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[vsnet-grb-info 41023] EP251202a / GRB 251202A: LCO r- and i-band optical detection
by GCN Circulars 02 Dec '25

02 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42948 SUBJECT: EP251202a / GRB 251202A: LCO r- and i-band optical detection DATE: 25/12/02 14:00:22 GMT FROM: Jonathan Quirola at Radboud University <jaquirola1990(a)gmail.com> J. Quirola-Vasquez (Radboud), J. Sanchez-Sierras (Radboud), D. B. Malesani (DAWN/NBI and Radboud), G. Corcoran (UCD), A. Martin-Carrillo (UCD), P. G. Jonker (Radboud), A. J. Levan (Radboud and Warwick), J. A. Chacón (PUC), F. E. Bauer (SSI and UTA), J. N. D. van Dalen (Radboud), A. P. C. van Hoof (Radboud) report on behalf of a larger collaboration: We observed the optical counterpart (Li et al., GCN 42934) of EP251202a (Zhang et al., GCN 42937, Liang et al., GCN 42946) and Fermi GRB 251202A (Fermi GBM team, GCN 42933) with a spectroscopic redshift of z = 2.785 (Zhu et al., GCN 42939) using the Las Cumbres Observatory (LCO) network at the McDonald Observatory, equipped with the SINISTRO camera. Observations were obtained in the r (6x200 s) and i (6x200 s) bands, starting on 2025-12-02 at 09:00:43 UTC (i.e., a mid-time observation of 7.35 and 7.75 hr after the EP/WXT trigger, respectively). Calibrated to nearby stars from the Pan-STARRS catalog, we measure AB magnitudes r = 19.22 +/- 0.06 and i = 19.12 +/- 0.06, not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/42948. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41022] GRB 251202A: GOTO optical afterglow detection
by GCN Circulars 02 Dec '25

02 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42947 SUBJECT: GRB 251202A: GOTO optical afterglow detection DATE: 25/12/02 13:55:02 GMT FROM: d.s.oneill(a)bham.ac.uk D. O’Neill, S. Moran, G. Ramsay, R. Starling, B. P. Gompertz, K. Ackley, M. Dyer, J. Lyman, K. Ulaczyk, D. Steeghs, D. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. Breton, J. Casares, L. Nuttall, B. Godson, T. Killestein, A. Kumar and M. Pursiainen report 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 251202A (Fermi GBM team, GCN 42923; Einstein Probe, GCN 42937). Targeted observations were performed beginning at 2025-12-02 03:00:49 UT, (+1.19h post trigger). Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations. We detect the counterpart (Moss et al., GCN 42924; Osborne et al., GCN 42927; Goyal et al., GCN 42925; Li et al., GCN 42931; Sbarufatti et al. GCN 42943) with magnitude L = 17.92 ± 0.04 AB mag (+1.71h), before fading to L = 18.83 ± 0.07 AB mag (+4.3h). 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/42947. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41021] EP251202a/GRB 251202A: refined analysis of the EP-WXT observations
by GCN Circulars 02 Dec '25

02 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42946 SUBJECT: EP251202a/GRB 251202A: refined analysis of the EP-WXT observations DATE: 25/12/02 12:20:05 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> R. D. Liang (NAOC) Z. M. Wang (BNU), Y. Wu (NJU), Y. J. Zhang (THU), H. N. Yang, H. Sun (NAOC) on behalf of the Einstein Probe (EP) team: The fast X-ray transient EP251202a triggered the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Zhang et al., GCN 42937), and was followed by several telescopes (Li et al., GCN 42934, Lipunov et al., GCN 42938 and Zhu et al., GCN 42939, Sbarufatti et al. GCN 42943). The refined analysis of the WXT data shows that the event started at T0=2025-12-02T01:48:23.9 (UTC) and lasted for ~400 s. Three peaks are detected in the lightcurve, whose spectra are characterized by photon indice of 2.33 (-0.90/+1.02), 1.12 (-0.48/+0.60) and 1.19 (-0.51/+1.1), respectively. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 6.48 x 10^20 cm^-2 and a photon index of 1.23 (-0.19/+0.19). The derived average unabsorbed 0.5-4 keV flux is 5.40 (-0.63/+0.70) x 10^(-10) erg/s/cm^2. 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/42946. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41020] GRB 251201A: GECAM-B observation of a burst
by GCN Circulars 02 Dec '25

02 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42945 SUBJECT: GRB 251201A: GECAM-B observation of a burst DATE: 25/12/02 12:08:00 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 251201A, at 2025-12-01T04:37:04.100 UTC (denoted as T0), which is also detected by MAXI/GSC (MAXI team, GCN #42913) and SVOM/GRM (Yue Wang et al., GCN #42932). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of multiple pulses followed by a possible flare with a total T90 of 47.7 +/-15.6 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb251201A.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/42945. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41019] GRB 251126A: SAO RAS optical marginal detection
by GCN Circulars 02 Dec '25

02 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42944 SUBJECT: GRB 251126A: SAO RAS optical marginal detection DATE: 25/12/02 12:05:32 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. Moskvitin, O. Spiridonova, V. Shergin (SAO RAS), A. Volnova (IKI), N. Pankov (HSE, IKI), A. Pozanenko (IKI) report on behalf of IKI-GRB-FuN and GRB follow-up team. We observed the field of the Swift GRB 251126A (Caputo et al., GCN 42843; Evans, GCN 42845; Goad et al., GCN 42851; Page et al., GCN 42860; Barthelmy et al., GCN 42876) with the Zeiss-1000 1m telescope of the SAO RAS starting on 2025-11-30 (UT) 00:19:43. The optical afterglow (Swain, GCN 42844; Fu et al., GCN 42848; Reguitti et al., GCN 42849; Broens et al., GCN 42850; Anguloet al., GCN 42855; Pulido-Torres et al; GCN 42856; Gupta et al., GCN 42857; Cotter et al., GCN 42858; Seki et al., GCN 42859; Volnova et al., GCN 42861; Breeveld and Caputo, GCN 42863; Gupta et al., GCN 42864; Burkhonov et al., GCN 42866; Maksut et al., GCN 42868; Moskvitin et al, GCN 42870; Adami et al., GCN 42871; Pankov et al., GCN 42875; Goranskij et al., GCN 42896; Yao et al., GCN 42941) is marginally detected in the stacked frame with the following brightness. Date UT start t-T0 Exp. Filter OT Err. UL (mid,days) (n*s) (3sigma) 2025-11-30 00:19:43 3.24019 13*300 Rc 24.3 0.4 24.3 The preliminary photometry is based on nearby stars from the USNO-B1 catalogue (R2 magnitudes) and is not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/42944. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41018] GRB 251202A: Swift-XRT afterglow detection
by GCN Circulars 02 Dec '25

02 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42943 SUBJECT: GRB 251202A: Swift-XRT afterglow detection DATE: 25/12/02 11:00:16 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> B. Sbarufatti (INAF-OAB), S. Lanava (PSU), S. Dichiara (PSU), J.A. Kennea (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), C. Salvaggio (INAF-OAB), M. Ferro (INAF-OAB) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of GRB 251202A. We searched for X-ray sources in 759 s of Photon Counting (PC) mode data. The total exposure at the position of the afterglow (see below) is 759 s, obtained between T0+2.4 ks and T0+24.0 ks. An uncatalogued X-ray source are clearly detected within the Einstein Probe/WXT error region. Using 411 s of PC mode data and 1 UVOT image, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 122.11512, +40.61228 which is equivalent to: RA (J2000): 08h 08m 27.63s Dec(J2000): +40d 36' 44.2" with an uncertainty of 2.4 arcsec (radius, 90% confidence). This position is 10.3 arcsec from the EP/FXT position (Zhang et al., GCN Circ. 42937) and 2.2 arcsec from the optical counterpart reported by Li et al. (GCN 42934). The light curve can be modelled with a power-law decay with a decay index of alpha=1.08 (+0.33, -0.24). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.93 (+0.45, -0.22). The best-fitting absorption column is consistent with the Galactic value of 6.5 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 3.4 x 10^-11 (3.9 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Galactic foreground: 6.5 x 10^20 cm^-2 Intrinsic column: 6 (+/-166) x 10^20 cm^-2 at z=2.785 Photon index: 1.93 (+0.45, -0.22) If the light curve continues to decay with a power-law decay index of 1.08, the count rate at T+24 hours will be 0.018 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 6.3 x 10^-13 (7.2 x 10^-13) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at https://www.swift.ac.uk/xrt_products/03000226. The results of the full analysis of the XRT observations are available at https://www.swift.ac.uk/EP/EP_FIELD00086. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42943. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41017] EP251129a/GRB 251129A: NOWT Detection
by GCN Circulars 02 Dec '25

02 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42942 SUBJECT: EP251129a/GRB 251129A: NOWT Detection DATE: 25/12/02 08:20:32 GMT FROM: Abdusamatjan Iskandar at XAO,CAS <abudu(a)xao.ac.cn> Shahidin Yaqup, Abdusamatjan Iskandar, Jinzhong Liu, report on behalf of optical group of the XAO: We imaged the field of the GRB 251129A/EP 251129a (GCN Circ. 42877, 42880, 42884 ) using the Nanshan One-meter Wide-field Telescope (NOWT) at Nanshan Station of Xinjiang Astronomical Observatory (XAO). We observed from 2025-11-29 20:08:26 to 20:32:43 UTC and obtained 6 x 300 s exposure in the V filter. The stack image photometry was calibrated using nearby stars from the GAIA synthesis catalog, without correction for Galactic extinction. We detect a source at the position (RA, DEC(J2000) = 14:57:18.88, +79:17:34.8) reported by GCN Circ.42880, with preliminary magnitude of V = 21.74+-0.64 mag. View this GCN Circular online at https://gcn.nasa.gov/circulars/42942. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41016] GRB 251126A: SVOM/VT optical observation
by GCN Circulars 02 Dec '25

02 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42941 SUBJECT: GRB 251126A: SVOM/VT optical observation DATE: 25/12/02 06:57:14 GMT FROM: zhyao(a)bao.ac.cn Z. H. Yao, Y. L. Qiu, C. Wu, H. L. Li, Y. N. Ma, L. P. Xin, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. R. Xu, J. S. Deng, J. Y. Wei (NAOC) and J. Palmerio (CEA) report on behalf of the SVOM/VT team. SVOM/VT performed a Target of Opportunity observation of GRB 251126A detected by Swift/BAT (Caputo et al., GCN 42843). SVOM/VT began observing the field at 2025-11-26T19:45:56.502 UTC, 35 minutes after T0, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. With X-band data available, the optical counterpart (Swain et al., GCN 42844; Lipunov et al. GCN 42847; Fu et al., GCN 42848; Reguitti et al., GCN 42849; Broens et al., GCN 42850; Angulo et al., GCN 42855; Pulido-Torres et al., GCN 42856; Gupta et al., GCN 42857; Cotter et al., GCN 42858; Seki et al., GCN 42859; Volnova et al., GCN 42861; Breeveld et al. GCN 42863; Gupta et al., GCN 42864; Burkhonov et al., GCN 42866; Maksut et al., GCN 42868; Moskvitin et al, GCN 42870; Adami et al., GCN 42871; Pankov et al., GCN 42875; Goranskij et al. GCN 42896) was detected in both VT_B and VT_R band within BAT (Caputo et al., GCN 42843; Barthelmy et al. GCN 42876) and XRT's (Caputo et al., GCN 42843; Evans et al., GCN 42845; Goad et al., GCN 42851) error box.We detect a clear fading with a decay slope of approximately 1.6, followed by a rebrightening bump occurring at ~13.48 h after the trigger. The most recent photometric measurement is as follows: mid time (h) | exposure time (s) | band | mag (AB) -------------|-------------------|------|---------------- 25.34 | 20*70 | VT_B | 22.87+/-0.12 25.34 | 20*70 | VT_R | 21.64+/-0.05 Our photometry was not corrected for Galactic extinction. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/42941. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41015] EP251130a: SVOM/VT optical observation
by GCN Circulars 02 Dec '25

02 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42940 SUBJECT: EP251130a: SVOM/VT optical observation DATE: 25/12/02 06:52:47 GMT FROM: Yinuo Ma <mayn(a)bao.ac.cn> Y. N. Ma, Y. L. Qiu, C. Wu, H. L. Li, L. P. Xin, Z. H. Yao, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA) report on behalf of the SVOM/VT team. SVOM performed a Target of Opportunity observation of EP251130a detected by EP/WXT (Wu et al., GCN 42903). SVOM/VT began observing the field at 2025-12-01T16:10:37 UTC, 29.05 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. With X-band data available, the optical counterpart (Dornic et al., GCN 42904; Lipunov et al., GCN 42906; 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) was detected within EP/FXT and Swift/XRT errorbox (Zhang et al., GCN 42915; Evans et al., GCN 42908) in both VT_B and VT_R bands. The magnitudes are: mid time (h) | exposure time (s) | band | mag (AB) | mag err -------------|-------------------|------|----------|-------- 29.61 | 23*50 | VT_B | 22.8 | 0.3 29.61 | 23*50 | VT_R | 20.54 | 0.08 Our photometry was not corrected for Galactic extinction. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/42940. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41014] EP251202a / GRB 251202A: NOT spectroscopic redshift z = 2.785
by GCN Circulars 02 Dec '25

02 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42939 SUBJECT: EP251202a / GRB 251202A: NOT spectroscopic redshift z = 2.785 DATE: 25/12/02 06:18:17 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> Z.P. Zhu (NAOC), D. B. Malesani (DAWN/NBI and Radboud), L. Izzo (INAF/OACN and DARK/NBI), A. de Ugarte Postigo (LAM), D. Xu, X. Liu, S.Q. Jiang, J. An, L.B. He (NAOC), A. Saccardi (CEA/Irfu), R. H. Rasmussen (NOT and Aarhus) report on behalf of a large collaboration: We observed the optical counterpart (Li et al., GCN 42934) of EP251202a (Zhang et al., GCN 42937), which is likely the same event of Fermi GRB 251202A (Fermi GBM team, GCN 42933), using the Nordic Optical Telescope (NOT), equipped with the ALFOSC camera and spectrograph. We obtained 10x120 s and 9x120 s exposures in the r and z bands, respectively, starting on 2025 Dec 2 at 02:51:32 UT. The afterglow is clearly detected in single images, with an AB magnitude of r = 17.27 +/- 0.01 at a mid time of 1.05 hr after the trigger. A sequence of 3 spectra by 1200 s each was then acquired using grism #4, covering the wavelength range 3500-9500 AA. Our first spectrum started on 2025 Dec 2.156 UT (1.93 hr after the EP/WXT trigger). Continuum is detected across the whole wavelength range. A spectral break is detected around 4610 AA, and the onset of the forest is seen blueward of this wavelength. We match existing features to a low-column density Lyman alpha and C IV (unresolved) at z = 2.785, which we believe to be the redshift of the burst. Intervening systems are also seen in Lyman alpha and C IV at z = 2.450 and 2.356. We acknowledge the use of the grbspec.eu tool to analyse this spectrum. View this GCN Circular online at https://gcn.nasa.gov/circulars/42939. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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