCN circ. 42439), Wu et al. (GCN circ. 42440), and Mohan et al. (GCN circ. 42447) is clearly detected in our image with a magnitude of g = 20.37 +/- 0.12 (AB), calibrated against PanSTARRS-1 DR2 stars and not corrected for galactic extinction. The optical counterpart position is consistent within the errors with the position of the X-ray afterglow measured by Swift-XRT (Beardmore et al. GCN circ. 42445). This work is based on observations made with the IAC80 telescope operated on the island of Tenerife by the Instituto de Astrofísica de Canarias in the Spanish Observatorio del Teide. We acknowledge the expert assistance of Roberto C. Álvarez and Borja Castañeda. These observations are part of a course in Astrophysical Techniques of the Master in Astrophysics of the Astrophysics Department of the University of La Laguna in collaboration with the Instituto de Astrofísica de Canarias (La Laguna, Tenerife, Canary Islands, Spain). This work made use of the Astro-COLIBRI platform (P. Reichherzer et al. 2021, ApJS, 256, 5). View this GCN Circular online at https://gcn.nasa.gov/circulars/42450. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40529] GRB 251025C: Fermi GBM Final Real-time Localization
by GCN Circulars 25 Oct '25

25 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42449 SUBJECT: GRB 251025C: Fermi GBM Final Real-time Localization DATE: 25/10/25 23:19:13 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 23:08:40 UT on 25 Oct 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251025C (trigger 783126525.293544 / 251025964). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 170.7, Dec = 54.9 (J2000 degrees, equivalent to J2000 11h 22m, 54d 53'), with a statistical uncertainty of 2.2 degrees. The angle from the Fermi LAT boresight is 103.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251025964/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251025964/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251025964/… View this GCN Circular online at https://gcn.nasa.gov/circulars/42449. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40528] Konus-Wind detection of GRB 251016B
by GCN Circulars 25 Oct '25

25 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42448 SUBJECT: Konus-Wind detection of GRB 251016B DATE: 25/10/25 20:36:05 GMT FROM: Anna Ridnaia at Ioffe Institute <ridnaia(a)mail.ioffe.ru> A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB 251016B (Ferm-GBM detection: The Fermi GBM team, GCN 42316; Godwin and Meegan, GCN 42383; CALET-GBM detection: Yamaoka et al., GCN 42320; AstroSat-CZTI detection: Harsha et al., GCN 42324; IPN triangulation: Kozyrev et al., GCN 42403) triggered Konus-Wind at T0=86340.495 s UT (23:59:00.495). The burst light curve shows a single pulse which starts at ~T0-0.5 s and has a total duration of ~18.5 s. The emission is seen up to ~6 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB251016_T86340/ As observed by Konus-Wind, the burst had a fluence of 3.50(-0.18,+0.18)x10^-5 erg/cm2, and a 64-ms peak flux, measured from T0+2.320 s, of 1.22(-0.11,+0.11)x10^-5 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+11.520 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.98(-0.06,+0.06), the high energy photon index beta = -2.29(-0.10,+0.08), the peak energy Ep = 226(-18,+19) keV (chi2 = 93/85 dof). The spectrum near the maximum count rate (measured from T0+0.256 to T0+3.328 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.85(-0.05,+0.06), the high energy photon index beta = -2.41(-0.11,+0.09), the peak energy Ep = 294(-21,+21) keV (chi2 = 67/67 dof). All the quoted errors are at the 68% confidence level. All the quoted values are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/42448. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40527] GRB 251025B: GROWTH-India Telescope optical observations
by GCN Circulars 25 Oct '25

25 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42447 SUBJECT: GRB 251025B: GROWTH-India Telescope optical observations DATE: 25/10/25 20:34:06 GMT FROM: V. Swain at IIT Bombay <vishwajeet.s(a)iitb.ac.in> T. Mohan, V. Swain, S. Patil, A.P. Saikia, V. Bhalerao (IITB), G.C. Anupama, S. Barway (IIA) and K. Angail (IAO) report on behalf of the GIT team: We observed the field of SVOM GRB 251025B (Hussein et al., GCN 42437), with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2025-10-25 15:47:08 UT, i.e., 1.38 hours after the SVOM trigger. Multiple exposures were obtained in the r′-filter, and we detect the optical counterpart in our stacked image. The photometry result follows as: | MJD (mid) | tmid - t0 (hours) | Filter | Exposure (s) | Magnitude (AB) | | --------- | ----------------- | ------ | ------------ | -------------- | |60973.68833| 2.12 | r' | 4 x 360 | 20.41 +- 0.11 | The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction. Our result is consistent with other optical observations (WU et al., GCN 42438; Gress et al., GCN 42439; Wu et al., GCN 42440). Further multiband optical observations are ongoing. The GROWTH India Telescope (GIT; Kumar et al. 2022) is a 70-cm telescope with a 0.7-degree field of view, set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports the operations of the telescope. Telescope technical details are available at https://sites.google.com/view/growthindia/. View this GCN Circular online at https://gcn.nasa.gov/circulars/42447. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40526] GRB 251025B: GROWTH-India Telescope optical observations
by GCN Circulars 25 Oct '25

25 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42447 SUBJECT: GRB 251025B: GROWTH-India Telescope optical observations DATE: 25/10/25 20:34:06 GMT FROM: V. Swain at IIT Bombay <vishwajeet.s(a)iitb.ac.in> T. Mohan, V. Swain, S. Patil, A.P. Saikia, V. Bhalerao (IITB), G.C. Anupama, S. Barway (IIA) and K. Angail (IAO) report on behalf of the GIT team: We observed the field of SVOM GRB 251025B (Hussein et al., GCN 42437), with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2025-10-25 15:47:08 UT, i.e., 1.38 hours after the SVOM trigger. Multiple exposures were obtained in the r′-filter, and we detect the optical counterpart in our stacked image. The photometry result follows as: | MJD (mid) | tmid - t0 (hours) | Filter | Exposure (s) | Magnitude (AB) | | --------- | ----------------- | ------ | ------------ | -------------- | |60973.68833| 2.12 | r' | 4 x 360 | 20.41 +- 0.11 | The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction. Our result is consistent with other optical observations (WU et al., GCN 42438; Gress et al., GCN 42439; Wu et al., GCN 42440). Further multiband optical observations are ongoing. The GROWTH India Telescope (GIT; Kumar et al. 2022) is a 70-cm telescope with a 0.7-degree field of view, set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports the operations of the telescope. Telescope technical details are available at https://sites.google.com/view/growthindia/. View this GCN Circular online at https://gcn.nasa.gov/circulars/42447. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40525] GRB 251024A: Swift/UVOT Upper Limits
by GCN Circulars 25 Oct '25

25 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42446 SUBJECT: GRB 251024A: Swift/UVOT Upper Limits DATE: 25/10/25 20:11:36 GMT FROM: Mike Siegel at PSU/Swift MOC <mhs18(a)psu.edu> M. H. Siegel and M. J. Moss (GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 251024A 132 s after the BAT trigger (Moss et al., GCN Circ. 42426). No optical afterglow consistent with the XRT position (Beardmore et al., GCN Circ. 42430) is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white_FC 132 282 147 >21.0 u_FC 290 540 246 >19.9 white 132 591 167 >21.0 v 622 641 19 >18.0 b 547 567 20 >19.8 u 290 540 246 >19.9 w2 597 617 20 >19.2 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.044 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/42446. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40524] GRB 251025B: Swift-XRT afterglow detection
by GCN Circulars 25 Oct '25

25 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42445 SUBJECT: GRB 251025B: Swift-XRT afterglow detection DATE: 25/10/25 19:52:19 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester), B. Sbarufatti (INAF-OAB), C. Salvaggio (INAF-OAB), M. Ferro (INAF-OAB), J.A. Kennea (PSU), D.N. Burrows (PSU), S. Lanava (PSU) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of GRB 251025B. We searched for X-ray sources in 1.7 ks of Photon Counting (PC) mode data obtained between T0+2.8 ks and T0+4.5 ks. An uncatalogued X-ray source is detected within the estimated 3-sigma SVOM/ECLAIRs error region (473 arcsec) and is above the RASS 3-sigma upper limit at this position, and is therefore likely the GRB afterglow. Using 1712 s of PC mode data and 1 UVOT image, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 29.53107, +30.30373 which is equivalent to: RA (J2000): 01h 58m 07.46s Dec(J2000): +30d 18' 13.4" with an uncertainty of 2.7 arcsec (radius, 90% confidence). This source is 1.25 arcsec from the SVOM/C-GFT position (Wu et al., GCN Circ. 42438) and 37 arcsec from the SVOM/MXT position (Hussein et al., GCN Circ. 42437). At present, the X-ray source shows no evidence of fading. A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.00 (+0.27, -0.25). The best-fitting absorption column is 1.9 (+0.9, -0.8) x 10^21 cm^-2, in excess of the Galactic value of 5.6 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.5 x 10^-11 (4.8 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.9 (+0.9, -0.8) x 10^21 cm^-2 Galactic foreground: 5.6 x 10^20 cm^-2 Excess significance: 2.8 sigma Photon index: 2.00 (+0.27, -0.25) The results of the XRT-team automatic analysis are available at https://www.swift.ac.uk/xrt_products/03000153. The results of the full analysis of the XRT observations are available at https://www.swift.ac.uk/SVOM/SVOM_FIELD00044. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42445. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40523] GRB 251024A: Swift-BAT refined analysis
by GCN Circulars 25 Oct '25

25 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42444 SUBJECT: GRB 251024A: Swift-BAT refined analysis DATE: 25/10/25 19:40:31 GMT FROM: Amy <yarleen(a)gmail.com> T. Sakamoto (AGU), S. D. Barthelmy (GSFC), R. Gupta (GSFC), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), M. J. Moss (GSFC), D. M. Palmer (LANL), T. Parsotan (GSFC), D. Sadaula (GSFC/UMBC) (i.e. the Swift-BAT team): Using the data set from T-240 to T+613 sec from the recent telemetry downlink, we report further analysis of BAT GRB 251024A (trigger #1406589) (Moss et al., GCN Circ. 42426). The BAT ground-calculated position is RA, Dec = 306.666, -68.576 deg which is RA(J2000) = 20h 26m 39.7s Dec(J2000) = -68d 34' 34.3" with an uncertainty of 2.4 arcmin, (radius, sys+stat, 90% containment). The partial coding was 84%. The mask-weighted light curve shows a weak pulse structure that starts at ~T+1 s and peaks at ~T+3 s. The main pulse structure ends at ~T+25 s, and there are some tail emissions that last till ~T+100 s. T90 (15-350 keV) is 82.66 +- 23.27 sec (estimated error including systematics). The time-averaged spectrum from T+1.16 to T+97.28 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.68 +- 0.30. The fluence in the 15-150 keV band is 6.5 +- 1.2 x 10^-07 erg/cm2. The 1-sec peak photon flux measured from T+2.16 sec in the 15-150 keV band is 0.5 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence level. The results of the batgrbproduct analysis are available at https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1406589 View this GCN Circular online at https://gcn.nasa.gov/circulars/42444. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40522] IceCube Alert 251025.57: Global MASTER-Net observations report
by GCN Circulars 25 Oct '25

25 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42443 SUBJECT: IceCube Alert 251025.57: Global MASTER-Net observations report DATE: 25/10/25 19:39:23 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-Tunka robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Applied Physics Institute, Irkutsk State University) started inspect of the IceCube Alert 251025.57 (trigger No 18513107,09h 42m 47.28s , +15d 19m 48.0s, R=1.19) errorbox 16456 sec after notice time and 16501 sec after trigger time at 2025-10-25 18:22:54 UT, with upper limit up to 17.6 mag. The observations began at zenith distance = 80 deg. The sun altitude is -47.0 deg. The galactic latitude b = 45 deg., longitude l = 219 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3023371 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 16531 | 2025-10-25 18:22:54 | MASTER-Tunka | (09h 42m 13.68s , +14d 52m 14.6s) | C | 60 | 17.6 | 16531 | 2025-10-25 18:22:54 | MASTER- | (09h 42m 26.98s , +14d 45m 50.3s) | C | 60 | 17.3 | 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/42443. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40521] GRB 251024A: Swift-XRT refined Analysis
by GCN Circulars 25 Oct '25

25 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42442 SUBJECT: GRB 251024A: Swift-XRT refined Analysis DATE: 25/10/25 18:09:15 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> S. Dichiara (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), V. D'Elia (SSDC & INAF-OAR), B. Sbarufatti (INAF-OAB), C. Salvaggio (INAF-OAB), J.A. Kennea (PSU), D.N. Burrows (PSU) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 4.4 ks of XRT data for GRB 251024A, from 113 s to 56.4 ks after the trigger. The data comprise 30 s in Windowed Timing (WT) mode (the first 10 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The late-time light curve (from T0+4.5 ks) is consistent with a constant source of mean count rate 4.5e-01 ct/sec. A power-law fit gives an index of -0.14 (+0.15, -0.14). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.06 (+0.16, -0.11). The best-fitting absorption column is consistent with the Galactic value of 3.7 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.2 x 10^-11 (3.6 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 3.7 (+/-2.8) x 10^20 cm^-2 Galactic foreground: 3.7 x 10^20 cm^-2 Excess significance: <1.6 sigma Photon index: 2.06 (+0.16, -0.11) The results of the XRT-team automatic analysis are available at https://www.swift.ac.uk/xrt_products/01406589. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42442. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40520] GRB 251025A (sb25102501): stellar flare confirmed
by GCN Circulars 25 Oct '25

25 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42441 SUBJECT: GRB 251025A (sb25102501): stellar flare confirmed DATE: 25/10/25 17:15:53 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Zhe Kang (CHO), Chao WU (NAOC), Liping Xin(NAOC), Xuhui Han(NAOC), Pinpin Zhang (NAOC), Xiaomeng Lu (NAOC), Zhenwei Li (CHO), You Lv (CHO), Ruosong Zhang (NAOC), Yujie Xiao(NAOC), Yulei Qiu(NAOC), Jing Wang (NAOC), Jinsong Deng(NAOC), Lei Huang(NAOC), Jianyan Wei (NAOC), Z.M. Wang (BNU), W.J. Tan (IHEP) report on behalf of the SVOM/C-GFT team: We observed the field of GRB 251025A (sb25102501) detected by SVOM/ECLAIRs (wang et al., GCN 42432) with LATIOS on SVOM/C-GFT. Observations started at 2025-10-25T09:36:54 UTC, ~92 seconds after the trigger. A sequence of images in the g, r, and i bands was obtained. The likely flaring star RX J2350.0+2659, reported by Li et al. (GCN 42435), is clearly detected. The source exhibited a fade in the i band from 9.68 to 11.38 mag over ~40 min, starting around T0+93 sec. Our observations confirm that this is a stellar flare. We thank the observation assistants Hongxu Xuan and Bowen Li at Jilin observatory for their excellent support. The Chinese Ground Follow-up Telescope (C-GFT) for the SVOM mission is located at Jilin Station, Changchun Observatory, National Astronomical Observatories, CAS. It features two instruments: (1) CATCH at the Cassegrain focus with a 21 arcsec x 21 arcsec FOV for simultaneous g/r/i-band imaging, and (2) LATIOS, a 4k x 4k CMOS camera at the prime focus with a 1.28 deg x 1.28 deg FOV that images in g, r, and i bands via filter switching. View this GCN Circular online at https://gcn.nasa.gov/circulars/42441. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40519] GRB 251025B: SVOM/VT optical observations with VHF data
by GCN Circulars 25 Oct '25

25 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42440 SUBJECT: GRB 251025B: SVOM/VT optical observations with VHF data DATE: 25/10/25 16:47:24 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> C. Wu., L.P. Xin, H.L. Li, Y. L. Qiu (NAOC), J. T. Palmerio (CEA), S. Hussein (IJCLab), M. Brunet (IRAP) report on behalf of the SVOM team. SVOM/VT performed an automatic slew on the burst triggered by SVOM/ECLAIRs (Hussein et al., GCN 42437). SVOM/VT began observing the field automatically at 2025-10-25T14:30:18 UTC, 373 seconds after the T0, with the slew of the platform triggered on-board, in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. We confirm the clear detection of the source reported by Wu et al.(GCN 42438) and Gress et al.(GCN 42439) in both the VT_B and VT_R bands with the downlinked VHF data. The AB magnitudes were derived as follows: -------------------------------------------- (T-T0)_mid exptime band mag 523 sec 300 sec VT_R 19.15 +/-0.02 523 sec 300 sec VT_B 18.61 +/-0.01 We note that the color of VT_B - VT_R ~ 0.5 mag may indicate a low-to-medium redshift event, following the analysis of Wang et al. (2020, RAA). Additional follow-up observations are encouraged. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/42440. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40518] GRB 251025B: MASTER OT detection
by GCN Circulars 25 Oct '25

25 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42439 SUBJECT: GRB 251025B: MASTER OT detection DATE: 25/10/25 16:28:10 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> O.Gress, N.Budnev (Irkutsk State University), V. Lipunov, P.Balanutsa, I.Panchenko, A.Kuznetsov, G.Antipov, E.Gorbovskoy, K.Zhirkov, N.Tiurina, A.Sankovich, Ya.Kechin, A.Chasovnikov, V.Topolev, D.Vlasenko, V.Senik, D.Vlasenko, V.Shumkov, K.Vetrov, Yu. Tselik(Lomonosov MSU, SAI, Moscow), R.Podesta, C.Francile, F. Podesta, E. Gonzalez (OAFA, San Juan Uni.,Argentina); D.Buckley (SAAO, South Africa), O.Ershova (ISU, Irkutsk), A.Sosnovskij (CrAO RAS), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), V.M.Pillet, R.Rebolo Lopez (The Instituto de Astrofisica de Canarias, Spain), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez,J.Martinez,A.R.Corella,L.H.Rodriguez (INAOE, Guillermo Haro Astrophysic Observatory, Mexico) MASTER Global Robotic Net [1-4] started Svom GRB 251025B (Hussein et al. GCN 42437, Ttrigger= 2025-10-25 14:24:05UT) at MASTER-Tunka and at MASTER-Kislovodsk. There is MASTER OT J015807.49+301814.0 with unfiltered m_OT=19.0 at at 2025-10-25 14:36:20 (mlim=20.5) Observation and reduction will be continued. This OT was discovered by SVOM (Chao Wu et al. GCN 42438, first image at 2025-10-25T14:25:38) [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 V., Kornilov V., Gorbovskoy E., Tiurina N., Kuznetsov A. 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics,Lomonosov MSU PRESS, 591pp. http://www.pereplet.ru/lipunov/625.html#625 View this GCN Circular online at https://gcn.nasa.gov/circulars/42439. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40517] GRB 251025B: SVOM/C-GFT optical counterpart detection
by GCN Circulars 25 Oct '25

25 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42438 SUBJECT: GRB 251025B: SVOM/C-GFT optical counterpart detection DATE: 25/10/25 15:50:39 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Chao WU (NAOC), Zhe Kang (CHO), Liping Xin(NAOC), Xuhui Han(NAOC), Pinpin Zhang (NAOC), Xiaomeng Lu (NAOC), Zhenwei Li (CHO), You Lv (CHO), Ruosong Zhang (NAOC), Yujie Xiao(NAOC), Yulei Qiu(NAOC), Jing Wang (NAOC), Jinsong Deng(NAOC), Lei Huang(NAOC), Jianyan Wei (NAOC),S.Hussein (IJCLab), M. Brunet (IRAP) report on behalf of the SVOM/C-GFT team: We observed the field of GRB 251025B (sb25102502) detected by SVOM/ECLAIRs (Hussein et al. GCN 42437) with LATIOS on SVOM/C-GFT. Observations started at 2025-10-25T14:25:38 UTC, ~93 seconds after the trigger. An uncatalogued optical source compared to PanStarrs1 catalogue is detected in our images within the SVOM/MXT localization error circle at: RA (J2000) = 01h58m07.49s = 29.53123 degrees Dec (J2000) = +30h18m14.5s = 30.30405 degrees with an uncertainty of ~0.5 arcsec. The magnitudes are: |[date-obs(mid-time)] | Mid_t-T0(s) | exposure time (s) | band | mag (AB) | mag_err| |--------------------|--------------|-------------------|------|----------|--------| | 2025-10-25T14:25:38| 98 | 10 | i | 17.49 | 0.12 | The photometry was calibrated against nearby Pan-STARRS1 stars and no correction for Galactic dust extinction was applied. The source exhibited ~1 mag decline in the i band over about 10 min. We propose that it is the optical counterpart of GRB 251025B. We thank the observation assistants Hongxu Xuan and Bowen Li at Jilin observatory for their excellent support. The Chinese Ground Follow-up Telescope (C-GFT) for the SVOM mission is located at Jilin Station, Changchun Observatory, National Astronomical Observatories, CAS. It features two instruments: (1) CATCH at the Cassegrain focus with a 21 arcsec x 21 arcsec FOV for simultaneous g/r/i-band imaging, and (2) LATIOS, a 4k x 4k CMOS camera at the prime focus with a 1.28 deg x 1.28 deg FOV that images in g, r, and i bands via filter switching. View this GCN Circular online at https://gcn.nasa.gov/circulars/42438. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40516] GRB 251025B: SVOM detection of a burst
by GCN Circulars 25 Oct '25

25 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42437 SUBJECT: GRB 251025B: SVOM detection of a burst DATE: 25/10/25 15:12:36 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> S. Hussein (IJCLab), M. Brunet (IRAP), U. Jacob (LUPM), D. Gotz (CEA), P. Maggi (ObAS), report on behalf of the SVOM mission team: At 2025-10-25T14:24:05 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 251025B (SVOM burst-id sb25102502). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was detected both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT), which produced a sequence of 13 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 17.67 in the [8-120] keV energy band over a time window of 10.20 seconds starting at 2025-10-25T14:24:00. The localization of the best alert is R.A., Dec. 29.5647, 30.2424 degrees (J2000) with a 90% confidence level (C.L.) radius of 4.80 arcmin (including systematic error of 2 arcmin added in quadrature). This burst was also detected by SVOM/GRM with a significance of 8.80. SVOM slewed to the burst. SVOM/MXT began observing the field at 2025-10-25T14:27:11 UTC, 186 seconds after T0. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec. 29.542, 30.308 degrees: R.A. (J2000) = 1h58m10.23s Dec. (J2000) = 30d18m32.2s with a 90% C.L. radius of 127.48 arcseconds. This location is 4.15 arcminutes from the ECLAIRs onboard position. This position may be improved as more data is received. VT began observing the field after the slew. The analysis of the data will be published in a future circular. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE. The Burst Advocate (BA) on shift for this alert is Shaymaa Hussein: hussein(a)astro.uni-tuebingen.de. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/42437. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40515] IceCube-251025A - IceCube observation of a high-energy neutrino candidate track-like event
by GCN Circulars 25 Oct '25

25 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42436 SUBJECT: IceCube-251025A - IceCube observation of a high-energy neutrino candidate track-like event DATE: 25/10/25 14:59:09 GMT FROM: A. Zegarelli at Ruhr University Bochum <azegarelli(a)icecube.wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: On 25-10-25 at 13:47:53.26 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 2.3507 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/141518_18513107.amon) more sophisticated reconstruction algorithms have been applied offline, with the direction refined to: Date: 25-10-25 Time: 13:47:53.26 UT RA: 145.63 (+0.88/-0.88 deg 90% PSF containment) J2000 Dec: 15.06 (+0.65/-0.62 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. No known gamma-ray sources listed in the Fermi 4FGL-DR4 or 3FHL catalogs are located within the 90% uncertainty region of the 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(a)icecube.wisc.edu View this GCN Circular online at https://gcn.nasa.gov/circulars/42436. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40514] IceCube-251025A - IceCube observation of a high-energy neutrino candidate track-like event
by GCN Circulars 25 Oct '25

25 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42436 SUBJECT: IceCube-251025A - IceCube observation of a high-energy neutrino candidate track-like event DATE: 25/10/25 14:59:09 GMT FROM: A. Zegarelli at Ruhr University Bochum <azegarelli(a)icecube.wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: On 25-10-25 at 13:47:53.26 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 2.3507 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/141518_18513107.amon) more sophisticated reconstruction algorithms have been applied offline, with the direction refined to: Date: 25-10-25 Time: 13:47:53.26 UT RA: 145.63 (+0.88/-0.88 deg 90% PSF containment) J2000 Dec: 15.06 (+0.65/-0.62 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. No known gamma-ray sources listed in the Fermi 4FGL-DR4 or 3FHL catalogs are located within the 90% uncertainty region of the 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(a)icecube.wisc.edu View this GCN Circular online at https://gcn.nasa.gov/circulars/42436. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40513] GRB 251025A (sb25102501): Likely a stellar flare by SVOM/VT
by GCN Circulars 25 Oct '25

25 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42435 SUBJECT: GRB 251025A (sb25102501): Likely a stellar flare by SVOM/VT DATE: 25/10/25 14:20:12 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, L. P. Xin, Y. L. Qiu, C. Wu, Z. H. Yao, Y. N. Ma, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, J. R. Xu, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA), Z. M. Wang (BNU), W. J. Tan (IHEP) report on behalf of the SVOM/VT team. SVOM/VT performed an automatic slew on the faint burst triggered by SVOM/ECLAIRs (sb25102501, Wang et al., GCN 42432). SVOM/VT began observing the field automatically on 2025-10-25T09:42:07, i.e., 405 sec with the slew of the platform triggered on-board, in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. With X band downlinked data, we find that the high proper motion star RX J2350.0+2659 was fading with the color from blue to red. It is located with a distance of 1.4 arcminutes from SVOM/MXT position (Wang et al., GCN 42432). The brightness was fading from 10.0 mag to 12.5 mag in VT_B during the first 1.6 hour after the trigger. The position of the source is consistent with XRT Source 1 (https://www.swift.ac.uk/SVOM/SVOM_FIELD00043/) Given the fading behavior in optical and the consistency in position between VT and XRT, we propose that this event was due to a stellar flare. Our photometry was estimated in AB magnitude. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/42435. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40512] GRB 251025A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
by GCN Circulars 25 Oct '25

25 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42434 SUBJECT: GRB 251025A: SVOM/COLIBRÍ (FM-GFT) optical upper limit DATE: 25/10/25 11:45:44 GMT FROM: nikos.mandarakas(a)lam.fr Nikos Mandarakas (LAM), Margarita Pereyra (UNAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Fredd Alvarez (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), 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), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), Z.M. Wang (BNU), W.J. Tan (IHEP): We imaged the field of the SVOM GRB 251025A (Wang et al., GCN Circ. 42432) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-10-25 09:58 to 11:00 UTC (from 0.39 to 1.41 hours after the trigger) and obtained 47 minutes of simultaneous exposure in the r and z filters. The data were analyzed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. In the stacked images, we do not detect any new source within the MXT localization region (Wang et al., GCN Circ. 42432) down to the following 5-sigma limits: r > 22.9 z > 21.7 These upper limits are consistent with the one reported by Wu et al. (GCN Circ. 42433). 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/42434. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40511] GRB 251025A: SVOM/VT VHF optical upper limit
by GCN Circulars 25 Oct '25

25 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42433 SUBJECT: GRB 251025A: SVOM/VT VHF optical upper limit DATE: 25/10/25 11:14:50 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> C. Wu, H. L. Li, L. P. Xin, Y. L. Qiu (NAOC), J. Palmerio (CEA), Z. M. Wang (BNU), W. J. Tan (IHEP) report on behalf of the SVOM/VT team. SVOM/VT began observing the field of GRB 251025A (Wang et al., GCN 42432) at 202025-10-25T09:43:10 UT, 7.8 minutes after T0, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. No optical candidate was detected within the position of MXT (Wang et al., GCN 42432), based on a preliminary analysis of the source list and 1-bit subimage downloaded via VHF network. The 3 sigma upper limits are about 21.5 mag in VT_R with an effective exposure time of 6*50 sec at 10.3 min post trigger. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. SVOM/VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/42433. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40510] GRB 251025A: SVOM detection of a faint burst
by GCN Circulars 25 Oct '25

25 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42432 SUBJECT: GRB 251025A: SVOM detection of a faint burst DATE: 25/10/25 10:15:26 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Z.M. Wang (BNU), W.J. Tan (IHEP), D. Turpin (CEA), B. Cordier(CEA), M. Moita (CEA), U. Jacob (LUPM) , report on behalf of the SVOM mission team: At 2025-10-25T09:35:22 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 251025A (SVOM burst-id sb25102501). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was only detected by the Image Trigger (IMT), which produced a sequence of 4 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 8.01 in the [5-20] keV energy band over a time window of 327.68 seconds starting at 2025-10-25T09:32:38. The localization of the best alert is R.A., Dec. 357.5739, 27.0002 degrees (J2000) with a 90% confidence level (C.L.) radius of 9.82 arcmin (including systematic error of 2 arcmin added in quadrature). SVOM slewed to the burst. SVOM/MXT began observing the field at 2025-10-25T09:41:11 UTC, 349 seconds after T0. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec. 357.5530, 26.9869 degrees: R.A. (J2000) = 23h50m12.72s Dec. (J2000) = 26d59m12.90s with a 90% C.L. radius of 25.08 arcseconds. This location is 1.37 arcminutes from the ECLAIRs onboard position. This position may be improved as more data is received. VT began observing the field after the slew. The analysis of the data will be published in a future circular. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE. The Burst Advocate (BA) on shift for this alert is Ziming Wang: zmwang489(a)mail.bnu.edu.cn. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/42432. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40509] GRB 251003A: VLA Detection
by GCN Circulars 24 Oct '25

24 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42431 SUBJECT: GRB 251003A: VLA Detection DATE: 25/10/24 22:49:01 GMT FROM: Sarah Chastain at University of New Mexico <sarahichastain(a)gmail.com> S. I. Chastain (TTU) and A. J. van der Horst (GWU) report: We carried out follow up observations of GRB 251003A, detected by Fermi (Fermi GBM Team, GCN 42069) and Swift (Beardmore et al., GCN 42070) with the Karl G. Jansky Very Large Array. At 18 days post-burst (2025-10-21 06:04:43.725), we significantly detect the afterglow at 9 GHz at 40 +/- 5 microJy/beam at the location: RA (J2000): 1:14:07.092 ± 0.003 seconds Dec (J2000): 56:29:27.94 ± 0.05 arcseconds These observations were taken as part of the Fermi GI project SF181025. We thank the VLA staff for scheduling and executing these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/42431. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40508] GRB 251024A: Enhanced Swift-XRT position
by GCN Circulars 24 Oct '25

24 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42430 SUBJECT: GRB 251024A: Enhanced Swift-XRT position DATE: 25/10/24 21:38:35 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> A.P. Beardmore, P.A. Evans, M.R. Goad and J.P. Osborne (U. Leicester) report on behalf of the Swift-XRT team. Using 1910 s of XRT Photon Counting mode data and 3 UVOT images for GRB 251024A, we find an astrometrically corrected X-ray position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 306.59782, -68.57239 which is equivalent to: RA (J2000): 20h 26m 23.48s Dec (J2000): -68d 34' 20.6" with an uncertainty of 2.2 arcsec (radius, 90% confidence). This position may be improved as more data are received. The latest position can be viewed at https://www.swift.ac.uk/xrt_positions. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177). This circular was automatically generated, and is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42430. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40507] GRB 251023C: Glowbug gamma-ray detection
by GCN Circulars 24 Oct '25

24 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42429 SUBJECT: GRB 251023C: Glowbug gamma-ray detection DATE: 25/10/24 21:38:04 GMT FROM: richard.s.woolf.civ(a)us.navy.mil R. Woolf, C.C. Cheung, M. Kerr, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report: The Glowbug gamma-ray telescope [1,2,3], operating on the International Space Station, reports the detection of GRB 251023C, which was also detected by Swift/BAT-GUANO (GCN 42412), CALET (GCN 42414), and AstroSat CZTI (GCN 42419). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2025-10-23 16:24:17.240 with a duration of 30.7 s and a total significance of about 110 sigma. The light curve comprises two primary peaks at ~T0+10s and ~T0+14s, and a tertiary peak around ~T0+28s. The Glowbug onset is ~7.7 s earlier than the CALET-reported T0 because we detect low-level emission prior to the first peak at ~T0+10s. The best-fit localization is RA, Decl. (J2000, deg) = 333.9, 58.4 with a radius of 2.1 deg (95% confidence), with a highly uncertain systematic uncertainty. We note that this localization is offset by ~40 deg from the Swift/BAT-GUANO-reported localization. The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS. Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC. It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS, and operated until 2024 April when it was put in safe storage on orbit. Glowbug was removed from storage and resumed operation on 2025 September 12. [1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959 [2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O [3] Woolf, R.S. et al. 2024, Proc. SPIE, 13151, id. 1315108 Distribution Statement A: Approved for public release. Distribution is unlimited. View this GCN Circular online at https://gcn.nasa.gov/circulars/42429. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40506] GRB 251024A: LCOGT Optical Afterglow Detection
by GCN Circulars 24 Oct '25

24 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42428 SUBJECT: GRB 251024A: LCOGT Optical Afterglow Detection DATE: 25/10/24 19:07:28 GMT FROM: Robert Strausbaugh at Eastern Illinois University <rstrausbaugh(a)eiu.edu> R. Strausbaugh (Eastern Illinois University), A. Cucchiara (NASA) report on behalf of a larger collaboration: We observed the Swift GRB 251024A field (Moss et al., GCN 42426) with the LCOGT 1-meter Sinistro instrument at the South African Astronomical Observatory site, on October 24, from 18:18 to 18:50 UT (corresponding to 0.51 to 1.05 hours after the GRB trigger time) with the Bessel I and R filters. We performed a series of 3x300s exposures in I-band and R-band. We detect an uncatalogued source in the XRT error region in both bands, which we propose to be the afterglow. The following magnitudes are calculated using the USNO-B1.0 catalog as reference: R = 21.2 +/- 0.1 I = 21.2 +/- 0.2 These magnitudes are not corrected for galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/42428. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40505] GRB 251022A: KAIT optical observations
by GCN Circulars 24 Oct '25

24 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42427 SUBJECT: GRB 251022A: KAIT optical observations DATE: 25/10/24 18:47:18 GMT FROM: Weikang Zheng at UC Berkeley <weikang(a)berkeley.edu> WeiKang Zheng (UCB) and Alexei V. Filippenko (UCB) report on behalf of the KAIT GRB team: The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at Lick Observatory, observed the field of GRB 251022A (Fermi GBM Team, GCN 42380; Di Lalla et al., GCN 42384; DeLaunay et al., GCN 42409; Mukherjee et al., GCN 42410) starting at ~0.46d and again at ~1.39d after the burst. A set of clear (roughly R) filter images were obtained. We detected the optical afterglow (O’Neill et al. GCN 42386; Becerra et al. GCN 42394; Lipunov et al. GCN 42395; Mandarakas et al. GCN 42397; Mohan et al. GCN 42413; Méndez et al., GCN 42423) in our coadd images. We estimate the afterglow to be 19.2 +/- 0.2 and 21.6 +/- 0.3 mag (Vega) at a mid time of ~0.47d and ~1.40d respectively. View this GCN Circular online at https://gcn.nasa.gov/circulars/42427. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40504] GRB 251024A: Swift detection of a burst
by GCN Circulars 24 Oct '25

24 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42426 SUBJECT: GRB 251024A: Swift detection of a burst DATE: 25/10/24 18:09:58 GMT FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk> M. J. Moss (GSFC), S. Dichiara (PSU), R. A. J. Eyles-Ferris (U Leicester), R. Gupta (NASA GSFC), J. A. Kennea (PSU), A. Y. Lien (U Tampa), K. L. Page (U Leicester) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 17:47:02.25 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 251024A (trigger= 1406589). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 306.622, -68.574 which is RA(J2000) = 20h 26m 29s Dec(J2000) = -68d 34' 25" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure with a duration of about 30 sec. The peak count rate was ~1000 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 17:49:11.3 UT, 129.1 seconds after the BAT trigger. Using promptly downlinked data we find a fading, uncatalogued X-ray source with an enhanced position: RA, Dec 306.59743, -68.57225 which is equivalent to: RA(J2000) = 20h 26m 23.38s Dec(J2000) = -68d 34' 20.1" with an uncertainty of 1.9 arcseconds (radius, 90% containment). This location is 32 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the Galactic value (3.73 x 10^20 cm^-2, Willingale et al. 2013), with an excess column of 3 (+2.09/-1.77) x 10^21 cm^-2 (90% confidence). UVOT took a finding chart exposure of 150 seconds with the White filter starting 132 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of the XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The list of sources is typically complete to about 18 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.044. Burst Advocate for this burst is M. J. Moss (mikejmoss3 AT gmail.com) Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/) View this GCN Circular online at https://gcn.nasa.gov/circulars/42426. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40503] Swift GRB251024.74: Global MASTER-Net observations report
by GCN Circulars 24 Oct '25

24 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42425 SUBJECT: Swift GRB251024.74: Global MASTER-Net observations report DATE: 25/10/24 17:54:39 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-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) was pointed to the Swift GRB251024.74 (trigger No 1406589,20h 26m 29.26s , -68d 34m 26.4s, R=0.05) errorbox 10 sec after notice time and 73 sec after trigger time at 2025-10-24 17:48:15 UT, with upper limit up to 16.5 mag. Observations started at twilight. The observations began at zenith distance = 38 deg. The sun altitude is -11.1 deg. The galactic latitude b = -34 deg., longitude l = 327 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3022698 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 78 | MASTER-SAAO | P\ | 10 | 16.2 | 78 | MASTER-SAAO | C | 10 | 16.1 | 112 | MASTER-SAAO | P\ | 20 | 16.5 | 112 | MASTER-SAAO | C | 20 | 16.3 | 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/42425. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40502] GRB 251023B / EP251023b: COLIBRÍ Confirmation of the Fading Nature of the Optical Candidate
by GCN Circulars 24 Oct '25

24 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42424 SUBJECT: GRB 251023B / EP251023b: COLIBRÍ Confirmation of the Fading Nature of the Optical Candidate DATE: 25/10/24 16:50:02 GMT FROM: Rosa Leticia Becerra Godínez at Instituto de Astronomía, UNAM <rbecerra(a)astro.unam.mx> Enrique Moreno Méndez (UNAM), Nikos Mandarakas (LAM), Alan M. Watson (UNAM), Rosa L. Becerra (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM): We reimaged the field of the GRB 251023B / EP251022b (Kang et al., GCN Circ. 42392; Nakahira et al., GCN Circ. 42402; Wu et al., GCN Circ. 42415; Cheung et al., GCN Circ. 42407), using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2025-10-24 07:06 to 08:12 UTC (from 22.3 to 23.4 hours after the trigger) and obtained 16 minutes of exposure in each of the r and i filters and 32 minutes of exposure in the z filter. The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. In our second epoch, we do not detect the optical candidate reported by Mandarakas et al. (GCN Circ. 42404) down to the following 3-sigma limits: r > 22.8 i > 22.4 z > 22.0 These values are consistent with the non-detection reported by Adami et al. (GCN Circ. 42421) and confirm the fading nature of the source, supporting its association with GRB 251023B / EP251022b. 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/42424. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40501] GRB 251022A: COLIBRÍ Further Multi-frequency Optical Observations
by GCN Circulars 24 Oct '25

24 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42423 SUBJECT: GRB 251022A: COLIBRÍ Further Multi-frequency Optical Observations DATE: 25/10/24 15:05:07 GMT FROM: Rosa Leticia Becerra Godínez at Instituto de Astronomía, UNAM <rbecerra(a)astro.unam.mx> Enrique Moreno Méndez (UNAM), Nikos Mandarakas (LAM), Alan M. Watson (UNAM), Rosa L. Becerra (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM): We reobserved the field of the Fermi GRB 251022A (Fermi GBM Team, GCN Circ. 42380; Di Lalla et al., GCN Circ. 42384) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2025-10-24 07:25 to 08:30 UTC (from 32.8 to 33.9 hours after the trigger) and obtained 10 minutes of exposure in each of the g, r, i, and z filters and 20 minutes of exposure in the y filter. The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. In our second epoch, we still detect the optical counterpart firstly reported by GOTO (O’Neill et al. GCN Circ. 42386) and subsequently followed-up by DDOTI (Becerra et al. GCN Circ. 42394), MASTER (Lipunov et al. GCN Circ. 42395), COLIBRÍ (Mandarakas et al. GCN Circ. 42397), and GROWTH (Mohan et al. GCN Circ. 42413) at preliminary magnitudes and upper limits of: g = 22.52 +/- 0.23 r = 22.05 +/- 0.20 i = 21.99 +/- 0.31 z = 21.95 +/- 0.65 y > 20.7 (3-sigma) Compared with the values reported in our first epoch (Mandarakas et al. GCN Circ. 42397), we estimate a temporal decay index of ~-2, consistent with a jet break. Our detection in g suggests that this is not a high-redshift GRB, but instead has z < 3. 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/42423. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40500] EP251023a: MAO/AZT-22 optical observations
by GCN Circulars 24 Oct '25

24 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42422 SUBJECT: EP251023a: MAO/AZT-22 optical observations DATE: 25/10/24 15:02:32 GMT FROM: Yodgor Rajabov at UBAI <rajabov(a)astrin.uz> Y. Rajabov, O. Burkhonov, B.Abidkhanov, S. Ehgamberdiev, Y. Tillayev (UBAI), T. Boyqobilov, A. Shaymanov (Maidanak Observatory/UBAI) report on behalf of UBAI team. We observed the field of EP transient EP251023a (Wu et al., GCN 42388), with the AZT-22 1.5m telescope of the Maidanak Observatory (MAO) starting on 2025-10-23 at 22:52:18 UT, i.e. ~10.37 hours since trigger. In total we obtained 6x300 s exposures in the R-band using 4kx4k CCD SNUCAM camera (Im et al., 2010). The optical afterglow initially detected by GOTO (Wortley et al., GCN 42387) and also observed (Li et al., GCN 42389; Liu et al., GCN 42391; Mandarakas et al., GCN 42400; Lipunov et al., GCN 42405; Selezneva et al., GCN 42406; Mohan et al., GCN 42411; Rakotondrainibe et al., GCN 42420) is detected in our individual and stacked frames. Preliminary photometry is as follows: Date UTstart Exptime t-T0 Filter OT Err. UL Site/Telescope (nxs) (mid, days) 2025-10-23 23:08:31 6x300 0.85928 R 20.56 0.03 22.99 MAO/AZT-22 All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained in Johnson Cousins filters were calibrated using the Gaia DR3 Synphot catalog. The data has not corrected for the Galactic extinction. Maidanak astronomical observatory (MAO) is an observational facility of the Ulugh Beg Astronomical Institute (UBAI), Uzbekistan Academy of Sciences (http://maidanak.uz/) View this GCN Circular online at https://gcn.nasa.gov/circulars/42422. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40499] GRB 251023B: OHP/T193 optical observations
by GCN Circulars 24 Oct '25

24 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42421 SUBJECT: GRB 251023B: OHP/T193 optical observations DATE: 25/10/24 13:26:31 GMT FROM: Ny Avo Rakotondrainibe at LAM <nyavo.rakotobe(a)gmail.com> C. Adami (LAM/Pytheas/AMU), N.A. Rakotondrainibe (LAM), E. Le Floc'h (CEA/Irfu), report on behalf of the MISTRAL GRB collaboration: We carried out observations of GRB 251023B (Cheung et al., GCN 42407; Mandarakas et al., GCN 42404; Nakahira et al., GCN 42402; Evans et al., GCN 42401; Kang et al., GCN 42392) using the T193cm telescope at Observatoire de Haute-Provence (France) equipped with the MISTRAL spectro-imager. We obtained 6 exposures of 15 min in the r-band at a midtime of 2025 10 24 01:51:23 UT, corresponding to T-T0 = 17.04 hours. We do not significantly detect the optical source identified by Mandarakas et al. (GCN 42404) at the 3-sigma upper limit of: r’ < 21.78 mag (AB) The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the magnitudes are not corrected for Galactic extinction. We used the STDWeb/STDPipe tools (Karpov 2025). We acknowledge the excellent support from the Observatoire de Haute-Provence and in particular Jean Balcaen. View this GCN Circular online at https://gcn.nasa.gov/circulars/42421. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40498] EP251023a: OHP/T193 optical observations
by GCN Circulars 24 Oct '25

24 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42420 SUBJECT: EP251023a: OHP/T193 optical observations DATE: 25/10/24 13:25:17 GMT FROM: Ny Avo Rakotondrainibe at LAM <nyavo.rakotobe(a)gmail.com> N.A. Rakotondrainibe (LAM), C. Adami (LAM/Pytheas/AMU), E. Le Floc'h (CEA/Irfu), report on behalf of the MISTRAL GRB collaboration: We carried out observations of EP251023a (Mohan et al., GCN 42411; Selezneva et al., GCN 42406; Lipunov et al., GCN 42405; Mandarakas et al., GCN 42400; Liu et al., GCN 42391; Li et al., GCN 42389; Wu et al., GCN 42388; Wortley et al., GCN 42387) using the T193cm telescope at Observatoire de Haute-Provence (France) equipped with the MISTRAL spectro-imager. We obtained 4 exposures of 15 min in the r-band at a midtime of 2025 10 24 03:17:52UT corresponding to T-T0 = 24.78 hours. The afterglow is well detected in r’ and we measured the following preliminary magnitude: r’ = 21.55+/-0.10 mag (AB) The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the magnitudes are not corrected for Galactic extinction. We used the STDWeb/STDPipe tools (Karpov 2025). We acknowledge the excellent support from the Observatoire de Haute-Provence and in particular Jean Balcaen. View this GCN Circular online at https://gcn.nasa.gov/circulars/42420. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40497] GRB 251023C: AstroSat CZTI detection
by GCN Circulars 24 Oct '25

24 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42419 SUBJECT: GRB 251023C: AstroSat CZTI detection DATE: 25/10/24 12:15:05 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> S. Salunke (IUCAA), M. Tembhurnikar (IUCAA), Harsha K. H. (IUCAA), A. Arya (IITB), A. Goyal (IITB), G. Waratkar (Caltech/IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a long,bright GRB 251023C which was also detected by SWIFT BAT (DeLaunay et. al., GCN Circ. 42412), and CALET (Asaoka et. al., GCN Circ. 42414). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2025-10-23 16:24:32.50 UTC. The measured peak count rate associated with the burst is 682 (+55, -51) counts/s above the background in the combined data of all quadrants, with a total of 4344 (+401, -229) counts. The local mean background count rate was 294 (+1, -7) counts/s. Using cumulative rates, we measure a T90 of 18.2 (+2.8, -1.6) s. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2025-10-23 16:24:28.05 UTC. The measured peak count rate associated with the burst is 942 (+83, -89) counts/s above the background in the combined data of all quadrants, with a total of 5554 (+521, -528) counts. The local mean background count rate was 1676 (+7, -8) counts/s. We measure a T90 of 15.8 (+1.9, -6.2) s from the cumulative Veto light curve. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project. CZTI GRB detections are reported regularly on the payload site at: http://astrosat.iucaa.in/czti/?q=grb View this GCN Circular online at https://gcn.nasa.gov/circulars/42419. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40496] GRB 251023C: AstroSat CZTI detection
by GCN Circulars 24 Oct '25

24 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42419 SUBJECT: GRB 251023C: AstroSat CZTI detection DATE: 25/10/24 12:15:05 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> S. Salunke (IUCAA), M. Tembhurnikar (IUCAA), Harsha K. H. (IUCAA), A. Arya (IITB), A. Goyal (IITB), G. Waratkar (Caltech/IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a long,bright GRB 251023C which was also detected by SWIFT BAT (DeLaunay et. al., GCN Circ. 42412), and CALET (Asaoka et. al., GCN Circ. 42414). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2025-10-23 16:24:32.50 UTC. The measured peak count rate associated with the burst is 682 (+55, -51) counts/s above the background in the combined data of all quadrants, with a total of 4344 (+401, -229) counts. The local mean background count rate was 294 (+1, -7) counts/s. Using cumulative rates, we measure a T90 of 18.2 (+2.8, -1.6) s. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2025-10-23 16:24:28.05 UTC. The measured peak count rate associated with the burst is 942 (+83, -89) counts/s above the background in the combined data of all quadrants, with a total of 5554 (+521, -528) counts. The local mean background count rate was 1676 (+7, -8) counts/s. We measure a T90 of 15.8 (+1.9, -6.2) s from the cumulative Veto light curve. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project. CZTI GRB detections are reported regularly on the payload site at: http://astrosat.iucaa.in/czti/?q=grb View this GCN Circular online at https://gcn.nasa.gov/circulars/42419. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40495] EP251023b/GRB 251023B: JinShan optical observation
by GCN Circulars 24 Oct '25

24 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42418 SUBJECT: EP251023b/GRB 251023B: JinShan optical observation DATE: 25/10/24 08:38:09 GMT FROM: L. B. He at NAOC <helb(a)bao.ac.cn> L.B. He, J. An, S.Q. Jiang, X. Liu, Z.P. Zhu, D. Xu (NAOC), S.Y. Fu, A.D. Zhu, L. Lei, H.Z. Wu (HUST), J.Z. Liu (XAO) report on behalf of a large collaboration: We observed the field of EP251023b/GRB 251023B (Kang et al., GCN 42392; Nakahira et al., GCN 42402; Wu et al., GCN 42415) using the 100C telescope of the JinShan project, located at Altay, Xinjiang, China. Observations started at 2025-10-23 16:01:41 UT, i. e. 7.3 hours after the trigger. The previously reported optical counterpart (Mandarakas et al., GCN 42404) was detected in our stacked z-band frame with a magnitude z~21.4 at a mid-time 9.75 hrs post-burst. The magnitude was callibrated with nearby PanSTARRS1 dr2 catalog without the Galactic extinction correction. We acknowledge the excellent support from T.Q. Chen and J.F. Zhang for enabling these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/42418. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40494] GRB 251022A: Swift-XRT detection of GOTO25iym
by GCN Circulars 24 Oct '25

24 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42417 SUBJECT: GRB 251022A: Swift-XRT detection of GOTO25iym DATE: 25/10/24 08:12:16 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> D.N. Burrows (PSU), S. Lanava (PSU), S. Dichiara (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), M. Capalbi (INAF-OAR), M. Perri (SSDC & INAF-OAR), V. D'Elia (SSDC & INAF-OAR) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the Fermi/LAT-detected burst GRB 251022A in a series of observations tiled on the sky. The total exposure time is 4.6 ks, distributed over 4 tiles; the maximum exposure at a single sky location in the tiling was 2.5 ks. The data were collected between T0+26.7 ks and T0+71.7 ks, and are entirely in Photon Counting (PC) mode. Seven uncatalogued X-ray sources have been detected, however none of them is above the RASS limit or shows definitive signs of fading in the X-rays. Source 4 is 2.6 arcsec from the reported optical transient GOTO25iym (O'Neill et al., GCN Circ. 42386) and thus is likely the counterpart to that transient and the GRB afterglow, though we cannot at present confirm fading in X-rays. The details of this source are: Source 4: RA (J2000.0): 65.4968 = 04h 21m 59.23s Dec (J2000.0): -18.9188 = -18d 55' 07.8" Error: 4.8 arcsec (radius, 90% conf.) Count-rate: 0.0110 [+0.0026, -0.0025] ct s^-1 Distance: 1463 arcsec from Fermi/LAT position. Flux: (2.96 [+0.71, -0.67])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV) The other 6 uncatalogued sources detected are enumerated below: Source 1: RA (J2000.0): 65.0135 = 04h 20m 03.25s Dec (J2000.0): -19.3306 = -19d 19' 50.1" Error: 6.3 arcsec (radius, 90% conf. [Enhanced position]) Count-rate: 0.0173 [+0.0061, -0.0050] ct s^-1 Distance: 1247 arcsec from Fermi/LAT position. Flux: (3.5 [+1.2, -1.0])e-12 erg cm^-2 s^-1 (observed, 0.3-10 keV) Source 2: RA (J2000.0): 65.0984 = 04h 20m 23.62s Dec (J2000.0): -19.2625 = -19d 15' 45.2" Error: 5.4 arcsec (radius, 90% conf.) Count-rate: 0.0115 [+0.0046, -0.0037] ct s^-1 Distance: 971 arcsec from Fermi/LAT position. Flux: (4.4 [+1.8, -1.4])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV) Source 5: RA (J2000.0): 65.3796 = 04h 21m 31.10s Dec (J2000.0): -18.9857 = -18d 59' 08.4" Error: 6.0 arcsec (radius, 90% conf.) Count-rate: (7.7 [+2.6, -2.1])e-3 ct s^-1 Distance: 1167 arcsec from Fermi/LAT position. Flux: (2.17 [+0.72, -0.60])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV) Source 6: RA (J2000.0): 65.5456 = 04h 22m 10.93s Dec (J2000.0): -19.1086 = -19d 06' 30.8" Error: 6.5 arcsec (radius, 90% conf.) Count-rate: (6.0 [+2.5, -2.0])e-3 ct s^-1 Distance: 917 arcsec from Fermi/LAT position. Flux: (9.1 [+3.9, -3.0])e-14 erg cm^-2 s^-1 (observed, 0.3-10 keV) Source 8: RA (J2000.0): 65.4382 = 04h 21m 45.16s Dec (J2000.0): -19.0268 = -19d 01' 36.6" Error: 7.8 arcsec (radius, 90% conf.) Count-rate: (3.2 [+1.8, -1.3])e-3 ct s^-1 Distance: 1038 arcsec from Fermi/LAT position. Flux: (6.8 [+3.9, -2.8])e-14 erg cm^-2 s^-1 (observed, 0.3-10 keV) Source 9: RA (J2000.0): 65.3956 = 04h 21m 34.95s Dec (J2000.0): -19.0576 = -19d 03' 27.4" Error: 6.3 arcsec (radius, 90% conf.) Count-rate: (3.6 [+2.1, -1.5])e-3 ct s^-1 Distance: 910 arcsec from Fermi/LAT position. Flux: (1.15 [+0.65, -0.48])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV) Two catalogued sources were also detected. The results of the XRT-team automatic analysis of the tiled XRT observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/xrt_products/TILED_GRB00139. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42417. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40493] EP251023b: Global MASTER-Net observations report
by GCN Circulars 24 Oct '25

24 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42416 SUBJECT: EP251023b: Global MASTER-Net observations report DATE: 25/10/24 06:18:23 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-Tunka robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Applied Physics Institute, Irkutsk State University) was pointed to the EP251023b ( EP Team et al., GCN 42415) errorbox 40434 sec after trigger time at 2025-10-23 20:02:41 UT, with upper limit up to 20.1 mag. The observations began at zenith distance = 38 deg. The sun altitude is -34.7 deg. The galactic latitude b = -18 deg., longitude l = 187 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3022366 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 40494 | 2025-10-23 20:02:41 | MASTER-Tunka | (04h 53m 57.12s , +12d 53m 42.1s) | C | 120 | 16.4 | 40494 | 2025-10-23 20:02:41 | MASTER- | (04h 53m 27.18s , +12d 59m 22.7s) | C | 120 | 18.8 | 40627 | 2025-10-23 20:04:54 | MASTER- | (04h 53m 23.22s , +13d 00m 50.4s) | C | 120 | 19.8 | 40628 | 2025-10-23 20:04:54 | MASTER-Tunka | (04h 53m 53.26s , +12d 55m 10.3s) | C | 120 | 16.4 | 40761 | 2025-10-23 20:07:07 | MASTER-Tunka | (04h 53m 53.45s , +12d 53m 31.3s) | C | 120 | 16.9 | 40761 | 2025-10-23 20:07:07 | MASTER- | (04h 53m 23.36s , +12d 59m 11.7s) | C | 120 | 19.9 | 41086 | 2025-10-23 20:13:02 | MASTER-Tunka | (04h 53m 57.11s , +12d 54m 43.4s) | C | 60 | 19.7 | 41176 | 2025-10-23 20:13:02 | MASTER-Tunka | (04h 53m 57.11s , +12d 54m 43.3s) | C | 240 | 20.0 | Coadd 41086 | 2025-10-23 20:13:02 | MASTER- | (04h 53m 26.63s , +13d 00m 28.7s) | C | 60 | 19.7 | 41159 | 2025-10-23 20:14:15 | MASTER-Tunka | (04h 53m 50.19s , +12d 54m 07.5s) | C | 60 | 19.7 | 41159 | 2025-10-23 20:14:15 | MASTER- | (04h 53m 19.72s , +12d 59m 52.6s) | C | 60 | 19.7 | 41263 | 2025-10-23 20:15:30 | MASTER-Tunka | (04h 53m 51.71s , +12d 55m 04.5s) | C | 120 | 19.8 | 41263 | 2025-10-23 20:15:30 | MASTER- | (04h 53m 21.21s , +13d 00m 49.4s) | C | 120 | 19.8 | 41398 | 2025-10-23 20:17:44 | MASTER-Tunka | (04h 53m 57.01s , +12d 54m 00.3s) | C | 120 | 19.8 | 41518 | 2025-10-23 20:17:44 | MASTER-Tunka | (04h 53m 57.02s , +12d 54m 00.4s) | C | 360 | 20.0 | Coadd 41398 | 2025-10-23 20:17:44 | MASTER- | (04h 53m 26.46s , +12d 59m 45.2s) | C | 120 | 19.8 | 41530 | 2025-10-23 20:19:57 | MASTER-Tunka | (04h 53m 50.71s , +12d 52m 55.2s) | C | 120 | 19.7 | 41530 | 2025-10-23 20:19:57 | MASTER- | (04h 53m 20.15s , +12d 58m 40.0s) | C | 120 | 19.7 | 41663 | 2025-10-23 20:22:10 | MASTER-Tunka | (04h 53m 57.82s , +12d 53m 08.0s) | C | 120 | 19.7 | 41663 | 2025-10-23 20:22:10 | MASTER- | (04h 53m 27.32s , +12d 58m 52.6s) | C | 120 | 19.7 | 41796 | 2025-10-23 20:24:22 | MASTER-Tunka | (04h 53m 54.06s , +12d 54m 19.5s) | C | 120 | 19.7 | 41916 | 2025-10-23 20:24:22 | MASTER-Tunka | (04h 53m 54.06s , +12d 54m 19.5s) | C | 360 | 20.1 | Coadd 41796 | 2025-10-23 20:24:22 | MASTER- | (04h 53m 23.57s , +13d 00m 03.9s) | C | 120 | 19.6 | 41929 | 2025-10-23 20:26:35 | MASTER-Tunka | (04h 53m 54.16s , +12d 52m 58.5s) | C | 120 | 19.8 | 41929 | 2025-10-23 20:26:35 | MASTER- | (04h 53m 23.66s , +12d 58m 43.0s) | C | 120 | 19.8 | 42062 | 2025-10-23 20:28:48 | MASTER-Tunka | (04h 53m 57.79s , +12d 54m 17.4s) | C | 120 | 19.9 | 42062 | 2025-10-23 20:28:48 | MASTER- | (04h 53m 27.25s , +13d 00m 01.6s) | C | 120 | 19.9 | 42195 | 2025-10-23 20:31:02 | MASTER-Tunka | (04h 53m 52.11s , +12d 53m 34.1s) | C | 120 | 19.9 | 42315 | 2025-10-23 20:31:02 | MASTER-Tunka | (04h 53m 52.11s , +12d 53m 34.1s) | C | 360 | 20.1 | Coadd 42195 | 2025-10-23 20:31:02 | MASTER- | (04h 53m 21.54s , +12d 59m 18.5s) | C | 120 | 19.9 | 42327 | 2025-10-23 20:33:13 | MASTER-Tunka | (04h 53m 50.56s , +12d 54m 30.9s) | C | 120 | 20.0 | 42327 | 2025-10-23 20:33:13 | MASTER- | (04h 53m 19.95s , +13d 00m 15.1s) | C | 120 | 19.9 | 42460 | 2025-10-23 20:35:27 | MASTER-Tunka | (04h 53m 57.26s , +12d 53m 27.1s) | C | 120 | 19.9 | 42460 | 2025-10-23 20:35:27 | MASTER- | (04h 53m 26.58s , +12d 59m 11.0s) | C | 120 | 19.9 | 42595 | 2025-10-23 20:37:41 | MASTER-Tunka | (04h 53m 52.25s , +12d 52m 22.4s) | C | 120 | 19.9 | 42685 | 2025-10-23 20:37:41 | MASTER-Tunka | (04h 53m 52.25s , +12d 52m 22.4s) | C | 300 | 20.1 | Coadd 42595 | 2025-10-23 20:37:41 | MASTER- | (04h 53m 21.54s , +12d 58m 06.1s) | C | 120 | 19.9 | 42730 | 2025-10-23 20:39:56 | MASTER-Tunka | (04h 53m 57.37s , +12d 52m 45.8s) | C | 120 | 20.0 | 42730 | 2025-10-23 20:39:56 | MASTER- | (04h 53m 26.63s , +12d 58m 29.3s) | C | 120 | 20.0 | 42833 | 2025-10-23 20:42:09 | MASTER-Tunka | (04h 53m 54.47s , +12d 53m 48.3s) | C | 60 | 19.9 | 42833 | 2025-10-23 20:42:09 | MASTER- | (04h 53m 23.67s , +12d 59m 31.7s) | C | 60 | 19.9 | 42907 | 2025-10-23 20:43:24 | MASTER-Tunka | (04h 53m 54.53s , +12d 52m 27.5s) | C | 60 | 19.8 | 42967 | 2025-10-23 20:43:24 | MASTER-Tunka | (04h 53m 54.54s , +12d 52m 27.5s) | C | 180 | 20.0 | Coadd 42907 | 2025-10-23 20:43:24 | MASTER- | (04h 53m 23.70s , +12d 58m 10.7s) | C | 60 | 19.8 | 42980 | 2025-10-23 20:44:36 | MASTER-Tunka | (04h 53m 56.90s , +12d 54m 01.3s) | C | 60 | 19.7 | 42980 | 2025-10-23 20:44:36 | MASTER- | (04h 53m 26.04s , +12d 59m 44.2s) | C | 60 | 19.7 | 43052 | 2025-10-23 20:45:49 | MASTER-Tunka | (04h 53m 52.30s , +12d 53m 09.6s) | C | 60 | 19.5 | 43052 | 2025-10-23 20:45:49 | MASTER- | (04h 53m 21.42s , +12d 58m 52.8s) | C | 60 | 19.5 | 43134 | 2025-10-23 20:47:11 | MASTER-Tunka | (04h 53m 51.00s , +12d 54m 07.5s) | C | 60 | 19.2 | 43194 | 2025-10-23 20:47:11 | MASTER-Tunka | (04h 53m 50.99s , +12d 54m 07.5s) | C | 180 | 19.7 | Coadd 43135 | 2025-10-23 20:47:11 | MASTER- | (04h 53m 20.10s , +12d 59m 50.4s) | C | 60 | 19.1 | 43208 | 2025-10-23 20:48:25 | MASTER-Tunka | (04h 53m 58.03s , +12d 53m 05.4s) | C | 60 | 19.2 | 43208 | 2025-10-23 20:48:25 | MASTER- | (04h 53m 27.12s , +12d 58m 48.7s) | C | 60 | 19.1 | 43284 | 2025-10-23 20:49:41 | MASTER-Tunka | (04h 53m 50.96s , +12d 52m 02.9s) | C | 60 | 19.0 | 43284 | 2025-10-23 20:49:41 | MASTER- | (04h 53m 20.05s , +12d 57m 45.8s) | C | 60 | 19.0 | 43358 | 2025-10-23 20:50:54 | MASTER-Tunka | (04h 53m 58.58s , +12d 52m 08.7s) | C | 60 | 18.8 | 43418 | 2025-10-23 20:50:54 | MASTER-Tunka | (04h 53m 58.58s , +12d 52m 08.7s) | C | 180 | 19.3 | Coadd 43358 | 2025-10-23 20:50:54 | MASTER- | (04h 53m 27.65s , +12d 57m 51.3s) | C | 60 | 18.7 | 43435 | 2025-10-23 20:52:12 | MASTER-Tunka | (04h 53m 54.73s , +12d 53m 32.9s) | C | 60 | 18.7 | 43435 | 2025-10-23 20:52:12 | MASTER- | (04h 53m 23.76s , +12d 59m 15.7s) | C | 60 | 18.7 | 43507 | 2025-10-23 20:53:24 | MASTER-Tunka | (04h 53m 54.77s , +12d 52m 13.3s) | C | 60 | 18.3 | 43507 | 2025-10-23 20:53:24 | MASTER- | (04h 53m 23.79s , +12d 57m 56.2s) | C | 60 | 18.2 | 43579 | 2025-10-23 20:54:36 | MASTER-Tunka | (04h 53m 57.61s , +12d 53m 34.0s) | C | 60 | 18.7 | 43639 | 2025-10-23 20:54:36 | MASTER-Tunka | (04h 53m 57.62s , +12d 53m 34.0s) | C | 180 | 19.9 | Coadd 43579 | 2025-10-23 20:54:36 | MASTER- | (04h 53m 26.61s , +12d 59m 16.6s) | C | 60 | 18.7 | 43654 | 2025-10-23 20:55:50 | MASTER-Tunka | (04h 53m 52.49s , +12d 52m 52.2s) | C | 60 | 19.6 | 43654 | 2025-10-23 20:55:50 | MASTER- | (04h 53m 21.48s , +12d 58m 34.6s) | C | 60 | 19.5 | 43727 | 2025-10-23 20:57:04 | MASTER-Tunka | (04h 53m 51.37s , +12d 53m 50.1s) | C | 60 | 19.5 | 43727 | 2025-10-23 20:57:04 | MASTER- | (04h 53m 20.37s , +12d 59m 32.4s) | C | 60 | 19.4 | 43800 | 2025-10-23 20:58:16 | MASTER-Tunka | (04h 53m 57.11s , +12d 52m 48.1s) | C | 60 | 19.6 | 43890 | 2025-10-23 20:58:16 | MASTER-Tunka | (04h 53m 57.11s , +12d 52m 48.2s) | C | 240 | 20.0 | Coadd 43800 | 2025-10-23 20:58:16 | MASTER- | (04h 53m 26.13s , +12d 58m 30.3s) | C | 60 | 19.6 | 43873 | 2025-10-23 20:59:30 | MASTER-Tunka | (04h 53m 52.86s , +12d 51m 46.0s) | C | 60 | 19.6 | 43873 | 2025-10-23 20:59:30 | MASTER- | (04h 53m 21.87s , +12d 57m 27.9s) | C | 60 | 19.5 | 43984 | 2025-10-23 21:00:51 | MASTER-Tunka | (04h 53m 58.73s , +12d 51m 48.7s) | C | 120 | 19.2 | 43984 | 2025-10-23 21:00:51 | MASTER- | (04h 53m 27.73s , +12d 57m 30.8s) | C | 120 | 19.2 | 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/42416. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40492] EP251023b/GRB 251023B : Einstein Probe detection of a fast X-ray transient
by GCN Circulars 24 Oct '25

24 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42415 SUBJECT: EP251023b/GRB 251023B : Einstein Probe detection of a fast X-ray transient DATE: 25/10/24 05:39:45 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y. Wu (NJU), D. F. Hu (PMO, CAS), H. N. Yang, T. Zhao, W. D. Zhang (NAO, CAS), on behalf of the Einstein Probe (EP) team: We report on the detection of a fast X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP251023b. The transient triggered EP-WXT (ID: 01709247298) at 2025-10-23T08:48:47 (UTC). The refined analysis of the WXT data shows that the event started at T0=2025-10-23T08:46:06 (UTC) and lasted for ~160 s. The WXT position of the source is R.A. = 73.502 deg, Dec. = 12.648 deg (J2000) with an uncertainty of 2.2 arcmin in radius (90% C.L. statistical and systematic). The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 2.69 x 10^(21) cm^-2 and a photon index of 1.66（-/+0.25）. The derived average unabsorbed 0.5-4 keV flux is 3.9 (-/+0.5) x 10^(-9) erg/s/cm^2. We performed a Target-of-Opportunity observation with the Follow-up X-ray Telescope on board EP. The observation began at 2025-10-23T14:40:06 (UTC).An uncatalogued X-ray source was detected within the WXT error circle at R.A. = 73.5021 deg, Dec. = 12.6574 deg (J2000), with a positional uncertainty of 10 arcsec in radius (90% confidence level, including both statistical and systematic uncertainties). The FXT 0.5-10 keV spectrum can be fitted with an absorbed power law with the same fixed Galactic hydrogen column density value and a photon index of 2.16 (-/+0.21). The derived average unabsorbed 0.5-10 keV flux is 2.03 (-0.29/+0.34) x 10^(-12) erg/s/cm^2. The source is spatially consistent with the counterpart reported (Kang et al. GCN 42392, Evans et al. GCN 42401, Nakahira et al. GCN 42402, Mandarakas et al. GCN 42404, Cheung et al. GCN 42407). 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). View this GCN Circular online at https://gcn.nasa.gov/circulars/42415. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40491] GRB 251023C: CALET Gamma-Ray Burst Monitor detection
by GCN Circulars 24 Oct '25

24 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42414 SUBJECT: GRB 251023C: CALET Gamma-Ray Burst Monitor detection DATE: 25/10/24 04:00:02 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University <kawakubo(a)phys.aoyama.ac.jp> Y. Asaoka (ICRR), A. Yoshida, T. Sakamoto, S. Sugita, Y. Kawakubo (AGU), K. Yamaoka (Nagoya U), S. Nakahira (JAXA), S. Torii, Y. Akaike, K. Kobayashi (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U), N. Cannady (GSFC/UMBC), M. L. Cherry (LSU), S. Ricciarini (U of Florence), P. S. Marrocchesi (U of Siena), and the CALET collaboration: The long GRB 251023C (Swift/BAT-GUANO localization skymap: DeLaunay et al., GCN Circ 42412) triggered the CALET Gamma-ray Burst Monitor (CGBM) at 16:24:24.93 UTC on 23 October 2025 (https://cgbm.calet.jp/cgbm_trigger/flight/1445271383/index.html) The burst signal was seen by all CGBM detectors. The burst light curve shows a multi-peaked structure that starts at T+1.9 sec, peaks at T+3.7 sec, and ends at T+23.4 sec. The T90 and T50 durations measured by the SGM data are 18.7 +/- 1.4 sec and 5.7 +/- 0.8 sec (40-1000 keV), respectively. The ground-processed light curve is available at https://cgbm.calet.jp/cgbm_trigger/ground/1445271383/ The CALET data used in this analysis are provided by the Waseda CALET Operation Center located at Waseda University. View this GCN Circular online at https://gcn.nasa.gov/circulars/42414. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40490] GRB 251022A: GROWTH-India Telescope optical observations
by GCN Circulars 24 Oct '25

24 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42413 SUBJECT: GRB 251022A: GROWTH-India Telescope optical observations DATE: 25/10/24 01:01:59 GMT FROM: V. Swain at IIT Bombay <vishwajeet.s(a)iitb.ac.in> T. Mohan, V. Swain, A.P. Saikia, V. Bhalerao (IITB), G.C. Anupama, S. Barway (IIA) and K. Angail (IAO) report on behalf of the GIT team: We observed the field of Fermi GRB 251022A (Fermi GBM team, GCN 42380), with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2025-10-23 22:25:05 UT, i.e., 23.85 hours after the Fermi trigger. Multiple exposures were obtained in the r'-band, and we clearly detect the optical counterpart in the stacked image. The photometry result follows as: | MJD (mid) | tmid - t0 (hours) | Filter | Exposure (s) | Magnitude (AB) | | --------- | ----------------- | ------ | ------------ | -------------- | |60971.94474| 24.1 | r' | 5 x 360 | 20.89 +- 0.12 | The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction. Our magnitude is consistent with other optical observations (O’Neill et al., GCN 42386; Becerra et al., GCN 42394; Lipunov et al., GCN 42395; Mandarakas et al., GCN 42397). The GROWTH India Telescope (GIT; Kumar et al. 2022) is a 70-cm telescope with a 0.7-degree field of view, set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports the operations of the telescope. Telescope technical details are available at https://sites.google.com/view/growthindia/. View this GCN Circular online at https://gcn.nasa.gov/circulars/42413. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40489] GRB 251023C: Swift/BAT-GUANO localization skymap of a burst
by GCN Circulars 24 Oct '25

24 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42412 SUBJECT: GRB 251023C: Swift/BAT-GUANO localization skymap of a burst DATE: 25/10/24 00:54:24 GMT FROM: Jimmy DeLaunay at Penn State <delauj2(a)gmail.com> James DeLaunay (PSU), Samuele Ronchini (GSSI), Aaron Tohuvavohu (Caltech), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC), Maia Williams (Northwestern) report: Swift/BAT did not localize GRB 251023C onboard (T0: 2025-10-23T16:24:24.92 UTC, CALET Trig 1445271383) The CALET notice, distributed in near real-time, triggered the Swift Mission Operations Center operated Gamma-ray Urgent Archiver for Novel Opportunities (GUANO; Tohuvavohu et al. 2020, ApJ, 900, 1). Upon trigger by this notice, GUANO sent a command to the Swift Burst Alert Telescope (BAT) to save 90 seconds of BAT event-mode data from [-45,+45] seconds around the time of the burst. All the requested event mode data was delivered to the ground. The BAT likelihood search, NITRATES (DeLaunay + Tohuvavohu 2022, ApJ, 941, 169), performed on the temporal window [T0-20 s, T0+20 s], detects the burst with a sqrt(TS) of 26.0 in a 8.192 s analysis time bin, starting at T0 + 2.048 s. Using the NITRATES analysis, parameter estimation was performed to obtain the localization of this burst in the form of a HEALPIX Multi-Order Coverage (MOC) skymap. This localization accounts for both statistical and systematic errors. More details in the creation and calibration of these maps will soon be published (DeLaunay et al. 2025. in prep) The 90% credible area is 1,100 deg2 and the 50% credible area is 229 deg2. The integrated probability inside the coded field of view is <1%. A plot of the probability skymap can be viewed here: [skymap_plot](https://guano.swift.psu.edu/trigger_report?id=782929501/#:~:te… The probability skymap file can be downloaded from the link here [skymap_fits_file](https://guano.swift.psu.edu/files/782929501/0_n_PROBMAP) Instructions on how to read and manipulate this map can be found here: https://guano.swift.psu.edu/documentation More details about this burst can be found on the trigger report page here: https://guano.swift.psu.edu/trigger_report?id=782929501 GUANO is a fully autonomous, extremely low latency, spacecraft commanding pipeline designed for targeted recovery of BAT event mode data around the times of compelling astrophysical events to enable more sensitive GRB searches. A live reporting of Swift/BAT event data recovered by GUANO can be found at: https://www.swift.psu.edu/guano/ View this GCN Circular online at https://gcn.nasa.gov/circulars/42412. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40488] EP251023a: GROWTH-India Telescope optical observations
by GCN Circulars 24 Oct '25

24 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42411 SUBJECT: EP251023a: GROWTH-India Telescope optical observations DATE: 25/10/24 00:12:04 GMT FROM: V. Swain at IIT Bombay <vishwajeet.s(a)iitb.ac.in> T. Mohan (IITB), D. Eappachen (IIA), V. Swain (IITB), A.P. Saikia (IITB), V. Bhalerao (IITB), G.C. Anupama (IIA), S. Barway (IIA) and K. Angail (IAO) report on behalf of the GIT team: We observed the field of EP transient EP251023a (Wu et al., GCN 42388), with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2025-10-23 20:05:36 UT, i.e., 17.57 hours after the EP trigger. We obtained multiple exposures in g', r', and i' filters. We detect the optical afterglow in our stacked images, at the position reported by GOTO (Wortley et al., GCN 42387). The photometry result follows as: | MJD (mid) | tmid - t0 (hours) | Filter | Exposure (s) | Magnitude (AB) | | --------- | ----------------- | ------ | ------------ | -------------- | |60971.87998| 18.60 | r' | 5 x 360 | 20.39+-0.09 | |60971.90145| 19.12 | i' | 5 x 360 | 20.24+-0.11 | |60971.92296| 19.63 | g' | 5 x 360 | 20.88+-0.10 | The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction. Our magnitude is consistent with other optical observations (Wortley et al., GCN 42387; Li et al., GCN 42389; Liu et al., GCN 42391; Mandarakas et al., GCN 42400; Lipunov et al., GCN 42405; Selezneva et al., GCN 42406). The GROWTH India Telescope (GIT; Kumar et al. 2022) is a 70-cm telescope with a 0.7-degree field of view, set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports the operations of the telescope. Telescope technical details are available at https://sites.google.com/view/growthindia/. View this GCN Circular online at https://gcn.nasa.gov/circulars/42411. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40487] GRB 251022A: Fermi GBM Observation
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42410 SUBJECT: GRB 251022A: Fermi GBM Observation DATE: 25/10/23 22:45:23 GMT FROM: oindabimukherjee(a)gmail.com O. Mukherjee (USRA) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 22:34:15.26 UT on 22 October 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251022A (trigger 782865260/251022940) which was also detected by Fermi-LAT ( N. Di Lalla et al. 2025, GCN 42384), MASTER OT (V. Lipunov et al. 2025, GCN 42395), and Swift/BAT-GUANO (James DeLaunay et al. 2025, GCN 42409). The Fermi GBM on-ground location is consistent with the Fermi-LAT position. The angle from the Fermi LAT boresight is 36.5 degrees. The GBM light curve consists of multiple emission episodes with a duration (T90) of about 99.6 s (50-300 keV). The time-averaged spectrum from T0-1 to T0+107.5 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.88 +/- 0.04 and the cutoff energy, parameterized as Epeak, is 154 +/- 5 keV. The event fluence (10-1000 keV) in this time interval is (2.16 +/- 0.05)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+100 s in the 10-1000 keV band is 12.4 +/- 0.3 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak= 138 +/- 7 keV, alpha = -0.8 +/- 0.05 and beta = -2.6 +/- 0.2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/" View this GCN Circular online at https://gcn.nasa.gov/circulars/42410. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40486] GRB 251022A: Swift/BAT-GUANO localization skymap of a burst
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42409 SUBJECT: GRB 251022A: Swift/BAT-GUANO localization skymap of a burst DATE: 25/10/23 20:18:12 GMT FROM: Jimmy DeLaunay at Penn State <delauj2(a)gmail.com> James DeLaunay (PSU), Samuele Ronchini (GSSI), Aaron Tohuvavohu (Caltech), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC), Maia Williams (Northwestern) report: Swift/BAT did not localize GRB 251022A onboard (T0: 2025-10-22T22:34:45.26 UTC, Fermi Trig 782865260) The Fermi notice, distributed in near real-time, triggered the Swift Mission Operations Center operated Gamma-ray Urgent Archiver for Novel Opportunities (GUANO; Tohuvavohu et al. 2020, ApJ, 900, 1). Upon trigger by this notice, GUANO sent a command to the Swift Burst Alert Telescope (BAT) to save 200 seconds of BAT event-mode data from [-50,+150] seconds around the time of the burst. All the requested event mode data was delivered to the ground. The BAT likelihood search, NITRATES (DeLaunay + Tohuvavohu 2022, ApJ, 941, 169), performed on the temporal window [T0-20 s, T0+50 s], detects the burst with a sqrt(TS) of 26.2 in a 2.048 s analysis time bin, starting at T0 + 32.560 s. The main peak was outside the typical search window of [T0-20 s, T0+20 s], so we expanded it in this case. Using the NITRATES analysis, parameter estimation was performed to obtain the localization of this burst in the form of a HEALPIX Multi-Order Coverage (MOC) skymap. This localization accounts for both statistical and systematic errors. More details in the creation and calibration of these maps will soon be published (DeLaunay et al. 2025. in prep) The 90% credible area is 2,100 deg2 and the 50% credible area is 380 deg2. The integrated probability inside the coded field of view is <1%. The NITRATES skymap is consistent with the Fermi localization reported in the final position notice (GCN 42380). The combined Fermi/GBM+NITRATES 90% credible area is 111 deg2 and the 50% credible area is 29 deg2. The NITRATES and combined Fermi/GBM+NITRATES skymaps are consistent with the Fermi/LAT (GCN 42384) and optical afterglow positions (GOTO GCN 42386, DDOTI GCN 42394, MASTER GCN 42395). A plot of the probability skymap can be viewed here: [skymap_plot](https://guano.swift.psu.edu/trigger_report?id=782865321/#:~:te… The probability skymap and joint skymap files can be downloaded from the links here [skymap_fits_file](https://guano.swift.psu.edu/files/782865321/0_n_PROBMAP) [joint_skymap_fits_file](https://guano.swift.psu.edu/files/782865321/0_n_JOI… Instructions on how to read and manipulate this map can be found here: https://guano.swift.psu.edu/documentation More details about this burst can be found on the trigger report page here: https://guano.swift.psu.edu/trigger_report?id=782865321 GUANO is a fully autonomous, extremely low latency, spacecraft commanding pipeline designed for targeted recovery of BAT event mode data around the times of compelling astrophysical events to enable more sensitive GRB searches. A live reporting of Swift/BAT event data recovered by GUANO can be found at: https://www.swift.psu.edu/guano/ View this GCN Circular online at https://gcn.nasa.gov/circulars/42409. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40485] GRB 251023A: Glowbug gamma-ray detection
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42408 SUBJECT: GRB 251023A: Glowbug gamma-ray detection DATE: 25/10/23 20:15:38 GMT FROM: richard.s.woolf.civ(a)us.navy.mil R. Woolf, C.C. Cheung, M. Kerr, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report: The Glowbug gamma-ray telescope [1,2,3], operating on the International Space Station, reports the detection of GRB 251023A, which was also detected by Fermi/GBM (GCN 42385). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2025-10-23 05:57:43.480 with a duration of 4.1 s and a total significance of about 9.1 sigma. The light curve comprises a single peak. Note that data from ~T0-1s to T0+1s suffered from deadtime in various detectors. The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS. Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC. It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS, and operated until 2024 April when it was put in safe storage on orbit. Glowbug was removed from storage and resumed operation on 2025 September 12. [1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959 [2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O [3] Woolf, R.S. et al. 2024, Proc. SPIE, 13151, id. 1315108 Distribution Statement A: Approved for public release. Distribution is unlimited. View this GCN Circular online at https://gcn.nasa.gov/circulars/42408. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40484] GRB 251023B: Glowbug gamma-ray detection
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42407 SUBJECT: GRB 251023B: Glowbug gamma-ray detection DATE: 25/10/23 19:43:30 GMT FROM: C.C. Cheung at Naval Research Lab <Teddy.Cheung(a)nrl.navy.mil> C.C. Cheung, R. Woolf, M. Kerr, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report: The Glowbug gamma-ray telescope [1,2,3], operating on the International Space Station, reports the detection of GRB 251023B, which was also detected by MAXI (as MAXI J0451+122; GCN 42392) and CALET (GCN 42402), and possibly associated with the Einstein Probe/WXT-detected source EP#01709247298 (GCN 42401). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2025-10-23 08:48:53.664 with a duration of 7.9 s and a total significance of about 7.0 sigma. The onset measured by Glowbug is 9.4 s prior to the MAXI-reported T0. The Glowbug light curve is dominated by a single peak corresponding to the maximum in the CALET light curve (GCN 42402). The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS. Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC. It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS, and operated until 2024 April when it was put in safe storage on orbit. Glowbug was removed from storage and resumed operation on 2025 September 12. [1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959 [2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O [3] Woolf, R.S. et al. 2024, Proc. SPIE, 13151, id. 1315108 Distribution Statement A: Approved for public release. Distribution is unlimited. View this GCN Circular online at https://gcn.nasa.gov/circulars/42407. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40483] EP251023a: ULL-ASTRO-MASTER detection of the optical afterglow with LCO 40-cm telescope at Teide Observatory
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42406 SUBJECT: EP251023a: ULL-ASTRO-MASTER detection of the optical afterglow with LCO 40-cm telescope at Teide Observatory DATE: 25/10/23 19:23:09 GMT FROM: Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf(a)iac.es> A. Selezneva, J. Basurto Merino, P.G. Berdayes, A. Caballero-Almagro, A. Cerón, M. Contreras, F. Díaz-Segado, T. Ferrer-Laviña, B. Gandolfi, V. Ghiraldo, J. Hernández Fung, L. Juliá-Maroto, E. Lekaroz-Urriza, M. Manzano García, E. Mejía-Martínez, J. Prieto Polo, M. Pulido-Torres, M. Quintana-Ansaldo, A. Schenone-Zanuzzi, T. Tundidor Rodríguez, E. Urquijo-Rodríguez (all ULL), M. Abdul-Masih (IAC and ULL), and I. Pérez-Fournon (IAC and ULL). Following the detection of the X-ray transient EP251023a by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (ID: 01709247295, Wu et al., GCN circ. 42388), we observed the field with one of the two Las Cumbres Observatory (LCO) 40-cm telescopes (Planewave Delta Rho 350 telescopes equipped with QHY600 CMOS cameras) located at the LCO node at Teide Observatory (Tenerife, Canary Islands, Spain). The observation, a single exposure of 300 sec in the SDSS r filter, started on 2025-10-23 at 06:09:24 UT, about 3.64 hours after the EP-WXT trigger. The optical counterpart detected by GOTO (GOTO25ixt, Wortley et al., GCN circ. 42387) is clearly detected in our image with a magnitude of r = 18.69 +/- 0.10 (AB), calibrated against PanSTARRS-1 DR2 stars and not corrected for galactic extinction, that is consistent with other optical detections at similar epochs (Li et al., GCN circ. 42389; Liu et al., GCN circ. 42391) and brighter than the COLIBRÍ detection at a later epoch (Mandarakas et al., GCN circ. 42400). A redshift of z = 2.232 has been measured by Chornock (GCN circ. 42398) using Keck/LRIS. Based on observations made with the Las Cumbres Observatory’s education network telescopes that were upgraded through generous support from the Gordon and Betty Moore Foundation (LCO program IAC2025B-010). These observations are part of a course in Astrophysical Techniques of the Master in Astrophysics of the Astrophysics Department of the University of La Laguna in collaboration with the Instituto de Astrofísica de Canarias (La Laguna, Tenerife, Canary Islands, Spain). This work made use of the Astro-COLIBRI platform (P. Reichherzer et al. 2021, ApJS, 256, 5). View this GCN Circular online at https://gcn.nasa.gov/circulars/42406. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40482] EP251023a: Global MASTER-Net observations report
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42405 SUBJECT: EP251023a: Global MASTER-Net observations report DATE: 25/10/23 17:18:38 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-Tunka robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Applied Physics Institute, Irkutsk State University) was pointed to the EP251023a ( EP Team et al., GCN 42388) errorbox 27379 sec after notice time and 51442 sec after trigger time at 2025-10-23 16:48:31 UT, with upper limit up to 18.2 mag. The observations began at zenith distance = 80 deg. The sun altitude is -50.5 deg. The galactic latitude b = 31 deg., longitude l = 204 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3021715 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 51472 | 2025-10-23 16:48:31 | MASTER-Tunka | (08h 28m 06.31s , +20d 38m 18.3s) | C | 60 | 18.2 | 51472 | 2025-10-23 16:48:31 | MASTER- | (08h 28m 21.58s , +20d 31m 55.6s) | C | 60 | 18.2 | 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/42405. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40481] GRB 251023B / EP#01709247298: COLIBRÍ optical counterpart candidate
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42404 SUBJECT: GRB 251023B / EP#01709247298: COLIBRÍ optical counterpart candidate DATE: 25/10/23 16:26:48 GMT FROM: nikos.mandarakas(a)lam.fr Nikos Mandarakas (LAM), Ramandeep Gill (UNAM), Jean-Grégoire Ducoin (CPPM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), 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): We imaged the field of the GRB 251023B / EP#01709247298, that might be associated with MAXI J0451+122 (Kang et al., GCN Circ. 42392) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2025-10-23 10:14:07 to 11:41:55 UTC (from 1.42 to 2.88 hours after the trigger) and obtained 32 minutes of simultaneous exposure in the r and z filters. The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). 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 detect an uncatalogued source consistent with the XRT 3.7 arcsec error circle (Evans et al., GCN Circ. 42401) at: RA(J2000) = 04:54:00.63 = 73.50263 degrees Dec(J2000) = 12:39:28.4 = 12.65789 degrees with an uncertainty of 0.5 arcsec. The preliminary magnitudes derived for that source is: r = 21.86 +/- 0.04 z = 20.45 +/- 0.04 Further observations are planned. 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/42404. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40480] IPN triangulation of GRB 251016B
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42403 SUBJECT: IPN triangulation of GRB 251016B DATE: 25/10/23 16:17:46 GMT FROM: Dmitry Svinkin at Ioffe Institute <svinkin(a)mail.ioffe.ru> A.S. Kozyrev, D.V. Golovin, M.L. Litvak, I.G. Mitrofanov, and A.B. Sanin on behalf of the MGNS/BepiColombo and HEND/Mars Odyssey teams, J. Benkhoff on behalf of the BepiColombo team, D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia, and T. Cline on behalf of the Konus-Wind team, A. Goldstein, M. S. Briggs, C. Wilson-Hodge, and E. Burns on behalf of the Fermi-GBM team, S. Barthelmy, J. Cummings, H. Krimm, D. Palmer, A. Tohuvavohu, and J. DeLaunay on behalf of the Swift-BAT team, and W. Boynton, C. Fellows, K. Harshman, H. Enos, R. Starr, and A.S. Gardner on on behalf of the GRS-Odyssey GRB team, report: The long-duration GRB 251016B (Ferm-GBM detection: The Fermi GBM team, GCN 42316; Godwin et al., GCN 42383; CALET-GBM detection: Yamaoka et al., GCN 42320; AstroSat-CZTI detection: Harsha et al., GCN 42324) was detected by Fermi (GBM trigger 782351945), CALET (GBM), AstroSat (CZTI), Konus-Wind, Swift (BAT), Mars-Odyssey (HEND), and BepiColombo (MGNS), at about 86340 s UT (23:59:00). The burst was outside the coded field of view of the BAT. We have triangulated it to a preliminary, 3 sigma error box whose coordinates are: --------------------------------------------- RA(2000), deg Dec(2000), deg --------------------------------------------- Center: 180.582 (12h 02m 20s) +57.856 (+57d 51' 21") Corners: 173.603 (11h 34m 25s) +54.048 (+54d 02' 53") 182.331 (12h 09m 19s) +58.703 (+58d 42' 09") 191.445 (12h 45m 47s) +61.827 (+61d 49' 37") 178.988 (11h 55m 57s) +57.018 (+57d 01' 07") --------------------------------------------- The error box area is 2295 sq. arcmin, and its maximum dimension is 12.186 deg (the minimum one is 5 arcmin). The Sun distance was 69 deg. This localization may be improved. A triangulation map and HEALPix FITS file are posted at http://www.ioffe.ru/LEA/GRBs/GRB251016_T86340/IPN/ The HEALPix triangulation map is the multi-order HEALPix in units of probability density. The Konus-Wind time history and spectrum will be given in a forthcoming GCN Circular. View this GCN Circular online at https://gcn.nasa.gov/circulars/42403. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40479] GRB 251023B: CALET Gamma-Ray Burst Monitor detection
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42402 SUBJECT: GRB 251023B: CALET Gamma-Ray Burst Monitor detection DATE: 25/10/23 16:16:02 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University <kawakubo(a)phys.aoyama.ac.jp> S. Nakahira (JAXA), A. Yoshida, T. Sakamoto, S. Sugita, Y. Kawakubo (AGU), K. Yamaoka (Nagoya U), Y. Asaoka (ICRR), S. Torii, Y. Akaike, K. Kobayashi (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U), N. Cannady (GSFC/UMBC), M. L. Cherry (LSU), S. Ricciarini (U of Florence), P. S. Marrocchesi (U of Siena), and the CALET collaboration: The long GRB 251023B (MAXI/GSC Detection: Kang et al., GCN Circ 42392) was detected in the ground analysis of the CALET Gamma-ray Burst Monitor (CGBM) data around 08:49:03 on 23 October 2025 (referenced to the MAXI detection: GCN Circ. 42392). (https://cgbm.calet.jp/cgbm_trigger/flight/1445244062/index.html) The burst signal was seen by all CGBM detectors. The burst light curve shows a multi-peaked structure that starts at T-31.7 sec and ends at T+8.2 sec. The T90 and T50 durations measured by the HXM2 data are 34.9 +/- 4.2 sec and 16.7 +/- 2.2 sec (7-100 keV), respectively. The ground-processed light curve is available at https://cgbm.calet.jp/cgbm_trigger/ground/1445244062/ The CALET data used in this analysis are provided by the Waseda CALET Operation Center located at Waseda University. View this GCN Circular online at https://gcn.nasa.gov/circulars/42402. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40478] EP#01709247298: Swift-XRT counterpart detection
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42401 SUBJECT: EP#01709247298: Swift-XRT counterpart detection DATE: 25/10/23 15:35:42 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P.A. Evans (U. Leicester), J.A. Kennea (PSU), E. Ambrosi (INAF-IASFPA) , A.P. Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB), R. Brivio (INAF-OAB), D.N. Burrows (PSU), S. Campana (INAF-OAB), M. Capalbi (INAF-OAR), A. D'Ai (INAF-IASFPA), P. D'Avanzo (INAF-OAB), V. D'Elia (SSDC & INAF-OAR), S. Dichiara (PSU), M. Ferro (INAF-OAB), A. Melandri (INAF-OAR), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), M. Perri (SSDC & INAF-OAR), C. Salvaggio (INAF-OAB), T. Sbarrato (INAF-OAB), B. Sbarufatti (INAF-OAB), M.A. Williams (PSU) report on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the Einstein Probe/WXT-detected source EP#01709247298, collecting 1.6 ks of Photon Counting (PC) mode data between T0+6.6 ks and T0+8.3 ks after the trigger. A likely counterpart has been found. This source is 43 arcmin from the position of the MAXI-detected transient GRB 251023B / MAXI J0451+122 (Kang et al., GCN Circ. 42392), well outside their error region, thus its association, while likely on temporal grounds, remains unconfirmed. The details of this source are: Source 1 (SWIFT J045400.4+123929): ================================== RA (J2000.0): 73.5018 = 04 54 00.43 Dec (J2000.0): +12.6583 = +12 39 29.9 Error: 3.7 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 22 arcsec from the Einstein Probe/WXT position. Mean rate: 0.152 +/- 0.011 ct s^-1 Mean flux: (5.94 +/- 0.44)e-12 erg cm^-2 s^-1 Peak rate: 0.221 +/- 0.049 ct s^-1 Peak flux: (8.6 +/- 1.9)e-12 erg cm^-2 s^-1 ECF: 3.91e-11 erg cm^-2 ct^-1 assuming NH=3.15e+21 cm^-2, gamma=1.97 determined from a spectral fit. XMM UL: 2.3e-12 erg cm^-2 s^-1, (0.3-10 keV) so the source is 3.2-sigma above this 3-sigma upper limit. All fluxes are 0.3-10 keV, observed. For all flux conversions and comparisons with catalogues and upper limits from other missions, we assumed a power-law spectrum with NH=3x10^20 cm^-2 and photon index (Gamma)=1.7 unless otherwise stated. The results of the XRT-team automatic analysis of the XRT observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/EP/EP_FIELD00077. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42401. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40477] EP251023a: COLIBRÍ optical observations
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42400 SUBJECT: EP251023a: COLIBRÍ optical observations DATE: 25/10/23 15:22:43 GMT FROM: nikos.mandarakas(a)lam.fr Nikos Mandarakas (LAM), Ramandeep Gill (UNAM), Jean-Grégoire Ducoin (CPPM), Alan M. Watson (UNAM), Noémie Globus (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Kin Ocelotl López (UNAM), 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): We imaged the field of the EP251023a (Wu et al., GCN Circ. 42388) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2025-10-23 09:29 to 10:57 UTC (from 7.0 to 8.4 hours after the trigger) and obtained 32 minutes of simultaneous exposure in the r and z filters, alternating with other observations. The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). 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 firstly identified by GOTO (Wortley et al., GCN Circ. 42387) and subsequently reported by Las Cumbres Observatory (Li et al., GCN Circ. 42389) and NOT (Liu et al., GCN Circ. 42391) at preliminary magnitudes of: r = 18.82 +/- 0.01 z = 18.52 +/- 0.01 Further observations are planned. 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/42400. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40476] GRB 251013C: further SAO RAS optical observations
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42399 SUBJECT: GRB 251013C: further SAO RAS optical observations DATE: 25/10/23 14:44:06 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. S. Moskvitin, O. I. Spiridonova, V. V. Vlasyuk (SAO RAS) report on behalf of GRB follow-up collaboration. We observed the field of the GRB 251013C (The Fermi GBM team, GCN 42221; Rakotondrainibe et al., GCN 42222) with the 1-m SAO RAS telescope Zeiss-1000 equipped with the CCD-photometer on October 20 and 21 nights. The optical afterglow (Palmerio et al., GCN 42223; Perez-Garcia et al., GCN 42225; Konno et al., GCN 42226; Martin-Carrillo et al., GCN 42227; Masi, GCN 42228; Palmerio et al., GCN 42229; Moskvitin et al., GCN 42230; Gompertz et al., GCN 42231; Lipunov et al., GCN 42235; Garnavich, GCN 42240; Watson et al., GCN 42241; López-Cámara et al., GCN 42242; Brosio et al., GCN 42251; Reguitti, GCN 42253; Quintana-Ansaldo et al., GCN 42254; Maksut et al., GCN 42256; Ghosh et al., GCN 42261; Quadri et al., GCN 42262; Adami et al., GCNs 42266, 42276, 42338; Peretto et al., GCN 42267; Ruocco et al., GCN 42269; Calapai, GCN 42275; Globus et al., GCN 42279; Evans, GCN 42281; Abidkhanov et al., GCN 42283; Siegel, GCN 42298; Leonini et al, GCN 42301; Méndez et al., GCN 42318; He et al., GCN 42319; Pavoni et al., GCN 42333; Bochenek and Perley, GCN 42334; Volnova et al., GCN 42396) is clearly detected in the stacked images with the following brightness. Date UT start t-T0 Exp. Filter OT Err. UL (mid, d) (s) 2025.10.20 19:59:38 7.12682 13 x 300 Rc 21.61 +/- 0.11 22.7 2025.10.21 17:02:31 8.01103 19 x 300 Rc 21.80 +/- 0.10 23.0 Preliminary photometry is based on the nearby SDSS objects (magnitudes converted with Lupton 2005 equations) and has not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/42399. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40475] EP251023a: Keck/LRIS spectroscopic redshift z=2.232
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42398 SUBJECT: EP251023a: Keck/LRIS spectroscopic redshift z=2.232 DATE: 25/10/23 14:39:53 GMT FROM: Ryan Chornock at UC Berkeley <chornock(a)berkeley.edu> R. Chornock (UC Berkeley) reports: We observed the optical afterglow (Wortley et al., GCN 42387; Li et al., GCN 42389; Liu et al. GCN 42391) of the X-ray transient EP251023a (Wu et al., GCN 42388) using the Low-Resolution Imaging Spectrometer on the Keck-I telescope at a mean time of 13:26UT on 2025 October 23 (~10.9 hours after the EP trigger). Observations covered the range 3100-10300 Angstroms. The afterglow remains bright and the continuum is well detected across the full spectral range. Multiple absorption systems are present, but the highest redshift absorber has many absorption lines (including Lyman-alpha, Si II, Si II*, O I, O I*, C II, Si IV, C IV, Fe II, Mg I and Mg II) present at a common redshift of z=2.232+/-0.001. View this GCN Circular online at https://gcn.nasa.gov/circulars/42398. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40474] GRB 251022A: COLIBRÍ optical observations
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42397 SUBJECT: GRB 251022A: COLIBRÍ optical observations DATE: 25/10/23 14:12:44 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Nikos Mandarakas (LAM), Ramandeep Gill (UNAM), Jean-Grégoire Ducoin (CPPM), Alan M. Watson (UNAM), Noémie Globus (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Kin Ocelotl López (UNAM), 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): We imaged the field of the Fermi GRB 251022A (Di Lalla et al., GCN Circ. 42384) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2025-10-23 06:12:44 to 07:32:34 UTC (from 7.64 to 8.97 hours after the trigger) and obtained 16 and 3 minutes of exposure in the r and z filters respectively. The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). 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 reported by O’Neill et al. (GCN Circ. 42386), Becerra et al. (GCN Circ. 42394), and Lipunov et al. (GCN Circ. 42395) at preliminary magnitudes of: r = 18.97 +/- 0.01 z = 18.54 +/- 0.04 Further observations are planned. 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/42397. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40473] GRB 251013C: ISON-Castelgrande observatory optical observations
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42396 SUBJECT: GRB 251013C: ISON-Castelgrande observatory optical observations DATE: 25/10/23 12:56:23 GMT FROM: Alina Volnova at IKI RAS <alinusss(a)gmail.com> A. Volnova (IKI), S. Schmalz (KIAM), A. Schmalz (KIAM), A. Pozanenko (IKI), N. Pankov (IKI, HSE), F. Graziani (GAUSS Srl) report on behalf of IKI GRB-FuN: We observed field of the GRB 251013C (Fermi GBM team, GCN 42221; Rakotondrainibe et al., GCN 42222) with ORI-22 telescope of ISON-Castelgrande observatory. Observation started on 2025-10-13 (UT) 21:40:38, i.e. ~2 hours after the GRB trigger. The series consists of 165 images with an exposure of 60 s in a Clear filter. The optical afterglow (Palmerio et al., GCN 42223; Perez-Garcia et al., GCN 42225; Konno et al., GCN 42226; Martin-Carrillo et al., GCN 42227; Masi, GCN 42228; Palmerio et al., GCN 42229; Moskvitin et al., GCN 42230; Gompertz et al., GCN 42231; Lipunov et al., GCN 42235; Garnavich, GCN 42240; Watson et al., GCN 42241; López-Cámara et al., GCN 42242; Brosio et al., GCN 42251; Reguitti, GCN 42253; Quintana-Ansaldo et al., GCN 42254; Maksut et al., GCN 42256; Ghosh et al., GCN 42261; Quadri et al., GCN 42262; Adami et al., GCNs 42266, 42276, 42338; Peretto et al., GCN 42267; Ruocco et al., GCN 42269; Calapai, GCN 42275; Globus et al., GCN 42279; Evans, GCN 42281; Abidkhanov et al., GCN 42283; Siegel, GCN 42298; Leonini et al, GCN 42301; Méndez et al., GCN 42318; He et al., GCN 42319; Pavoni et al., GCN 42333; Bochenek and Perley, GCN 42334) is clearly detected, and the preliminary photometry of the stacked frames is the following: Date UT start t-T0 Exp. Filter OT Err. UL (mid,days) (n*s) (3sigma) 2025-10-13 21:40:38 0.17290 15*60 Clear 16.75 0.10 18.0 2025-10-13 21:56:47 0.18487 15*60 Clear 16.86 0.08 18.0 2025-10-13 22:15:08 0.19875 20*60 Clear 17.00 0.10 18.1 2025-10-13 22:37:50 0.21452 20*60 Clear 17.19 0.11 18.1 2025-10-13 22:59:27 0.23325 30*60 Clear 17.47 0.12 18.3 2025-10-13 23:31:46 0.25573 30*60 Clear 17.35 0.13 18.1 2025-10-14 00:04:13 0.28013 35*60 Clear 17.54 0.19 17.9 The photometry is based on several nearby SDSS stars (R-magnitudes Lupton's transformation) and is not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/42396. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40472] GRB 251022A: MASTER OT detection
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42395 SUBJECT: GRB 251022A: MASTER OT detection DATE: 25/10/23 12:43:30 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V. Lipunov, I.Panchenko, A.Kuznetsov, O.Gress, G.Antipov, P.Balanutsa, E.Gorbovskoy, K.Zhirkov, N.Tiurina, A.Sankovich, Ya.Kechin, A.Chasovnikov, V.Topolev, D.Vlasenko, V.Senik, D.Vlasenko, V.Shumkov, K.Vetrov, Yu. Tselik, M.Shilova(Lomonosov MSU, SAI, Moscow), R.Podesta, C.Francile, F. Podesta, E. Gonzalez (OAFA, San Juan Uni.,Argentina); D.Buckley (SAAO, South Africa), N.Budnev (ISU, Irkutsk), A.Sosnovskij (CrAO RAS), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), V.M.Pillet, R.Rebolo Lopez (The Instituto de Astrofisica de Canarias, Spain), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez,J.Martinez,A.R.Corella,L.H.Rodriguez (INAOE, Guillermo Haro Astrophysic Observatory, Mexico) MASTER Global Robotic Net [1-4] started Fermi GRB 251022A (GCNC 42380, Ttrigger=2025-10-22 22:34:15.26 ,GBM_notice=2025-10-22 22:43:43, LAT_notice=2025-10-23 03:04:17UT, LAT_center=04 21 31.18 -19 18 35.6 +-0.32deg (Di Lalla et al. GCN 42384) at MASTER-SAAO and MASTER-OAFA (Lipunov et al. GCNC 42381) 13s after LAT_notice_time (16215s after trigger time) There is MASTER OT J042159.34-185510.4 since 2025-10-23 03:04:54UT with unfiltered m_OT=18.0. This OT can be on MASTER very wide field images at earlier images in MASTER-Tunka, that started GBM error-filed observations in alert mode, the reduction will be continued. This OT was discovered by GOTO (O'Neill et al. GCNC 42386) and also observed by DDOTI (Becerra et al. GCNC 42394) We analyzed SWIFT XRT candidates (Evans et al. GCNC42382, https://www.swift.ac.uk/xrt_products/TILED_GRB00139/ ) The first one ( 04h 20m 03.25s -19° 19′ 50.1″) coincides with QSO (UV/GALEX, xray/eROSITA detection) in 2.8" from center of SWIFT error-box. The second one (04 20 23.62 -19 15 45.2) coincides with second QSO (see VIZIER for full information) in 2.5" from the center of Swift error-box. Both has complicated light curves without significant details at 23 oct 2025. Observation and reduction will be continued. [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 V., Kornilov V., Gorbovskoy E., Tiurina N., Kuznetsov A. 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics,Lomonosov MSU PRESS, 591pp. http://www.pereplet.ru/lipunov/625.html#625 View this GCN Circular online at https://gcn.nasa.gov/circulars/42395. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40471] GRB 251022A: DDOTI Optical Detection
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42394 SUBJECT: GRB 251022A: DDOTI Optical Detection DATE: 25/10/23 11:09:52 GMT FROM: Rosa Leticia Becerra Godínez at Instituto de Astronomía, UNAM <rbecerra(a)astro.unam.mx> Rosa L. Becerra (U Roma), Simone Dichiara (Penn State University), Eleonora Troja (U Roma), Alan M. Watson (UNAM), Camila Angulo Valdez (UNAM), Sahil Atri (U Roma), Nat Butler (ASU), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Océlotl López (UNAM) and Margarita Pereyra (UNAM) report: We observed the field of GRB 251022A detected by Fermi/GBM (Fermi GBM Team, GCN Circ. 42380) and Fermi/LAT (Di Lalla et al., GCN Circ. 42384) with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on Sierra San Pedro Mártir (http://ddoti.astroscu.unam.mx) on the night of 2025-10-23 UTC. DDOTI covered the entire Fermi/GBM error region from 07:00 UTC to 10:16 UTC (from T+8.4 h to T+ 11.7 h after the trigger), obtaining a total exposure of 80 minutes, alternating with other scientific programs. Comparing our observations to the USNO-B1 and Pan-STARRS PS1 DR2 catalogues, our system automatically identified the fading nature of the optical candidate previously reported by GOTO (O’Neill et al., GCN Circ. 42386) with a preliminary AB magnitude of: w = 19.45 +/- 0.04. Further observations and analysis are on going. 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/42394. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40470] EP251021b/GRB 251021A: SVOM/VT optical candidate
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42393 SUBJECT: EP251021b/GRB 251021A: SVOM/VT optical candidate DATE: 25/10/23 10:18:34 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H.L. Li , L.P. Xin, Y. L. Qiu, C. Wu, Y.N. Ma, Z.H. Yao, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA) report on behalf of the SVOM/VT team. SVOM/VT performed ToO observation to the field of EP251021b/GRB 251021A (Dai et al., GCN 42377; Ravasio et al., GCN 42379). The observation stared at 2025-10-22T20:09:33 UTC, I.e., 29.69 hours post trigger in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. Within the error box of EP-FXT (Dai et al., GCN 42377), an uncatalogued source was detected, compared to the Legacy survey DR9 catalog. The position is at R.A., Dec. = 306.745094, -38.3034732 degrees, equivalent to: R.A. (J2000) = 20:26:58.82 Dec. (J2000) = -38:18:12.50 with an uncertainty of 0.5 arcsec. The candidate's magnitudes are given below: Mid_time Band Exposure Time Magnitude (AB) 30.75 hour VT_B 45*70 sec 23.62+/-0.25 mag 30.75 hour VT_R 54*70 sec 22.80+/-0.20 mag Our photometry was derived in AB magnitude and not corrected for Galactic extinction. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/42393. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40469] GRB 251023B / MAXI J0451+122: MAXI/GSC detection
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42392 SUBJECT: GRB 251023B / MAXI J0451+122: MAXI/GSC detection DATE: 25/10/23 10:08:49 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University <kawakubo(a)phys.aoyama.ac.jp> C. Kang (Ehime U.), M. Nakajima (Nihon U.), Y. Kawakubo (AGU), H. Negoro, K. Takagi, H. Takahashi, H. Nishio (Nihon U.), T. Mihara, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN), T. Sakamoto, M. Serino, S. Sugita, H. Hiramatsu, Y. Kondo, A. Yoshida (AGU), Y. Tsuboi, H. Sugai, N. Nagashima, Y. Ishihara (Chuo U.), M. Shidatsu, T. Nakamoto (Ehime U.), I. Takahashi, Y. Yatsu (Science Tokyo), S. Nakahira, S. Ueno, H. Tomida, M. Ishikawa, S. Ogawa, M. Kurihara (JAXA), Y. Ueda, K. Fujiwara (Kyoto U.), M. Yamauchi, M. Nishio, C. Hiraizumi (Miyazaki U.), K. Yamaoka (Nagoya U.), M. Sugizaki (Kanazawa U.), W. Iwakiri (Chiba U.), T. Kawamuro (Osaka U.), S. Yamada (Tohoku U) report on behalf of the MAXI team: The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient source at 08:49:03 UT on October 23, 2025. Assuming that the source flux was constant over the transit, we obtain the source position at (R.A., Dec) = (72.930 deg, 12.205 deg) = (04 51 43, +12 12 18) (J2000) with a statistical 90% C.L. elliptical error region with long and short radii of 0.15 deg and 0.13 deg, respectively. The roll angle of long axis from the north direction is 71.0 deg counterclockwise. There is an additional systematic uncertainty of 0.1 deg (90% containment radius). The X-ray flux averaged over the scan was 341 +- 36 mCrab (4.0-10.0keV, 1 sigma error). Without assumptions on the source constancy, we obtain a rectangular error box for the transient source with the following corners: (72.360, 11.893) deg = (04 49 26, +11 53 34) (J2000) (72.539, 11.711) deg = (04 50 09, +11 42 39) (J2000) (73.436, 12.551) deg = (04 53 44, +12 33 03) (J2000) (73.256, 12.734) deg = (04 53 01, +12 44 02) (J2000) There was no significant excess flux in the previous transit at 07:16 UT with an upper limit of 20 mCrab for each. View this GCN Circular online at https://gcn.nasa.gov/circulars/42392. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40468] EP251023a: NOT optical counterpart detection
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42391 SUBJECT: EP251023a: NOT optical counterpart detection DATE: 25/10/23 10:01:31 GMT FROM: liuxing(a)nao.cas.cn X. Liu, Z.P. Zhu, L.B. He, J. An, S.Q. Jiang, D. Xu (NAOC), J.P.U. Fynbo (DAWN/NBI), Niko Pyykkinen (NOT) report on behalf of a large collaboration: We observed the field of the EP251023a (Wu et al., GCN 42388) using the 2.56m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observation started at 05:55:11 UTC on 2025-10-23, i.e., 3.4 hours after the EP trigger, and a series of frames were obtained in the Sloan r- and z- bands. Within the EP/FXT localization error region (Wu et al., GCN 42388), the optical counterpart (Wortley et al., GCN 42387; Li et al., GCN 42389) is also clearly detected in both r- and z- bands with magnitudes as follows: T-mid (hr) | Filter | Exposure | Mag 3.49 | r | 3x200s | 18.57 +- 0.01 3.72 | z | 5x150s | 18.36 +- 0.01 calibrated against nearby Pan-STARRS stars and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/42391. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40467] Fermi GRB 251023A: Global MASTER-Net observations report
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42390 SUBJECT: Fermi GRB 251023A: Global MASTER-Net observations report DATE: 25/10/23 09:15:24 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-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) started inspect of the Fermi GRB 251023A ( Fermi GBM team, GCN 42385) errorbox 665 sec after notice time and 686 sec after trigger time at 2025-10-23 06:09:10 UT, with upper limit up to 20.7 mag. The observations began at zenith distance = 29 deg. The sun altitude is -40.0 deg. The galactic latitude b = -56 deg., longitude l = 180 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3021658 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 717 | 2025-10-23 06:09:10 | MASTER-OAFA | (02h 36m 41.44s , -06d 42m 24.3s) | C | 60 | 20.6 | 792 | 2025-10-23 06:10:25 | MASTER-OAFA | (02h 36m 48.65s , -06d 42m 09.1s) | C | 60 | 20.6 | 880 | 2025-10-23 06:11:53 | MASTER-OAFA | (02h 51m 27.06s , -04d 47m 02.9s) | C | 60 | 20.4 | 956 | 2025-10-23 06:13:09 | MASTER-OAFA | (02h 51m 25.90s , -04d 46m 08.3s) | C | 60 | 20.4 | 1045 | 2025-10-23 06:14:38 | MASTER-OAFA | (02h 29m 25.20s , -08d 34m 50.8s) | C | 60 | 20.3 | 1120 | 2025-10-23 06:15:53 | MASTER-OAFA | (02h 37m 24.96s , -08d 34m 57.2s) | C | 60 | 20.4 | 1197 | 2025-10-23 06:17:10 | MASTER-OAFA | (02h 29m 18.79s , -08d 34m 44.5s) | C | 60 | 20.3 | 1272 | 2025-10-23 06:18:25 | MASTER-OAFA | (02h 37m 30.89s , -08d 35m 06.2s) | C | 60 | 20.4 | 1353 | 2025-10-23 06:19:46 | MASTER-OAFA | (02h 44m 42.03s , -08d 34m 33.8s) | C | 60 | 20.6 | 1429 | 2025-10-23 06:21:02 | MASTER-OAFA | (02h 52m 48.50s , -08d 32m 57.2s) | C | 60 | 20.5 | 1503 | 2025-10-23 06:22:16 | MASTER-OAFA | (02h 44m 48.52s , -08d 34m 42.6s) | C | 60 | 20.7 | 1579 | 2025-10-23 06:23:32 | MASTER-OAFA | (02h 52m 49.17s , -08d 35m 05.7s) | C | 60 | 20.4 | 1654 | 2025-10-23 06:24:47 | MASTER-OAFA | (02h 44m 47.30s , -08d 35m 42.7s) | C | 60 | 20.6 | 1733 | 2025-10-23 06:26:07 | MASTER-OAFA | (02h 52m 04.95s , -06d 40m 17.4s) | C | 60 | 20.2 | 1895 | 2025-10-23 06:28:48 | MASTER-OAFA | (02h 51m 58.29s , -06d 40m 20.1s) | C | 60 | 20.2 | 1981 | 2025-10-23 06:30:14 | MASTER-OAFA | (02h 30m 14.33s , -10d 30m 32.8s) | C | 60 | 20.2 | 2057 | 2025-10-23 06:31:30 | MASTER-OAFA | (02h 38m 20.88s , -10d 28m 16.3s) | C | 60 | 20.5 | 2132 | 2025-10-23 06:32:45 | MASTER-OAFA | (02h 38m 22.92s , -10d 28m 22.0s) | C | 60 | 20.4 | 2215 | 2025-10-23 06:34:08 | MASTER-OAFA | (02h 59m 21.23s , -06d 41m 00.5s) | C | 60 | 20.0 | 2369 | 2025-10-23 06:36:42 | MASTER-OAFA | (02h 59m 20.42s , -06d 42m 09.2s) | C | 60 | 20.1 | 3339 | 2025-10-23 06:52:52 | MASTER-OAFA | (02h 39m 52.78s , -06d 23m 46.0s) | C | 60 | 19.5 | 3405 | 2025-10-23 06:53:58 | MASTER-OAFA | (02h 39m 52.75s , -06d 23m 44.1s) | C | 60 | 19.5 | 3470 | 2025-10-23 06:55:03 | MASTER-OAFA | (02h 39m 52.71s , -06d 23m 42.5s) | C | 60 | 19.6 | 3536 | 2025-10-23 06:56:09 | MASTER-OAFA | (02h 39m 52.68s , -06d 23m 41.2s) | C | 60 | 20.6 | 3601 | 2025-10-23 06:57:15 | MASTER-OAFA | (02h 39m 52.66s , -06d 23m 39.7s) | C | 60 | 20.6 | 3667 | 2025-10-23 06:58:20 | MASTER-OAFA | (02h 39m 52.65s , -06d 23m 38.5s) | C | 60 | 20.6 | 3734 | 2025-10-23 06:59:27 | MASTER-OAFA | (02h 39m 52.64s , -06d 23m 37.5s) | C | 60 | 20.6 | 3800 | 2025-10-23 07:00:33 | MASTER-OAFA | (02h 39m 52.62s , -06d 23m 36.4s) | C | 60 | 20.5 | 3865 | 2025-10-23 07:01:38 | MASTER-OAFA | (02h 39m 52.61s , -06d 23m 35.4s) | C | 60 | 20.5 | 3931 | 2025-10-23 07:02:44 | MASTER-OAFA | (02h 39m 52.60s , -06d 23m 34.4s) | C | 60 | 20.4 | 3997 | 2025-10-23 07:03:50 | MASTER-OAFA | (02h 39m 52.60s , -06d 23m 33.5s) | C | 60 | 20.5 | 4063 | 2025-10-23 07:04:56 | MASTER-OAFA | (02h 39m 52.59s , -06d 23m 32.6s) | C | 60 | 20.6 | 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/42390. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40466] EP251023a: GSP Optical Counterpart Detection
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42389 SUBJECT: EP251023a: GSP Optical Counterpart Detection DATE: 25/10/23 09:13:54 GMT FROM: Wenxiong Li at NAOC <liwenxiong1992(a)gmail.com> W. X. Li, S. J. Xue (NAOC); M. Andrews, J. Farah, D. A. Howell, M. Newsome, E. Padilla Gonzalez, C. McCully, and G. Terreran (Las Cumbres Observatory), on behalf of a larger collaboration, report optical follow-up observations of EP251023a (Wu et al. GCN 42388) obtained with a Las Cumbres Observatory (LCO) 1-m telescope at Teide Observatory, Tenerife, ~3.6 hours after the EP-WXT trigger. We acquired 2 × 300 s exposures using the broad optical w band. The optical counterpart reported by Wortley et al. (GCN 42387) is detected. Preliminary photometry, calibrated to the r band, yields r ≈ 18.5 mag (not corrected for Galactic extinction). No known source is found at this position in the MPC or other major catalogs. These observations were taken as part of the Global Supernova Project (GSP). View this GCN Circular online at https://gcn.nasa.gov/circulars/42389. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40465] EP251023a: Einstein Probe detection of an X-ray transient
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42388 SUBJECT: EP251023a: Einstein Probe detection of an X-ray transient DATE: 25/10/23 09:11:35 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y. Wu (NJU), D. F. Hu (PMO, CAS), H. N. Yang, T. Zhao, W. D. Zhang (NAO, CAS), on behalf of the Einstein Probe (EP) team: We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP251023a. The transient triggered EP-WXT (ID: 01709247295) at 2025-10-23T02:31:09 (UTC). The WXT position of the source is R.A. = 127.151 deg, Dec. = 20.871 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). We performed a Target-of-Opportunity observation with the Follow-up X-ray Telescope on board EP. The observation began at 2025-10-23T07:44:08 (UTC).An uncatalogued X-ray source was detected within the WXT error circle at R.A. = 127.1368 deg, Dec. = 20.8634 deg (J2000), with a positional uncertainty of 20 arcsec in radius (90% confidence level, including both statistical and systematic uncertainties). The source is spatially consistent with the counterpart reported in optical bands (Wortley et al. GCN 42387). Further information will be updated when the telemetry data is received. 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). View this GCN Circular online at https://gcn.nasa.gov/circulars/42388. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40464] EP/WXT 01709247295: GOTO optical afterglow candidate.
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42387 SUBJECT: EP/WXT 01709247295: GOTO optical afterglow candidate. DATE: 25/10/23 08:44:08 GMT FROM: d.s.oneill(a)bham.ac.uk M. E. Wortley, D. O'Neill, G. Ramsay, B. P. Gompertz, B. Godson, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, and J. Casares report on behalf of the GOTO collaboration: We report on optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to Einstein Probe alert 01709247295. Serendipitous imaging covered the position at 2025-10-23 05:25:22 (+2.9h post trigger) and targeted observations at 2025-10-23 05:36:01 UT, (+3.08h post trigger). The observations consisted of 4x45s and 4x90s exposures respectively in the GOTO L-band (400-700 nm). Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations. A new optical source, GOTO25ixt, is identified within the WXT 90% localisation region with coordinates: RA,DEC (J2000) =127.134217, 20.86431 | 08:28:32.21, +20:51:51.51 The source was initially detected with magnitude L = 18.57 ± 0.06 AB mag (+2.9h), with marginal fading to L = 18.64 ± 0.04 AB mag (+3.08h). The source was not detected in ATLAS forced photometry (Shingles et al 2021) at 2025-10-22 15:04:55 (11.44 hours pre-trigger), with a 5-sigma limiting magnitude of o > 19.45 AB mag. Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction. GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/42387. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40463] GRB 251022A: GOTO optical counterpart detection
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42386 SUBJECT: GRB 251022A: GOTO optical counterpart detection DATE: 25/10/23 08:26:52 GMT FROM: d.s.oneill(a)bham.ac.uk D. O’Neill, M. Wortley, B. P. Gompertz, R. Starling K. Ackley, M. Dyer, J. Lyman, K. Ulaczyk, D. Steeghs, D. Galloway, V. Dhillon, P. O'Brien, G. Ramsay, K. Noysena, R. Kotak, R. Breton, J. Casares, L. Nuttall, B. Godson, T. Killestein, A. Kumar, M. Pursiainen report on behalf of GOTO collaboration: We report on observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to GRB 251022A (Fermi GBM team, GCN 42380; Di Lalla et al. GCN 42384). Targeted observations were performed beginning at 2025-10-23 00:58:21 UT, (+2.4h post trigger) and continued through to 2025-10-23 05:04:03 UT (+6.5h post trigger). 161 images were taken, across 10 unique pointings, covering 219.8 square degrees within the 90% localisation contour. ~89.9% of the total 2D localisation probability was covered, with an average 5-sigma depth of 20.5 mag. Each observation consisted of 4x90s exposures in the GOTO L-band (400-700 nm). Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations of the same pointings. We detect a new optical source, GOTO25iym, with coordinates: RA,DEC (J2000) = 65.497023, -18.9195 | 04:21:59.29, -18:55:10.19 This position lies on the 92% contour of the Fermi/GBM localisation and is offset by 0.41 degrees from the Fermi/LAT position (90% statistical uncertainty: 0.32 deg; Di Lalla et al., GCN 42384). The source was initially detected with AB magnitude L = 18.21 ± 0.03 mag (+2.4h), before fading to L = 18.82 ± 0.06 mag (+4.67h). We find no evidence of this source prior to the GRB trigger time in the previous GOTO observation taken at 2025-10-22 14:20:35 UT (8.23h pre-trigger) down to a 5-sigma depth of L > 19.54 AB mag. Despite the mild inconsistency with the Fermi/LAT position, which may be explained by the unaccounted-for systematic uncertainty, the power-law decay seen across three epochs combined with the recent deeper non-detection at the position pre-GRB strongly suggest that GOTO25iym is the afterglow of GRB 251022A. Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction. GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/42386. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40462] GRB 251023A: Fermi GBM Final Localization Correction
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42385 SUBJECT: GRB 251023A: Fermi GBM Final Localization Correction DATE: 25/10/23 07:33:17 GMT FROM: A. Holzmann Airasca at University of Trento and INFN Bari <a.holzmannairasca(a)unitn.it> The Fermi GBM team reports the detection of a likely LONG GRB "At 05:57:43.66 UT on 23 October 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251023A (trigger 782891868/251023248). This trigger was initially classified as distant particles by the flight software, but is in fact a GRB. The on-ground calculated location, using the Fermi GBM trigger data, is RA = 39.87, Dec = -6.53 (J2000 degrees, equivalent to J2000 02h 39m, -06d 31'), with a statistical uncertainty of 3.12 degrees. The angle from the Fermi LAT boresight is 89 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251023248/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251023248/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251023248/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/42385. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40461] GRB 251022A: Fermi-LAT detection
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42384 SUBJECT: GRB 251022A: Fermi-LAT detection DATE: 25/10/23 07:29:47 GMT FROM: Elisabetta Bissaldi at Politecnico and INFN Bari <elisabetta.bissaldi(a)ba.infn.it> N. Di Lalla (Stanford Univ.), D. Kocevski (NASA/MSFC), N. Omodei (Stanford Univ.), S. Cutini (INFN Perugia) A. Holzmann Airasca (UniTrento and INFN Bari), F. Longo (University and INFN, Trieste) and E. Bissaldi (Politecnico and INFN Bari) report on behalf of the Fermi-LAT Collaboration: On October 22, 2025, Fermi-LAT detected high-energy emission from GRB 251022A, which was also detected by Fermi-GBM (trigger 782865260 / 251022940, GCN 42380). The best LAT on-ground location is found to be: RA, Dec = 65.38, -19.31 (J2000) with an error radius of 0.32 deg (90 % containment, statistical error only). This was 36 deg from the LAT boresight at the time of the GBM trigger (T0 = 22:34:15.26 UT). The data from the Fermi-LAT shows a significant increase in the event rate that is spatially and temporally correlated with the GBM emission with high significance. The photon flux above 100 MeV in the time interval 0 - 300 s after the GBM trigger is (5.4 ± 2.0) E-6 ph/cm2/s. The estimated photon index above 100 MeV is -2.5 ± 0.5. The highest-energy photon is a 2 GeV event which is observed ~ 71 seconds after the GBM trigger. A Swift ToO has been approved for this burst. The Fermi-LAT point of contact for this burst is Sara Cutini (sara.cutini(a)pg.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. View this GCN Circular online at https://gcn.nasa.gov/circulars/42384. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40460] GRB 251016B: Fermi GBM Detection
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42383 SUBJECT: GRB 251016B: Fermi GBM Detection DATE: 25/10/23 06:22:48 GMT FROM: Matt Godwin <msg0028(a)uah.edu> Matt Godwin (UAH) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 23:59:00.72 UT on 16 October 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251016B (trigger 782351945/251016999). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 183.64, Dec = 59.60 (J2000 degrees, equivalent to J2000 12h 14m, +59d 36'), with a statistical uncertainty of 1.00 degrees. (radius, 1-sigma containment, statistical only; there is additionally a systematic error which we have characterized as a mixture of two Gaussians, one with a radius of 1.8 degrees (52% contribution) and one with a radius of 4.1 degrees (47% contribution) [A. Goldstein et al. 2020, ApJ, 895, 1]). The angle from the Fermi LAT boresight is 46 degrees. The GBM light curve consists of a single bright emission episode with a duration (T90) of about 7.1 s (50-300 keV). The time-averaged spectrum from T0-0.8 to T0+13.5 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.07 +/- 0.01 and the cutoff energy, parameterized as Epeak, is 310 +/- 1 keV. The event fluence (10-1000 keV) in this time interval is (2.27 +/- 0.05)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+2.4 s in the 10-1000 keV band is 37.5 +/- 0.5 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak= 222 +/- 1 keV, alpha = -0.96 +/- 0 and beta = -2 +/- 0.01. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/" View this GCN Circular online at https://gcn.nasa.gov/circulars/42383. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40459] GRB 251022A: Tiled Swift observations
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42382 SUBJECT: GRB 251022A: Tiled Swift observations DATE: 25/10/23 05:56:57 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P. A. Evans (U. Leicester) reports on behalf of the Swift team: Swift has initiated a series of observations, tiled on the sky, of the Fermi/LAT GRB 251022A. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/xrt_products/TILED_GRB00139 Any uncatalogued X-ray sources detected in this analysis will be reported on this website and via GCN COUNTERPART notices. The probability of finding serendipitous sources, unrelated to the Fermi/LAT event is high: any X-ray source considered to be a probable afterglow candidate will be reported via a GCN Circular after manual consideration. Details of the XRT automated analysis methods are detailed in Evans et al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8). This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42382. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40458] LAT GRB251022.94: Global MASTER-Net observations report
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42381 SUBJECT: LAT GRB251022.94: Global MASTER-Net observations report DATE: 25/10/23 03:11:21 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-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) was pointed to the LAT GRB251022.94 (trigger No 782865260,04h 21m 31.18s , -19d 18m 35.6s, R=0.32) errorbox 13 sec after notice time and 16215 sec after trigger time at 2025-10-23 03:04:30 UT, with upper limit up to 17.2 mag. Observations started at twilight. The observations began at zenith distance = 32 deg. The sun altitude is -10.1 deg. The galactic latitude b = -41 deg., longitude l = 216 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3021522 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 16245 | 2025-10-23 03:04:30 | MASTER-SAAO | (04h 21m 02.62s , -19d 31m 07.4s) | C | 60 | 17.2 | 16245 | 2025-10-23 03:04:30 | MASTER-SAAO | (04h 19m 05.26s , -19d 15m 42.2s) | P\ | 60 | 16.7 | 16324 | 2025-10-23 03:05:49 | MASTER-SAAO | (04h 21m 02.39s , -19d 31m 03.5s) | C | 60 | 16.7 | 16324 | 2025-10-23 03:05:49 | MASTER-SAAO | (04h 19m 05.05s , -19d 15m 37.8s) | P\ | 60 | 16.6 | 16404 | 2025-10-23 03:07:08 | MASTER-SAAO | (04h 19m 04.85s , -19d 15m 33.5s) | P\ | 60 | 16.6 | 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/42381. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40457] GRB 251022A: Fermi GBM Final Real-time Localization
by GCN Circulars 22 Oct '25

22 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42380 SUBJECT: GRB 251022A: Fermi GBM Final Real-time Localization DATE: 25/10/22 22:44:50 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 22:34:15 UT on 22 Oct 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251022A (trigger 782865260.264246 / 251022940). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 74.5, Dec = -22.7 (J2000 degrees, equivalent to J2000 04h 58m, -22d 41'), with a statistical uncertainty of 1.9 degrees. The angle from the Fermi LAT boresight is 29.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251022940/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251022940/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251022940/… View this GCN Circular online at https://gcn.nasa.gov/circulars/42380. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40456] GRB 251013C: SAO RAS optical observations
by GCN Circulars 22 Oct '25

22 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42230 SUBJECT: GRB 251013C: SAO RAS optical observations DATE: 25/10/13 21:31:40 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. S. Moskvitin, O. I. Spiridonova, V. V. Vlasyuk (SAO RAS), N. Pankov (HSE, IKI), A. Pozanenko (IKI), A. Ghosh, S. Razzaque (CAPP, University of Johannesburg), Tao An and Yuanqi Liu (Shanghai Astronomical Observatory) report on behalf of GRB follow-up collaboration and IKI-GRB-FuN. We observed the field of the GRB 251013C (The Fermi GBM team, GCN 42221; Rakotondrainibe et al., GCN 42222) with the 1-m SAO RAS telescope Zeiss-1000 equipped with the CCD-photometer. The observations started on 2025.10.13T19:47:54 UT (t_mid - T0 = 2.1369 hours). The OT (Palmerio et al., GCN 42223; Perez-Garcia et al., GCN 42225; Konno et al., GCN 42226; Martin-Carrillo et al., GCN 42227; Masi, GCN 42228; Palmerio et al, GCN 42229) is clearly detected in the individual images with the following brightness. Date UT start t-T0 Exp. Filter OT Err. (mid, d) (s) 2025.10.13 19:47:54 0.09078 300 Rc 15.84 +/- 0.01 2025.10.13 20:04:02 0.10082 100 Rc 16.05 +/- 0.01 2025.10.13 20:15:34 0.10883 100 Rc 16.21 +/- 0.01 Preliminary photometry is based on the nearby SDSS objects (magnitudes converted with Lupton 2005 equations) and has not corrected for the Galactic extinction. The observations with the 1-m telescope in BVRI filters and also with the 0.5-m telescope AS-500/2 are ongoing. View this GCN Circular online at https://gcn.nasa.gov/circulars/42230. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40455] GRB 251021A/EP251021b: Fermi-GBM Sub-Threshold Detection
by GCN Circulars 22 Oct '25

22 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42379 SUBJECT: GRB 251021A/EP251021b: Fermi-GBM Sub-Threshold Detection DATE: 25/10/22 13:56:22 GMT FROM: mariaedvige.ravasio(a)ru.nl M. E. Ravasio (Radboud Univ.), E. Burns (LSU), and P.G. Jonker (Radboud Univ.) report on behalf of the Fermi-GBM Team: Fermi-GBM had full spatial and temporal coverage of the transient EP251021b detected by EP-WXT (Dai et al., GCN 42377). There was no Fermi-GBM onboard trigger around the EP starting time at T0=2025-10-21T14:28:05 UTC. The GBM Targeted Search [1], the most sensitive, coherent search for GRB-like signals, was run in the time interval [-50;+500] s from the EP T0. A transient was found most significantly at ~T0+7 s on a 4.096 s timescale, with a false alarm rate of 4.9e-05 Hz. The localization is consistent with the EP one, with a spatial association probability of 99.2%. Among the three spectral templates tested, the transient was best-fit with a "soft" spectrum (i.e., a Band function with Epeak = 70 keV, alpha = -1.9, beta = -3.7) for a GRB. [1] Goldstein et al. 2019 arXiv:1903.12597 View this GCN Circular online at https://gcn.nasa.gov/circulars/42379. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40454] EP251021b: BOOTES-7 optical upper limit
by GCN Circulars 22 Oct '25

22 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42378 SUBJECT: EP251021b: BOOTES-7 optical upper limit DATE: 25/10/22 09:05:45 GMT FROM: I. Perez-Garcia at Institute of Astrophysics of Andalusia <ipg(a)iaa.es> I. Perez-Garcia, S.-Y. Wu, E. Fernandez-Garcia, M. D. Caballero-Garcia, R. Sanchez-Ramirez, S. Guziy and A. J. Castro-Tirado (IAA-CSIC, Granada), C. Perez del Pulgar, A. Castellon, A. Reina (Univ. de Malaga),Y.-D. Hu (GXU), L. Hernandez-Garcia (Univ. de Valparaiso), M. Gritsevich (Univ. of Helsinki), D. R. Xiong (Yunnan Observatories of CAS), B.-B. Zhang (Nanjing Univ.) and A. Maury (Space, San Pedro de Atacama), on behalf of a larger collaboration, report: Following the detection of the fast X-ray transient EP251021b by the Einstein Probe (Dai et al. GCN 42377), the 0.6m BOOTES-7 robotic telescope at San Pedro de Atacama (Chile) observed the fast X-ray transient location starting on Oct 22, 03:57 UT (~13.08 h after trigger) in different optical bands. No new optical source is detected on the first co-added clear-filter images (mid exposure time 2025-10-22 04:07:57) within the EP/FXT 20 arcsec radius error circle down to 20.0 mag. We thank the staff at San Pedro de Atacama Celestial Explorations observatory for their excellent support. View this GCN Circular online at https://gcn.nasa.gov/circulars/42378. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40453] EP251021b: Einstein Probe detection of a fast X-ray transient
by GCN Circulars 22 Oct '25

22 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42377 SUBJECT: EP251021b: Einstein Probe detection of a fast X-ray transient DATE: 25/10/22 08:30:35 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> C. Y. Dai (NJU), Q. J. Huang(PMO), W. F. Wen (SZTU), J. H. Wu (GZHU), H. W. Pan (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of a fast X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP251021b. The transient triggered EP-WXT (ID: 01709247263) at 2025-10-21T14:28:28 (UTC). The ground analysis of the WXT data shows that the event started at T0=2025-10-21T14:28:05 (UTC) and lasted for around 30 s. The WXT position of the source is R.A. = 306.742 deg, Dec. = -38.286 deg (J2000) with an uncertainty of 2.3 arcmin in radius (90% C.L. statistical and systematic). We performed a Target-of-Opportunity observation with the Follow-up X-ray Telescope on board EP. The observation began at 2025-10-22T04:41:25 (UTC), around 14 hours after the trigger. An uncatalogued X-ray source was detected within the WXT error circle at R.A. = 306.7451 deg, Dec. = –38.3048 deg (J2000), with a positional uncertainty of 20 arcsec in radius (90% confidence level, including both statistical and systematic uncertainties). Further information will be updated when the telemetry data is received. 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). View this GCN Circular online at https://gcn.nasa.gov/circulars/42377. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0