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[vsnet-grb-info 41152] GRB 251211B: Fermi GBM Final Real-time Localization
by GCN Circulars 11 Dec '25

11 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43072 SUBJECT: GRB 251211B: Fermi GBM Final Real-time Localization DATE: 25/12/11 20:42:26 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 20:32:04 UT on 11 Dec 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251211B (trigger 787177929.268096 / 251211856). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 176.2, Dec = -11.6 (J2000 degrees, equivalent to J2000 11h 44m, -11d 35'), with a statistical uncertainty of 4.5 degrees. The angle from the Fermi LAT boresight is 56.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251211856/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251211856/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251211856/… View this GCN Circular online at https://gcn.nasa.gov/circulars/43072. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41151] IceCube-251210A: DDOTI Optical Upper Limit
by GCN Circulars 11 Dec '25

11 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43071 SUBJECT: IceCube-251210A: DDOTI Optical Upper Limit DATE: 25/12/11 05:40:15 GMT FROM: Rosa Leticia Becerra at Instituto de Astronomía, UNAM <rbecerra(a)astro.unam.mx> Rosa L. Becerra (UNAM), Simone Dichiara (Penn State University), Alan M. Watson (UNAM), Camila Angulo Valdez (UNAM), Nat Butler (ASU), 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-251210A (gold) event (IceCube Collaboration, GCN Circ. 43064) 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 2025-12-11 UTC. DDOTI observed from 01:54 UTC to 04:34 UTC (T+14.8 h to T+17.5 h after the trigger), with a total exposure time of 81 minutes, covering the entire error region reported by IceCube (IceCube Collaboration, GCN Circ. 43064). Comparing our observations to the USNO-B1 and PanSTARRS PS1 DR2 catalogues, we detect no uncatalogued or credible fading sources within the observed field to a 10-sigma limiting AB magnitude of: w > 20.5 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/43071. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41150] SVOM GRB251211.12: Global MASTER-Net observations report
by GCN Circulars 11 Dec '25

11 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43070 SUBJECT: SVOM GRB251211.12: Global MASTER-Net observations report DATE: 25/12/11 03:00:33 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 [1] located in Argentina (OAFA observatory of San Juan National University) started inspect of the SVOM GRB251211.12 (trigger No 1765421306,03h 46m 48.22s , +23d 45m 06.5s, R=1) errorbox 27 sec after notice time and 61 sec after trigger time at 2025-12-11 02:49:27 UT, with upper limit up to 18.7 mag. The observations began at zenith distance = 55 deg. The sun altitude is -31.1 deg. The galactic latitude b = -23 deg., longitude l = 167 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3067906 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 67 | 2025-12-11 02:49:27 | MASTER-OAFA | (03h 47m 09.45s , +23d 52m 13.3s) | C | 10 | 18.7 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/43070. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41149] GRB 251211A: Fermi GBM Final Real-time Localization
by GCN Circulars 11 Dec '25

11 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43069 SUBJECT: GRB 251211A: Fermi GBM Final Real-time Localization DATE: 25/12/11 02:51:35 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 02:40:59 UT on 11 Dec 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251211A (trigger 787113664.18548 / 251211112). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 181.9, Dec = -32.3 (J2000 degrees, equivalent to J2000 12h 07m, -32d 17'), with a statistical uncertainty of 6.4 degrees. The angle from the Fermi LAT boresight is 28.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251211112/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251211112/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251211112/… View this GCN Circular online at https://gcn.nasa.gov/circulars/43069. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41148] GRB 251209A: Fermi GBM observation
by GCN Circulars 10 Dec '25

10 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43068 SUBJECT: GRB 251209A: Fermi GBM observation DATE: 25/12/10 22:23:56 GMT FROM: Elisabetta Bissaldi at Politecnico and INFN Bari <elisabetta.bissaldi(a)ba.infn.it> E. Bissaldi (Politecnico and INFN Bari) reports on behalf of the Fermi GBM Team: "At 13:24:03.99 UT on 9 December 2025, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 251209A (trigger 786979448 / 251209558). The Fermi GBM Final Real-time Localization is reported in GCN 43048. The angle from the Fermi LAT boresight at the GBM trigger time is 52 degrees. The GBM light curve consists of several structured emission episodes with a duration (T90) of about 57 s (50-300 keV). The time-averaged spectrum from T0-4 s to T0+81 s is best fit by a Band function with Epeak = 105 +/- 4 keV, alpha = -1.63 +/- 0.01, and beta = -2.37 +/- 0.06. The event fluence (10-1000 keV) in this time interval is (6.89 +/- 0.05)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+49.7 s in the 10-1000 keV band is 38.4 +/- 0.6 ph/s/cm^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/43068. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41147] GRB 251205A: 1.3m DFOT optical upper limit
by GCN Circulars 10 Dec '25

10 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43067 SUBJECT: GRB 251205A: 1.3m DFOT optical upper limit DATE: 25/12/10 20:44:22 GMT FROM: ANSHIKA GUPTA at ARIES <anshika05180(a)gmail.com> Anshika Gupta, Debalina Kar, Koshvendra Singh, Dhruv Jain, Pankaj Pawar, and Kuntal Misra (ARIES) report: We observed the field of GRB 251205A detected by Swift (Lanava et al. 2025, GCN 43005) with the 1.3m Devasthal Fast Optical Telescope (DFOT), located at the Devasthal Observatory of the Aryabhatta Research Institute of Observational Sciences (ARIES), India. The observations were started on 2025-12-09 at 23:15:22.00 UT, i.e., ~ 3.98 days after the Swift trigger. We have taken multiple frames with an exposure time of 300s in the R filter. We stacked the images after the alignment. We could not detect the optical emission in our stacked image within the error box of Swift/UVOT (Lanava et al. 2025, GCN 43005). We obtain the following 3-sigma upper limit in the stacked image: Date Start_UT T_start-T0 (Days) Filter Exp time (s) Magnitude =============================================================== 2025-12-09 23:15:22.00 ~3.98 R 300s*11 >22.9 The non-detection of the burst is consistent with (Lipunov et al. 2025, GCN 43004; Lanava et al. 2025, GCN 43005; Lipunov et al. 2025, GCN 43006; de Ugarte Postigo et al. 2025, GCN 43008; Malesani et al. 2025, GCN 43009; O’Neill et al. 2025, GCN 43010; Mandarakas et al. 2025, GCN 43011; Pankov et al. 2025, GCN 43012; Bochenek et al. 2025, GCN 43015; Klinger et al. 2025, GCN 43016; Patil et al. 2025, GCN 43019; Pérez-Fournon et al. 2025, GCN 43020; Bochenek et al. 2025, GCN 43024; Busmann et al. 2025, GCN 43026; Hagio et al. 2025, GCN 43029; Bochenek et al. 2025, GCN 43038; Mo et al. 2025, GCN 43044). The magnitude is not corrected for the Galactic extinction in the direction of the burst. Photometric calibration is performed using the standard stars from the USNO-B1.0 catalogue. View this GCN Circular online at https://gcn.nasa.gov/circulars/43067. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41146] GRB 251209A: AstroSat CZTI detection
by GCN Circulars 10 Dec '25

10 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43066 SUBJECT: GRB 251209A: AstroSat CZTI detection DATE: 25/12/10 16:59:18 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> M. Tembhurnikar (IUCAA), S. Salunke (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 251209A which was also detected by Fermi GBM (Fermi GBM Team, GCN Circ. 43048). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2025-12-09 13:24:31.50 UTC. The measured peak count rate associated with the burst is 358 (+38, -34) counts/s above the background in the combined data of three quadrants (out of four), with a total of 5908 (+328, -277) counts. The local mean background count rate was 208 (+1, -2) counts/s. Using cumulative rates, we measure a T90 of 38 (+4, -3) s. In the preliminary analysis, we find 594 Compton events associated with this event. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2025-12-09 13:24:35.75 UTC. The measured peak count rate associated with the burst is 435 (+68, -32) counts/s above the background in the combined data of all quadrants, with a total of 6675 (+484, -624) counts. The local mean background count rate was 1160 (+3, -3) counts/s. We measure a T90 of 33 (+5, -3) 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/43066. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41145] IceCube Alert 251210.46: Global MASTER-Net observations report
by GCN Circulars 10 Dec '25

10 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43065 SUBJECT: IceCube Alert 251210.46: Global MASTER-Net observations report DATE: 25/12/10 15:13:19 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 [1] located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) was pointed to the IceCube Alert 251210.46 (trigger No 43378962,02h 22m 57.84s , +20d 42m 14.4s, R=0.72) errorbox 11898 sec after notice time and 11947 sec after trigger time at 2025-12-10 14:25:22 UT, with upper limit up to 18.0 mag. Observations started at twilight. The observations began at zenith distance = 52 deg. The sun altitude is -8.9 deg. The galactic latitude b = -37 deg., longitude l = 151 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3067269 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 12008 | 2025-12-10 14:25:22 | MASTER-Kislovodsk | (02h 19m 29.66s , +20d 34m 40.7s) | P- | 120 | 13.1 | 12008 | 2025-12-10 14:25:22 | MASTER-Kislovodsk | (02h 19m 38.74s , +20d 11m 50.3s) | P| | 120 | 15.4 | 12148 | 2025-12-10 14:27:42 | MASTER-Kislovodsk | (02h 19m 29.78s , +20d 34m 42.4s) | P- | 120 | 14.5 | 12148 | 2025-12-10 14:27:42 | MASTER-Kislovodsk | (02h 19m 38.65s , +20d 11m 54.3s) | P| | 120 | 16.8 | 12288 | 2025-12-10 14:30:02 | MASTER-Kislovodsk | (02h 19m 29.78s , +20d 34m 47.8s) | P- | 120 | 15.0 | 12288 | 2025-12-10 14:30:02 | MASTER-Kislovodsk | (02h 19m 38.50s , +20d 11m 56.8s) | P| | 120 | 17.3 | 12428 | 2025-12-10 14:32:22 | MASTER-Kislovodsk | (02h 19m 29.82s , +20d 34m 52.9s) | P- | 120 | 15.3 | 12428 | 2025-12-10 14:32:22 | MASTER-Kislovodsk | (02h 19m 38.48s , +20d 12m 01.1s) | P| | 120 | 17.4 | 12568 | 2025-12-10 14:34:42 | MASTER-Kislovodsk | (02h 19m 29.68s , +20d 34m 59.2s) | P- | 120 | 15.3 | 12568 | 2025-12-10 14:34:42 | MASTER-Kislovodsk | (02h 19m 38.42s , +20d 12m 06.0s) | P| | 120 | 17.5 | 12708 | 2025-12-10 14:37:02 | MASTER-Kislovodsk | (02h 19m 29.59s , +20d 35m 05.6s) | P- | 120 | 15.5 | 12708 | 2025-12-10 14:37:02 | MASTER-Kislovodsk | (02h 19m 38.42s , +20d 12m 11.9s) | P| | 120 | 17.5 | 12848 | 2025-12-10 14:39:22 | MASTER-Kislovodsk | (02h 19m 38.40s , +20d 12m 19.1s) | P| | 120 | 17.7 | 12848 | 2025-12-10 14:39:22 | MASTER-Kislovodsk | (02h 19m 29.44s , +20d 35m 13.4s) | P- | 120 | 15.5 | 12987 | 2025-12-10 14:41:41 | MASTER-Kislovodsk | (02h 19m 38.43s , +20d 12m 25.5s) | P| | 120 | 17.7 | 12987 | 2025-12-10 14:41:41 | MASTER-Kislovodsk | (02h 19m 29.28s , +20d 35m 20.8s) | P- | 120 | 15.4 | 13128 | 2025-12-10 14:44:01 | MASTER-Kislovodsk | (02h 19m 29.39s , +20d 35m 24.2s) | P- | 120 | 15.5 | 13128 | 2025-12-10 14:44:01 | MASTER-Kislovodsk | (02h 19m 38.43s , +20d 12m 31.5s) | P| | 120 | 17.9 | 13267 | 2025-12-10 14:46:21 | MASTER-Kislovodsk | (02h 19m 38.43s , +20d 12m 39.0s) | P| | 120 | 17.9 | 13267 | 2025-12-10 14:46:21 | MASTER-Kislovodsk | (02h 19m 29.15s , +20d 35m 34.0s) | P- | 120 | 15.5 | 13407 | 2025-12-10 14:48:41 | MASTER-Kislovodsk | (02h 19m 38.45s , +20d 12m 46.7s) | P| | 120 | 17.9 | 13407 | 2025-12-10 14:48:41 | MASTER-Kislovodsk | (02h 19m 29.08s , +20d 35m 41.2s) | P- | 120 | 15.7 | 13547 | 2025-12-10 14:51:01 | MASTER-Kislovodsk | (02h 19m 38.48s , +20d 12m 54.0s) | P| | 120 | 17.9 | 13547 | 2025-12-10 14:51:01 | MASTER-Kislovodsk | (02h 19m 28.90s , +20d 35m 48.4s) | P- | 120 | 15.7 | 13687 | 2025-12-10 14:53:21 | MASTER-Kislovodsk | (02h 19m 28.84s , +20d 35m 56.4s) | P- | 120 | 15.6 | 13687 | 2025-12-10 14:53:21 | MASTER-Kislovodsk | (02h 19m 38.55s , +20d 13m 01.8s) | P| | 120 | 17.9 | 13827 | 2025-12-10 14:55:41 | MASTER-Kislovodsk | (02h 19m 28.68s , +20d 36m 03.8s) | P- | 120 | 15.8 | 13827 | 2025-12-10 14:55:41 | MASTER-Kislovodsk | (02h 19m 38.61s , +20d 13m 09.1s) | P| | 120 | 17.8 | 13967 | 2025-12-10 14:58:01 | MASTER-Kislovodsk | (02h 19m 28.52s , +20d 36m 10.3s) | P- | 120 | 15.8 | 13967 | 2025-12-10 14:58:01 | MASTER-Kislovodsk | (02h 19m 38.69s , +20d 13m 15.4s) | P| | 120 | 17.9 | 14107 | 2025-12-10 15:00:21 | MASTER-Kislovodsk | (02h 19m 38.76s , +20d 13m 21.0s) | P| | 120 | 18.0 | 14107 | 2025-12-10 15:00:21 | MASTER-Kislovodsk | (02h 19m 28.32s , +20d 36m 15.6s) | P- | 120 | 15.6 | The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/43065. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41144] IceCube-251210A - IceCube observation of a high-energy neutrino candidate track-like event
by GCN Circulars 10 Dec '25

10 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43064 SUBJECT: IceCube-251210A - IceCube observation of a high-energy neutrino candidate track-like event DATE: 25/12/10 14:20:41 GMT FROM: A. Zegarelli at Ruhr University Bochum <azegarelli(a)icecube.wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: On 25-12-10 at 11:06:14.40 UT IceCube detected a track-like event with a high probability of being of astrophysical origin. The event was selected by the ICECUBE_Astrotrack_GOLD alert stream. The average astrophysical neutrino purity for Gold alerts is 50%. This alert has an estimated false alarm rate of 0.7301 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/141715_43378962.amon) more sophisticated reconstruction algorithms have been applied offline, with the direction refined to: Date: 25-12-10 Time: 11:06:14.40 UT RA: 35.29 (+0.68/-0.69 deg 90% PSF containment) J2000 Dec: 20.34 (+0.64/-0.71 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/43064. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41143] EP251124a: Mondy optical upper limit
by GCN Circulars 10 Dec '25

10 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43063 SUBJECT: EP251124a: Mondy optical upper limit DATE: 25/12/10 11:55:55 GMT FROM: Alina Volnova at IKI RAS <alinusss(a)gmail.com> A. A. Volnova (IKI), E. Klunko (ISTP), A. S. Pozanenko, N. S. Pankov (HSE, IKI) (IKI) report on behalf of IKI-GRB-FuN: We observed the field of the EP251124a triggered by EP/WXT (Zhou et al., GCN 42816; GCN 42832) with the AZT-33IK 1.5m telescope of the Sayan Solar Observatory (Mondy) taking several 120-second expositions in R-band starting on Nov.24 UT 14:36:01 in the R filter. In the error boxes reported by Zhou et al. (GCN 42816) we do not detect any new optical transient in the stacked frame. The photometry and observational details are the following: Date UT start t-T0 Exp. Filter UL Site/Telescope (mid,days) (n*s) (3sigma) 2025-11-24 14:36:01 0.16386 30*120 R 22.3 Mondy/AZT-33IK The photometry is based on several nearby stars from the USNO-B1 catalogue (R2 magnitudes) and is not corrected for the Galactic extinction. Our upper limit is in agreement with previously reported limits (Mohan et al., GCN 42817; Wang et al., GCN 42824; Lipunov et al., GCN 42828; van Hoof et al., GCN 42829; Ma et al, GCN 42833; Gillanders et al., GCN 42862). View this GCN Circular online at https://gcn.nasa.gov/circulars/43063. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41142] GRB 251129A/EP251129a: AbAO and Mondy optical observations
by GCN Circulars 10 Dec '25

10 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43062 SUBJECT: GRB 251129A/EP251129a: AbAO and Mondy optical observations DATE: 25/12/10 09:30:07 GMT FROM: Alina Volnova at IKI RAS <alinusss(a)gmail.com> N. S. Pankov (HSE, IKI), E. Klunko (ISTP), R. Ya. Inasaridze (AbAO), A. A. Volnova (IKI), A. S. Pozanenko (IKI) report on behalf of IKI-GRB-FuN: We observed the field of GRB 251129A initially detected by SVOM (Tan et al., GCN 42877) and also detected by Einstein Probe as EP251129a (Wu et al., GCN 42884) and Swift (Evans, GCN 42888; Page et al., GCN 42891). The observations were carried out with the AS-32 0.7m telescope of the Abastumani Observatory (AbAO) and the 1.5m telescope of the Sayan Solar Observatory (Mondy). The observations started on 2025-11-29 at 18:58 UT at AbAO. The optical afterglow (Angulo et al., GCN 42880; Wu et al., GCN 42882; Watson, GCN 42883; Masi, GCN 42885; Li et al., GCN 42887; Lipunov et al., GCN 42892; Moskvitin & Spiridonova, GCN 42897; Guziy et al., GCN 42899; Sanchez-Ramirez et al., GCN 42900; Yaqup et al., GCN 42942; Kuin and Cenko, GCN 42959; Xin et al., GCN 42972) is only visible in the stacked images from Mondy. The preliminary photometry and the observation properties are presented above: Date UT start t-T0 Exp. Filter OT Err. UL Site/Telescope (mid,days) (n*s) (3sigma) 2025-11-29 18:58:15 0.70255 51*60 R n/d n/d 17.6 AbAO/AS-32 2025-11-29 20:15:26 0.75928 30*120 R 21.57 0.15 22.2 Mondy/AZT-33IK 2025-11-30 19:50:56 1.75199 44*120 R 21.47 0.13 22.2 Mondy/AZT-33IK The photometry is based on nearby stars from the USNO-B1 catalog (R2 magnitudes) and is not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/43062. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41141] EP251130a: Mondy and AbAO optical observations
by GCN Circulars 10 Dec '25

10 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43061 SUBJECT: EP251130a: Mondy and AbAO optical observations DATE: 25/12/10 09:19:25 GMT FROM: Alina Volnova at IKI RAS <alinusss(a)gmail.com> A. A. Volnova (IKI), E. Klunko (ISTP), R. Ya. Inasaridze (AbAO), N. S. Pankov (HSE, IKI), A. S. Pozanenko (IKI) report on behalf of IKI-GRB-FuN: We continued observations of the field of the X-ray transient EP251130a (Wu et al., GCN 42903; Zhang et al., GCN 42915), also detected by Swift/XRT (Evans et al., GCN 42908) with the AZT-33IK 1.5m telescope of the Sayan Solar Observatory (Mondy), and the AS-32 0.7m telescope of Abastumani Observatory (AbAO) taking several frames in R-band. Further observations at AZT-33IK started on Dec. 01 at 20:11 (~1.4 days after the trigger), then followed by AbAO on Dec. 3 starting at 23:01 UT (~3.5 days after the trigger). The optical counterpart (Dornic et al., GCN 42904; He et al. GCN 42914; Gupta et al. GCN 42916; Zheng et al. GCN 42917; van Dalen et al., GCN 42918; Moskvitin and Spiridonova, GCN 42919; Aryan et al., GCN 42921; Volnova et al., GCN 42922; Ma et al., GCN 42940; Corcoran et al., GCN 42951; Tundidor Rodríguez et al., GCN 42963; Abidkhanov et al., GCN 42969; Fu et al., GCN 42990) is seen in the stacked AZT-33IK frame and is not detected in the stacked frame from AS-32. The photometry and observational details are the following: Date UT start t-T0 Exp. Filter OT Err. UL Site/Instrum (mid,days) (n*s) (3sigma) 2025-12-01 20:11:34 1.40888 45*120 R 21.83 0.15 22.5 Mondy/AZT-33IK 2025-12-03 23:01:52 3.56284 285*30 R n/d n/d 21.0 AbAO/AS-32 The photometry is based on several nearby stars from the USNO-B1 catalogue (R2 magnitudes) and is not corrected for the Galactic extinction. Our observations together with other published magnitudes confirm the steep decay (Tundidor Rodríguez et al., GCN 42963) after the re-brightening: the R-band light curve slope changed from ~1.3 at 0.06-0.19 days to ~4 at 0.9-1.4 days in the observer frame. View this GCN Circular online at https://gcn.nasa.gov/circulars/43061. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41140] GRB 251208A: AstroSat CZTI detection
by GCN Circulars 10 Dec '25

10 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43060 SUBJECT: GRB 251208A: AstroSat CZTI detection DATE: 25/12/10 06:31:41 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> A. Goyal (IITB), A. Arya (IITB), M. Tembhurnikar (IUCAA), S. Salunke (IUCAA), Harsha K. H. (IUCAA), 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 short duration GRB 251208A which was also detected by Fermi GBM (Fermi GBM Team, GCN Circ. 43027), and SVOM/GRM (Wang et. al., GCN Circ. 43042). The source was clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2025-12-08 09:25:56.97 UTC. The measured peak count rate associated with the burst is 337 (+63, -72) counts/s above the background in the combined data of all quadrants, with a total of 526 (+239, -300) counts. The local mean background count rate was 1251 (+7, -6) counts/s. Due to the intrinsic 1 s binning of veto data, we cannot reliably estimate a T90 for this short burst. The source was also faintly detected in the CZT detectors in the 20-200 keV energy range. 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/43060. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41139] Fermi GBM Sub-Threshold Detection of GRB 251205A
by GCN Circulars 09 Dec '25

09 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43059 SUBJECT: Fermi GBM Sub-Threshold Detection of GRB 251205A DATE: 25/12/09 22:38:52 GMT FROM: rhamburg(a)usra.edu R. Hamburg and P. Veres report on behalf of the Fermi-GBM Team: The Swift/BAT detected GRB 251205A on 2025-12-05 at 23:39:47 UTC (Lanava et al 2025, GCN 43005) and a redshift of z = 1.1 has been measured by GTC/OSIRIS (de Ugarte Postigo et al 2025, GCN 43008). There was no Fermi-GBM onboard trigger around this event time. An automated, blind search for gamma-ray bursts below the onboard triggering threshold in Fermi-GBM identified no candidates. The GBM Targeted Search [1], the most sensitive coherent search for GRB-like signals in GBM, identified a transient starting about 2 seconds after the Swift/BAT trigger time, most significantly on the 8 s timescale with an SNR of 7.1 and a false alarm rate of 8.1e-05 Hz. The Targeted Search event was found with highest significance using a hard spectrum (i.e., Comptonized function with Epeak = 1500 keV, alpha = -0.5) for a GRB. The Targeted Search localization is found to be spatially consistent with the Swift BAT location. [1] Goldstein et al. 2019, arXiv:1903.12597 View this GCN Circular online at https://gcn.nasa.gov/circulars/43059. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41138] GRB 251208A: Glowbug gamma-ray detection
by GCN Circulars 09 Dec '25

09 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43058 SUBJECT: GRB 251208A: Glowbug gamma-ray detection DATE: 25/12/09 18:40:44 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 251208A, which was also detected by Fermi/GBM (GCN 43027), SVOM/GRM (GCN 43042), and GECAM-B (GCN 43054). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2025-12-08 09:25:56.376 with a duration of 2.05 s and a total significance of about 13.5 sigma. The light curve comprises a single peak. 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/43058. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41137] GRB 251208B: COLIBRÍ optical upper limits
by GCN Circulars 09 Dec '25

09 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43057 SUBJECT: GRB 251208B: COLIBRÍ optical upper limits DATE: 25/12/09 18:32:15 GMT FROM: Alan Watson at UNAM <alan(a)astro.unam.mx> Francesco Magnani (CPPM), Diego López-Cámara (UNAM), Alan M. Watson (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), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García-García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), 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/Swift GRB 251208B (Fermi GBM Team, GCN Circ. 43028; DeLaunay et al., GCN Circ. 43033; Bissaldi et al., GCN Circ. 43034) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2025-12-09 12:13 to 13:13 UTC (from 25.9 to 26.9 hours after the Fermi/GBM trigger) and obtained 45 minutes of simultaneous exposure in the r and z filters. The data were reduced, coadded, and analyzed with the ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. In our stacked images, at the position of the XRT afterglow candidate (Kennea et al., GCN Circ. 43050) we do not detect any new source to the following 3-sigma limits: r > 23.7 z > 22.7 Furthermore, we do not detect any new source at the LAT uncertainty region (Bissaldi et al., GCN Circ. 43034) down to the following 5-sigma limits: r > 23.1 z > 22.1 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/43057. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41136] EP251118a / GRB 251118C: VLT/MUSE redshift confirmation
by GCN Circulars 09 Dec '25

09 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43056 SUBJECT: EP251118a / GRB 251118C: VLT/MUSE redshift confirmation DATE: 25/12/09 17:24:40 GMT FROM: Andrea Saccardi at CEA/Irfu <andrea.saccardi(a)cea.fr> A. Saccardi (CEA/Irfu), D. B. Malesani (DAWN/NBI and Radboud), L. Izzo (INAF/OACn & DARK/NBI), V. D’Elia (ASI/SSDC), J. An, D. Xu (NAOC), M. De Pasquale (U. of Messina) report on behalf of the Stargate collaboration: We observed the field of EP251118a / GRB 251118C detected by EP (Jiang et al., GCN 42749; Shi et al., GCN 42754), Konus-Wind (Frederiks et al., GCN 42765), SVOM/GRM (Wang et al., GCN 42766), Swift/BAT (Delaunay et al., GCN 42770), and Glowbug (Woolf et al., GCN 42771), using the ESO VLT UT4 (Yepun) equipped with the MUSE spectrograph. Our observation started at 07:17:25 UT on 2025 November 19 (14.6 hr after the GRB trigger), and consisted of 3 exposures of 700 s each. The optical counterpart (Malesani et al., GCN 42751; Lipunov et al., GCN 42755; Belkin et al., GCN 42758; Yadav et al., GCN 42760; Busmann et al., GCN 42763; Francile et al., GCN 42767; Urquijo-Rodríguez et al., GCN 42773; Li et al., GCN 42776; Lee et al., GCN 42780; Moskvitin and Spiridonova, GCN 42785; Gupta et al., GCN 42787; Liu et al., GCN 42793; Aryan et al., GCN 42798; Gupta et al., GCN 42810; Volnova et al., GCN 42926) is well detected in the wavelength-stacked “white light” image. Our spectra cover the wavelength range 4750 - 9330 AA. In a preliminary reduction, we detect a continuum over the entire covered wavelength range. From the detection of several absorption features that we identify as Fe II, Mg II, Mg I, and Ca II, we infer a redshift of z = 1.217 for the GRB. Additionally, we note the presence of the [O II] 3726,3729 doublet in emission at a comparable redshift (z = 1.218). Our result is thus fully consistent with, and improves, the value previously reported by the Nordic Optical Telescope (An et al., GCN 42756). We acknowledge expert support from the observing staff in Paranal, in particular Cedric Ledoux, Fuyan Bian, and Juan Carlos Olivares. View this GCN Circular online at https://gcn.nasa.gov/circulars/43056. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41135] GRB 251208C: GECAM-B observation of a short burst
by GCN Circulars 09 Dec '25

09 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43055 SUBJECT: GRB 251208C: GECAM-B observation of a short burst DATE: 25/12/09 16:16:20 GMT FROM: Yue Wang <m18509381757(a)163.com> Yue Wang, Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered on-ground by GRB 251208C, at 2025-12-08T12:52:32.600 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #43030) and SVOM/GRM (Yue Wang et al., GCN #43041). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of a single pulse with a duration (T90) of 0.3 +0.2/-0.2 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb251208C.png Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS). View this GCN Circular online at https://gcn.nasa.gov/circulars/43055. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41134] GRB 251208A: GECAM-B observation of a short burst
by GCN Circulars 09 Dec '25

09 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43054 SUBJECT: GRB 251208A: GECAM-B observation of a short burst DATE: 25/12/09 16:15:06 GMT FROM: Yue Wang <m18509381757(a)163.com> Yue Wang, Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered on-ground by GRB 251208A, at 2025-12-08T09:25:57.550 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #43027) and SVOM/GRM (Yue Wang et al., GCN #43042). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of a single pulse with a duration (T90) of 2.4 +0.7/-1.2 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb251208A.png Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS). View this GCN Circular online at https://gcn.nasa.gov/circulars/43054. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41133] Fermi GRB 251209A: Global MASTER-Net observations report
by GCN Circulars 09 Dec '25

09 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43053 SUBJECT: Fermi GRB 251209A: Global MASTER-Net observations report DATE: 25/12/09 15:30:41 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 [1] located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB 251209A ( Fermi GBM team, GCN 43048) errorbox 4838 sec after notice time and 4882 sec after trigger time at 2025-12-09 14:45:26 UT, with upper limit up to 15.1 mag. Observations started at twilight. The observations began at zenith distance = 80 deg. The sun altitude is -12.3 deg. The galactic latitude b = 66 deg., longitude l = 80 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3065758 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 4912 | 2025-12-09 14:45:26 | MASTER-Kislovodsk | (14h 17m 04.16s , +45d 00m 13.7s) | C | 60 | 15.1 | 4912 | 2025-12-09 14:45:26 | MASTER-Kislovodsk | (14h 22m 26.41s , +44d 40m 31.0s) | C | 60 | 15.0 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/43053. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41132] Fermi GRB 251208C: Global MASTER-Net observations report
by GCN Circulars 09 Dec '25

09 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43052 SUBJECT: Fermi GRB 251208C: Global MASTER-Net observations report DATE: 25/12/09 15:30:32 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Kislovodsk robotic telescope [1] located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB 251208C ( Fermi GBM team, GCN 43030) errorbox 1 days 6304 sec after notice time and 1 days 6326 sec after trigger time at 2025-12-09 14:37:58 UT, with upper limit up to 15.6 mag. Observations started at twilight. The observations began at zenith distance = 77 deg. The sun altitude is -11.0 deg. The galactic latitude b = -39 deg., longitude l = 14 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3064550 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 92816 | 2025-12-09 14:37:58 | MASTER-Kislovodsk | (20h 51m 14.16s , -30d 11m 05.4s) | C | 180 | 12.8 | 93444 | 2025-12-09 14:49:26 | MASTER-Kislovodsk | (20h 51m 12.38s , -29d 02m 48.7s) | C | 60 | 13.6 | 93444 | 2025-12-09 14:49:26 | MASTER-Kislovodsk | (20h 46m 31.77s , -28d 42m 11.8s) | C | 60 | 14.3 | 93525 | 2025-12-09 14:50:47 | MASTER-Kislovodsk | (21h 01m 36.94s , -30d 57m 36.2s) | C | 60 | 12.5 | 93525 | 2025-12-09 14:50:47 | MASTER-Kislovodsk | (20h 56m 51.84s , -30d 36m 58.9s) | C | 60 | 13.2 | 93604 | 2025-12-09 14:52:07 | MASTER-Kislovodsk | (20h 56m 03.09s , -27d 10m 45.4s) | C | 60 | 14.7 | 93604 | 2025-12-09 14:52:07 | MASTER-Kislovodsk | (20h 51m 26.46s , -26d 50m 06.8s) | C | 60 | 15.1 | 93684 | 2025-12-09 14:53:27 | MASTER-Kislovodsk | (21h 00m 18.16s , -28d 43m 43.1s) | C | 60 | 14.0 | 93684 | 2025-12-09 14:53:27 | MASTER-Kislovodsk | (21h 04m 59.03s , -29d 04m 22.4s) | C | 60 | 13.9 | 93765 | 2025-12-09 14:54:47 | MASTER-Kislovodsk | (20h 38m 01.33s , -26d 48m 57.8s) | C | 60 | 14.5 | 93765 | 2025-12-09 14:54:47 | MASTER-Kislovodsk | (20h 42m 37.44s , -27d 09m 35.3s) | C | 60 | 14.1 | 93845 | 2025-12-09 14:56:07 | MASTER-Kislovodsk | (20h 32m 54.99s , -28d 43m 10.7s) | C | 60 | 13.1 | 93845 | 2025-12-09 14:56:07 | MASTER-Kislovodsk | (20h 37m 34.74s , -29d 03m 45.7s) | C | 60 | 12.5 | 93925 | 2025-12-09 14:57:27 | MASTER-Kislovodsk | (20h 48m 49.10s , -25d 15m 12.4s) | C | 60 | 14.9 | 93925 | 2025-12-09 14:57:27 | MASTER-Kislovodsk | (20h 44m 16.39s , -24d 54m 32.9s) | C | 60 | 15.3 | 94005 | 2025-12-09 14:58:47 | MASTER-Kislovodsk | (21h 02m 06.24s , -25d 16m 49.4s) | C | 60 | 15.1 | 94005 | 2025-12-09 14:58:47 | MASTER-Kislovodsk | (20h 57m 32.94s , -24d 56m 08.5s) | C | 60 | 15.6 | 94085 | 2025-12-09 15:00:07 | MASTER-Kislovodsk | (21h 09m 35.36s , -27d 08m 43.7s) | C | 60 | 14.6 | 94085 | 2025-12-09 15:00:07 | MASTER-Kislovodsk | (21h 04m 58.34s , -26d 48m 02.7s) | C | 60 | 14.9 | 94697 | 2025-12-09 15:10:19 | MASTER-Kislovodsk | (21h 10m 53.04s , -30d 37m 42.3s) | C | 60 | 12.2 | 94857 | 2025-12-09 15:12:59 | MASTER-Kislovodsk | (20h 35m 32.24s , -25d 17m 04.5s) | C | 60 | 13.9 | 94947 | 2025-12-09 15:14:29 | MASTER-Kislovodsk | (21h 18m 27.36s , -29d 04m 37.5s) | C | 60 | 13.4 | 94947 | 2025-12-09 15:14:29 | MASTER-Kislovodsk | (21h 13m 59.27s , -28d 44m 11.1s) | C | 60 | 13.7 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/43052. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41131] GRB 251206A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
by GCN Circulars 09 Dec '25

09 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43051 SUBJECT: GRB 251206A: SVOM/COLIBRÍ (FM-GFT) optical upper limit DATE: 25/12/09 14:48:58 GMT FROM: Alan Watson at UNAM <alan(a)astro.unam.mx> Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Jean-Luc Atteia (IRAP), Noémie Globus (UNAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), 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), 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), Antonio de Ugarte Postigo (LAM), and Marius Brunet (IRAP) report: We imaged the field of the SVOM GRB 251206A (Brunet et al., GCN Circ. 43031) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-12-09 04:39 to 0625 UTC (from 55.8 to 57.2 hours after the trigger) and obtained 80 minutes of simultaneous exposure in the r and z filters. The data were reduced, coadded, and analyzed with the ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. In the stacked image, we do not detect any new source inside the ECLAIRs uncertainty region (Brunet et al., GCN Circ. 43031) to the following 5-sigma limits: r > 23.3 z > 22.3 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/43051. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41130] GRB 251208B: Swift-XRT afterglow detection
by GCN Circulars 09 Dec '25

09 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43050 SUBJECT: GRB 251208B: Swift-XRT afterglow detection DATE: 25/12/09 13:53:09 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> J.A. Kennea (PSU), D.N. Burrows (PSU), A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester), M. Ferro (INAF-OAB), R. Brivio (INAF-OAB), A. D'Ai (INAF-IASFPA), 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 the GUANO (DeLaunay et al. GCN 43033) and Fermi/LAT-detected (Bissaldi et al. GCN 43034) burst GRB 251208B. We searched for X-ray sources in 4.8 ks of Photon Counting (PC) mode data. The total exposure at the position of the afterglow (see below) is 4.8 ks, obtained between T0+33.1 ks and T0+45.4 ks. Three uncatalogued X-ray sources are detected within the estimated 3-sigma Fermi/LAT error region (414 arcsec), of which one ("Source 1") is 2.9 sigma above the RASS limit and it is fading with 2.2 sigma significance and thus is believed to be the GRB afterglow. Using 4576 s of PC mode data and 5 UVOT images, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 228.48108, +29.04575 which is equivalent to: RA (J2000): 15h 13m 55.46s Dec(J2000): +29d 02' 44.7" with an uncertainty of 2.3 arcsec (radius, 90% confidence). This position is 87 arcsec from the Fermi/LAT position. The light curve is consistent with a constant source of mean count rate 5.0e-02 ct/sec. A power-law fit gives an index of 1.2 (+/-1.2). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.2 (+0.4, -0.3). The best-fitting absorption column is 1.4 (+1.1, -0.8) x 10^21 cm^-2, in excess of the Galactic value of 2.6 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 3.1 x 10^-11 (4.4 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.4 (+1.1, -0.8) x 10^21 cm^-2 Galactic foreground: 2.6 x 10^20 cm^-2 Excess significance: 2.3 sigma Photon index: 2.2 (+0.4, -0.3) The results of the XRT-team automatic analysis are available at https://www.swift.ac.uk/xrt_products/00021893. The results of the full analysis of the XRT observations are available at https://www.swift.ac.uk/ToO_GRBs/00021893. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/43050. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41129] GRB 251208D: LAST optical upper limit
by GCN Circulars 09 Dec '25

09 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43049 SUBJECT: GRB 251208D: LAST optical upper limit DATE: 25/12/09 13:50:40 GMT FROM: Ruslan Konno at Weizmann Institute of Science <ruslankonno(a)gmail.com> R. Konno (WIS), S. Garrappa (WIS), E. A. Zimmerman (WIS), A. Horowicz (WIS), E. O. Ofek (WIS), S. Ben-Ami (WIS), D. Polishook (WIS), O. Yaron (WIS), S. Fainer (WIS), A. Krassilchtchikov (WIS), Y. M. Shani (WIS), E. Segre (WIS), A. Gal-Yam (WIS), and S. Spitzer (WIS) report on behalf of the LAST Collaboration. We report observations of GRB 251208D, detected by SVOM (Lin et al., GCN 43032). Observations were conducted with the Large Array Survey Telescope (LAST; Ofek et al. 2023, PASP 135, 5001; Ben-Ami et al. 2023, PASP 135, 5002). We observed the field of GRB 251208D using 4 divergent telescopes (each with a 7.4 deg^2 FoV) in clear band (similar to the Gaia Bp band) over 5 sequential epochs. Each epoch consists of 20x20s exposures. We began observations at 2025-12-08 17:22:15 UTC (T-T0 = 0.53h). We coadd a total of 100x20s exposure images and perform image subtraction using a reference image of the field. We do not detect any new optical source up to a limiting magnitude of 20.33 (AB) within the error region reported in Lin et al., GCN 43032. LAST is a survey telescope array of the Weizmann Astrophysical Observatory (https://www.weizmann.ac.il/wao/) View this GCN Circular online at https://gcn.nasa.gov/circulars/43049. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41128] GRB 251209A: Fermi GBM Final Real-time Localization
by GCN Circulars 09 Dec '25

09 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43048 SUBJECT: GRB 251209A: Fermi GBM Final Real-time Localization DATE: 25/12/09 13:34:44 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 13:24:03 UT on 9 Dec 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251209A (trigger 786979448.987734 / 251209558). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 214.2, Dec = 43.1 (J2000 degrees, equivalent to J2000 14h 16m, 43d 06'), with a statistical uncertainty of 1.0 degrees. The angle from the Fermi LAT boresight is 52.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251209558/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251209558/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251209558/… View this GCN Circular online at https://gcn.nasa.gov/circulars/43048. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41127] GRB 251208D: LCO analysis of the XRT sources
by GCN Circulars 09 Dec '25

09 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43047 SUBJECT: GRB 251208D: LCO analysis of the XRT sources DATE: 25/12/09 12:07:14 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> D. B. Malesani (DAWN/NBI and Radboud), D. Turpin, A. Saccardi (CEA/Irfu), Z.-Y. Lin, F. Cangemi (APC), report on behalf of the SVOM mission team: Following the report of two X-ray sources detected by Swift/XRT (Evans et al., GCN 43043), we inspected again our images taken with LCO (Turpin et al., GCN 43037) of the field of the SVOM GRB 251208A (Lin et al., GCN 43032). * XRT source #1 matches the high proper-motion star TYC 5226-156-1 (distance ~500 pc). We measure a magnitude of r = 11.34 +- 0.02, consistent with the APASS archival value r = 11.34 +- 0.06. * XRT source #2 is consistent with SDSS J223038.66-003108.3, a known QSO at z = 1.32 with magnitude r = 20.34 (from SDSS) and r = 20.65 (from Pan-STARRS), possibly indicating some long-term variability. We measure r = 20.73 +- 0.12, indicating that the object is not in a particularly active state. Our observations suggest that neither sources are likely related to the high-energy emission observed by SVOM. This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/43047. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41126] GRB 251208B: Fermi GBM Observation
by GCN Circulars 09 Dec '25

09 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43046 SUBJECT: GRB 251208B: Fermi GBM Observation DATE: 25/12/09 11:51:58 GMT FROM: Andreas von Kienlin at MPE <azk(a)mpe.mpg.de> A. von Kienlin (MPE) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 10:17:17.29 UT on 08 December 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251208B (trigger 786881842/251208429). which was also detected by Fermi-LAT (E. Bissaldi et al. 2025, GCN 43034) and Swift/BAT-GUANO (GCN #43033). The Fermi GBM on-ground location was reported by the Fermi-GBM team in GCN 43028 and is consistent with the Fermi-LAT and Swift/BAT positions. The GBM light curve shows a structured emission episode with a duration (T90) of about 62.5 s (50-300 keV). The time-averaged spectrum from T0-4.1 to T0+61.4 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.67 +/- 0.08 and the cutoff energy, parameterized as Epeak, is 250 +/- 20 keV. The event fluence (10-1000 keV) in this time interval is (9.5 +/- 0.5)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+55 s in the 10-1000 keV band is 2 +/- 0.2 ph/s/cm^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/43046. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41125] GRB 251208B: GROWTH-India Telescope optical upper limits
by GCN Circulars 09 Dec '25

09 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43045 SUBJECT: GRB 251208B: GROWTH-India Telescope optical upper limits DATE: 25/12/09 09:02:28 GMT FROM: V. Swain at IIT Bombay <vishwajeet.s(a)iitb.ac.in> A. Kumar, 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 Fermi GBM transient (Fermi GBM Team, GCN 43028), with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2025-12-08T23:43:57 UT, i.e., about 13.4 hours after the Fermi GBM Trigger. Exposures were obtained in r' and i' filters. We did not detect any transient in our images within the Fermi-LAT on-ground localization region (Bissaldi et al., GCN 43034). Additionally, we checked the source 1 and 5 of Swift-XRT ToO observations (Evans at al., GCN 43035), and did not detect any optical counterpart at their respective position and uncertainty. The photometric upper limits are as follows: | MJD (mid) | Filter | tmid-t0 (hrs) | Exposure Time (sec) | Upper limit (AB) | | ------------ | ------ | ------------- | ------------------- | ---------------- | | 61018.007928 | r' | 13.90 | 3 x 360 | 20.6 | | 61018.020746 | i' | 14.21 | 2 x 360 | 17.4 | The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction. 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/43045. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41124] GRB 251205A: J-band detection with WINTER
by GCN Circulars 09 Dec '25

09 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43044 SUBJECT: GRB 251205A: J-band detection with WINTER DATE: 25/12/09 02:23:58 GMT FROM: Geoffrey Mo at Caltech / Carnegie Observatories <gmo(a)mit.edu> Geoffrey Mo (Caltech/Carnegie), Tomas Ahumada (NOIRLab), Benjamin Schneider (LAM), 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 251205A (Lanava et al., GCN 43005; Beardmore et al., GCN 43007; Dichiara et al., GCN 43017; Krimm et al., GCN 43018) 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 2025-12-06T10:27:54 UTC in the J band (~10.8 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 source at the optical counterpart location (Lipunov et al., GCN 43004; Lanava et al., GCN 43005; Lipunov et al., GCN 43006; de Ugarte Postigo et al., GCN 43008; Malesani et al., GCN 43009; O’Neill et al., GCN 43010; Mandarakas et al., GCN 43011; Pankov et al., GCN 43012; Bochenek et al., GCN 43015; Klinger et al., GCN 43016; Patil et al., GCN 43019; Pérez-Fournon et al., GCN 43020; Bochenek et al., GCN 43024; Busmann et al., GCN 43026; Hagio et al., GCN 43029; Bochenek et al., GCN 43038), with magnitude J = 17.9 ± 0.1 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/43044. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41123] GRB 251208D: Swift-XRT observations
by GCN Circulars 09 Dec '25

09 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43043 SUBJECT: GRB 251208D: Swift-XRT observations DATE: 25/12/09 02:01:30 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 sb25120806 (GCN 43032), collecting 2.4 ks of Photon Counting (PC) mode data between T0+5.2 ks and T0+11 ks after the trigger. We have detected 2 sources. These have been automatically classified as follows: * 0 likely counterparts * 0 candidate counterparts * 1 uncatalogued X-ray source * 1 known X-ray source Uncatalogued X-ray sources -------------------------- Source 2 (SWIFT J223038.6-003107): ================================== RA (J2000.0): 337.6610 = 22 30 38.64 Dec (J2000.0): -0.5186 = -00 31 07.0 Error: 5.8 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 10.7 arcmin from the SVOM/ECLAIRs position. Mean rate: (4.6 [+2.2, -1.7])e-3 ct s^-1 Mean flux: (4.6 [+2.2, -1.7])e-13 erg cm^-2 s^-1 Peak rate: (4.6 [+2.2, -1.7])e-3 ct s^-1 Peak flux: (4.6 [+2.2, -1.7])e-13 erg cm^-2 s^-1 ECF: 1.02e-10 erg cm^-2 ct^-1 assuming NH=3.34e+21 cm^-2, gamma=0.47 determined from a spectral fit. RASS UL: 1.6e-01 ct s^-1 (converted to XRT; 0.3-10 keV) so the source is not above this 3-sigma upper limit. There is no evidence for fading. A SIMBAD object `SDSS J223038.66-003108.3' is 1.2" away. Known X-ray sources ------------------- Source 1 (SWIFT J222951.0-001338): ================================== RA (J2000.0): 337.4626 = 22 29 51.02 Dec (J2000.0): -0.2273 = -00 13 38.3 Error: 5.2 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 10.8 arcmin from the SVOM/ECLAIRs position. Mean rate: (5.6 [+2.4, -1.9])e-3 ct s^-1 Mean flux: (2.41 [+1.05, -0.81])e-13 erg cm^-2 s^-1 Peak rate: (5.6 [+2.4, -1.9])e-3 ct s^-1 Peak flux: (2.41 [+1.05, -0.81])e-13 erg cm^-2 s^-1 This matches a catalogued X-ray source 4XMM J222950.9-001339 in the XMM-NEWTON/XMMSSC catalogue. Details: Separation: 2.0" from the XRT source Cat Rate: 5.9e-02 +/- 8.2e-03 ct s^-1 Cat Flux: 6.0e-13 +/- 8.3e-14 erg cm^-2 s^-1 (0.3-10 keV) so the source is not above the catalogued flux. There is no evidence for fading. A SIMBAD object `TYC 5226-156-1' is 1" away. There is 1 2MASS object 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_FIELD00056. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/43043. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41122] GRB 251208A: SVOM/GRM observation of a short burst
by GCN Circulars 09 Dec '25

09 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43042 SUBJECT: GRB 251208A: SVOM/GRM observation of a short burst DATE: 25/12/09 01:54:54 GMT FROM: Yue Wang <m18509381757(a)163.com> SVOM/GRM team: Yue Wang, Chen-Wei Wang, Wen-Jun Tan, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Frédéric Daigne (IAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by GRB 251208A (SVOM trigger reference: sb25120804) at 2025-12-08T09:25:58.000 (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #43027). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a single pulse with a T90 of 2.2 +0.9/-0.5 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb251208A.png In addition, the position of this burst, as determined by Fermi/GBM (RA = 32.8, Dec = -66.7, position uncertainty = 3.9, GCN #43027), is located at about 61 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. With this localization, the time-averaged spectrum from T0-1 to T0+2 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.20 +0.19/-0.18 and the cutoff energy, parameterized as Epeak, is 135 +51/-27 keV. The event fluence (10-1000 keV) in this time interval is (1.29 +0.19/-0.14)E-06 erg/cm^2. The 1s peak spectrum, measured from T0-0.6 to T0+0.4 s, if fitted by a power law function with an exponential high-energy cutoff, the power law index is -0.98 +0.17/-0.18 and the cutoff energy, parameterized as Epeak, is 139 +33/-21 keV. The flux (10-1000 keV) in this time interval is (7.79 +0.91/-0.72)E-07 erg/cm^2/s. The localization of GRB 251208A in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb251208A_amati.png The localization of GRB 251201A in the 'Yonetoku' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb251208A_yonetoku.png In the absence of a measured redshift, the duration, soft spectrum, and position in the Amati diagram do not allow us to determine whether this burst is type I or type II. 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/GRM point of contact for this burst is: Yue Wang (IHEP) (yuewang(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/43042. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41121] GRB 251208C: SVOM/GRM observation of a short burst
by GCN Circulars 09 Dec '25

09 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43041 SUBJECT: GRB 251208C: SVOM/GRM observation of a short burst DATE: 25/12/09 01:00:49 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> SVOM/GRM team: Chen-Wei Wang, Yue Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Frédéric Daigne (IAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by GRB 251208C (SVOM trigger reference: sb25120805) at 2025-12-08T12:52:32.600 (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #43030). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a single pulse with a T90 of 0.36 +0.06/-0.08 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb251208C.png In addition, the position of this burst, as determined by Fermi/GBM (RA = 312.8 deg, Dec = -30.7 deg, Error=4.8 deg, GCN #43030), is located at about 84 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. With this localization, the time-averaged spectrum from T0-0.12 to T0+0.04 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.54 +0.22/-0.19 and the cutoff energy, parameterized as Epeak, is 617 +241/-151 keV. The event fluence (10-1000 keV) in this time interval is (1.18 +0.09/-0.12)E-06 erg/cm^2. The localization of GRB 251208C in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb251208C_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/GRM 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/43041. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41120] GRB 251129A: e-MERLIN C-band observations
by GCN Circulars 09 Dec '25

09 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43040 SUBJECT: GRB 251129A: e-MERLIN C-band observations DATE: 25/12/09 00:50:36 GMT FROM: Tao An at SHAO, CAS <antao(a)shao.ac.cn> Tao An (SHAO), Ailing Wang (IHEP), Emmanuel Bempong-Manful (UoM), Zigao Dai (USTC), and collaborators report on e-MERLIN observations of GRB 251129A. We observed GRB 251129A (GCN 42877, 42879, 42880, 42882, 42884, 42887, 42888, 42891, 42897, 42900, 42902, 42959, 42972, 42985) with the e-MERLIN array in the C band between 2025 December 3, 17:40 UT and December 5, 04:19 UT (project RR20009). Four antennas, Pickmere (Pi), Darnhall (Da), Knockin (Kn), and Cambridge (Cm), participated in the observation. Observing setup: - Frequency coverage: 4.82–5.33 GHz (C band), total bandwidth 512 MHz - Antennas: Pi, Da, Kn, Cm - Polarizations: Right and left circular - Spectral setup: 4 × 128 MHz spectral windows, 128 × 1 MHz channels per window (post-averaging) - Observation span: 2025-12-03 17:40 UT to 2025-12-05 04:19 UT The data were processed using the standard e-MERLIN pipeline followed by calibration and imaging in CASA. No significant radio emission was detected at the position of GRB 251129A. We place a 3σ upper limit of 0.066 mJy beam⁻¹ on the flux density. We encourage coordinated and continued radio follow-up to further constrain the flux density and probe potential variability at C band and complementary frequencies. We thank the e-MERLIN TAG and operations teams for their support. View this GCN Circular online at https://gcn.nasa.gov/circulars/43040. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41119] LAT GRB251208.43: Global MASTER-Net observations report
by GCN Circulars 09 Dec '25

09 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43039 SUBJECT: LAT GRB251208.43: Global MASTER-Net observations report DATE: 25/12/09 00:11:28 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 [1] located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) was pointed to the LAT GRB251208.43 (trigger No 786881842,15h 13m 55.20s , +29d 04m 12.0s, R=0.07) errorbox 23885 sec after notice time and 49564 sec after trigger time at 2025-12-09 00:03:21 UT, with upper limit up to 12.9 mag. The observations began at zenith distance = 82 deg. The sun altitude is -47.7 deg. The galactic latitude b = 58 deg., longitude l = 45 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3064689 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 49654 | 2025-12-09 00:03:21 | MASTER-Kislovodsk | (15h 12m 35.31s , +29d 07m 16.4s) | C | 180 | 12.9 | 49654 | 2025-12-09 00:03:21 | MASTER-Kislovodsk | (15h 12m 31.18s , +28d 44m 43.8s) | C | 180 | 12.6 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/43039. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41118] GRB 251205A: Liverpool Telescope further optical follow-up observations
by GCN Circulars 08 Dec '25

08 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43038 SUBJECT: GRB 251205A: Liverpool Telescope further optical follow-up observations DATE: 25/12/08 21:58:15 GMT FROM: A. Bochenek at Liverpool John Moores University <a.m.bochenek(a)2023.ljmu.ac.uk> A. Bochenek, D. A. Perley (LJMU), report: We observed the field of GRB 251205A (Lanava et al., GCN 43005) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 4x100s exposures in the SDSS i and r filters starting at 2025-12-08 05:21:03 UT, approximately 2.24 days after trigger. We report detections in the stacked images of both filters, at the position first reported by Lanava et al., GCN 43005: MJD (mid) T_mid-T_0 Filter Mag. (AB) 61017.22543 53.8 h i 21.02 ± 0.19 61017.23156 53.9 h r 21.14 ± 0.26 The photometry was obtained using nearby PanSTARRS secondary standards and was not corrected for extinction. The photometry is consistent with late-time optical measurements by Mandarakas et al., GCN 43011; Pérez-Fournon et al., GCN 43020; Bochenek & Perley, GCN 43024; and Hagio et al., GCN 43029. View this GCN Circular online at https://gcn.nasa.gov/circulars/43038. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41117] GRB 251208D: LCO optical upper limits
by GCN Circulars 08 Dec '25

08 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43037 SUBJECT: GRB 251208D: LCO optical upper limits DATE: 25/12/08 20:27:36 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> D. Turpin, A. Saccardi (CEA/Irfu), D. B. Malesani (DAWN/NBI and Radboud), Z.-Y. Lin, F. Cangemi (APC), report on behalf of the SVOM mission team: We observed the field of the SVOM GRB 251208D (Lin et al., GCN 43032) with the LCO 1m telescope at South African Astronomical Observatory equipped with the Sinistro instrument. Our observation started on 2025-12-08 at 19:02:27 UT (about 2.18 hr after the trigger) and we obtained 3x200 s exposures in the SDSS r and 3x200 s exposures in the Pan-STARRS z filters. In the stacked image, we do not detect any new source within the ECLAIRs error circle. We measure the following upper limits calibrated against the PanSTARRS DR1 catalog, and not corrected for Galactic extinction: r > 21.6 AB (mid-time 2.27 hr after the trigger); z > 19.7 AB (mid-time 2.65 hr after the trigger). This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/43037. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41116] SVOM GRB251208.70: Global MASTER-Net observations report
by GCN Circulars 08 Dec '25

08 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43036 SUBJECT: SVOM GRB251208.70: Global MASTER-Net observations report DATE: 25/12/08 19:28:32 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Kislovodsk robotic telescope [1] located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) was pointed to the SVOM GRB251208.70 (trigger No 1765212621,22h 30m 08.33s , -00d 23m 30.5s, R=0.1962) errorbox 6047 sec after notice time and 7322 sec after trigger time at 2025-12-08 18:52:23 UT, with upper limit up to 13.3 mag. The observations began at zenith distance = 73 deg. The sun altitude is -56.3 deg. MASTER-SAAO robotic telescope located in South Africa (South African Astronomical Observatory) was pointed to the SVOM GRB251208.70 errorbox 7366 sec after notice time and 8641 sec after trigger time at 2025-12-08 19:14:22 UT, with upper limit up to 19.0 mag. The observations began at zenith distance = 56 deg. The sun altitude is -17.9 deg. The galactic latitude b = -47 deg., longitude l = 66 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3064681 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 7382 | 2025-12-08 18:52:23 | MASTER-Kislovodsk | (22h 29m 37.06s , -00d 21m 55.6s) | C | 120 | 12.6 | 7382 | 2025-12-08 18:52:23 | MASTER-Kislovodsk | (22h 29m 37.94s , -00d 00m 13.8s) | C | 120 | 13.2 | 8671 | 2025-12-08 19:14:22 | MASTER-SAAO | (22h 28m 00.88s , -00d 37m 02.0s) | C | 60 | 18.9 | 8671 | 2025-12-08 19:14:22 | MASTER-SAAO | (22h 26m 18.28s , -00d 21m 13.1s) | C | 60 | 18.5 | 8764 | 2025-12-08 19:15:54 | MASTER-SAAO | (22h 27m 55.90s , -00d 37m 31.3s) | C | 60 | 19.0 | 8764 | 2025-12-08 19:15:54 | MASTER-SAAO | (22h 26m 13.40s , -00d 21m 40.9s) | C | 60 | 18.6 | 8867 | 2025-12-08 19:17:38 | MASTER-SAAO | (22h 26m 12.54s , -00d 20m 34.9s) | C | 60 | 18.5 | 8892 | 2025-12-08 19:18:03 | MASTER-Kislovodsk | (22h 29m 36.09s , -00d 22m 32.0s) | C | 60 | 12.2 | 8892 | 2025-12-08 19:18:03 | MASTER-Kislovodsk | (22h 29m 39.94s , -00d 01m 05.5s) | C | 60 | 13.2 | 8972 | 2025-12-08 19:19:22 | MASTER-Kislovodsk | (22h 29m 33.23s , -00d 02m 12.0s) | C | 60 | 13.3 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/43036. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41115] GRB 251208B: Swift ToO observations
by GCN Circulars 08 Dec '25

08 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43035 SUBJECT: GRB 251208B: Swift ToO observations DATE: 25/12/08 19:26:56 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 ToO observation of the Fermi/LAT-detected event GRB 251208B. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/ToO_GRBs/00021893 Any uncatalogued X-ray sources detected in this analysis will be reported on this website and via GCN COUNTERPART notices. These are not necessarily related to the Fermi/LAT event. 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/43035. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41114] GRB 251208B: Fermi-LAT detection
by GCN Circulars 08 Dec '25

08 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43034 SUBJECT: GRB 251208B: Fermi-LAT detection DATE: 25/12/08 18:51:48 GMT FROM: chiara.bartolini-1(a)unitn.it E. Bissaldi (Politecnico and INFN Bari), N. Di Lalla (Stanford University), R. Gupta (NASA/GSFC), A. Holzmann Airasca (UniTrento and INFN Bari), C. Bartolini (UniTrento and INFN Bari) and F. Longo (University and INFN, Trieste) report on behalf of the Fermi-LAT team: At 10:17:17.29 UT on December, 08, 2025 Fermi-LAT detected high-energy emission from GRB 251208B, which was also detected by Fermi-GBM (trigger 786881842 / 251208429, GCN #43028) and Swift/BAT-GUANO (GCN #43033). The best LAT on-ground location is found to be RA, Dec = 228.48, 29.07 (J2000) with an error radius of 0.07 deg (90 % containment, statistical error only), which is consistent with the Swift/BAT-GUANO localization. This was 39 deg from the LAT boresight at the time of the trigger. The data from the Fermi-LAT show a significant increase in the event rate that is spatially and temporally correlated with the trigger with high significance. The photon flux above 100 MeV in the time interval 0 - 1 ks after the GBM trigger is (3.13 ± 0.09)E-6 ph/cm2/s. The estimated photon index above 100 MeV is -2.01 ± 0.23. The highest-energy photon is a 17 GeV event which is observed 419 seconds after the GBM trigger. A Swift ToO has been approved for this burst. The Fermi-LAT point of contact for this burst is Chiara Bartolini (chiara.bartolini(a)ba.infn.it) The Fermi-LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden. View this GCN Circular online at https://gcn.nasa.gov/circulars/43034. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41113] GRB 251208B: Swift/BAT-GUANO arcminute localization of a burst
by GCN Circulars 08 Dec '25

08 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43033 SUBJECT: GRB 251208B: Swift/BAT-GUANO arcminute localization of a burst DATE: 25/12/08 18:03:30 GMT FROM: Jimmy DeLaunay at Penn State <delauj2(a)gmail.com> James DeLaunay (PSU), Aaron Tohuvavohu (Cosmic Frontier), Samuele Ronchini (GSSI), Gayathri Raman (PSU), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC), Maia Williams (Northwestern) report: Swift/BAT did not localize GRB 251208B onboard (T0: 2025-12-08T10:17:17.29 UTC, Fermi Trig 786881842). 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), detects the burst in a 8.192 s analysis time bin starting at T0 - 2.048 s with a sqrt(TS) of 17.6. An arcminute localization is found with DeltaLLHOut of 43 and a DeltaLLHPeak of 30.0. See Section 9.1 and Figures 10 and 17 in the NITRATES paper for brief descriptions and interpretations of sqrt(TS), DeltaLLHPeak, and DeltaLLHOut. The BAT position is RA, Dec = 228.453, 29.044 deg which is RA(J2000) = 15h 13m 48.72s Dec(J2000) = 29d 02’ 38.4″ with an estimated uncertainty of 5 arcmin radius. More details about this burst can be found on the trigger report page here: https://guano.swift.psu.edu/trigger_report?id=786881874 XRT and UVOT follow-up has been requested. Results of follow-up observations will be reported in future circulars. 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/43033. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41112] GRB 251208D: SVOM possible detection of a faint burst
by GCN Circulars 08 Dec '25

08 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43032 SUBJECT: GRB 251208D: SVOM possible detection of a faint burst DATE: 25/12/08 17:25:54 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Z.-Y. Lin, F. Cangemi (APC), D. Turpin, S. Schanne (CEA/Irfu), F. Daigne (IAP) At 2025-12-08T16:51:43 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 251208D (SVOM burst-id sb25120806). 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 1 alert. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 6.64 in the [8-120] keV energy band over a time window of 81.92 seconds starting at 2025-12-08T16:50:21. The localization of the best alert is R.A., Dec. 337.5347, -0.3918 degrees: R.A. (J2000) = 22h30m08.33s Dec. (J2000) = -0d23m30.32s with a 90% confidence level (C.L.) radius of 11.77 arcmin (including systematic error of 2 arcmin added in quadrature). Due to the detection significance being below the slew threshold, no immediate slew was performed on this burst. A SVOM ToO has been requested. MXT and VT ToO observation results will be reported in dedicated GCN Circulars. 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 Zhe-Yu Lin: zheyu.lin(a)apc.in2p3.fr. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/43032. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41111] GRB 251206A: SVOM detection of a burst through offline search
by GCN Circulars 08 Dec '25

08 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43031 SUBJECT: GRB 251206A: SVOM detection of a burst through offline search DATE: 25/12/08 16:55:31 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. Brunet, J.-L. Atteia (IRAP), N. Dagoneau (CEA), report on behalf of the SVOM team: The SVOM/ECLAIRs telescope detected a transient source, labelled GRB 251206A, starting at 2025-12-06T20:48:20.92 UTC (T0), through an offline search with the event-by-event data downloaded through the X-band ground station. The burst was detected within several energy ranges and timescales. The best detection is obtained by the Image Trigger (IMT) with a signal-to-noise ratio of 8.5 within 4-20 keV over a time window of 20.48 seconds starting at T0-20.48s. The lightcurve shows an asymmetric double-peaked structure, with a minor peak followed by a major peak, lasting around 20 s. The localization of the source is RA, Dec = 1.843, -4.404 degrees: RA (J2000) = 00h07m22.32s Dec (J2000) = -04d24m16.85s with a 90% C.L. radius of 10.9 arcmin (including systematic error of 6 arcmin added in quadrature). We note that no bright catalogued X-ray sources are found in the error box. The time-averaged spectrum from T0 to T0+20.48s in the energy range 5-120 keV is best fitted by a power law. The powerlaw index is -1.96 -0.15/+0.17. With this model, the total fluence in 4-120 keV is (3.56 +0.28/-0.57)e-7 erg/cm^2. All quoted errors are at the 68% confidence level. The Space 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. ECLAIRs was developed jointly by APC, CEA, CNES, and IRAP. The SVOM point of contact for this event is : Marius Brunet : marius.brunet at irap.omp.eu Please contact him by email if you require additional information regarding the SVOM follow-up of this burst. View this GCN Circular online at https://gcn.nasa.gov/circulars/43031. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41110] GRB 251208C: Fermi GBM Final Real-time Localization
by GCN Circulars 08 Dec '25

08 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43030 SUBJECT: GRB 251208C: Fermi GBM Final Real-time Localization DATE: 25/12/08 13:03:09 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 SHORT GRB At 12:52:32 UT on 8 Dec 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251208C (trigger 786891157.548312 / 251208536). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 312.8, Dec = -30.7 (J2000 degrees, equivalent to J2000 20h 51m, -30d 41'), with a statistical uncertainty of 4.8 degrees. The angle from the Fermi LAT boresight is 84.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251208536/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251208536/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251208536/… View this GCN Circular online at https://gcn.nasa.gov/circulars/43030. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41109] GRB 251205A : MITSuME Akeno optical afterglow candidate detection
by GCN Circulars 08 Dec '25

08 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43029 SUBJECT: GRB 251205A : MITSuME Akeno optical afterglow candidate detection DATE: 25/12/08 10:54:40 GMT FROM: hagio.h.ffca(a)m.isct.ac.jp H. Hagio, Y. Kubo, I. Takahashi, M. Sasada, H. Seki, A. Ochi, R. Kato, S. Joshima, Y. Yatsu and N. Kawai (Science Tokyo) report on behalf of the MITSuME collaboration: We observed the field of GRB 251205A detected by Swift (Lanava et al., GCN 43005) with the optical three-color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50-cm telescope Akeno. The observation started at 2025-12-06 16:56:58 UT (16.3 hr after the trigger). We stacked the images taken under good conditions. We detected a point source in the Rc- and Ic-band images at a position of the reported optical candidate (Lipunov et al., GCN 43004; Lanava et al., GCN 43005; Lipunov et al., GCN 43006; Malesani et al., GCN 43009; O'Neill et al., GCN 43010; Mandarakas et al., GCN 43011; Pankov et al., GCN 43012; Bochenek et al., GCN 43015; Klingler et al., GCN 43016; Patil et al., GCN 43019; Pérez-Fournon et al., GCN 43020; Bochenek et al., GCN 43024; Busmann et al., GCN 43026 ). Our photometric results can be contaminated by the flux from the nearby galaxy. Here we report the preliminary magnitudes of the source as follows. T0+[sec] | MID-UT | T-EXP[sec] | magnitudes --------------------------------------------------------------------------------------------------------------- 68759 | 2025-12-06 18:45:46 | 4860 | Rc=19.1+/-0.2, Ic=18.8+/-0.2 --------------------------------------------------------------------------------------------------------------- T0+ : Elapsed time after the trigger T-EXP: Total exposure time We used the PS1 catalog for flux calibration. The catalog magnitudes in PS1 g, r and i bands were converted to our g', Rc and Ic band magnitudes following Tonry et al. (2012), Table 6. The magnitudes are expressed in the AB system. The images were processed in real-time through the MITSuME GPU reduction pipeline (Niwano et al. 2021, PASJ; https://github.com/MNiwano/Eclaire) View this GCN Circular online at https://gcn.nasa.gov/circulars/43029. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41108] GRB 251208B: Fermi GBM Final Real-time Localization
by GCN Circulars 08 Dec '25

08 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43028 SUBJECT: GRB 251208B: Fermi GBM Final Real-time Localization DATE: 25/12/08 10:27:53 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 10:17:17 UT on 8 Dec 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251208B (trigger 786881842.294214 / 251208429). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 212.3, Dec = 30.1 (J2000 degrees, equivalent to J2000 14h 09m, 30d 06'), with a statistical uncertainty of 5.8 degrees. The angle from the Fermi LAT boresight is 25.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251208429/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251208429/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251208429/… View this GCN Circular online at https://gcn.nasa.gov/circulars/43028. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41107] GRB 251208A: Fermi GBM Final Real-time Localization
by GCN Circulars 08 Dec '25

08 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43027 SUBJECT: GRB 251208A: Fermi GBM Final Real-time Localization DATE: 25/12/08 09:36:35 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 SHORT GRB At 09:25:57 UT on 8 Dec 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251208A (trigger 786878762.38767 / 251208393). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 32.8, Dec = -66.7 (J2000 degrees, equivalent to J2000 02h 11m, -66d 42'), with a statistical uncertainty of 3.9 degrees. The angle from the Fermi LAT boresight is 56.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251208393/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251208393/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251208393/… View this GCN Circular online at https://gcn.nasa.gov/circulars/43027. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41106] GRB 251205A: FTW optical and NIR observations
by GCN Circulars 07 Dec '25

07 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43026 SUBJECT: GRB 251205A: FTW optical and NIR observations DATE: 25/12/07 23:06:48 GMT FROM: Malte Busmann at Ludwig-Maximilians-Universität München <m.busmann(a)physik.lmu.de> Malte Busmann (LMU), Xander J. Hall (CMU), Jule Augustin (LMU), Brendan O’Connor (CMU), Daniel Gruen (LMU), and Antonella Palmese (CMU) report: We observed the counterpart of GRB 251205A (Lavana et al. GCN 43005) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i, z, J, and Ks bands. We detect the counterpart across all bands. | Start Time | t - t0 (days) | Filter | Exposures | Magnitude (AB) | |---------------------|---------------|--------|-----------------------|----------------| | 2025-12-06T03:25:42 | 0.157 | r' | 5 x 150 s + 5 x 180 s | 18.09 +/- 0.05 | | 2025-12-06T03:25:42 | 0.157 | i' | 5 x 150 s | 18.10 +/- 0.05 | | 2025-12-06T03:41:46 | 0.168 | z' | 5 x 180 s | 17.74 +/- 0.05 | | 2025-12-06T03:42:00 | 0.168 | J | 5 x 180 s | 17.46 +/- 0.05 | | 2025-12-06T03:25:55 | 0.157 | Ks | 10 x 60 s | 17.13 +/- 0.05 | These measurements are consistent with the magnitudes reported by Lavana et al. (GCN 43005), Lipunov et al. (GCN 43006), Malesani et al. (GCN 43009), O’Neill et al. (GCN 43010), Mandarakas et al. (GCN 43011), Bochenek & Perley (GCN 43015), Klinger et al. (GCN 43016), Patil et al. (GCN 43019), Pérez-Fournon et al. (GCN 43020), and Bochenek et al. (GCN 13024). The r, i, and z-band magnitudes are calibrated against the PS1 catalog, and the J and Ks-band magnitudes are calibrated with the 2MASS Catalog. All magnitudes are provided in the AB system and are not corrected for Galactic extinction. We thank Michael Schmidt from the Wendelstein Observatory for obtaining these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/43026. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41105] EP-WXT trigger 01709249380: KAIT confirmation of a stellar flare
by GCN Circulars 07 Dec '25

07 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43025 SUBJECT: EP-WXT trigger 01709249380: KAIT confirmation of a stellar flare DATE: 25/12/07 22:39:57 GMT FROM: Weikang Zheng at UC Berkeley <weikang(a)berkeley.edu> WeiKang Zheng (UCB), Xuhui Han (NAOC), Pinpin Zhang (NAOC) 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, automatically responded to the EP-WXT trigger 01709249380 (Li et al. GCN 43021) starting at 09:30 UT, about 11 minutes after the trigger. A set of clear (roughly R) filter images were obtained and lasted for ~2 hours. We performed the photometry on the suggested flare star 2MASS J05100460-0428037 and see its brightness decreased from ~10.8 mag to ~11.2 mag in about 15 minutes, then remained ~11.2 mag afterward, thus confirming the EP X-ray trigger is related to the stellar flare. Our result also confirms the observations from Perez-Garcia et al. (GCN 43022) who reported similar decrease in mag from the flare star. View this GCN Circular online at https://gcn.nasa.gov/circulars/43025. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41104] GRB 251205A: Liverpool Telescope further optical follow-up observations
by GCN Circulars 07 Dec '25

07 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43024 SUBJECT: GRB 251205A: Liverpool Telescope further optical follow-up observations DATE: 25/12/07 16:36:22 GMT FROM: A. Bochenek at Liverpool John Moores University <a.m.bochenek(a)2023.ljmu.ac.uk> A. Bochenek, D. A. Perley (LJMU), report: We observed the field of GRB 251205A (Lanava et al., GCN 43005) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 4x100s exposures the SDSS i and r filters starting at 2025-12-07 04:57:54 UT, approximately 29.3 hours after trigger. Some exposures were affected by telescope wobble or poor seeing and had to be discarded before stacking. We report detections in both filters, at the position first reported by Lanava et al., GCN 43005: MJD (mid) T_mid-T_0 Filter Mag. (AB) 61016.21035 29.4 h i 19.57 ± 0.06 61016.21529 29.5 h r 19.72 ± 0.07 The photometry is consistent with measurements by Lanava et al. GCN 43005; Lipunov et al. GCN 43006; de Ugarte Postigo et al. GCN 43008; Malesani et al. GCN 43009; O’Neill et al., GCN 43010; Mandarakas et al. GCN 43011; Pankov et al., GCN 43012; Bochenek and Perley, GCN 43015; Klingler et al., GCN 43016; Patil et al., GCN 43019; and Pérez-Fournon et al., GCN 43020. The photometry was obtained using nearby PanSTARRS secondary standards and was not corrected for extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/43024. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41103] SVOM GRB251206.86: Global MASTER-Net observations report
by GCN Circulars 07 Dec '25

07 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43023 SUBJECT: SVOM GRB251206.86: Global MASTER-Net observations report DATE: 25/12/07 12:28:31 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 [1] located in Russia (Applied Physics Institute, Irkutsk State University) started inspect of the SVOM GRB251206.86 (trigger No 1765053354,20h 01m 18.62s , -04d 30m 48.6s, R=1) errorbox 53447 sec after notice time and 53742 sec after trigger time at 2025-12-07 11:31:36 UT, with upper limit up to 17.8 mag. The observations began at zenith distance = 71 deg. The sun altitude is -22.6 deg. The galactic latitude b = -18 deg., longitude l = 37 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3062682 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 53773 | 2025-12-07 11:31:36 | MASTER-Tunka | (20h 01m 24.73s , -04d 19m 35.9s) | C | 60 | 17.8 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/43023. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41102] EP-WXT trigger 01709249380: confirmation of a stellar flare by BOOTES-5
by GCN Circulars 07 Dec '25

07 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43022 SUBJECT: EP-WXT trigger 01709249380: confirmation of a stellar flare by BOOTES-5 DATE: 25/12/07 10:30:51 GMT FROM: I. Perez-Garcia at Institute of Astrophysics of Andalusia <ipg(a)iaa.es> I. Perez-Garcia, E. J. Fernandez-Garcia, M. D. Caballero-Garcia, S.-Y. Wu, R. Sanchez-Ramirez, S. Guziy and A. J. Castro-Tirado (IAA-CSIC, Granada), I. M. Carrasco (SMA), M. Gritsevich (Univ. of Helsinki), C. Perez del Pulgar (Univ. of Malaga), Y.-D. Hu (GXU), S. Jeong (ADD, Daejeon), G. Garcia-Segura and D. Hiriart (IA-UNAM, Ensenada), D. R. Xiong (Yunnan Observatories of CAS, Kunming), and W. H. Lee (UNAM, Mexico DF), on behalf of a larger collaboration, report: Following the detection of trigger 01709249380 by EP-WXT (Li et al. GCN 43021), the 0.6m robotic telescopes BOOTES-5/JGU robotic telescope at San Pedro Martir Observatory (Mexico) responded to the alert on Dec 07, 9:25 UT (i.e. 6 min after the detection). Within the reported EP-FXT error circle we find the star 2MASS J05100460-0428037 decreasing 0.3 mag in brightness (g filter) and 0.15 mag (r filter) during a 50 min time interval, confirming the EP X-ray trigger due to a stellar flare. We would like to thank the staff at San Pedro Martir Observatory for their excellent support. View this GCN Circular online at https://gcn.nasa.gov/circulars/43022. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41101] The EP-WXT trigger 01709249380 is likely a flaring star
by GCN Circulars 07 Dec '25

07 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43021 SUBJECT: The EP-WXT trigger 01709249380 is likely a flaring star DATE: 25/12/07 09:58:15 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> R.-Z. Li (YNAO, CAS), K. R. Ni (CCNU), Y. J. Yi (BNU) , X. X. Sun and C. C. Jin (NAO,CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709249380 at the time of 2025-12-07T09:19:14, is likely a stellar flare associated with 2MASS J05100460-0428037 (T Tauri Star). The estimated flux of the flare is around 8e-11erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 6.5e31 erg/s erg/s. 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/43021. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41100] GRB 251205A: ZTF and ATLAS optical afterglow detections
by GCN Circulars 07 Dec '25

07 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43020 SUBJECT: GRB 251205A: ZTF and ATLAS optical afterglow detections DATE: 25/12/07 09:28:50 GMT FROM: Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf(a)iac.es> I. Pérez-Fournon (IAC and ULL), 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, A. Selezneva, T. Tundidor Rodríguez, E. Urquijo-Rodríguez (all ULL) and M. Abdul-Masih (IAC and ULL). We report on ZTF and ATLAS detections of the optical afterglow of the Swift GRB 251205A (Lanava et al., GCN Circ. 43005; Beardmore et al., GCN Circ. 43007; Dichiara et al., GCN Circ. 43017; and Krimm et al., GCN Circ. 43018) at a spectroscopic redshift of z = 1.100 (de Ugarte Postigo et al., GCN Circ. 43008). Both ZTF and ATLAS detected the optical afterglow of GRB 251205A during standard observations of these time-domain surveys. ZTF first detected this transient (ZTF25acgbeof) on 2025-12-06 at 12:16:12 UT at a ZTF g-band magnitude of g-ZTF = 19.168 +/- 0.169. It was reported to the Transient Name Server by Rehemtulla et al. (AT 2025afws, TNS Astronomical Transient Report No. 279483). Using the ATLAS forced-photometry server (Shingles et al. 2021, Transient Name Server AstroNote 2021-7), we find three ATLAS detections, as reported in the following table of ZTF and ATLAS photometry: MJD mag (AB) error survey filter 61015.511250 19.168 0.169 ZTF g 61015.543854 18.788 0.105 ZTF r 61015.625035 19.062 0.279 ATLAS orange 61015.628805 19.225 0.321 ATLAS orange 61015.646040 18.889 0.229 ATLAS orange These ZTF and ATLAS detections are consistent with other reported UV and optical detections: Lanava et al. (GCN Circ. 43005), Lipunov et al. (GCN Circ. 43006), de Ugarte Postigo et al. (GCN Circ. 43008), Malesani et al. (GCN Circ. 43009), O'Neill et al. (GCN Circ. 43010), Mandarakas et al. (GCN Circ. 43011), Pankov et al. (GCN Circ. 43012), Bochenek and Perley (GCN Circ. 43015), Klingler et al. (GCN Circ. 43016), and Patil et al. (GCN Circ. 43019). The ZTF coordinates of ZTF25acgbeof / AT 2025afws are RA (J2000) = 13:21:05.324, Dec (J2000) = 29:55:43.64, consistent within the errors with the optical and X-ray positions of the GRB 251205A afterglow reported by Lanava et al. (GCN Circ. 43005), Lipunov et al. (GCN Circ. 43006), Beardmore et al. (GCN Circ. 43007), de Ugarte Postigo et al. (GCN Circ. 43008), and Klingler et al. (GCN Circ. 43016). 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/43020. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41099] GRB 251205A: GROWTH-India Telescope optical observations
by GCN Circulars 07 Dec '25

07 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43019 SUBJECT: GRB 251205A: GROWTH-India Telescope optical observations DATE: 25/12/07 08:44:48 GMT FROM: V. Swain at IIT Bombay <vishwajeet.s(a)iitb.ac.in> S. Patil, A.P. Saikia, V. Swain, V. Vijaykumar, T. Mohan, 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 Swift GRB 251205A (Lanava et al., GCN Circ. 43005), with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2025-12-05T23:46:13 UT, i.e., 6.43 minutes after the Swift BAT trigger. We obtained multiple exposures in r' filter. We detected the optical afterglow in our stacked image of r' filter at position reported by Swift UVOT (Lanava et al., GCN Circ. 43005). The photometry results are as follow: | MJD (mid) | Filter | t-t0 (in minutes) |Total Exposure Time (sec) | Magnitude (AB) | | ------------- | ------ |-----| ------------------ | -------------- | | 61014.99251157 | r' | 9.43 | 360 | 16.84 +/- 0.06 | | 61015.00966435 | r' | 34.13 | 360 | 17.02 +/- 0.06 | 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 (Lipunov et al., GCN 43004, de Ugarte Postigo et al., GCN 43008, Malesani et al. GCN 43009, O'Neill et al. 43010, Mandarakas et al. GCN 43011, Pankov et al. 43012, Bochenek et al. 43015, Klingler et al. 43016, ). 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/43019. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41098] GRB 251205A: Swift-BAT refined analysis
by GCN Circulars 07 Dec '25

07 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43018 SUBJECT: GRB 251205A: Swift-BAT refined analysis DATE: 25/12/07 04:06:20 GMT FROM: Amy <yarleen(a)gmail.com> H. A. Krimm (NSF), S. D. Barthelmy (GSFC), R. Gupta (GSFC), S. Laha (GSFC/UMBC), S. Lanava (PSU), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), M. J. Moss (GSFC), D. M. Palmer (LANL), T. Parsotan (GSFC), D. Sadaula (GSFC/UMBC), T. Sakamoto (AGU) (i.e. the Swift-BAT team): Using the data set from T-239 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 251205A (trigger #1420873) (Lanava et al., GCN Circ. 43005). The BAT ground-calculated position is RA, Dec = 200.260, 29.906 deg which is RA(J2000) = 13h 21m 02.5s Dec(J2000) = +29d 54' 21.2" with an uncertainty of 2.1 arcmin, (radius, sys+stat, 90% containment). The partial coding was 45%. The mask-weighted light curve shows a weak pulse that starts at ~T0 and peaks at ~T+9 s. The main pulse ends at ~T+40s, followed by a weak tail emission that lasts till ~T+140 s. T90 (15-350 keV) is 128.00 +- 65.97 sec (estimated error including systematics). The time-averaged spectrum from T+0.94 to T+144.94 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.67 +- 0.27. The fluence in the 15-150 keV band is 1.1 +- 0.2 x 10^-06 erg/cm2. The 1-sec peak photon flux measured from T+8.44 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/1420873 View this GCN Circular online at https://gcn.nasa.gov/circulars/43018. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41097] GRB 251205A: Swift-XRT refined Analysis
by GCN Circulars 07 Dec '25

07 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43017 SUBJECT: GRB 251205A: Swift-XRT refined Analysis DATE: 25/12/07 03:50:01 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> S. Dichiara (PSU), J.A. Kennea (PSU), D.N. Burrows (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), C. Salvaggio (INAF-OAB), M. Ferro (INAF-OAB), R. Brivio (INAF-OAB) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 6.3 ks of XRT data for GRB 251205A, from 129 s to 94.1 ks after the trigger. The data comprise 352 s in Windowed Timing (WT) mode (the first 9 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The late-time light curve (from T0+9.7 ks) can be modelled with a power-law decay with a decay index of alpha=0.77 (+0.12, -0.11). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 2.14 (+/-0.06). The best-fitting absorption column is 5.6 (+1.3, -1.2) x 10^20 cm^-2, in excess of the Galactic value of 1.2 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.95 (+0.16, -0.15) and a best-fitting absorption column of 3.8 (+3.5, -2.6) x 10^20 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.4 x 10^-11 (3.7 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 3.8 (+3.5, -2.6) x 10^20 cm^-2 Galactic foreground: 1.2 x 10^20 cm^-2 Excess significance: <1.6 sigma Photon index: 1.95 (+0.16, -0.15) The results of the XRT-team automatic analysis are available at https://www.swift.ac.uk/xrt_products/01420873. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/43017. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41096] GRB 251205A: Swift/UVOT Detection
by GCN Circulars 06 Dec '25

06 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43016 SUBJECT: GRB 251205A: Swift/UVOT Detection DATE: 25/12/06 18:47:19 GMT FROM: N. Klingler at NASA-GSFC/UMBC/CRESST II <noelklingler(a)gmail.com> N. Klingler (NASA-GSFC / UMBC / CRESST II) and Sophia Lanava (PSU) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 251205A 149 s after the BAT trigger (Lanava et al., GCN Circ. 43005). A source consistent with the XRT position (RA, Dec = 13h 21m 05.26s, +29d 55' 44.2"; Beardmore et al., GCN Circ. 43007) is detected in the initial UVOT exposures. The preliminary UVOT position is: RA (J2000) = 13:21:05.34 = 200.27223 (deg.) Dec (J2000) = +29:55:44.0 = 29.92890 (deg.) with an estimated uncertainty of 0.43 arc sec. (radius, 90% confidence). Preliminary detections using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: Filter T_start(s) T_stop(s) Mag white 148.9 298.7 17.61 +/- 0.06 white 586.8 606.5 16.96 +/- 0.09 white 759.1 869.1 16.89 +/- 0.08 white 16513.5 17308.6 17.77 +/- 0.05 b 562.4 582.2 17.32 +/- 0.17 b 734.9 754.7 17.29 +/- 0.18 b 15601.3 16508.4 18.18 +/- 0.05 u 306.8 556.6 16.65 +/- 0.06 u 710.3 730.0 16.57 +/- 0.16 u 22323.1 22838.7 17.51 +/- 0.06 v 636.4 656.2 17.10 +/- 0.27 v 808.6 828.4 16.92 +/- 0.24 v 10660.9 11393.6 18.45 +/- 0.10 uvw1 685.8 705.5 16.18 +/- 0.18 uvw1 21416.9 22316.6 17.83 +/- 0.07 uvw2 9754.6 10654.4 18.44 +/- 0.10 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.014 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/43016. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41095] GRB 251205A: Liverpool Telescope optical follow-up observations
by GCN Circulars 06 Dec '25

06 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43015 SUBJECT: GRB 251205A: Liverpool Telescope optical follow-up observations DATE: 25/12/06 18:26:59 GMT FROM: A. Bochenek at Liverpool John Moores University <a.m.bochenek(a)2023.ljmu.ac.uk> A. Bochenek, D. A. Perley (LJMU), report: We observed the field of GRB 251205A (Lanava et al., GCN 43005) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 4x100s exposures the SDSS i and r filters starting at 2025-12-06 05:37:14 UT, approximately 5.95 hours after trigger. Some exposures were affected by telescope movement and had to be discarded. We report detections in both filters, at the position first reported by Lanava et al. GCN 43005: MJD (mid) T_mid-T_0 Filter Mag. (AB) 61015.23465 5.97 h i 17.93 ± 0.05 61015.24283 6.16 h r 18.06 ± 0.03 The photometry is consistent with measurements by Lanava et al. GCN43005; Lipunov et al. GCN 43006; de Ugarte Postigo et al. GCN 43008; Malesani et al. GCN 43009; O’Neill et al., GCN 43010; Mandarakas et al. GCN 43011 and Pankov et al., GCN 43012. The photometry was obtained using nearby PanSTARRS secondary standards and was not corrected for extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/43015. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41094] GRB 251203C: Swift/UVOT Upper Limit
by GCN Circulars 06 Dec '25

06 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43014 SUBJECT: GRB 251203C: Swift/UVOT Upper Limit DATE: 25/12/06 18:22:42 GMT FROM: N. Klingler at NASA-GSFC/UMBC/CRESST II <noelklingler(a)gmail.com> Swift/UVOT has performed follow-up observations of the field of GRB 251203C, starting 20.3 ks after the SVOM trigger sb25120305 (Brunet et al; GCN Circ. 42976). No source is detected at the position of the optical counterpart (R.A., Dec. = 51.701538, -7.382688) reported by Li et al. (GCN Circ. 42987) and Turpin et al. (GCN Circ. 42988). 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) are: Filter T_start(s) T_stop(s) Exp(s) Mag(AB) u 20269 20514 241 >20.69 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.046 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/43014. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41093] Konus-Wind detection of GRB 251118A
by GCN Circulars 06 Dec '25

06 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43013 SUBJECT: Konus-Wind detection of GRB 251118A DATE: 25/12/06 16:38:47 GMT FROM: Valentina Panteleeva at Ioffe Institute <panteleevav228(a)gmail.com> V. Panteleeva, D. Frederiks, A. Lysenko, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB 251118A (Fermi-GBM detection: The Fermi GBM team, GCN 42743; Palafox and Meegan, GCN 42783; BALROG localization: Preis and Greiner, GCN 42745; Fermi-LAT detection: Gupta and Khalil, GCN 42752; GECAM-B detection: Ren et al., GCN 42779; Glowbug detection: Cheung et al., GCN 42784) triggered Konus-Wind at T0=73904.449 s UT (20:31:44.449). The burst light curve starts, at ~T0-20.5 s, with a short soft initial pulse (precursor) which had a duration of about 25.8 s. The precursor is followed, starting at ~T0+32 s, by the main episode, lasting for ~25 s. The total duration of the burst is ~48 s. The emission in the main episode is seen up to ~3 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB251118_T73904/ As observed by Konus-Wind, the burst had the total fluence of 1.07(-0.03,+0.03)x10^-4 erg/cm2, and the 64-ms peak flux, measured from T0+35.776 s, of 2.03(-0.15,+0.15)x10^-5 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the initial pulse (measured from T0 to T0+8.448 s) is best described in the 20 keV - 10 MeV range by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -1.94(-0.03,+0.12) and Ep < 41 keV (chi2 = 89/85 dof). Fitting this spectrum by a GRB (Band) model results in the same estimates of alpha and Ep, and gives only an upper limit on the high energy photon index beta of -2.8 (chi2 = 89/84 dof). The time-averaged spectrum of the main episode (measured from T0+33.024 to T0+65.536 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 = -1.29(-0.03,+0.04), the high energy photon index beta = -2.56(-0.08,+0.07), the peak energy Ep = 154(-5,+5) keV (chi2 = 110/97 dof). The spectrum near the maximum count rate (measured from T0+33.024 to T0+36.608 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 = -0.74(-0.05,+0.06), the high energy photon index beta = -2.53(-0.10,+0.08), the peak energy Ep = 251(-12,+12) keV (chi2 = 68/69 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/43013. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41092] GRB 251205A: Zeiss-1000 Koshka observatory optical observations
by GCN Circulars 06 Dec '25

06 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43012 SUBJECT: GRB 251205A: Zeiss-1000 Koshka observatory optical observations DATE: 25/12/06 14:44:43 GMT FROM: Alexei Pozanenko at IKI, Moscow <grb.alex(a)gmail.com> N. Pankov (HSE,IKI), A. Novichonok (Petrozavodsk State University, KIAM), S. Schmalz (KIAM), A. Volnova (IKI), A. Pozanenko (IKI) report on behalf of IKI GRB-FuN: We observed the optical afterglow of GRB 251205A (Lanava et al., GCN 43005; Lipunov et al., GCN 43006; de Ugarte Postigo et al., GCN 43008; Malesani et al., GCN 43009; O'Neill et al., GCN 43010) using the Zeiss-1000 telescope at Koshka observatory (INASAN). The observations started/ended on 2025-12-06 (UT) 00:57:28/04:07:07. Preliminary photometry of the initial stacked image is the following Date UT start t-T0 Exp. Filter OT Err. UL(3sigma) (mid, days) (s) 2025-12-06 00:57:28 0.05747 10*90 R 17.92 0.06 20.5 The photometry is based on nearby USNO-B1.0 stars and not corrected for Galaxy extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/43012. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41091] GRB 251205A: Zeiss-1000 Koshka observatory optical observations
by GCN Circulars 06 Dec '25

06 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43012 SUBJECT: GRB 251205A: Zeiss-1000 Koshka observatory optical observations DATE: 25/12/06 14:44:43 GMT FROM: Alexei Pozanenko at IKI, Moscow <grb.alex(a)gmail.com> N. Pankov (HSE,IKI), A. Novichonok (Petrozavodsk State University, KIAM), S. Schmalz (KIAM), A. Volnova (IKI), A. Pozanenko (IKI) report on behalf of IKI GRB-FuN: We observed the optical afterglow of GRB 251205A (Lanava et al., GCN 43005; Lipunov et al., GCN 43006; de Ugarte Postigo et al., GCN 43008; Malesani et al., GCN 43009; O'Neill et al., GCN 43010) using the Zeiss-1000 telescope at Koshka observatory (INASAN). The observations started/ended on 2025-12-06 (UT) 00:57:28/04:07:07. Preliminary photometry of the initial stacked image is the following Date UT start t-T0 Exp. Filter OT Err. UL(3sigma) (mid, days) (s) 2025-12-06 00:57:28 0.05747 10*90 R 17.92 0.06 20.5 The photometry is based on nearby USNO-B1.0 stars and not corrected for Galaxy extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/43012. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41090] GRB 251205A: Zeiss-1000 Koshka observatory optical observations
by GCN Circulars 06 Dec '25

06 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43012 SUBJECT: GRB 251205A: Zeiss-1000 Koshka observatory optical observations DATE: 25/12/06 14:44:43 GMT FROM: Alexei Pozanenko at IKI, Moscow <grb.alex(a)gmail.com> N. Pankov (HSE,IKI), A. Novichonok (Petrozavodsk State University, KIAM), S. Schmalz (KIAM), A. Volnova (IKI), A. Pozanenko (IKI) report on behalf of IKI GRB-FuN: We observed the optical afterglow of GRB 251205A (Lanava et al., GCN 43005; Lipunov et al., GCN 43006; de Ugarte Postigo et al., GCN 43008; Malesani et al., GCN 43009; O'Neill et al., GCN 43010) using the Zeiss-1000 telescope at Koshka observatory (INASAN). The observations started/ended on 2025-12-06 (UT) 00:57:28/04:07:07. Preliminary photometry of the initial stacked image is the following Date UT start t-T0 Exp. Filter OT Err. UL(3sigma) (mid, days) (s) 2025-12-06 00:57:28 0.05747 10*90 R 17.92 0.06 20.5 The photometry is based on nearby USNO-B1.0 stars and not corrected for Galaxy extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/43012. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41089] GRB 251205A: COLIBRÍ optical observations
by GCN Circulars 06 Dec '25

06 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43011 SUBJECT: GRB 251205A: COLIBRÍ optical observations DATE: 25/12/06 12:07:07 GMT FROM: nikos.mandarakas(a)lam.fr Nikos Mandarakas (LAM), Margarita Pereyra (UNAM), 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), 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), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM): We imaged the field of the Swift GRB 251205A (S. Lanava et al., GCN Circ. 43005) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2025-12-06 10:04:31 to 10:47:46 UTC (from 10.41 to 11.13 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 detected the optical counterpart S. Lanava et al. (GCN Circ. 43005); V. M. Lipunov et al. (GCN Circ. 43006); A. de Ugarte Postigo et al. (GCN Circ. 43008); D. B. Malesani et al. (GCN Circ. 43009) and D. O’Neill et al. (GCN Circ. 43010), at a preliminary magnitude of: r = 18.26 +/- 0.03 z = 17.97 +/- 0.02 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/43011. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41088] GRB 251205A: GOTO optical afterglow detection
by GCN Circulars 06 Dec '25

06 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43010 SUBJECT: GRB 251205A: GOTO optical afterglow detection DATE: 25/12/06 11:03:38 GMT FROM: d.s.oneill(a)bham.ac.uk D. O'Neill, G. Ramsay, A. Kumar, B. Gompertz, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, S. Belkin, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien,, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, D. Pollacco, J. Casares Vel'azquez, T. Killestein, B. Godson on behalf of 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 the GRB 251205A. Serendipitous observations from the all-sky survey covered the position of the counterpart (Malesani et al., GCN 43009; Lanava et al., GCN 43005; Lipunov et al., GCN 43006; de Ugarte Postigo et al., GCN 43008) at 2025-12-06 06:12:01 UT, (+6.5h post trigger). Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations. The counterpart was detected in the GOTO L-band (400-700nm) mag = 18.16 ± 0.12 (AB). Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and 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, the University of Birmingham and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/43010. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41087] GRB 251205A: NOT optical observations
by GCN Circulars 06 Dec '25

06 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43009 SUBJECT: GRB 251205A: NOT optical observations DATE: 25/12/06 09:45:00 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), A. K. Aris-Kiss (Helsinki), M. Korp-Lagg (Aalto University), S. Wedemeyer (Oslo), S. Armas Perez (NOT) report on behalf of a larger collaboration: We observed the optical afterglow of GRB 251205A (Lanava et al., GCN 43005; Lipunov et al., GCN 43006; de Ugarte Postigo et al., GCN 43008) using the Nordic Optical Telescope (NOT) equipped with the StanCam camera. Observations started on 2025-12-06 at 05:25:33 UT (5.75 hr after the trigger). Five 150 s observations were taken using the StanCam “interference i” filter. The optical afterglow is well detected in single images. At a mean time of 5.90 hr after the trigger, we measure a magnitude i = 17.93 +- 0.03. This magnitude is in the AB system and is not corrected for Galactic extinction. We note that, due to the small field-of-view of StanCam, only one star from the Pan-STARRS catalog could be used for photometric calibration. Considering that the StanCam i filter is (slightly) different from the Pan-STARRS one, an extra systematic error of 0.1 mag should be conservatively added to the photometric error budget. View this GCN Circular online at https://gcn.nasa.gov/circulars/43009. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41086] GRB 251205A: GTC/OSIRIS+ redshift z = 1.100
by GCN Circulars 06 Dec '25

06 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43008 SUBJECT: GRB 251205A: GTC/OSIRIS+ redshift z = 1.100 DATE: 25/12/06 09:08:39 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> A. de Ugarte Postigo (LAM), S. Geier (GTC), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), C. C. Thoene (AbAO), L. Izzo (INAF/OACN and DARK/NBI), J. F. Agui Fernandez (CAHA), M. A. Aloy (UV), J. P. U. Fynbo (DAWN/NBI), L. Galbany (IEEC-CSIC), G. Lombardi (GTC), N. A. Rakotondrainibe (LAM), B. Schneider (LAM), N. R. Tanvir (Univ. Leicester), D. Perez Valladares (GTC) report: We observed the optical counterpart of GRB 251205A (Lanava et al., GCN 43005; Lipunov et al., GCN 43006) using the Gran Telescopio Canarias (GTC) equipped with the OSIRIS+ instrument. In the 30-s acquisition image (beginning on 2025-12-06 at 05:21:34 UT, that is 5.68 hr after trigger), the optical afterglow is well detected with a magnitude i = 17.78 +- 0.03 AB, calibrated against nearby Pan-STARRS objects, and not corrected for Galactic extinction. We also report the following, improved coordinates (0.3" accuracy): RA(J2000) = 13:21:05.32 Dec(J2000) = +29:55:43.6 A total of 4 spectra by 900 s were secured, starting on 2025-12-06 at 05:31:22 UT (5.86 hr after trigger), using grism R1000B. Continuum is detected over the range 3750-7750 AA. A number of absorption features are detected, which we interpret as due to Fe II 2344, 2383, 2586, 2600, Mg II 2796, 2803, and Mg I 2852, all at a common redshift z = 1.100, which we suggest to be the redshift of GRB 251205A. Given the redshift value measured in absorption, it is thus unlikely that the GRB is associated with the nearby, bright galaxy with photometric redshift z = 0.25 noted by Lipunov et al. (GCN 43006). View this GCN Circular online at https://gcn.nasa.gov/circulars/43008. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41085] GRB 251205A: Enhanced Swift-XRT position
by GCN Circulars 06 Dec '25

06 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43007 SUBJECT: GRB 251205A: Enhanced Swift-XRT position DATE: 25/12/06 03:12:58 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 366 s of XRT Photon Counting mode data and 1 UVOT images for GRB 251205A, 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 = 200.27190, +29.92894 which is equivalent to: RA (J2000): 13h 21m 05.26s Dec (J2000): +29d 55' 44.2" with an uncertainty of 2.4 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/43007. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41084] Swift GRB 251205A : MASTER OT detection with host galaxy
by GCN Circulars 06 Dec '25

06 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43006 SUBJECT: Swift GRB 251205A : MASTER OT detection with host galaxy DATE: 25/12/06 01:42:41 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.M. Lipunov (Lomonosov MSU), V.Senik, E.Gorbovskoy, A.Kuznetsov, I.Panchenko, G.Antipov, P.Balanutsa, K.Zhirkov, N. Tiurina, Ya.Kechin,A.Chasovnikov, D.Vlasenko, Yu.Tselik(Lomonosov MSU, SAI, Moscow), O.A.Gress, N.M.Budnev, O.Ershova (Irkutsk State University), R. Podesta, C.Francile, F. Podesta, E. Gonzalez (OAFA, San JuanUni.,Argentina); D.Buckley (SAAO), A. Sosnovskij (CrAO RAS), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysic Observatory, Mexico) V.M.Pillet, R.Rebolo Lopez (The Instituto de Astrofisica de Canarias,Spain) MASTER-Kislovodsk robotic telescope of MASTER Global Robotic Net (Lipunov et al. [1-4], http://observ.pereplet.ru ), started Swift GRB 251205A (Lanava et al GCN 43005) error-box observations in alert mode (PP filters) 19s after notice time at at 2025-12-05 23:41:19 UT, Lipunov et al. GCN 43004 MASTER auto-detection system found optical counterpart MASTER OT J132105.37+295545.8 , first publishied by Swift (GCN 43005) with unfiltered m_OT~18.1m We have also prompt wide-field cameras images, the reduction will be later. There is host(possible) galaxy in 4.36" from GRB counterpart with z_phot=0.25470(Cavuoti et al. 2014) Real time updated cover map and OT position are available here: https://master.sai.msu.ru/site/master2/observ.php?id=3062088 Observation and reduction will continue. [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/43006. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41083] GRB 251205A: Swift detection of a burst with an optical afterglow
by GCN Circulars 06 Dec '25

06 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43005 SUBJECT: GRB 251205A: Swift detection of a burst with an optical afterglow DATE: 25/12/06 00:02:39 GMT FROM: David Palmer at LANL <palmer(a)lanl.gov> S. Lanava (PSU), S. Dichiara (PSU), C. Gronwall (PSU), R. Gupta (NASA GSFC), N. P. M. Kuin (UCL-MSSL), A. Y. Lien (U Tampa), D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 23:39:47 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 251205A (trigger=1420873). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 200.243, +29.962 which is RA(J2000) = 13h 20m 58s Dec(J2000) = +29d 57' 45" 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 ~500 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 23:42:07.0 UT, 139.8 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 200.2707, 29.9296 which is equivalent to: RA(J2000) = 13h 21m 4.97s Dec(J2000) = +29d 55' 46.6" with an uncertainty of 5.3 arcseconds (radius, 90% containment). This location is 145 arcseconds from the BAT onboard position, within the BAT error circle. No event data are yet available to determine the column density using X-ray spectroscopy. The initial flux in the 2.5 s image was 1.44e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 148 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 13:21:05.34 = 200.27223 DEC(J2000) = +29:55:44.0 = 29.92888 with a 90%-confidence error radius of about 0.75 arc sec. This position is 5.4 arc sec. from the center of the XRT error circle. The estimated magnitude is 17.54 with a 1-sigma error of about 0.14. No correction has been made for the expected extinction corresponding to E(B-V) of 0.014. Burst Advocate for this burst is S. Lanava (sml7284 AT psu.edu) 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/43005. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41082] Swift GRB251205.99: Global MASTER-Net observations report
by GCN Circulars 05 Dec '25

05 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43004 SUBJECT: Swift GRB251205.99: Global MASTER-Net observations report DATE: 25/12/05 23:48:53 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 [1] located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) was pointed to the Swift GRB251205.99 (trigger No 1420873,13h 20m 58.42s , +29d 57m 45.0s, R=0.05) errorbox 19 sec after notice time and 92 sec after trigger time at 2025-12-05 23:41:19 UT, with upper limit up to 17.0 mag. The observations began at zenith distance = 68 deg. The sun altitude is -51.1 deg. The galactic latitude b = 83 deg., longitude l = 55 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3062088 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 103 | MASTER-Kislovodsk | P- | 20 | 16.6 | 103 | MASTER-Kislovodsk | P| | 20 | 16.5 | 131 | MASTER-Kislovodsk | P- | 20 | 16.3 | 131 | MASTER-Kislovodsk | P| | 20 | 16.5 | 164 | MASTER-Kislovodsk | P- | 30 | 16.8 | 164 | MASTER-Kislovodsk | P| | 30 | 16.8 | 208 | MASTER-Kislovodsk | P- | 40 | 16.8 | 208 | MASTER-Kislovodsk | P| | 40 | 16.8 | 261 | MASTER-Kislovodsk | P- | 50 | 17.0 | 261 | MASTER-Kislovodsk | P| | 50 | 17.0 | The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/43004. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41081] GRB 251126B: Fermi GBM Final Localization
by GCN Circulars 05 Dec '25

05 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43003 SUBJECT: GRB 251126B: Fermi GBM Final Localization DATE: 25/12/05 17:22:08 GMT FROM: Boyan A. Hristov at UAH <bah0046(a)uah.edu> The Fermi GBM team reports the detection of a likely LONG GRB "At 15:57:02.80 UT on 26 November 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251126B (trigger 785865427/251126665). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 321.15, Dec = -28.24 (J2000 degrees, equivalent to J2000 21h 24m, -28d 14'), with a statistical uncertainty of 14.32 degrees. The angle from the Fermi LAT boresight is 73 degrees. The skymap can be found here: sftp://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251126665/q… The HEALPix FITS file, including the estimated localization systematic, can be found here: sftp://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251126665/q… The GBM light curve can be found here: sftp://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251126665/q…" View this GCN Circular online at https://gcn.nasa.gov/circulars/43003. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41080] GRB 251203A: Insight-HXMT/HE detection
by GCN Circulars 05 Dec '25

05 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43002 SUBJECT: GRB 251203A: Insight-HXMT/HE detection DATE: 25/12/05 15:48:13 GMT FROM: renyz16607(a)163.com Yang-Zhao Ren, Chen-Wei Wang, Cheng-Kui Li, Shao-Lin Xiong, and Chao Zheng (IHEP) report on behalf of the Insight-HXMT team: At 2025-12-03T08:18:50.250 (T0), Insight-HXMT/HE detected a long burst, GRB 251203A, which is also detected by Fermi/GBM (Fermi GBM team, GCN#42968), SVOM/GRM (Ren et al., GCN#42995), and GECAM-B (Ren et al., GCN#42996). The Insight-HXMT/HE light curve mainly consists of multiple pulses with T90 of 11 +5/-5 s. The 1s peak rate, measured from T0-0.5 s, is 351 cnts/sec. Insight-HXMT/HE detected a total of 1399 counts from this burst. The Insight-HXMT /HE light curve can be found here: https://www.bursthub.cn//admin/static/hxmtgrb251203A.png All measurements above are made with the CsI detectors of Insight-HXMT/HE operating in the Low-Gain mode with the energy range of about 300-3000 keV (deposited energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope. Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://www.hxmt.org View this GCN Circular online at https://gcn.nasa.gov/circulars/43002. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41079] GRB 251203C: SVOM/ECLAIRs refined analysis
by GCN Circulars 05 Dec '25

05 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43001 SUBJECT: GRB 251203C: SVOM/ECLAIRs refined analysis DATE: 25/12/05 14:17:52 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> N. Dagoneau (CEA), M. Brunet, N. A. Webb (IRAP) Using the event-by-event data downloaded through the X-band ground station, we report further analysis of ECLAIRs observations of GRB 251203C (SVOM burst-id sb25120305). The burst that triggered ECLAIRs onboard (GCN 42976) consists of a multiple peaks lightcurve with a duration of T90 = 13.0 -4.7/+1.6 s in the 4-120 keV energy band. The time-averaged spectrum (from T0-3.59s to T0+9.49s) in the energy range 5-120 keV is best fit by a simple power-law model with a photon index -1.98 -0.17/+0.18. The total fluence in the 4-120 keV band is (3.63 -0.59/+0.27)e-7 erg/cm^2. All the quoted errors are at the 68% confidence level. 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/43001. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41078] SVOM/sb25120502: SVOM detection of a faint X-ray transient candidate
by GCN Circulars 05 Dec '25

05 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43000 SUBJECT: SVOM/sb25120502: SVOM detection of a faint X-ray transient candidate DATE: 25/12/05 13:40:22 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> W. J. Xie, D. H. Zhao (NAOC), S. Schanne (CEA/Irfu), Marius Brunet, J.-L. Atteia (IRAP) report on behalf of the SVOM mission team: At 2025-12-05T02:57:15 UTC (T0), SVOM/ECLAIRs triggered and located a possible X-ray transient (SVOM burst-id sb25120502). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The transient was only detected by the Image Trigger (IMT), which produced a sequence of 1 alert. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 6.58 in the [8-50] keV energy band over a time window of 20.48 seconds starting at 2025-12-05T02:56:55. After the reception over X-band of the photon by photon data, those have been replayed on ground in the Offline trigger as well as a ground copy of the On-board trigger, by varying the trigger timescales. The event is still detected as a point-like source at the same position in the same energy band as given by the on-board trigger, over the same 20.48 s time-window. The sky images obtained are clean and show no sign of the source before and after that time period. The localization of the best alert is R.A., Dec. 80.9924, -18.2171 degrees: R.A. (J2000) = 5h23m58.16s Dec. (J2000) = -18d13m01.48s with a 90% confidence level (C.L.) radius of 11.88 arcmin (including systematic error of 2 arcmin added in quadrature). No immediate slew was performed on this burst. No X-ray observation could be performed by SVOM/MXT for the time being. No optical observation could be performed by SVOM/VT for the time being. We notice the presence of the High Proper Motion star LP 777-23, located at 9.3 arcmin from the trigger position. 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 contact point for this alert is Wenjin XIE: xiewj(a)bao.ac.cn Please contact by the email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/43000. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41077] SVOM/sb25120502: SVOM detection of a faint X-ray transient candidate
by GCN Circulars 05 Dec '25

05 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43000 SUBJECT: SVOM/sb25120502: SVOM detection of a faint X-ray transient candidate DATE: 25/12/05 13:40:22 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> W. J. Xie, D. H. Zhao (NAOC), S. Schanne (CEA/Irfu), Marius Brunet, J.-L. Atteia (IRAP) report on behalf of the SVOM mission team: At 2025-12-05T02:57:15 UTC (T0), SVOM/ECLAIRs triggered and located a possible X-ray transient (SVOM burst-id sb25120502). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The transient was only detected by the Image Trigger (IMT), which produced a sequence of 1 alert. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 6.58 in the [8-50] keV energy band over a time window of 20.48 seconds starting at 2025-12-05T02:56:55. After the reception over X-band of the photon by photon data, those have been replayed on ground in the Offline trigger as well as a ground copy of the On-board trigger, by varying the trigger timescales. The event is still detected as a point-like source at the same position in the same energy band as given by the on-board trigger, over the same 20.48 s time-window. The sky images obtained are clean and show no sign of the source before and after that time period. The localization of the best alert is R.A., Dec. 80.9924, -18.2171 degrees: R.A. (J2000) = 5h23m58.16s Dec. (J2000) = -18d13m01.48s with a 90% confidence level (C.L.) radius of 11.88 arcmin (including systematic error of 2 arcmin added in quadrature). No immediate slew was performed on this burst. No X-ray observation could be performed by SVOM/MXT for the time being. No optical observation could be performed by SVOM/VT for the time being. We notice the presence of the High Proper Motion star LP 777-23, located at 9.3 arcmin from the trigger position. 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 contact point for this alert is Wenjin XIE: xiewj(a)bao.ac.cn Please contact by the email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/43000. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41076] GRB 251202A / EP251202a: ULL-ASTRO-MASTER detection of the optical afterglow with LCO 40-cm and 1-m telescopes at McDonald Observatory
by GCN Circulars 05 Dec '25

05 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42999 SUBJECT: GRB 251202A / EP251202a: ULL-ASTRO-MASTER detection of the optical afterglow with LCO 40-cm and 1-m telescopes at McDonald Observatory DATE: 25/12/05 12:55:58 GMT FROM: Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf(a)iac.es> M. Contreras, J. Basurto Merino, P.G. Berdayes, A. Caballero-Almagro, A. Cerón, 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, A. Selezneva, T. Tundidor Rodríguez, E. Urquijo-Rodríguez (all ULL), M. Abdul-Masih (IAC and ULL), and I. Pérez-Fournon (IAC and ULL). We report on observations of the optical counterpart of GRB 251202A / EP251202a, detected by Fermi/GBM (Fermi GBM Team, GCN Circ. 42933; and Bala, GCN Circ. 42957), Einstein Probe (EP) (Zhang et al., GCN Circ. 42937; and Liang et al., GCN Circ. 42946), Swift-XRT (Sbarufatti et al., GCN Circ. 42943), AstroSat CZTI (Arya et al., GCN Circ. 42967), Insight-HXMT/HE (Guo et al., GCN Circ. 42970), and SVOM/GRM (Guo et al., GCN Circ. 42997). We observed the field of GRB 251202A / EP251202a with the Las Cumbres Observatory (LCO) 40-cm telescope and one of the two LCO 1-m telescopes located at the LCO node at McDonald Observatory, Texas. The first observation, with the 40-cm telescope, started on 2025-12-02 at 06:29:14 UT, about 4.67 hours after the Fermi and EP trigger. The optical counterpart first reported by Li et al. (GCN Circ. 42934), at a spectroscopic redshift of z = 2.785 (Zhu et al., GCN Circ. 42939), is clearly detected in our images with the following AB magnitudes, calibrated against PanSTARRS-1 DR2 stars and not corrected for Galactic extinction: Date | UT start | mag | error | filter | exposure time (sec) | telescope --------------------------------------------------------------------------------------- 2025-12-02 06:29:14 18.76 0.18 SDSS r' 300 LCO 40-cm 2025-12-02 07:43:09 19.19 0.08 SDSS g' 180 LCO 1-m 2025-12-02 07:46:39 18.91 0.07 SDSS r' 180 LCO 1-m 2025-12-02 07:50:11 18.71 0.08 SDSS i' 180 LCO 1-m Our results are consistent with other UV and optical observations: Li et al. (GCN Circ. 42934), Lipunov et al. (GCN Circ. 42938), Zhu et al. (GCN Circ. 42939), O’Neill et al. (GCN Circ. 42947), Quirola-Vasquez et al. (GCN Circ. 42948), Kuin and Moss (GCN Circ. 42956), Zheng et al. (GCN Circ. 42964), Ma et al. (GCN Circ. 42966), and Bochenek et al . (GCN Circ. 42977). This work makes use of observations from the Las Cumbres Observatory global telescope network (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/42999. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41075] GRB 251203C: SVOM/COLIBRÍ (FM-GFT) optical upper limit
by GCN Circulars 05 Dec '25

05 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42998 SUBJECT: GRB 251203C: SVOM/COLIBRÍ (FM-GFT) optical upper limit DATE: 25/12/05 11:31:43 GMT FROM: nikos.mandarakas(a)lam.fr Nikos Mandarakas (LAM), Alan M. Watson (UNAM), Fredd Sanchez Alvarez (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), 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), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), M. Brunet (IRAP), N. A. Webb (IRAP): We imaged the field of the SVOM GRB 251203C (Brunet et al., GCN 42976) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-12-05T04:55:27 to 2025-12-05T06:22:35 UTC (from 34.36 to 35.81 hours after the trigger) and obtained 3840 seconds of exposure in the r and z filters. The data were reduced, coadded, and analyzed with the COLIBRÍ pipeline. The photometry was calibrated using nearby stars from the Pan-STARRS-DR1 catalog, is in the AB system, and was not corrected for Galactic extinction. In the stacked image, we no longer detect the optical counterpart reported by H.L. Li (GCN Circ. 42987) and D. Turpin et al. (CGN Circ. 42988), down to the following 3σ limit: r > 22.91 z > 22.47 We do detect a nearby extended source with coordinates RA = 51.782, Dec = -7.31, which is also seen in the Pan-STARRS-DR1 catalog, and could potentially correspond to the host of the GRB. The magnitudes we detect are: r = 22.34 +/- 0.14 z = 21.96 +/- 0.14 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/42998. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41074] GRB 251202A: SVOM/GRM observation
by GCN Circulars 05 Dec '25

05 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42997 SUBJECT: GRB 251202A: SVOM/GRM observation DATE: 25/12/05 08:13:34 GMT FROM: guohx(a)ihep.ac.cn SVOM/GRM team: Hao-Xuan Guo, Chao Zheng, Xing-Hao Luo, Chen-Wei Wang, Zheng-Hang Yu, Yue Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Nicolas Dagoneau (CEA) Report on behalf of the SVOM team: SVOM/GRM was triggered on-ground by EP251202a/GRB 251202A at 2025-12-02T01:51:02.000 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN #42933 and #42957), Einstein Probe (Einstein Probe (EP) team, GCN #42934, #42937 and #42946), GOTO (GOTO collaboration, GCN #42947) and Insight-HXMT (Insight-HXMT team, GCN #42970). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a single pulse with a T90 of 16 +8/-4 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb251202A.png In addition, the position of this burst, as determined by Swift-XRT (RA = 122.11512, Dec = 40.61228, GCN #42943), is located at about 134 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. ECLAIRs was not collecting data at the time of this burst. 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: Hao-Xuan Guo (IHEP)(guohx(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/42997. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41073] GRB 251203A: GECAM-B observation of a burst
by GCN Circulars 05 Dec '25

05 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42996 SUBJECT: GRB 251203A: GECAM-B observation of a burst DATE: 25/12/05 07:58:43 GMT FROM: renyz16607(a)163.com Yang-Zhao Ren, Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered on-ground by GRB 251203A, at 2025-12-03T08:18:45.150 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #42968), and SVOM/GRM (Ren et al., GCN #42995). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of multiple pulses with a duration (T90) of 14 +1/-3 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb251203A.png Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS). View this GCN Circular online at https://gcn.nasa.gov/circulars/42996. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41072] GRB 251203A: SVOM/GRM observation
by GCN Circulars 05 Dec '25

05 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42995 SUBJECT: GRB 251203A: SVOM/GRM observation DATE: 25/12/05 05:45:12 GMT FROM: renyz16607(a)163.com SVOM/GRM team: Yang-Zhao Ren, Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Nicolas Dagoneau (CEA), Jean-Luc Atteia (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered on-ground by GRB 251203A at 2025-12-03T08:18:45.150 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN #42968). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multiple pulses with a T90 of 14.5 +2.5/-1.5 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb251203A.png In addition, the position of this burst, as determined by Fermi/GBM (RA = 165.5, Dec = -46.9, GCN #42968), is located at about 94 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+20 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.40 +0.23/-0.28 and the cutoff energy, parameterized as Epeak, is 185 +83/-42 keV. The event fluence (10-1000 keV) in this time interval is (7.87 +0.94/-0.88)E-06 erg/cm^2. The 1s peak spectrum, measured from T0+14.85 to T0+15.85 s, if fitted by a power law function with an exponential high-energy cutoff, the power law index is -1.65 +0.14/-0.17 and the cutoff energy, parameterized as Epeak, is 1040 +1700/-630 keV. The flux (10-1000 keV) in this time interval is (1.41 +0.13/-0.14)E-06 erg/cm^2/s. The localization of GRB 251203A in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb251203A_amati.png The localization of GRB 251203A in the 'Yonetoku' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb251203A_yonetoku.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: Yang-Zhao Ren (IHEP)(renyz(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/42995. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41071] GRB 251201B: SALT spectroscopic redshift z = 1.599
by GCN Circulars 04 Dec '25

04 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42994 SUBJECT: GRB 251201B: SALT spectroscopic redshift z = 1.599 DATE: 25/12/04 23:55:00 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> D. B. Malesani (DAWN/NBI and Radboud), A. J. Levan (Radboud and Warwick), S. de Wet (DTU Space), A. de Ugarte Postigo (LAM), D. A. H. Buckley (SAAO), A. Martin-Carrillo (UCD), P. M. Vreeswijk (Radboud) report on behalf of a larger collaboration: We observed the optical afterglow of the Swift and Fermi GRB 251201B (Moss et al., GCN 42924; Palafox & Meegan, GCN 42965), using the Robert Stobie Spectrograph (RSS) installed on the 9.2 m Southern African Large Telescope (SALT) at the Sutherland observatory (South Africa). In a 10-s acquisition image, taken with the SALTICAM instrument on 2025 Dec 1.871 UT (4.47 hr after trigger), we measure a magnitude i = 19.25 +- 0.09 AB, calibrated against nearby stars from the Pan-STARRS catalog, and not corrected for Galactic extinction. A 2400-s spectrum was acquired using the PG0700 grating, covering the wavelength range 3600-7500 AA. Faint continuum is detected across the entire spectrum, setting a secure upper limit to the redshift z < 2. Towards the red end, we identify a few weak absorption features, which we match to Mg I 2852, Mg II 2804, 2796, Fe II 2600, 2587, 2383, all at a common redshift of z = 1.599, which we suggest to be the redshift of GRB 251201B. We acknowledge excellent support from the SALT observing staff, in particular Alexei Kniazev and Veronica Van Dyk. View this GCN Circular online at https://gcn.nasa.gov/circulars/42994. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41070] GRB 251203C: J-band observations with WINTER
by GCN Circulars 04 Dec '25

04 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42993 SUBJECT: GRB 251203C: J-band observations with WINTER DATE: 25/12/04 21:59:48 GMT FROM: Geoffrey Mo at Caltech / Carnegie Observatories <gmo(a)mit.edu> Geoffrey Mo (Caltech/Carnegie), Benjamin Schneider (LAM), Tomas Ahumada (NOIRLab), Robert Stein (UMD), Viraj Karambelkar (Columbia), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report: We observed the field of GRB 251203C (Brunet et al., GCN 42976; Wu et al., GCN 42986) 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 2025-12-04T02:48:19 UTC in the J band (~8.2 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 do not detect a source at the optical counterpart location (Turpin et al., GCN 42980; Li et al., GCN 42987; Turpin et al., GCN 42988). We obtain the following 5-sigma upper limit: J ~ 19.3 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/42993. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41069] GRB 251129B: Glowbug gamma-ray detection of a short burst
by GCN Circulars 04 Dec '25

04 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42992 SUBJECT: GRB 251129B: Glowbug gamma-ray detection of a short burst DATE: 25/12/04 21:03:54 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, confirms the detection of the short GRB 251129B, which was detected by AstroSat/CZTI (GCN 42958), Konus-Wind, Swift/BAT, Mars-Odyssey/HEND (GCN 42960), and GECAM-B (GCN 42984). The light curve comprises a single peak at 2025-11-29 09:51:33.20 with a duration of 0.16s. 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/42992. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41068] GRB 251203A: AstroSat CZTI detection
by GCN Circulars 04 Dec '25

04 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42991 SUBJECT: GRB 251203A: AstroSat CZTI detection DATE: 25/12/04 18:21:20 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> Harsha K. H. (IUCAA), S. Salunke (IUCAA), M. Tembhurnikar (IUCAA), A. Arya (IITB), A. Goyal (IITB), U. Pathak (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 GRB 251203A which was also detected by Fermi GBM (Fermi GBM Team, GCN Circ. 42968), and Konus-IPN (via IPN Notices). 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 2025-12-03 08:19:00.50 UTC. The measured peak count rate associated with the burst is 148 (+38, -16) counts/s above the background in the combined data of three quadrants (out of four), with a total of 775 (+165, -169) counts. The local mean background count rate was 225 (+3, -3) counts/s. Using cumulative rates, we measure a T90 of 15 (+2, -3) 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 2025-12-03 08:18:47.01 UTC. The measured peak count rate associated with the burst is 150 (+70, -22) counts/s above the background in the combined data of all quadrants, with a total of 989 (+427, -457) counts. The local mean background count rate was 1321 (+7, -8) counts/s. We measure a T90 of 15 (+1, -7) 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/42991. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41067] EP251130a: JinShan near-infrared observations
by GCN Circulars 04 Dec '25

04 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42990 SUBJECT: EP251130a: JinShan near-infrared observations DATE: 25/12/04 16:38:15 GMT FROM: syfu(a)nao.cas.cn S.Y. Fu (HUST), L.B. He (NAOC), A.D. Zhu, L. Lei, H.Z. Wu, W.H. Lei (HUST), J. An, S.Q. Jiang, X. Liu, Z.P. Zhu, D. Xu (NAOC), J.Z. Liu (XAO) We continued monitoring the optical counterpart of EP251130a (Wu et al., GCN 42903) using the 100C telescope, equipped with the INS-BIue SWIR camera, of the JinShan project, located at Altay, Xinjiang, China. Observation started at 2025-12-01 16:29:07 UT, i.e., 1.22 days post-burst, and a series of J-band frames were obtained. The previously reported optical counterpart (Dornic et al., GCN 42904; He et al. GCN 42914; Gupta et al. GCN 42916; Zheng et al. GCN 42917; Dalen et al. GCN 42918; Moskvitin & Spiridonova, GCN 42919; Aryan et al. GCN 42921; Volnova et al. GCN 42922; Ma et al. GCN 42940; Corcoran et al. GCN 42951; Rodríguez et al. GCN 42963; Abidkhanov et al. GCN 42969) was detected in our stacked J-band frame with magnitude J = 19.19 +/- 0.12 (Vega) at a mid-time 1.32 days post-burst. The magnitude was calibrated with the nearby 2MASS catalog and 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/42990. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41066] Fermi Gamma-ray Burst Monitor trigger 786496343/251203967 is not a GRB
by GCN Circulars 04 Dec '25

04 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42989 SUBJECT: Fermi Gamma-ray Burst Monitor trigger 786496343/251203967 is not a GRB DATE: 25/12/04 16:12:47 GMT FROM: Suman Bala at USRA <sumanbala2210(a)gmail.com> S. Bala (USRA) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "The Fermi Gamma-ray Burst Monitor (GBM) trigger 786496343/251203967 at 23:12:18.62 UT on 03 December 2025, tentatively classified as a GRB, is in fact not due to a GRB. This trigger is likely due to background fluctuation (accidental)." View this GCN Circular online at https://gcn.nasa.gov/circulars/42989. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41065] GRB 251203C: LCO optical afterglow confirmation
by GCN Circulars 04 Dec '25

04 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42988 SUBJECT: GRB 251203C: LCO optical afterglow confirmation DATE: 25/12/04 14:54:55 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> D. Turpin, A. Saccardi (CEA/Irfu), D. B. Malesani (DAWN/NBI and Radboud), J. T. Palmerio (CEA/Irfu), L. P. Xin, C. Wu (NAOC), B. Cordier (CEA/Irfu), M. Brunet, N. A. Webb (IRAP), report on behalf of the SVOM mission team: Following the report of an optical counterpart by SVOM/VT (Li et al., GCN 42987) of the SVOM GRB 251203C (Brunet et al., GCN 42976), we inspected again our stacked image from LCO (Turpin et al., GCN 42980). The VT candidate afterglow is detected in our r-band image. At a mean epoch of 37 min after trigger, we measure an SDSS r-band magnitude of r = 19.91 +/- 0.14 (AB, which is significantly brighter than the SVOM/VT magnitudes (despite the filter system difference) measured at a later epoch (> 3.3 hr after trigger). This further confirms that this source is the optical afterglow of GRB 251203C. The z-band upper limit reported by Turpin et al. (GCN 42980) is still confirmed. This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/42988. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41064] GRB 251203C: SVOM/VT optical counterpart
by GCN Circulars 04 Dec '25

04 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42987 SUBJECT: GRB 251203C: SVOM/VT optical counterpart DATE: 25/12/04 14:05:47 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H.L. Li (NAOC), D. Turpin (CEA), Y.N. Ma, L.P. Xin, Y. L. Qiu, C. Wu, Z.H. Yao, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. R. Xu, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA), M. Brunet, N. A. Webb (IRAP) report on behalf of the SVOM/VT team. SVOM/VT performed ToO observation to the field of GRB 251203C triggered by SVOM (Brunet et al., GCN 42976). The observation started at 2025-12-03T21:46:05 UTC, i.e., 3.2 hours post trigger in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. An uncatalogued source was detected within the ECLAIRs's error box (Brunet et al., GCN 42976), compared to the Legacy survey catalog. The position is at R.A., Dec. = 51.701538, -7.382688 degrees, equivalent to: R.A. (J2000) = 03:26:48.36 Dec. (J2000) = -07:22:57.67 with an uncertainty of 0.5 arcsec. The measurements in AB magnitudes are given below: Mid_time Band Exposure Time Magnitude (AB) 3.3 hour VT_B 970 sec 22.1+/-0.1 mag 3.3 hour VT_R 970 sec 21.7+/-0.1 mag 9.7 hour VT_B 4430 sec 23.0+/-0.3 mag 9.7 hour VT_R 4430 sec 22.4+/-0.2 mag Our photometry was not corrected for Galactic extinction. As this source has significantly faded during our observations, we suggest it is the optical afterglow of GRB 251203C. 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/42987. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41063] GRB 251203C: EP-FXT follow-up observation
by GCN Circulars 04 Dec '25

04 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42986 SUBJECT: GRB 251203C: EP-FXT follow-up observation DATE: 25/12/04 14:02:16 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> H.Z. Wu (HUST), Y. Wu (NJU), H. Y. Ren, Tian-Yu Liu, G. J. Yang, W. D. Zhang (NAO, CAS) on behalf of the Einstein Probe (EP) team: EP-FXT performed a follow-up observation of the SVOM/ECLAIRs-detected burst GRB 251203C (SVOM/sb25120305, Brunet et al., GCN #42976) at 2025-12-03 20:12:47 (UTC), about 52 minutes after the SVOM/ECLAIRs trigger, with an exposure time of 4569 s. Four uncataloged sources are detected within the ECLAIRs error circle. Preliminary analysis on these sources is automatically conducted, and the details are listed as follows. EPF_J032718.1-071802 RA (J2000): 51.8268 Dec (J2000): -7.3024 Flux: 9.24 x 10^-14 erg/s/cm2 (observed, 0.5-10 keV) Flux_err: 2.78 x 10^-14 erg/s/cm2 (1 sigma) EPF_J032703.9-072334 RA (J2000): 51.7662 Dec (J2000): -7.3929 Flux: 1.07 x 10^-13 erg/s/cm2 (observed, 0.5-10 keV) Flux_err: 3.23 x 10^-14 erg/s/cm2 (1 sigma) EPF_J032718.1-071802 RA (J2000): 51.8255 Dec (J2000): -7.3005 Flux: 5.85 x 10^-14 erg/s/cm2 (observed, 0.5-10 keV) Flux_err: 2.12 x 10^-14 erg/s/cm2 (1 sigma) EPF_J032658.4-072128 RA (J2000): 51.7434 Dec (J2000): -7.3577 Flux: 1.12 x 10^-13 erg/s/cm2 (observed, 0.5-10 keV) Flux_err: 2.77x 10^-14 erg/s/cm2 (1 sigma) 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/42986. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41062] GRB 251129A/EP251129a : SVOM/ECLAIRs refined analysis
by GCN Circulars 04 Dec '25

04 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42985 SUBJECT: GRB 251129A/EP251129a : SVOM/ECLAIRs refined analysis DATE: 25/12/04 09:35:09 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> H. Yang, M. Brunet, O. Godet, J.-L. Atteia (IRAP), W. J. Xie (NAOC), W. J. Tan (IHEP), D. F. Kong (GXU) Using the event-by-event data downloaded through the X-band ground stations, we report further analysis of ECLAIRs observations of GRB 251129A/EP251129a (SVOM burst-id sb25112901, GCN 42877) detected at T0 = 2025-11-29T02:32:05 UT, which was also detected by EP/WXT (GCN 42884). The burst that triggered ECLAIRs shows a featureless light curve, and is detected from T0-41 s to T0+3200 s in the 4-120 keV energy band, indicating that it may be an ultra-long GRB or a very bright afterglow or a combination of both. The peculiar multi-wavelength temporal behavior of this event makes it a burst of great interest. ECLAIRs observations of GRB 251129A/EP251129a were interrupted by a slew and by a pass through the SAA, which divides the data into three time intervals for the time-averaged spectra analysis. The time-averaged spectrum from T0-41 s to T0+77 s (before the slew) in the 4-120 keV is well fitted by a power-law model with a photon index of 1.7+/-0.1 and a corresponding 4-120 keV flux of (1.5+/-0.2)e-8 erg/cm^2/s. The spectrum from T0+190 s to T0+585 s (after the slew and before the SAA transit) in the 4-120 keV is well fitted by a power-law model with a photon index of 2.1+/-0.1, with a 4-120 keV flux of (3.9+0.5-0.4)e-9 erg/cm^2/s. The spectrum from T0+1600 s to T0+3200 s (after the SAA transit) in the 4-120 keV is well fitted by a power-law model with a photon index of 2.0+/-0.1, with a 4-120 keV flux of (1.5+0.1-0.3)e-9 erg/cm^2/s. Overall, the ECLAIRs spectral analysis shows that GRB 251129A/EP251129a is decreasing in fluxes, and shows no significant spectral evolution from T0+190 s to T0+3200 s. The photon index measured from T0+190 s to T0+3200 s is consistent with that measured from EP/FXT at T0+2643 s (GCN 42902). The long-lasting emission seen by ECLAIRs matches the X-ray emission of the uncatalogued source seen by SVOM/MXT (GCN 42877). All the quoted errors are at the 68% confidence level. 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. ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. The SVOM/ECLAIRs point of contact for this burst is: Hui Yang (IRAP) (hui.yang(a)irap.omp.eu) View this GCN Circular online at https://gcn.nasa.gov/circulars/42985. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41061] GRB 251129B: GECAM-B observation of a burst
by GCN Circulars 04 Dec '25

04 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42984 SUBJECT: GRB 251129B: GECAM-B observation of a burst DATE: 25/12/04 08:30:50 GMT FROM: xueyuan zao <zaoxueyuan(a)gmail.com> Xue-Yuan Zao, Yue Wang, Zheng-Hang Yu, Chen-Wei Wang, Chao Zheng, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered in-flight and on-ground by a short/hard burst GRB 251129B at 2025-11-29T09:51:34.250 UTC (denoted as T0). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of a single pulse main emission with a duration (T90) of 0.25 +0.10/-0.15 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb251129B.png Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS). View this GCN Circular online at https://gcn.nasa.gov/circulars/42984. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41060] GRB 251203B: Swift-XRT observations
by GCN Circulars 03 Dec '25

03 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42983 SUBJECT: GRB 251203B: Swift-XRT observations DATE: 25/12/03 22:35:55 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> S. Lanava (PSU), 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 sb25120304, collecting 972 s of Photon Counting (PC) mode data between T0+4.6 ks and T0+5.7 ks after the trigger. A candidate counterpart has been found. The details of this source are: Source 1 (SWIFT J011326.9+000111): ================================== RA (J2000.0): 18.3625 = 01 13 27.00 Dec (J2000.0): +0.0198 = +00 01 11.3 Error: 3.5 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 5.9 arcmin from the SVOM/ECLAIRs position. Mean rate: 1.785 +/- 0.088 ct s^-1 Mean flux: (5.76 +/- 0.28)e-11 erg cm^-2 s^-1 Peak rate: 2.72 +/- 0.62 ct s^-1 Peak flux: (8.8 +/- 2.0)e-11 erg cm^-2 s^-1 ECF: 3.23e-11 erg cm^-2 ct^-1 assuming NH=1.00e+21 cm^-2, gamma=2.03 determined from a spectral fit. This matches a catalogued X-ray source 4XMM J011326.8+000107 in the XMM-NEWTON/XMMSSC catalogue. Details: Separation: 3.3" from the XRT source Cat Rate: 2.7e-01 +/- 1.0e-02 ct s^-1 Cat Flux: 2.4e-12 +/- 8.9e-14 erg cm^-2 s^-1 (0.3-10 keV) so the source is 4.3-sigma above the catalogued flux. The source may be fading, at the 0.3-sigma level. A SIMBAD object `Gaia DR3 2534635509050352256' is 4.2" away. There is 1 2MASS object within the source's 3-sigma error radius. As pointed out by Malesani et al. (GCNs 42979), Brunet et al. (GCN 42981) and Perez-Garcia at al. (GCN 42982) this suggest that the transient is due to flaring activity from this star. We have detected a total of 4 sources. These have been automatically classified as follows: * 0 likely counterparts * 1 candidate counterpart * 3 uncatalogued X-ray sources * 0 known X-ray sources Uncatalogued X-ray sources -------------------------- Source 2 (SWIFT J011329.9-000900): ================================== RA (J2000.0): 18.3746 = 01 13 29.90 Dec (J2000.0): -0.1502 = -00 09 00.7 Error: 7.9 (arcsec, radius, 90% confidence). Detect flag: POOR Distance: 10.3 arcmin from the SVOM/ECLAIRs position. Mean rate: (6.9 [+4.4, -3.1])e-3 ct s^-1 Mean flux: (3.0 [+1.9, -1.3])e-13 erg cm^-2 s^-1 Peak rate: (6.9 [+4.4, -3.1])e-3 ct s^-1 Peak flux: (3.0 [+1.9, -1.3])e-13 erg cm^-2 s^-1 XMM UL: 1.8e-14 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. Source 3 (SWIFT J011422.6+000036): ================================== RA (J2000.0): 18.5945 = 01 14 22.68 Dec (J2000.0): +0.0102 = +00 00 36.7 Error: 8.3 (arcsec, radius, 90% confidence). Detect flag: POOR Distance: 8.1 arcmin from the SVOM/ECLAIRs position. Mean rate: (6.2 [+4.0, -2.8])e-3 ct s^-1 Mean flux: (2.6 [+1.7, -1.2])e-13 erg cm^-2 s^-1 Peak rate: (6.2 [+4.0, -2.8])e-3 ct s^-1 Peak flux: (2.6 [+1.7, -1.2])e-13 erg cm^-2 s^-1 XMM UL: 1.1e-14 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. Source 4 (SWIFT J011327.9-000300): ================================== RA (J2000.0): 18.3663 = 01 13 27.91 Dec (J2000.0): -0.0501 = -00 03 00.4 Error: 9.4 (arcsec, radius, 90% confidence). Detect flag: POOR Distance: 6.4 arcmin from the SVOM/ECLAIRs position. Mean rate: (-1.0 +/- -1.0)e0 ct s^-1 Mean flux: (-4.3 +/- -4.3)e-11 erg cm^-2 s^-1 Peak rate: (4.0 [+3.3, -2.3])e-3 ct s^-1 Peak flux: (1.7 [+1.4, -1.0])e-13 erg cm^-2 s^-1 XMM UL: 3.6e-14 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. There is 1 2MASS object 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_FIELD00054. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42983. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41059] GRB 251203B: confirmation of a stellar flare by BOOTES-2
by GCN Circulars 03 Dec '25

03 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42982 SUBJECT: GRB 251203B: confirmation of a stellar flare by BOOTES-2 DATE: 25/12/03 21:59:40 GMT FROM: I. Perez-Garcia at Institute of Astrophysics of Andalusia <ipg(a)iaa.es> I. Perez-Garcia, M.D. Caballero-Garcia, E. J. Fernandez-Garcia, R. Sanchez-Ramirez, S.-Y. Wu, S. Guziy, and A. J. Castro-Tirado (IAA-CSIC, Granada), Y.-D. Hu (GXU), C. Perez del Pulgar and A. Reina (Univ. of Malaga), M. Gritsevich (Univ. of Helsinki), R. Fernandez-Munoz (IHSM/UMA-CSIC), D. R. Xiong (Yunnan Observatories of CAS), and M. Jelinek (ASU-CAS, Ondrejov Obs.), on behalf of a larger collaboration, report: Following the detection of trigger sb25120304 by SVOM (Brunet et al. GCN 42973), the 0.6m robotic telescope BOOTES-2/TELMA at IHSM La Mayora/UMA-CSIC (Malaga, Spain) responded to the alert on Dec 3, 18:16 UT (i.e. 7 min after detection). A serie of 3 sec images in clear fiter were taken. As reported by Palmerio et al. (GCN 42978) and Malesani et al. (GCN 42979) we measure the star Gaia DR3 2534635509050352256 to fade by ~1.8 mag over a ~20 min interval, consistent with a stellar flare and confirming its non-GRB origin, as stated in Brunet et al. (GCN 42981). We thank the staff at IHSM La Mayora/UMA-CSIC for their excellent support. View this GCN Circular online at https://gcn.nasa.gov/circulars/42982. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41058] GRB 251203B : SVOM trigger sb25120304 is not a GRB
by GCN Circulars 03 Dec '25

03 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42981 SUBJECT: GRB 251203B : SVOM trigger sb25120304 is not a GRB DATE: 25/12/03 21:50:09 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. Brunet, N. A. Webb (IRAP), D. B. Malesani (DAWN/NBI and Radboud),report on behalf of the SVOM mission team: At 2025-12-03T18:10:27 SVOM issued an alert with burst-id: sb25120304. The following circulars have been published regarding this event: GCN 42973, GCN 42974, GCN 42978, GCN 42979, with the event labelled as GRB 252103B. Given the VT (Palmerio et al., GCN 42978), LCO (Malesani et al., GCN 42979), and XRT observations (https://www.swift.ac.uk/SVOM/SVOM_FIELD00054/) this event is most likely associated with a flare from the star Gaia DR3 2534635509050352256 (also a historical X-ray emitter), and is no longer considered a GRB. We apologize for any inconvenience this may have caused. The Burst Advocate (BA) on shift for this alert is Marius Brunet: mbrunet(a)irap.omp.eu. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/42981. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41057] GRB 251203C: LCO optical upper limits
by GCN Circulars 03 Dec '25

03 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42980 SUBJECT: GRB 251203C: LCO optical upper limits DATE: 25/12/03 21:31:09 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> D. Turpin, A. Saccardi (CEA/Irfu), D. B. Malesani (DAWN/NBI and Radboud), J. T. Palmerio (CEA/Irfu), L. P. Xin, C. Wu (NAOC), B. Cordier (CEA/Irfu), M. Brunet, N. A. Webb (IRAP), report on behalf of the SVOM mission team: We observed the field of the SVOM GRB 251203C (Brunet et al., GCN 42976) with the LCO 1m telescope at South African Astronomical Observatory equipped with the Sinistro instrument. Our observation started on 2025-12-03 at 19:05:17 UT (about 31 min after the trigger) and we obtained 3x200 s exposures in the SDSS r and 2x200 s exposures in the Pan-STARRS z filters. In the stacked image, we do not detect any new source within the ECLAIRs error circle. We measure the following upper limits calibrated against the Pan-STARRS catalog, and not corrected for Galactic extinction: r > 20.2 AB (mid-time 37 min after the trigger); z > 19.0 AB (mid-time 58 min after the trigger). This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/42980. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41056] GRB 251203B: LCO optical upper limits
by GCN Circulars 03 Dec '25

03 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42979 SUBJECT: GRB 251203B: LCO optical upper limits DATE: 25/12/03 21:22:36 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> D. B. Malesani (DAWN/NBI and Radboud), D. Turpin, A. Saccardi, J. T. Palmerio (CEA/Irfu), L. P. Xin, C. Wu (NAOC), B. Cordier (CEA/Irfu), M. Brunet, N. A. Webb (IRAP), report on behalf of the SVOM mission team: We observed the field of the SVOM GRB 251203B (Brunet et al., GCN 42973) with the LCO 1m telescope at South African Astronomical Observatory equipped with the Sinistro instrument. Our observation started on 2025-12-03 at 19:14:38 UT (about 64 min after the trigger) and we obtained 3x200 s exposures in the SDSS r and 3x200 s exposures in the PanSTARRS z filters. In the stacked image, we do not detect any new source within the MXT error circle. We measure the following upper limits calibrated against the Pan-STARRS catalog, and not corrected for Galactic extinction: r > 20.8 AB (mid-time 1.16 hr after the trigger); z > 20.1 AB (mid-time 1.29 hr after the trigger). As already noted by Brunet et al. (GCN 42973) and Palmerio et al. (GCN 42978), within the MXT error circle there is a bright star at RA = 01:13:26.89, Dec = +00:01:07.7, also a possible historical X-ray emitter. Recent Swift/XRT observations (https://www.swift.ac.uk/SVOM/SVOM_FIELD00054/) show this star to be coincident with the only X-ray source within the MXT error circle. This suggests the transient is due to activity from this star. In our z-band image, the star appears about 0.6 mag brighter than its archival Pan-STARRS magnitude (though we caution possible saturation effects), a behavior also consistent with a stellar flare origin of the burst. This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/42979. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41055] GRB 251203B: SVOM/VT optical observation
by GCN Circulars 03 Dec '25

03 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42978 SUBJECT: GRB 251203B: SVOM/VT optical observation DATE: 25/12/03 20:48:28 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> J. T. Palmerio (CEA), D. B. Malesani (DAWN/NBI and Radboud), Y. L. Qiu, C. Wu, H. L. Li, L. P. Xin (NAOC) on behalf of the SVOM/VT team. After the trigger by SVOM/ECLAIRs at 2025-12-03T18:10:27 UTC (T0), SVOM performed an automatic slew on the burst location (Brunet et al., GCN 42973). SVOM/VT began observing the field at 2025-12-03T18:16:09, 341.62 seconds after T0, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. From a preliminary analysis of the 1-bit subimage and source list downloaded via VHF network, no credible candidate is identified down to VT_R~21 mag within the error box provided by MXT (Brunet et al. GCN 42973). We note the presence of the bright star Gaia DR3 2534635509050352256 within the error box of MXT which appeared to fade in our observations from magnitude VT_B = 12.4 to 14.0 over the course of ~1 hr. Despite the difference in photometric filters, this is brighter than its catalogued magnitude of mag g = 15.2 in Pan-STARRS1. 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/42978. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41054] GRB 251202A / EP251202a: Liverpool Telescope optical follow-up observations
by GCN Circulars 03 Dec '25

03 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42977 SUBJECT: GRB 251202A / EP251202a: Liverpool Telescope optical follow-up observations DATE: 25/12/03 20:41:04 GMT FROM: A. Bochenek at Liverpool John Moores University <a.m.bochenek(a)2023.ljmu.ac.uk> A. Bochenek, D. A. Perley (LJMU) and A. Y. Q. Ho (Cornell) report: We observed the field of GRB 251202A/EP251202a (Fermi GBM team, GCN 42933; Bala et al., GCN 42957; Zhang et al., GCN 42937; Liang et al., GCN 42946) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained two epochs, separated by ~30 minutes, of 6x120s exposures with the SDSS r filter starting at 2025-12-03 03:24: UT, approximately 25.8 hours after trigger. We report detections in both epochs, at the position of the afterglow first reported by Li et al., GCN 42934: MJD (mid) T_mid-T_0 Filter Mag. (AB) 61012.15590 25.89 h r 19.99 ± 0.05 61012.17610 26.38 h r 20.18 ± 0.09 The seeing was poor throughout the observations, with the second epoch being more affected. The photometry was calibrated using nearby PanSTARRS secondary standards and was not corrected for extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/42977. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41053] GRB 251203C: SVOM detection of a burst
by GCN Circulars 03 Dec '25

03 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42976 SUBJECT: GRB 251203C: SVOM detection of a burst DATE: 25/12/03 19:20:15 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. Brunet, N. A. Webb (IRAP), N. Dagoneau, M. Moita, D. Turpin (CEA) report on behalf of the SVOM mission team At 2025-12-03T18:33:50 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 251203C (SVOM burst-id sb25120305). 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. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 11.74 in the [8-50] keV energy band over a time window of 10.20 seconds starting at 2025-12-03T18:33:45. The localization of the best alert is R.A., Dec. 51.7804, -7.3100 degrees: R.A. (J2000) = 3h27m07.31s Dec. (J2000) = -7d18m36.09s with a 90% confidence level (C.L.) radius of 6.85 arcmin (including systematic error of 2 arcmin added in quadrature). No immediate slew was performed on this burst. A SVOM ToO has been programmed for follow-up. 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 Marius Brunet: mbrunet(a)irap.omp.eu. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/42976. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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